WO2012014998A1

WO2012014998A1 - Lithium secondary battery

Info

Publication number: WO2012014998A1
Application number: PCT/JP2011/067328
Authority: WO
Inventors: 上剃春樹; 御書至; 松尾和貴; 川端雄介; 長岡修一; 河野聡; 稲葉章; 山田將之; 阿部浩史
Original assignee: 日立マクセルエナジー株式会社
Priority date: 2010-07-29
Filing date: 2011-07-28
Publication date: 2012-02-02
Also published as: CN103038928A; KR20130033425A; KR101485382B1; JPWO2012014998A1

Abstract

The lithium secondary battery of the present invention is provided with a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator, and is characterized by: the positive electrode including a current collector and a positive electrode mixture layer formed on top of the current collector; the positive electrode mixture layer including a positive electrode active material; the positive electrode active material including a lithium-containing complex oxide containing lithium and nickel; the molar ratio of lithium to nickel in the total volume of the lithium-containing complex oxide being 0.5-1.05%; and the nonaqueous electrolyte including 0.5-20% by weight of a phosphonoacetate compound represented in Formula (1). In Formula (1), R¹, R² and R³ all independently represent C_1-12 alkyl groups that can be substituted with halogen atoms, and n represents an integer of 0 to 6.

Description

Lithium secondary battery

The present invention relates to a lithium secondary battery having a high capacity and good charge / discharge cycle characteristics and storage characteristics.

In recent years, along with the development of portable electronic devices such as mobile phones and notebook personal computers, and the practical application of electric vehicles, secondary batteries and capacitors with small and light weight and high capacity have been required.

Such lithium secondary batteries have been continuously improved for the purpose of improving battery characteristics. For example, Patent Document 1 discloses a lithium ion secondary that has a low gas generation amount, a high capacity, and excellent storage characteristics and charge / discharge cycle characteristics by including a non-aqueous electrolyte solution with a specific compound of a phosphate ester type. A battery is disclosed.

Conventionally, lithium cobaltate (LiCoO ₂ ), which has been used as a positive electrode material for lithium secondary batteries, is easy to manufacture and easy to handle, and is therefore frequently used as a suitable active material. However, since LiCoO ₂ is produced using cobalt (Co), which is a rare metal, as a raw material, it is expected that resource shortages will become serious in the future. Further, since the price of cobalt itself is high and the price fluctuates greatly, development of a positive electrode material that is inexpensive and stable in supply is desired.

Therefore, with the aim of further increasing the capacity, as an approach from the positive electrode active material, a positive electrode active material replacing LiCoO ₂ has been developed. For example, Patent Document 2 discloses nickel (Ni), manganese (Mn). , Cobalt (Co) and other substitutional elements M, the content ratio of each element is defined, and the atomic ratio a of M to Mn, Ni, Co on the surface of the positive electrode active material particles A positive electrode active material that is larger than the average atomic ratio of M to Mn, Ni, and Co is disclosed.

Further, as an approach from a negative electrode active material for the purpose of increasing the capacity, it is possible to use SiO _x having a structure in which ultrafine particles of silicon (Si) are dispersed in SiO ₂ as a negative electrode material. 5.

JP 2008-262908 A JP 2006-202647 A Japanese Patent Laid-Open No. 2004-047404 Japanese Patent Laid-Open No. 2005-259697 JP 2008-210618A

However, when a battery is configured using a positive electrode using a lithium-containing composite oxide containing Ni or Mn, which has a higher capacity than LiCoO ₂ , as a positive electrode active material, the battery swells when stored in a charged state, particularly at high temperatures. This is remarkable as compared with a battery using LiCoO ₂ alone as a positive electrode active material. Furthermore, there is also a problem that the recovery rate of the capacity that has decreased after storage at high temperature is smaller than that before high temperature storage.

These problems are thought to be caused by the inclusion of Ni in the positive electrode active material. In general, Ni is unstable in a high temperature environment. Therefore, Ni in the positive electrode active material reacts with the electrolyte under high-temperature storage, generating gas and causing the battery to swell, and the reaction product accumulates on the Ni interface, increasing the resistance of the battery and storing at high temperature. This is thought to reduce the recovery capacity later.

In addition, since the SiO _x has a large volume expansion / contraction associated with the charge / discharge reaction, particles are pulverized for each charge / discharge cycle of the battery, and Si deposited on the surface reacts with the nonaqueous electrolyte solvent and is irreversible. It is also known that problems such as an increase in capacity occur.

Under such circumstances, the SiO _x utilization rate is limited to suppress volume expansion / contraction associated with charge / discharge reactions, or halogen-substituted cyclic carbonates (for example, 4-fluoro-1,3-dioxolane- There has also been proposed a technique for improving the charge / discharge cycle characteristics of a battery by using a non-aqueous electrolytic solution to which 2-one or the like is added (see Patent Document 5).

According to the technique described in Patent Document 5, a lithium secondary battery having good charge / discharge cycle characteristics, for example, can be obtained while increasing capacity by using SiO _x as a negative electrode active material. The produced cyclic carbonate easily causes the battery to swell, and in this respect, the technique described in Patent Document 5 still leaves room for improvement.

In view of the above problems, the present invention provides a lithium secondary battery having a high capacity, a small battery swelling after high-temperature storage, a high capacity recovery rate, and good charge / discharge cycle characteristics.

The first lithium secondary battery of the present invention is a lithium secondary battery including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, and the positive electrode is formed on a current collector and the current collector. A positive electrode mixture layer, the positive electrode mixture layer contains a positive electrode active material, the positive electrode active material contains a first lithium-containing composite oxide containing lithium and nickel, and the first lithium The molar ratio of nickel to lithium in the total amount of the composite oxide containing is 0.05 to 1.05, and the non-aqueous electrolyte is a phosphonoacetate compound represented by the following general formula (1) Is contained in an amount of 0.5 to 20% by mass.

In the general formula (1), R ¹ , R ² and R ³ are each independently an alkyl group having 1 to 12 carbon atoms which may be substituted with a halogen atom, and n is an integer of 0 to 6 It is.

The second lithium secondary battery of the present invention is a lithium secondary battery including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, and the negative electrode is disposed on the current collector and the current collector. A negative electrode mixture layer formed, the negative electrode mixture layer contains a negative electrode active material, the negative electrode active material contains a material containing silicon and oxygen as constituent elements, and the non-aqueous electrolyte is: A halogen-substituted cyclic carbonate and a phosphonoacetate compound represented by the following general formula (1), wherein in the non-aqueous electrolyte, the content of the phosphonoacetate compound is the halogen-substituted cyclic carbonate It is characterized by being below the content of.

According to the present invention, it is possible to provide a lithium secondary battery having a high capacity, a small battery swelling after high-temperature storage, a high capacity recovery rate, and good charge / discharge cycle characteristics.

1A is a plan view showing an example of the lithium secondary battery of the present invention, and FIG. 1B is a cross-sectional view of FIG. 1A. FIG. 2 is a perspective view showing an example of the lithium secondary battery of the present invention.

Hereinafter, embodiments of the present invention will be described. However, these are merely examples of embodiments of the present invention, and the present invention is not limited to these contents.

(Embodiment 1)
The first lithium secondary battery of the present invention includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator. The positive electrode includes a current collector and a positive electrode mixture layer formed on the current collector, the positive electrode mixture layer includes a positive electrode active material, and the positive electrode active material includes lithium and A first lithium-containing composite oxide containing nickel is included, and a molar ratio of the nickel to the lithium in the total amount of the first lithium-containing composite oxide is 0.05 to 1.05. Further, the nonaqueous electrolytic solution contains 0.5 to 20% by mass of a phosphonoacetate compound represented by the following general formula (1).

[Positive electrode]
For the positive electrode according to the first lithium secondary battery of the present invention, for example, one having a structure having a positive electrode mixture layer containing a positive electrode active material, a binder, a conductive additive and the like on one side or both sides of a current collector is used. it can.

<Positive electrode active material>
The positive electrode active material used for the positive electrode of the first lithium secondary battery of the present invention includes a first lithium-containing composite oxide containing lithium (Li) and nickel (Ni). The first lithium-containing composite oxide may contain other metals such as cobalt (Co) and manganese (Mn) as constituent elements. Furthermore, the ratio (molar ratio) of Ni to Li in the total amount of the first lithium-containing composite oxide is set to 0.05 to 1.05. Since Ni contributes to an increase in battery capacity, if Ni is contained in the positive electrode active material, the battery capacity increases. However, since Ni lacks stability under high-temperature storage, electrolysis including a phosphonoacetate compound is necessary. By using the solution together and setting the molar ratio of Ni to Li to 0.05 to 1.05, more preferably 0.2 to 0.9, a battery having a high capacity and stable even under high temperature storage can be obtained. it can.

The molar ratio of Ni to Li in the total amount of the first lithium-containing composite oxide defined in the present invention is calculated as follows. Taking LiNi _0.8 Co _0.2 O ₂ as an example of the lithium-nickel-containing composite oxide, the composition ratio of Li: Ni in this lithium-nickel-containing composite oxide is 1: 0.8. In this case, the molar ratio of Ni to Li in LiNi _0.8 Co _0.2 O ₂ is 0.8 / 1 = 0.8.

The composition analysis of the lithium-containing composite oxide can be performed as follows using an ICP (Inductive Coupled Plasma) method. First, 0.2 g of a lithium-containing composite oxide to be measured is collected and placed in a 100 mL container. Thereafter, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were added in order and dissolved by heating. After cooling, the mixture was further diluted 25 times with pure water, and an ICP analyzer “ICP-757” manufactured by JARRELASH was used. The composition is analyzed by a calibration curve method. The composition formula can be derived from the obtained results.

In view of other characteristics of the positive electrode active material such as thermal stability and high potential stability, the first lithium-containing composite oxide used in the present invention is particularly represented by the following general composition formula (2). It is preferable to use one.

Li _{1 + y} MO ₂ (2)
However, in the general composition formula (2), −0.15 ≦ y ≦ 0.15, and M represents an element group containing Ni, Co, and Mn, and is based on the total number of elements in the element group M. When the ratio of the number of elements Ni, Co and Mn contained in the element group M is a (mol%), b (mol%) and c (mol%), respectively, 25 ≦ a ≦ 90, 5 ≦ b ≦ 35, 5 ≦ c ≦ 35, and 10 ≦ b + c ≦ 70.

When the total number of elements in the element group M in the general composition formula (2) representing the first lithium-containing composite oxide is 100 mol%, the Ni ratio a is a viewpoint of improving the capacity of the lithium-containing composite oxide. Therefore, it is preferable to set it as 25 mol% or more, and it is more preferable to set it as 50 mol% or more. However, if the proportion of Ni in the element group M is too large, for example, the amount of Co or Mn is reduced, and the effects of these may be reduced. Therefore, when the total number of elements in the element group M in the general composition formula (2) representing the first lithium-containing composite oxide is 100 mol%, the Ni ratio a is preferably 90 mol% or less, More preferably, it is 70 mol% or less.

In addition, Co contributes to the capacity of the lithium-containing composite oxide and acts to improve the packing density in the positive electrode mixture layer. On the other hand, too much Co may cause an increase in cost and a decrease in safety. Therefore, when the total number of elements in the element group M in the general composition formula (2) representing the first lithium-containing composite oxide is 100 mol%, the Co ratio b is 5 mol% or more and 35 mol% or less. Is preferred.

In the first lithium-containing composite oxide, when the total number of elements in the element group M in the general composition formula (2) is 100 mol%, the ratio c of Mn is 5 mol% or more and 35 mol% or less. It is preferable. By including Mn in the lithium-containing composite oxide in the amount as described above, and by always allowing Mn to be present in the crystal lattice, the thermal stability of the lithium-containing composite oxide can be improved, and the safety is further improved. It is possible to construct a battery with a high value.

Furthermore, in the first lithium-containing composite oxide, by containing Co, fluctuations in the valence of Mn due to Li doping and dedoping during charging and discharging of the battery are suppressed, and the average valence of Mn is 4 It is possible to stabilize the value in the vicinity of the valence, and to further improve the reversibility of charge / discharge. Therefore, by using such a lithium-containing composite oxide, it becomes possible to configure a battery with more excellent charge / discharge cycle characteristics.

In addition, in the first lithium-containing composite oxide, from the viewpoint of favorably securing the above-described effect by using Co and Mn together, the total number of elements in the element group M in the general composition formula (2) is 100 mol. %, The sum b + c of the Co ratio b and the Mn ratio c is preferably 10 mol% or more and 70 mol% or less, and more preferably 10 mol% or more and 50 mol% or less.

The element group M in the general composition formula (2) representing the first lithium-containing composite oxide may contain elements other than Ni, Co, and Mn. For example, titanium (Ti), chromium (Cr) , Iron (Fe), copper (Cu), zinc (Zn), aluminum (Al), germanium (Ge), tin (Sn), magnesium (Mg), silver (Ag), thallium (Tl), niobium (Nb) , Boron (B), phosphorus (P), zirconium (Zr), calcium (Ca), strontium (Sr), barium (Ba) and the like. However, in the first lithium-containing composite oxide, in order to sufficiently obtain the above-described effect by containing Ni, Co, and Mn, Ni is obtained when the total number of elements in the element group M is 100 mol%. When the sum of the ratios (mol%) of elements other than Co, Mn is expressed by f, f is preferably 15 mol% or less, and more preferably 3 mol% or less.

For example, in the first lithium-containing composite oxide, when Al is present in the crystal lattice, the crystal structure of the lithium-containing composite oxide can be stabilized, and the thermal stability thereof can be improved. It becomes possible to constitute a lithium secondary battery with higher safety. In addition, since Al is present at the grain boundaries and surfaces of the lithium-containing composite oxide particles, the stability over time and side reactions with the electrolytic solution can be suppressed, and a longer-life lithium secondary battery is constructed. It becomes possible.

However, since Al cannot participate in the charge / discharge capacity, increasing the content in the first lithium-containing composite oxide may cause a decrease in capacity. Therefore, in the general composition formula (2) representing the first lithium-containing composite oxide, when the total number of elements in the element group M is 100 mol%, the Al ratio is preferably 10 mol% or less. In order to better secure the above-described effect by including Al, in the general composition formula (2) representing the first lithium-containing composite oxide, the total number of elements in the element group M is set to 100 mol%. Sometimes, the Al ratio is preferably 0.02 mol% or more.

In the first lithium-containing composite oxide, when Mg is present in the crystal lattice, the crystal structure of the lithium-containing composite oxide can be stabilized and its thermal stability can be improved, so that it is safer. It becomes possible to constitute a lithium secondary battery with high performance. In addition, when a phase transition of the lithium-containing composite oxide occurs due to Li doping and dedoping during charging and discharging of a lithium secondary battery, Mg is rearranged to relax the irreversible reaction, and the lithium-containing composite Since reversibility of the crystal structure of the oxide can be increased, a lithium secondary battery having a longer charge / discharge cycle life can be configured. In particular, in the general composition formula (2) representing the first lithium-containing composite oxide, when y <0 and the lithium-containing composite oxide has a Li-deficient crystal structure, Mg is substituted for Li. A lithium-containing composite oxide can be formed so as to enter the Li site, and a stable compound can be obtained.

However, since Mg has little influence on the charge / discharge capacity, if the content in the lithium-containing composite oxide is increased, the capacity may be reduced. Therefore, in the general composition formula (2) representing the first lithium-containing composite oxide, when the total number of elements in the element group M is 100 mol%, the ratio of Mg is preferably 10 mol% or less. On the other hand, in order to better secure the above-described effect by containing Mg, in the general composition formula (2) representing the first lithium-containing composite oxide, the total number of elements in the element group M is set to 100 mol%. In this case, the Mg ratio is preferably 0.02 mol% or more.

In the first lithium-containing composite oxide, when Ti is contained in the particles, in the LiNiO ₂ type crystal structure, Ti is arranged in a crystal defect portion such as an oxygen vacancy to stabilize the crystal structure. The reversibility of the reaction of the lithium-containing composite oxide is increased, and a lithium secondary battery having more excellent charge / discharge cycle characteristics can be configured. In order to secure the above-mentioned effect satisfactorily, in the general composition formula (2) representing the first lithium-containing composite oxide, the ratio of Ti when the total number of elements in the element group M is 100 mol% Is preferably 0.01 mol% or more, and more preferably 0.1 mol% or more. On the other hand, when the content of Ti increases, Ti does not participate in charging / discharging, so that the capacity may be reduced or a heterogeneous phase such as Li ₂ TiO ₃ may be easily formed, leading to a deterioration in characteristics. Therefore, in the general composition formula (2) representing the first lithium-containing composite oxide, when the total number of elements in the element group M is 100 mol%, the ratio of Ti is preferably 10 mol% or less. More preferably, it is 5 mol% or less, and further preferably 2 mol% or less.

In addition, the first lithium-containing composite oxide contains at least one element M ′ selected from Ge, Ca, Sr, Ba, B, Zr and Ga as the element group M in the general composition formula (2). When it contains, it is preferable at the point which can ensure the following effect, respectively.

In the case where the first lithium-containing composite oxide contains Ge, the crystal structure of the composite oxide after Li is eliminated is stabilized, so that the reversibility of the reaction during charge and discharge is improved. Therefore, it is possible to configure a lithium secondary battery that is higher in safety and more excellent in charge / discharge cycle characteristics. In particular, when Ge is present on the particle surface or grain boundary of the lithium-containing composite oxide, disorder of the crystal structure due to Li desorption / insertion at the interface is suppressed, greatly contributing to improvement of charge / discharge cycle characteristics. be able to.

When the first lithium-containing composite oxide contains an alkaline earth metal such as Ca, Sr, or Ba, the growth of primary particles is promoted, and the crystallinity of the lithium-containing composite oxide is increased. In order to improve, the active site can be reduced, the stability over time when a coating material for forming a positive electrode mixture layer (a positive electrode mixture-containing composition described later) is improved, and the lithium secondary battery has Irreversible reaction with the non-aqueous electrolyte can be suppressed. Furthermore, since these elements are present on the particle surfaces and grain boundaries of the lithium-containing composite oxide, the CO ₂ gas in the battery can be trapped. It becomes possible to do. In particular, when the lithium-containing composite oxide contains Mn, the primary particles tend to be difficult to grow. Therefore, the addition of an alkaline earth metal such as Ca, Sr, or Ba is more effective.

Even when B is contained in the first lithium-containing composite oxide, the growth of primary particles is promoted and the crystallinity of the lithium-containing composite oxide is improved, so that the active sites can be reduced, Irreversible reactions with the moisture in the atmosphere, the binder used for forming the positive electrode mixture layer, and the non-aqueous electrolyte of the battery can be suppressed. For this reason, stability over time when it is used as a coating material for forming the positive electrode mixture layer is improved, gas generation in the battery can be suppressed, and a lithium secondary battery having better storage and a longer life can be obtained. It can be configured. In particular, when the lithium-containing composite oxide contains Mn, the addition of B is more effective because primary particles tend to be difficult to grow.

When Zr is contained in the first lithium-containing composite oxide, the presence of Zr at the grain boundaries and surfaces of the lithium-containing composite oxide particles results in electrochemical characteristics of the lithium-containing composite oxide. Therefore, it is possible to construct a lithium secondary battery having a better shelf life and a longer life.

When Ga is contained in the first lithium-containing composite oxide, the growth of primary particles is promoted and the crystallinity of the lithium-containing composite oxide is improved. Therefore, active sites can be reduced, Stability over time when a coating material for forming the positive electrode mixture layer is improved, and irreversible reaction with the non-aqueous electrolyte can be suppressed. Further, by dissolving Ga in the crystal structure of the lithium-containing composite oxide, the layer spacing of the crystal lattice can be expanded, and the rate of lattice expansion / contraction due to insertion and desorption of Li can be reduced. . For this reason, the reversibility of a crystal structure can be improved and it becomes possible to comprise a lithium secondary battery with a longer charge-discharge cycle life. In particular, when the lithium-containing composite oxide contains Mn, the addition of Ga is more effective because primary particles tend to be difficult to grow.

In order to easily obtain the effect of the element M ′ selected from Ge, Ca, Sr, Ba, B, Zr, and Ga, the ratio is 0.1 mol% or more in all elements of the element group M. It is preferable. Further, the ratio of these elements M ′ in all elements of the element group M is preferably 10 mol% or less.

Elements other than Ni, Co, and Mn in the element group M may be uniformly distributed in the first lithium-containing composite oxide, or may be segregated on the particle surface or the like.

In the general composition formula (2) representing the first lithium-containing composite oxide, when the relationship between the Co ratio b and the Mn ratio c in the element group M is b> c, By promoting the growth of lithium-containing composite oxide particles, it is possible to obtain a lithium-containing composite oxide that has a high packing density at the positive electrode (the positive electrode mixture layer) and is more reversible. Further improvement in capacity can be expected.

On the other hand, in the general composition formula (2) representing the first lithium-containing composite oxide, when the relationship between the Co ratio b and the Mn ratio c in the element group M is b ≦ c, A lithium-containing composite oxide having high thermal stability can be obtained, and further improvement in the safety of a battery using the lithium-containing composite oxide can be expected.

The first lithium-containing composite oxide having the above composition has a large true density of 4.55 to 4.95 g / cm ³ and becomes a material having a high volume energy density. The true density of the lithium-containing composite oxide containing Mn in a certain range varies greatly depending on its composition. However, since the structure is stabilized and the uniformity can be improved in the narrow composition range as described above, for example, LiCoO ₂ This is considered to be a large value close to the true density of. Moreover, the capacity | capacitance per mass of lithium containing complex oxide can be enlarged, and it can be set as the material excellent in reversibility.

The true density of the first lithium-containing composite oxide increases particularly when the composition is close to the stoichiometric ratio. Specifically, in the general composition formula (2), −0.15 ≦ It is preferable to satisfy y ≦ 0.15, and the true density and reversibility can be improved by adjusting the value of y in this way. y is more preferably −0.05 or more and 0.05 or less. In this case, the true density of the lithium-containing composite oxide can be set to a higher value of 4.6 g / cm ³ or more. .

The first lithium-containing composite oxide represented by the general composition formula (2) includes a Li-containing compound (lithium hydroxide monohydrate and the like), a Ni-containing compound (such as nickel sulfate), and a Co-containing compound (sulfuric acid). Cobalt and the like), a Mn-containing compound (such as manganese sulfate), and a compound containing other elements contained in the element group M (such as aluminum sulfate and magnesium sulfate) are mixed and fired. Further, in order to synthesize the lithium-containing composite oxide with higher purity, a composite compound (hydroxide, oxide, etc.) containing a plurality of elements contained in the element group M and a Li-containing compound are mixed and fired. It is preferable to do.

The firing conditions can be, for example, 800 to 1050 ° C. for 1 to 24 hours, but once heated to a temperature lower than the firing temperature (for example, 250 to 850 ° C.) and maintained at that temperature, preheating is performed. After that, it is preferable to raise the temperature to the firing temperature to advance the reaction. There is no particular limitation on the preheating time, but it is usually about 0.5 to 30 hours. The atmosphere during firing can be an atmosphere containing oxygen (that is, in the air), a mixed atmosphere of an inert gas (such as argon, helium, or nitrogen) and oxygen gas, or an oxygen gas atmosphere. The oxygen concentration (volume basis) is preferably 15% or more, and more preferably 18% or more.

The positive electrode active material may contain one kind of the first lithium-containing composite oxide, or may contain two or more kinds.

The positive electrode active material may further contain a second lithium-containing composite oxide containing lithium and a transition metal, in addition to the first lithium-containing composite oxide described above. Examples of the second lithium-containing composite oxide include lithium cobalt oxides such as LiCoO ₂ ; lithium manganese oxides such as LiMnO ₂ and Li ₂ MnO ₃ ; LiMn ₂ O ₄ and Li _4/3 Ti _5/3 O. A lithium-containing composite oxide having a spinel structure such as ₄ ; a lithium-containing composite oxide having an olivine structure such as LiFePO ₄ ; an oxide in which these oxides have a basic composition and a part of the constituent elements is substituted with another element; Etc.

The positive electrode active material may contain one kind of the second lithium-containing composite oxide, or may contain two or more kinds.

When using the first lithium-containing composite oxide and the second lithium-containing composite oxide as the positive electrode active material, it is particularly preferable to use LiCoO ₂ as the second lithium-containing composite oxide.

In addition, when the first lithium-containing composite oxide and the second lithium-containing composite oxide are used as the positive electrode active material, the effect of using the first lithium-containing composite oxide is ensured satisfactorily. From the viewpoint, the content of the first lithium-containing composite oxide in the total amount of the positive electrode active material is preferably 10% by mass or more, and more preferably 30% by mass or more. Further, in order to better achieve the effect of improving the storage characteristics and charge / discharge cycle characteristics at high temperatures of the lithium secondary battery of the present invention, the inclusion of the first lithium-containing composite oxide in the total amount of the positive electrode active material The amount is preferably 80% by mass or less, and more preferably 60% by mass or less.

In addition, when using the first lithium-containing composite oxide and the second lithium-containing composite oxide as the positive electrode active material, in order to obtain a lithium secondary battery that has a high capacity and is stable even under high-temperature storage, The total molar ratio of total nickel to total lithium in the total amount of the positive electrode active material is preferably 0.05 to 1.0.

When the first lithium-containing composite oxide and the second lithium-containing composite oxide are used as the positive electrode active material, the total molar ratio R of all nickel to the total lithium in the total amount of the positive electrode active material is It can be calculated by equation (3).

R = ΣN _j × a _j / ΣL _j × a _j (3)
Here, in the formula (3), N _j : molar composition ratio of Ni contained in the component j, a _j : mixing mass ratio of the component j, L _j : molar composition ratio of Li contained in the component j.

For example, LiNi _0.8 Co _0.1 Mn _0.1 O ₂ as the first lithium-containing composite oxide and LiCoO ₂ as the second lithium-containing composite oxide may have a mass ratio of 1: 1 ( That is, when the mixed mass ratio is 0.5) for both the first lithium-containing composite oxide and the second lithium-containing composite oxide, the total molar ratio R is as follows.

R = (0.8 × 0.5) / (1.0 × 0.5 + 1.0 × 0.5) = 0.4

The average particle size of the first lithium-containing composite oxide and the second lithium-containing oxide used in the present invention is preferably 5 to 25 μm, particularly preferably 10 to 20 μm. These particles may be secondary aggregates in which primary particles are aggregated, and the average particle size in this case means the average particle size of the secondary aggregates. Further, the average particle diameter of various particles in the present specification was measured by, for example, using a laser scattering particle size distribution analyzer “LA-920” manufactured by Horiba, Ltd., dispersing these fine particles in a medium in which the measurement particles are not dissolved. The average particle diameter D is 50%. Furthermore, the specific surface area by the BET method is preferably 0.1 to 0.4 m ² / g for reasons such as ensuring reactivity with lithium ions and suppressing side reactions with the electrolyte. . The specific surface area by the BET method can be measured, for example, using a specific surface area measuring device “Macsorb HM model-1201” manufactured by Mounttech using a nitrogen adsorption method.

<Binder of positive electrode mixture layer>
As the binder used for the positive electrode mixture layer relating to the positive electrode of the first lithium secondary battery of the present invention, any thermoplastic resin or thermosetting resin can be used as long as it is chemically stable in the battery. . Among them, for example, it is preferable to use a tetrafluoroethylene-vinylidene fluoride copolymer (hereinafter referred to as “P (TFE-VDF)”) other than the PVDF polymer together with polyvinylidene fluoride (PVDF). By the action of P (TFE-VDF), the adhesion between the positive electrode mixture layer and the current collector can be moderately suppressed.

In addition, as the binder of the positive electrode mixture layer, binders other than these can be used together with PVDF and P (TFE-VDF) or independently. Examples of such binders include polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoro. Propylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), propylene-tetrafluoroethylene copolymer Polymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), or ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-acrylic Methyl methacrylate copolymer, ethylene - methyl methacrylate copolymer and the like Na ion crosslinked product thereof copolymer.

When PVDF and P (TFE-VDF) and other binders are used, the amount of these other binders used in the positive electrode mixture layer is 1 mass in the total amount of binder in the positive electrode mixture layer. % Or less is preferable.

The total content of the binder in the positive electrode mixture layer is preferably 4% by mass or less, and more preferably 3% by mass or less. If the amount of the binder in the positive electrode mixture layer is too large, the adhesion between the positive electrode mixture layer and the current collector becomes too high, and the positive electrode mixture layer is formed on the inner peripheral side of the wound electrode body using this positive electrode. Defects such as cracks are likely to occur.

Further, from the viewpoint of improving the capacity of the positive electrode, it is preferable to increase the content of the positive electrode active material by reducing the amount of the binder in the positive electrode mixture layer, but if the amount of the binder in the positive electrode mixture layer is too small, The flexibility of the mixture layer is lowered, the shape of the wound electrode body using this positive electrode (especially the shape on the outer peripheral side) is deteriorated, and the productivity of the positive electrode and further the productivity of the battery using this are impaired. There is a risk that. Therefore, the total content of the binder in the positive electrode mixture layer is preferably 1% by mass or more, and more preferably 1.4% by mass or more.

In the positive electrode mixture layer, when the total of PVDF and P (TFE-VDF) is 100% by mass, the ratio of P (TFE-VDF) is 10% by mass or more, preferably 20% by mass or more. can do. Thereby, even as a positive electrode mixture layer containing a lithium-containing composite oxide having a large Ni ratio and PVDF, it is possible to moderately suppress the adhesion with the current collector.

However, if the amount of P (TFE-VDF) in the sum of PVDF and P (TFE-VDF) is too large, the electrode adhesion strength is reduced, battery resistance is increased, and the load characteristics of the battery are reduced. Sometimes. Therefore, when the total of PVDF and P (TFE-VDF) in the positive electrode mixture layer is 100% by mass, the ratio of P (TFE-VDF) is preferably 30% by mass or less.

<Conductive aid for positive electrode mixture layer>
As a conductive support agent used for the positive mix layer concerning the positive electrode of the 1st lithium secondary battery of this invention, what is chemically stable should just be in a battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black (trade name), channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fiber and metal fiber; aluminum Metallic powders such as powders; Fluorinated carbon; Zinc oxide; Conductive whiskers made of potassium titanate; Conductive metal oxides such as titanium oxide; Organic conductive materials such as polyphenylene derivatives; One species may be used alone, or two or more species may be used in combination. Among these, highly conductive graphite and carbon black excellent in liquid absorption are preferable. Further, the form of the conductive auxiliary agent is not limited to primary particles, and secondary aggregates and aggregated forms such as chain structures can also be used. Such an assembly is easier to handle and has better productivity.

Among them, it is preferable that carbon fibers having an average fiber length of 10 nm or more and less than 1000 nm and an average fiber diameter of 1 nm or more and 100 nm or less are contained in an amount of 0.25 mass% or more and 1.5 mass% or less. Use carbon fibers having an average fiber length of 10 nm or more and less than 1000 nm and an average fiber diameter of 1 nm or more and 100 nm or less in an amount of 0.25 mass% or more and 1.5 mass% or less in the positive electrode mixture layer. Thus, for example, it is possible to increase the density of the positive electrode mixture layer, leading to an increase in battery capacity. Although the details of the reason are unclear, the carbon fibers of the size are easily dispersed well in the positive electrode mixture layer, and since many carbon fibers having a short fiber length are included, the distance between the positive electrode active material particles is small. This is considered to be because the components in the positive electrode mixture layer become shorter and can be filled satisfactorily. Furthermore, since the dispersion of the carbon fiber, which is a conductive auxiliary agent, becomes better, the reaction in the positive electrode mixture layer is averaged over the entire area, so that the area of the positive electrode mixture layer actually involved in the reaction becomes larger and the load is increased. The characteristics are improved, and further, the local reaction of the positive electrode mixture layer is suppressed, and the deterioration of the positive electrode when charging / discharging is repeated is suppressed. Therefore, it is considered that the charge / discharge cycle characteristics are also improved.

The average fiber length of the carbon fibers is preferably 30 nm or more, and preferably 500 nm or less. Furthermore, the average fiber diameter of the carbon fiber is preferably 3 nm or more, and preferably 50 nm or less.

The average fiber length and average fiber diameter of the carbon fiber referred to in this specification are accelerated by a transmission electron microscope (TEM, for example, “JEM series” manufactured by JEOL Ltd., “H-700H” manufactured by Hitachi, Ltd.), etc. The voltage is 100 kV or 200 kV and is measured from the photographed TEM image. When viewing the average fiber length, TEM images of 100 samples were taken at 20,000 to 40,000 magnification, and when viewing the average fiber diameter at 200,000 to 400,000 magnification. The length and diameter are measured one by one with a metal scale certified to the first grade of the industry standard (JIS), and the average of the measured values is taken as the average fiber length and average fiber diameter.

Further, in the positive electrode mixture layer, a conductive auxiliary other than carbon fibers having an average fiber length of 10 nm or more and less than 1000 nm and an average fiber diameter of 1 nm or more and 100 nm or less (hereinafter, referred to as “other conductive assistant”). Can be used in combination with the carbon fiber. Examples of the other conductive assistants include conductive assistants used for positive electrodes of lithium secondary batteries that are conventionally known, such as natural graphite (such as flake graphite) and graphite such as artificial graphite; acetylene black, Carbon black such as ketjen black, channel black, furnace black, lamp black, thermal black; carbon fiber having an average fiber length of less than 1 nm or 1000 nm or more, carbon fiber having an average fiber diameter of less than 1 nm or more than 100 nm; Examples thereof include carbon materials.

In particular, the graphite is preferably used in combination with carbon fibers having an average fiber length of 10 nm or more and less than 1000 nm and an average fiber diameter of 1 nm or more and 100 nm or less. In this case, the carbon in the positive electrode mixture layer is used. The dispersibility of the fibers becomes better, and the load characteristics and charge / discharge cycle characteristics of the lithium secondary battery using the positive electrode of the present embodiment can be further improved.

When the carbon fiber and graphite are used in combination, when the total of the carbon fiber content and the graphite content in the positive electrode mixture layer is 100% by mass, the graphite content is 25% by mass or more. It is preferable that the above-mentioned effects can be ensured more favorably by using the carbon fiber and graphite together. However, if the amount of graphite in the total of the carbon fiber and graphite in the positive electrode mixture layer is excessively increased, the amount of the conductive auxiliary agent in the positive electrode mixture layer is excessively increased and the filling amount of the positive electrode active material is decreased. However, the effect of increasing the capacity may be reduced. Therefore, when the total of the carbon fiber content and the graphite content in the positive electrode mixture layer is 100% by mass, the graphite content is preferably 87.5% by mass or less.

Moreover, also when using 2 or more types together as a conductive support agent which concerns on a positive mix layer, when the sum total of the said carbon fiber and said other conductive support agent in a positive mix layer is 100 mass% The content of the other conductive aid is preferably 25 to 87.5% by mass.

<Current collector of positive electrode>
The current collector used for the positive electrode of the first lithium secondary battery of the present invention can be the same as that used for the positive electrode of a conventionally known lithium secondary battery. A 10-30 μm aluminum foil is preferred.

<Method for producing positive electrode>
For the positive electrode, for example, a positive electrode mixture-containing composition in the form of a paste or slurry in which the positive electrode active material, binder and conductive additive described above are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) is prepared. (However, the binder may be dissolved in a solvent.) After applying this to one or both sides of the current collector and drying, it can be produced through a process of calendering if necessary. . The manufacturing method of a positive electrode is not necessarily restricted to the said method, It can also manufacture with another manufacturing method.

<Positive electrode mixture layer>
As the composition of the positive electrode mixture layer, for example, the amount of the positive electrode active material is preferably 60 to 95% by mass, the amount of the binder is preferably 1 to 15% by mass, and the amount of the conductive auxiliary agent is 3%. It is preferably ˜20% by mass.

Further, after the calendar treatment, the thickness of the positive electrode mixture layer is preferably 15 to 200 μm per one side of the current collector. Furthermore, after the calendar treatment, the density of the positive electrode mixture layer is preferably 3.2 g / cm ³ or more, and more preferably 3.6 g / cm ³ or more. By using a positive electrode having such a high-density positive electrode mixture layer, higher capacity can be achieved. However, if the density of the positive electrode mixture layer is too large, the porosity becomes small and the permeability of the non-aqueous electrolyte may be reduced. It is preferably 2 g / cm ³ or less. As the calendering process, for example, roll pressing can be performed at a linear pressure of about 1 to 30 kN / cm. By such a process, the positive electrode mixture layer having the above density can be obtained.

Further, the density of the positive electrode mixture layer referred to in the present specification is a value measured by the following method. The positive electrode is cut into a predetermined area, its mass is measured using an electronic balance with a minimum scale of 0.1 mg, and the mass of the current collector is subtracted to calculate the mass of the positive electrode mixture layer. On the other hand, the total thickness of the positive electrode was measured at 10 points with a micrometer having a minimum scale of 1 μm, and the volume of the positive electrode mixture layer was determined from the average value obtained by subtracting the thickness of the current collector from these measured values and the area. calculate. Then, the density of the positive electrode mixture layer is calculated by dividing the mass of the positive electrode mixture layer by the volume.

[Negative electrode]
The negative electrode according to the lithium secondary battery of the present invention has, for example, a structure having a negative electrode mixture layer containing a negative electrode active material, a binder, and a conductive auxiliary agent, if necessary, on one side or both sides of a current collector. Can be used.

<Negative electrode active material>
The negative electrode active material used for the negative electrode of the first lithium secondary battery of the present invention includes a negative electrode active material conventionally used for lithium secondary batteries, that is, a material capable of inserting and extracting lithium ions. If there is no restriction in particular. For example, carbon-based materials that can occlude and release lithium ions, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers. One kind or a mixture of two or more kinds is used as the negative electrode active material. In addition, elements such as silicon (Si), tin (Sn), germanium (Ge), bismuth (Bi), antimony (Sb), indium (In), and alloys thereof, lithium such as lithium-containing nitride or lithium-containing oxide A compound that can be charged and discharged at a low voltage close to that of a metal, or a lithium metal or lithium / aluminum alloy can also be used as the negative electrode active material. Specially, as the anode active material, a material represented by SiO _x containing the constituent elements silicon and oxygen, a complex with SiO _x and the carbon material, and in combination with SiO _x and the graphitic carbon material is preferred.

The SiO _x may contain Si microcrystal or amorphous phase. In this case, the atomic ratio of Si and O is a ratio including Si microcrystal or amorphous phase Si. That is, SiO _x includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and this amorphous SiO ₂ is dispersed in the SiO ₂ matrix. It is sufficient that the atomic ratio x satisfies 0.5 ≦ x ≦ 1.5 in combination with Si. For example, in the case of a material in which Si is dispersed in an amorphous SiO ₂ matrix and the material has a molar ratio of SiO ₂ to Si of 1: 1, x = 1, so that the structural formula is represented by SiO. The In the case of a material having such a structure, for example, in X-ray diffraction analysis, a peak due to the presence of Si (microcrystalline Si) may not be observed, but when observed with a transmission electron microscope, the presence of fine Si Can be confirmed.

Then, SiO _x is preferably a complex complexed with carbon materials, for example, it is desirable that the surface of the SiO _x is coated with a carbon material. Usually, since SiO _x has poor conductivity, when using it as a negative electrode active material, from the viewpoint of ensuring good battery characteristics, a conductive material (conductive aid) is used, and SiO _x in the negative electrode is electrically conductive. It is necessary to form an excellent conductive network by making good mixing and dispersion with the conductive material. If complexes complexed with carbon material SiO _x, for example, simply than with a material obtained by mixing a conductive material such as SiO _x and the carbon material, good conductive network in the negative electrode Formed.

That is, the specific resistance value of SiO _x is usually 10 ³ to 10 ⁷ kΩcm, whereas the specific resistance value of the carbon material exemplified above is usually 10 ⁻⁵ to 10 kΩcm. The composite of SiO _x and the carbon material may further have a material layer (a material layer containing non-graphitizable carbon) that covers the carbon material coating layer on the particle surface.

The complex of the SiO _x and the carbon material, as described above, other although the surface of the SiO _x coated with carbon material, such as granules of SiO _x and the carbon material can be cited.

In addition, since the composite in which the surface of SiO _x is coated with a carbon material is further combined with a conductive material (carbon material or the like), a better conductive network can be formed in the negative electrode. Therefore, it is possible to realize a lithium secondary battery with higher capacity and more excellent battery characteristics (for example, charge / discharge cycle characteristics). The complex of the SiO _x and the carbon material coated with a carbon material, for example, like granules the mixture was further granulated with SiO _x and the carbon material coated with a carbon material.

Further, as SiO _x whose surface is coated with a carbon material, the surface of a composite (for example, a granulated body) of SiO _x and a carbon material having a smaller specific resistance value is further coated with a carbon material. Those can also be preferably used. In the non-aqueous secondary battery having a negative electrode containing SiO _x as a negative electrode active material, it is possible to form a better conductive network when SiO _x and the carbon material are dispersed inside the granule. Battery characteristics such as load discharge characteristics can be further improved.

Preferred examples of the carbon material that can be used to form a composite with SiO _x include carbon materials such as low crystalline carbon, carbon nanotubes, and vapor grown carbon fibers.

The details of the carbon material include at least one selected from the group consisting of fibrous or coiled carbon materials, carbon black (including acetylene black and ketjen black), artificial graphite, graphitizable carbon, and non-graphitizable carbon. A seed material is preferred. A fibrous or coiled carbon material is preferable in that it easily forms a conductive network and has a large surface area. Carbon black (including acetylene black and ketjen black), graphitizable carbon, and non-graphitizable carbon have high electrical conductivity and high liquid retention, and further, SiO _x particles expand and contract. Is preferable in that it has a property of easily maintaining contact with the particles.

Among the carbon materials exemplified above, a fibrous carbon material is particularly preferable for use when the composite with SiO _x is a granulated body. The fibrous carbon material has a thin thread shape and high flexibility so that it can follow the expansion and contraction of SiO _x that accompanies charging / discharging of the battery, and because of its large bulk density, it has a large amount of SiO _x particles. It is because it can have the following junction point. Examples of the fibrous carbon include polyacrylonitrile (PAN) -based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber, and carbon nanotube, and any of these may be used. The fibrous carbon material can be formed on the surface of the SiO _x particles by, for example, a vapor phase method.

When a composite of SiO _x and a carbon material is used for the negative electrode, the ratio of SiO _x and the carbon material is based on SiO _x : 100 parts by mass from the viewpoint of satisfactorily exerting the effect of the composite with the carbon material. The carbon material is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more. Further, in the composite, if the ratio of the carbon material to be combined with SiO _x is too large, it may lead to a decrease in the amount of SiO _x in the negative electrode mixture layer, and the effect of increasing the capacity may be reduced. SiO _x: relative to 100 parts by weight, the carbon material, and more preferably preferably not more than 50 parts by weight, more than 40 parts by weight.

The composite of the SiO _x and the carbon material can be obtained, for example, by the following method.

First, a manufacturing method in the case of combining SiO _x will be described. A dispersion liquid in which SiO _x is dispersed in a dispersion medium is prepared, and sprayed and dried to produce composite particles including a plurality of particles. For example, ethanol or the like can be used as the dispersion medium. It is appropriate to spray the dispersion liquid in an atmosphere of 50 to 300 ° C. In addition to the above method, similar composite particles can be produced also by a granulation method by a mechanical method using a vibration type or planetary type ball mill or rod mill.

In the case of producing a granulated body of SiO _x and a carbon material having a specific resistance value smaller than that of SiO _x , the carbon material is added to a dispersion in which SiO _x is dispersed in a dispersion medium, and the dispersion is The composite particles (granulated body) may be obtained by the same method as that used when combining SiO _x . Further, by granulation process according to the similar mechanical method, it is possible to produce a granular material of the SiO _x and the carbon material.

Next, when the surface of SiO _x particles (SiO _x composite particles or a granulated body of SiO _x and a carbon material) is coated with a carbon material to form a composite, for example, the SiO _x particles and the hydrocarbon-based material The gas is heated in the gas phase, and carbon generated by pyrolysis of the hydrocarbon-based gas is deposited on the surface of the particles. As described above, according to the vapor deposition (CVD) method, the hydrocarbon-based gas spreads to every corner of the composite particle, and the surface of the particle and the pores in the surface are thin and contain a conductive carbon material. Since a uniform film (carbon material coating layer) can be formed, the SiO _x particles can be imparted with good conductivity with a small amount of carbon material.

In the production of SiO _x coated with a carbon material, the processing temperature (atmosphere temperature) of the vapor deposition (CVD) method varies depending on the type of hydrocarbon gas, but usually 600 to 1200 ° C. is appropriate. Among these, the temperature is preferably 700 ° C. or higher, and more preferably 800 ° C. or higher. This is because the higher the treatment temperature, the fewer impurities remain and the formation of a coating layer containing carbon having high conductivity.

As the liquid source of the hydrocarbon-based gas, toluene, benzene, xylene, mesitylene and the like can be used, but toluene that is easy to handle is particularly preferable. A hydrocarbon-based gas can be obtained by vaporizing them (for example, bubbling with nitrogen gas). Moreover, methane gas, acetylene gas, etc. can also be used.

In addition, after the surface of SiO _x particles (SiO _x composite particles or a granulated body of SiO _x and a carbon material) is covered with a carbon material by a vapor deposition (CVD) method, a petroleum-based pitch or a coal-based pitch is used. At least one organic compound selected from the group consisting of a thermosetting resin and a condensate of naphthalene sulfonate and aldehydes is attached to a coating layer containing a carbon material, and then the organic compound is attached. The obtained particles may be fired.

Specifically, a dispersion liquid in which a SiO _x particle (SiO _x composite particle or a granulated body of SiO _x and a carbon material) coated with a carbon material and the organic compound are dispersed in a dispersion medium is prepared, The dispersion is sprayed and dried to form particles coated with the organic compound, and the particles coated with the organic compound are fired.

Isotropic pitch can be used as the pitch, and phenol resin, furan resin, furfural resin, or the like can be used as the thermosetting resin. As the condensate of naphthalene sulfonate and aldehydes, naphthalene sulfonic acid formaldehyde condensate can be used.

As a dispersion medium for dispersing the SiO _x particles coated with the carbon material and the organic compound, for example, water or alcohols (ethanol or the like) can be used. It is appropriate to spray the dispersion liquid in an atmosphere of 50 to 300 ° C. The firing temperature is usually 600 to 1200 ° C., preferably 700 ° C. or higher, and more preferably 800 ° C. or higher. This is because the higher the treatment temperature, the fewer impurities remain and the formation of a coating layer containing a high-quality carbon material with high conductivity. However, the processing temperature needs to be lower than the melting point of SiO _x .

As the negative electrode active material, it is preferable to use a graphitic carbon material together with SiO _x . By reducing the ratio of SiO _x in the negative electrode active material using a graphitic carbon material, while suppressing the decrease in the effect of increasing the capacity due to the reduction in SiO _x as much as possible, the negative electrode accompanying charging / discharging of the battery ( It is possible to suppress a change in volume of the negative electrode mixture layer) and suppress a decrease in battery characteristics that may be caused by the volume change.

Also, the graphitic carbon material used in combination with SiO _x as the anode active material, it can also be used as a carbon material according to the complex of the SiO _x and the carbon material. Graphite carbon material, like carbon black, has high electrical conductivity and high liquid retention, and even when SiO _x particles expand and contract, it is easy to maintain contact with the particles. Since it has properties, it can be preferably used for forming a complex with SiO _x .

Examples of the graphitic carbon material used as the negative electrode active material include artificial graphite obtained by graphitizing natural graphite such as scaly graphite; graphitizable carbon such as pyrolytic carbons, MCMB, and carbon fiber at 2800 ° C. or higher. And so on.

Wherein the negative electrode, from the viewpoint of satisfactorily ensuring the effect of the high capacity by using a SiO _x, the content of the complex of the SiO _x and the carbon material in the anode active material is more than 0.01 wt% It is preferable that it is 1 mass% or more, and it is more preferable that it is 3 mass% or more. Further, from the viewpoint of better avoiding the problem due to the volume change of SiO _x accompanying charge / discharge, the content of the composite of SiO _x and carbon material in the negative electrode active material is preferably 20% by mass or less. More preferably, it is 15 mass% or less.

<Binder of negative electrode mixture layer>
Examples of the binder used in the negative electrode mixture layer include starch, polyvinyl alcohol, polyacrylic acid, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose, diacetylcellulose, and other polysaccharides and modified products thereof; polyvinylchloride, Thermoplastic resins such as polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyamide, and their modified products; polyimide; ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene Rubber (SBR), butadiene rubber, polybutadiene, fluororubber, polyethylene oxide and other polymers having rubbery elasticity, and modified products thereof. May be used alone or two or more al.

<Conductive aid for negative electrode mixture layer>
A conductive material may be further added to the negative electrode mixture layer as a conductive aid. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery. For example, carbon black (thermal black, furnace black, channel black, ketjen black, acetylene black, etc.), carbon It is possible to use one or more materials such as fiber, metal powder (powder of copper, nickel, aluminum, silver, etc.), metal fiber, polyphenylene derivative (described in JP-A-59-20971). it can. Among these, carbon black is preferably used, and ketjen black and acetylene black are more preferable.

The particle diameter of the carbon fiber used as the conductive additive is, for example, an average particle diameter determined by the same method as the method for determining the average fiber length described above, and is preferably 0.01 μm or more, and 0.02 μm or more. More preferably, it is preferably 10 μm or less, and more preferably 5 μm or less.

<Negative electrode current collector>
As the current collector used for the negative electrode, a foil made of copper or nickel, a punching metal, a net, an expanded metal, or the like can be used, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is 5 μm in order to ensure mechanical strength. Is desirable.

<Method for producing negative electrode>
The negative electrode is, for example, a paste-like or slurry-like negative electrode in which the above-described negative electrode active material and binder, and further, if necessary, a conductive additive are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) or water. A step of preparing a mixture-containing composition (however, the binder may be dissolved in a solvent), applying this to one or both sides of the current collector, drying, and then subjecting to a calender treatment if necessary It is manufactured through. The manufacturing method of a negative electrode is not necessarily restricted to the said manufacturing method, It can also manufacture with another manufacturing method.

<Negative electrode mixture layer>
In the negative electrode mixture layer, the total amount of the negative electrode active material is preferably 80 to 99% by mass and the amount of the binder is preferably 1 to 20% by mass. In addition, when a conductive material is separately used as the conductive auxiliary agent, these conductive materials in the negative electrode mixture layer are used in a range in which the total amount of the negative electrode active material and the binder amount satisfy the above-described preferable values. It is preferable. The thickness of the negative electrode mixture layer is preferably 10 to 100 μm, for example.

[Non-aqueous electrolyte]
The nonaqueous electrolytic solution according to the first lithium secondary battery of the present invention is a solution in which a lithium salt is dissolved in an organic solvent, and contains a phosphonoacetate compound represented by the following general formula (1). Is used.

Examples of the phosphonoacetate compound include the following compounds.

<Compound with n = 0 in the general formula (1)>
Trimethylphosphonoformate, methyldiethylphosphonoformate, methyldipropylphosphonoformate, methyldibutylphosphonoformate, triethylphosphonoformate, ethyldimethylphosphonoformate, ethyldipropylphosphonoformate, ethyl Dibutylphosphonoformate, tripropylphosphonoformate, propyldimethylphosphonoformate, propyldiethylphosphonoformate, propyldibutylphosphonoformate, tributylphosphonoformate, butyldimethylphosphonoformate, butyldiethylphospho Noformate, butyldipropylphosphonoformate, methylbis (2,2,2-trifluoroethyl) phosphonoformate, ethylbis (2,2,2-to Trifluoroethyl) phosphonoacetate formate, propyl bis (2,2,2-trifluoroethyl) phosphonoacetate formate, butyl bis (2,2,2-trifluoroethyl) phosphonoacetate formate and the like.

<Compound with n = 1 in the general formula (1)>
Trimethylphosphonoacetate, methyldiethylphosphonoacetate, methyldipropylphosphonoacetate, methyldibutylphosphonoacetate, triethylphosphonoacetate, ethyldimethylphosphonoacetate, ethyldipropylphosphonoacetate, ethyldibutylphosphonoacetate, tripropyl Phosphonoacetate, propyldimethylphosphonoacetate, propyldiethylphosphonoacetate, propyldibutylphosphonoacetate, tributylphosphonoacetate, butyldimethylphosphonoacetate, butyldiethylphosphonoacetate, butyldipropylphosphonoacetate, methylbis (2, 2,2-trifluoroethyl) phosphonoacetate, ethylbis (2,2,2-trifluoroethyl) phosphonoacetate , Propyl bis (2,2,2-trifluoroethyl) phosphonoacetate, butyl bis (2,2,2-trifluoroethyl) phosphonoacetate, and the like.

<Compound with n = 2 in the general formula (1)>
Trimethyl-3-phosphonopropionate, methyldiethyl-3-phosphonopropionate, methyldipropyl-3-phosphonopropionate, methyldibutyl-3-phosphonopropionate, triethyl-3-phosphonopro Pionate, ethyldimethyl-3-phosphonopropionate, ethyldipropyl-3-phosphonopropionate, ethyldibutyl-3-phosphonopropionate, tripropyl-3-phosphonopropionate, propyldimethyl- 3-phosphonopropionate, propyldiethyl-3-phosphonopropionate, propyldibutyl 3-phosphonopropionate, tributyl-3-phosphonopropionate, butyldimethyl-3-phosphonopropionate, Butyldiethyl-3-phosphonopropionate, butyldipropyl 3-phosphonopropionate, methylbis (2,2,2-trifluoroethyl) -3-phosphonopropionate, ethylbis (2,2,2-trifluoroethyl) -3-phosphonopropionate, Propylbis (2,2,2-trifluoroethyl) -3-phosphonopropionate, butylbis (2,2,2-trifluoroethyl) -3-phosphonopropionate, and the like.

<Compound with n = 3 in the general formula (1)>
Trimethyl-4-phosphonobutyrate, methyldiethyl-4-phosphonobutyrate, methyldipropyl-4-phosphonobutyrate, methyldibutyl-4-phosphonobutyrate, triethyl-4-phosphonobutyrate, ethyldimethyl -4-phosphonobutyrate, ethyldipropyl-4-phosphonobutyrate, ethyldibutyl-4-phosphonobutyrate, tripropyl-4-phosphonobutyrate, propyldimethyl-4-phosphonobutyrate, propyldiethyl -4-phosphonobutyrate, propyldibutyl 4-phosphonobutyrate, tributyl-4-phosphonobutyrate, butyldimethyl-4-phosphonobutyrate, butyldiethyl-4-phosphonobutyrate, butyldipropyl- 4-phosphonobutyrate and the like.

Of the above-mentioned phosphonoacetate compounds, triethylphosphonoacetate is most preferable.

Usually, non-aqueous electrolytes used for batteries include, for example, vinylene carbonate, fluoroethylene carbonate, anhydride, sulfonate ester, dinitrile, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, t -Additives (including their derivatives) such as butylbenzene and succinonitrile as appropriate, for example, charge / discharge cycle characteristics, high-temperature blistering suppression, overcharge prevention, and other safety characteristics Additives corresponding to were added.

As described above, when a lithium-containing composite oxide containing Ni is used as the positive electrode active material, the swelling of the battery under high temperature storage becomes larger than when only LiCoO ₂ is used as the positive electrode active material. This is because Ni is unstable at high temperatures, and therefore, the reactivity between Ni in a highly charged state and a solvent or additive is high, and it is considered that it is likely to become an active site. For this reason, excessive reaction between the Ni active sites and the solvent or additive generates excessive gas, causing the battery to swell, or the reaction product accumulates at the Ni interface to increase the resistance of the battery. The subsequent capacity recovery rate is greatly reduced. Therefore, as a countermeasure, it has been indispensable to add additives such as 1,3-propane sultone and succinonitrile to suppress the above excess reaction.

However, with conventional additives, the high-temperature storage property is improved and the swelling of the battery can be suppressed, but the charge / discharge cycle characteristics often deteriorate. This is because even when the addition amount is small, conventional additives such as 1,3-propane sultone and succinonitrile react with other than the active sites of the positive electrode active material, resulting in the deposition of reaction products, resulting in a decrease in capacity. This is thought to be due to an increase in resistance.

The inventors use a lithium-containing composite oxide containing Ni as the positive electrode active material, and when the phosphonoacetate compound is contained in the nonaqueous electrolytic solution, the charge / discharge cycle characteristics are not deteriorated. In addition, the inventors have found that the high temperature storage property is improved and the swelling of the battery is suppressed. The reason for this is not clear, but it is presumed that the phosphonoacetate compound mainly coats the active sites of Ni that react with the electrolyte and becomes the starting point of gas generation, thereby inactivating the Ni active sites. Is done.

Furthermore, in the negative electrode, a film is formed by the phosphonoacetate compound at the first charge / discharge after the battery is manufactured. However, the film by the phosphonoacetate compound has high thermal stability and low resistance. However, it is considered that the coating is hardly decomposed and the increase in resistance is suppressed.

In the electrolyte solution of the first lithium secondary battery of the present invention, these phosphonoacetate compounds are contained in a non-aqueous electrolyte solution (a non-aqueous electrolyte solution used for battery assembly, the same applies hereinafter). 5 mass% or more is contained, Preferably 1 mass% or more is contained. If the content is too small, the effect of suppressing gas generation is recognized, but the Ni active sites are not covered and the swelling of the battery cannot be suppressed. However, if there is too much phosphonoacetate compound in the electrolytic solution, it causes a reaction other than the active site of the positive electrode material, and increases the resistance like other additives, so the content is preferably 20% by mass or less, preferably Is 10% by mass or less, more preferably 5% by mass or less.

Conventional additives such as vinylene carbonate, fluoroethylene carbonate, anhydride, sulfonic acid ester, dinitrile, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, t-butylbenzene described above (these (Including derivatives) may be used in combination as appropriate depending on the desired battery characteristics.

In particular, the electrolytic solution of the first lithium secondary battery of the present invention preferably further contains, for example, a halogen-substituted cyclic carbonate such as fluoroethylene carbonate (FEC) and vinylene carbonate (VC).

As the halogen-substituted cyclic carbonate, a compound represented by the following general formula (4) can be used.

In the general formula (4), R ⁴ , R ⁵ , R ⁶ and R ⁷ are hydrogen, a halogen element or an alkyl group having 1 to 10 carbon atoms, and part or all of the hydrogen in the alkyl group is a halogen element. may be ^substituted, at least one of R ^4, R 5, ^{R 6} and ^{R 7} are ^halogen, R ^4, R 5, ^{R 6} and ^{R 7,} which may be different from each Two or more may be the same. When R ⁴ , R ⁵ , R ⁶ and R ⁷ are alkyl groups, the smaller the number of carbon atoms, the better. As the halogen element, fluorine is particularly preferable.

Among such cyclic carbonates substituted with a halogen element, 4-fluoro-1,3-dioxolan-2-one (FEC) is particularly preferable.

The halogen-substituted cyclic carbonate and VC content in the non-aqueous electrolyte used for the battery are halogen-substituted cyclic carbonate and halogen-substituted cyclic carbonate from the viewpoint of ensuring the above-mentioned effects by VC. The content of is 1% by mass or more, preferably 1.5% by mass or more, and the content of VC is 1% by mass or more, preferably 1.5% by mass or more. . On the other hand, when the halogen-substituted cyclic carbonate weight and the amount of VC nonaqueous electrolytic solution is too large, the SiO _x is contained in the anode active material, it may decrease the activity of SiO _x, during film formation There is a possibility that excessive gas is generated and causes the battery outer body to swell. Therefore, in the nonaqueous electrolytic solution used for the battery, the content of the halogen-substituted cyclic carbonate is 10% by mass or less, preferably 5% by mass or less, and the VC content is 10% by mass. % Or less, and preferably 5% by mass or less.

The lithium salt used in the non-aqueous electrolyte is not particularly limited as long as it dissociates in a solvent to form lithium ions and does not easily cause a side reaction such as decomposition in a voltage range used as a battery. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ and other inorganic lithium salts, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (2 ≦ n ≦ 7), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] or the like is used. be able to.

The concentration of this lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / L, more preferably 0.9 to 1.25 mol / L.

The organic solvent used in the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause side reactions such as decomposition in the voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; dimethoxyethane, Chain ethers such as diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; ethylene Sulfites such as glycol sulfite; and the like. These may be used in combination of two or more. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high electrical conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate.

[Separator]
The separator according to the first lithium secondary battery of the present invention has a property that the pores are blocked at 80 ° C. or higher (more preferably 100 ° C. or higher) and 170 ° C. or lower (more preferably 150 ° C. or lower) (ie, shutdown function). ), And separators used in ordinary lithium secondary batteries, for example, microporous membranes made of polyolefin such as polyethylene (PE) and polypropylene (PP) can be used. The microporous film constituting the separator may be, for example, one using only PE or one using PP, or a laminate of a PE microporous film and a PP microporous film. There may be.

The separator according to the first lithium secondary battery of the present invention has a porous layer (I) mainly composed of a resin having a melting point of 140 ° C. or lower, a resin that does not melt at a temperature of 150 ° C. or lower, or a heat resistant temperature of 150 ° C. It is preferable to use a laminated separator having a porous layer (II) mainly containing the above inorganic filler. Here, the “melting point” means the melting temperature measured using a differential scanning calorimeter (DSC) in accordance with the provisions of JIS K 7121. In addition, “does not melt at a temperature of 150 ° C. or lower” means that the melting temperature measured using DSC exceeds 150 ° C. in accordance with the provisions of JIS K 7121. This means that the melting behavior is not exhibited at the temperature. Furthermore, “the heat resistant temperature is 150 ° C. or higher” means that deformation such as softening is not observed at least at 150 ° C.

The porous layer (I) according to the laminated separator is mainly for ensuring a shutdown function, and the melting point of the resin, which is a component in which the lithium secondary battery is the main component of the porous layer (I) When the temperature reaches the value, the resin related to the porous layer (I) melts and closes the pores of the separator, thereby causing a shutdown that suppresses the progress of the electrochemical reaction.

Examples of the resin having a melting point of 140 ° C. or lower, which is the main component of the porous layer (I), include PE, and the form thereof is a substrate such as a microporous film used in the above-described lithium secondary battery or a nonwoven fabric. And a dispersion obtained by applying a dispersion containing PE particles and drying. Here, in all the constituent components of the porous layer (I), the volume of the resin having a main melting point of 140 ° C. or less is 50% by volume or more, and more preferably 70% by volume or more. For example, when the porous layer (I) is formed of the microporous film of PE, the volume of the resin having a melting point of 140 ° C. or lower is 100% by volume.

The porous layer (II) according to the multilayer separator has a function of preventing a short circuit due to direct contact between the positive electrode and the negative electrode even when the internal temperature of the lithium secondary battery is increased. The function is secured by a resin that does not melt at a temperature of ℃ or less or an inorganic filler with a heat resistant temperature of 150 ℃ or more. That is, when the battery becomes high temperature, even if the porous layer (I) shrinks, the porous layer (II) which does not easily shrink can directly generate positive and negative electrodes that can be generated when the separator is thermally contracted. It is possible to prevent a short circuit due to the contact. Moreover, since this heat-resistant porous layer (II) acts as a skeleton of the separator, the thermal contraction of the porous layer (I), that is, the thermal contraction of the entire separator itself can be suppressed.

When the porous layer (II) is formed mainly of a resin having a melting point of 150 ° C. or higher, for example, a microporous film formed of a resin that does not melt at a temperature of 150 ° C. or lower (for example, the above-mentioned PP micro battery cell The porous layer (I) is laminated on the porous layer (I), or a dispersion liquid containing resin particles that do not melt at a temperature of 150 ° C. or lower is applied to the porous layer (I) and dried to form a porous layer ( Examples thereof include a coating lamination type form in which the porous layer (II) is formed on the surface of I).

Resins that do not melt at temperatures below 150 ° C include PP; crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, crosslinked styrene-divinylbenzene copolymer, polyimide, melamine resin, phenolic resin, benzoguanamine-formaldehyde condensation And various crosslinked polymer fine particles; polysulfone; polyether sulfone; polyphenylene sulfide; polytetrafluoroethylene; polyacrylonitrile; aramid; polyacetal and the like.

When using resin particles that do not melt at a temperature of 150 ° C. or lower, the average particle size is, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, It is preferably 10 μm or less, and more preferably 2 μm or less. As described above, the average particle size of the various particles referred to in the present specification is measured by, for example, using a laser scattering particle size distribution analyzer “LA-920” manufactured by Horiba, Ltd., and dispersing these fine particles in a medium that does not dissolve the resin. The average particle diameter D is 50%.

When the porous layer (II) is mainly formed of an inorganic filler having a heat resistant temperature of 150 ° C. or higher, for example, a dispersion containing an inorganic filler having a heat resistant temperature of 150 ° C. or higher is applied to the porous layer (I). Examples of the coating-laminated type in which the porous layer (II) is formed by drying.

The inorganic filler related to the porous layer (II) has a heat resistant temperature of 150 ° C. or higher, is stable to the non-aqueous electrolyte of the battery, and is electrochemically stable to be hardly oxidized or reduced in the battery operating voltage range. However, fine particles are preferable from the viewpoint of dispersion, and alumina, silica, and boehmite are preferable. Alumina, silica, and boehmite have high oxidation resistance, and the particle size and shape can be adjusted to the desired numerical values, making it easy to control the porosity of the porous layer (II) with high accuracy. It becomes. As the inorganic filler having a heat resistant temperature of 150 ° C. or higher, for example, one of the above-mentioned examples may be used alone, or two or more may be used in combination. Further, an inorganic filler having a heat resistant temperature of 150 ° C. or higher may be used in combination with a resin that does not melt at a temperature of 150 ° C. or lower.

There is no restriction | limiting in particular about the shape of the inorganic filler whose heat resistant temperature which concerns on porous layer (II) is 150 degreeC or more, A substantially spherical shape (a true spherical shape is included), a substantially ellipsoid shape (an ellipsoid shape is included), a board Various shapes such as shapes can be used.

Further, the average particle diameter of the inorganic filler having a heat resistant temperature of 150 ° C. or higher related to the porous layer (II) is preferably 0.3 μm or more because the ion permeability is lowered if it is too small. More preferably, it is 5 μm or more. In addition, if the inorganic filler having a heat resistant temperature of 150 ° C. or higher is too large, the electrical characteristics are likely to be deteriorated. Therefore, the average particle diameter is preferably 5 μm or less, and more preferably 2 μm or less.

In the porous layer (II), the resin that does not melt at a temperature of 150 ° C. or lower and the inorganic filler having a heat resistant temperature of 150 ° C. or higher are mainly contained in the porous layer (II). Amount in (II) [when the porous layer (II) contains only one of a resin that does not melt at a temperature of 150 ° C. or less and an inorganic filler that has a heat resistant temperature of 150 ° C. or more, is the amount, If both are included, the total amount. The same applies hereinafter in the porous layer (II) of the resin that does not melt at a temperature of 150 ° C. or lower and the inorganic filler having a heat resistant temperature of 150 ° C. or higher. ] Is 50% by volume or more in the total volume of the constituent components of the porous layer (II), preferably 70% by volume or more, more preferably 80% by volume or more, and 90% by volume or more. More preferably it is. By making the heat-resistant material in the porous layer (II) high as described above, even when the lithium secondary battery becomes high temperature, it is possible to satisfactorily suppress the thermal contraction of the entire separator, Generation | occurrence | production of the short circuit by the direct contact of a positive electrode and a negative electrode can be suppressed more favorably.

As will be described later, since it is preferable that the porous layer (II) also contains an organic binder, in the porous layer (II) of a resin that does not melt at a temperature of 150 ° C. or less and an inorganic filler having a heat resistant temperature of 150 ° C. or more. The amount is preferably 99.5% by volume or less in the total volume of the constituent components of the porous layer (II).

In the porous layer (II), a resin that does not melt at a temperature of 150 ° C. or less or an inorganic filler having a heat resistant temperature of 150 ° C. or higher is bound, or the porous layer (II) and the porous layer (I) For integration or the like, it is preferable to contain an organic binder. Organic binders include ethylene-vinyl acetate copolymers (EVA, structural units derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylic acid copolymers such as ethylene-ethyl acrylate copolymers, fluorine-based binders Examples include rubber, SBR, CMC, hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), cross-linked acrylic resin, polyurethane, and epoxy resin. A heat-resistant binder having a heat-resistant temperature is preferably used. As the organic binder, those exemplified above may be used singly or in combination of two or more.

Among the organic binders exemplified above, highly flexible binders such as EVA, ethylene-acrylic acid copolymer, fluorine rubber, and SBR are preferable. Specific examples of such highly flexible organic binders include EVA “Evaflex Series” from Mitsui DuPont Polychemical Co., Ltd., EVA from Nippon Unicar Co., Ltd., and “Evaflex” ethylene-acrylic acid copolymer from Mitsui DuPont Polychemical Co., Ltd. -EEA series ", EEA of Nihon Unicar, Daikin Industries, Ltd.'s fluoro rubber" Daiel Latex Series ", JSR's SBR" TRD-2001 ", Zeon's SBR" BM-400B ".

When the organic binder is used for the porous layer (II), it may be used in the form of an emulsion dissolved or dispersed in a solvent of a composition for forming the porous layer (II) described later.

The coating-laminated separator is, for example, a composition for forming a porous layer (II) containing a resin particle that does not melt at a temperature of 150 ° C. or lower, an inorganic filler having a heat resistant temperature of 150 ° C. or higher (liquid such as slurry). The composition etc.) can be applied to the surface of the microporous membrane for constituting the porous layer (I) and dried at a predetermined temperature to form the porous layer (II).

The composition for forming the porous layer (II) contains resin particles that do not melt at a temperature of 150 ° C. or lower and / or an inorganic filler having a heat resistant temperature of 150 ° C. or higher, and an organic binder as necessary. Is dispersed in a solvent (including a dispersion medium; the same shall apply hereinafter). The organic binder can be dissolved in a solvent. The solvent used in the composition for forming the porous layer (II) can uniformly disperse resin particles and inorganic filler that do not melt at a temperature of 150 ° C. or lower, and can dissolve or disperse the organic binder uniformly. Common organic solvents such as aromatic hydrocarbons such as toluene; furans such as tetrahydrofuran; ketones such as methyl ethyl ketone and methyl isobutyl ketone; are preferably used. For the purpose of controlling the interfacial tension, alcohols (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added to these solvents. In addition, when the organic binder is water-soluble or used as an emulsion, water may be used as a solvent. In this case, alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) are appropriately added. It is also possible to control the interfacial tension.

The composition for forming the porous layer (II) has a solid content containing, for example, a resin particle that does not melt at a temperature of 150 ° C. or lower and / or an inorganic filler having a heat resistant temperature of 150 ° C. or higher, and an organic binder. It is preferable to set it to 80 mass%.

In the laminated separator, the porous layer (I) and the porous layer (II) do not have to be one each, and a plurality of layers may be present in the separator. For example, the porous layer (I) may be arranged on both sides of the porous layer (II), or the porous layer (II) may be arranged on both sides of the porous layer (I). However, increasing the number of layers may increase the thickness of the separator and increase the internal resistance of the battery or decrease the energy density. Therefore, it is not preferable to increase the number of layers. The total number of layers of the porous layer (I) and the porous layer (II) is preferably 5 or less.

The thickness of the separator (the separator made of a polyolefin microporous film or the laminated separator) according to the first lithium secondary battery of the present invention is preferably 10 to 30 μm, for example.

In the laminated separator, the thickness of the porous layer (II) [when the separator has a plurality of porous layers (II), the total thickness thereof. same as below. ] Is preferably 3 μm or more from the viewpoint of more effectively exerting the above-described functions of the porous layer (II). However, if the porous layer (II) is too thick, the energy density of the battery may be lowered. Therefore, the thickness of the porous layer (II) is preferably 8 μm or less.

Furthermore, in the laminated separator, the thickness of the porous layer (I) [when the separator has a plurality of porous layers (I), the total thickness thereof. same as below. ] Is preferably 6 μm or more, more preferably 10 μm or more, from the viewpoint of more effectively exerting the above-described action (particularly the shutdown action) due to the use of the porous layer (I). However, if the porous layer (I) is too thick, there is a possibility that the energy density of the battery may be lowered. In addition, the force that the porous layer (I) tends to shrink is increased, and the heat of the entire separator is increased. There is a possibility that the action of suppressing the shrinkage becomes small. Therefore, the thickness of the porous layer (I) is preferably 25 μm or less, more preferably 20 μm or less, and still more preferably 14 μm or less.

The porosity of the separator as a whole is preferably 30% or more in a dry state in order to ensure the amount of electrolyte retained and to improve ion permeability. On the other hand, from the viewpoint of securing separator strength and preventing internal short circuit, the separator porosity is preferably 70% or less in a dry state. The porosity of the separator: P (%) can be calculated by calculating the sum of each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following formula (5).

P = {1−m / (Σa _i ρ _i × t)} × 100 (5)
Here, in the above formula (5), a _i : ratio of component i expressed by mass%, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of the separator (g / cm ² ), t: thickness (cm) of the separator.

In the case of the multilayer separator, in the above formula (5), m is the mass per unit area (g / cm ² ) of the porous layer (I), and t is the thickness of the porous layer (I) ( cm), the porosity: P (%) of the porous layer (I) can also be obtained using the formula (5). The porosity of the porous layer (I) obtained by this method is preferably 30 to 70%.

Further, in the case of the laminated separator, in the formula (5), m is the mass per unit area (g / cm ² ) of the porous layer (II), and t is the thickness of the porous layer (II) ( cm), the porosity: P (%) of the porous layer (II) can also be obtained using the formula (5). The porosity of the porous layer (II) obtained by this method is preferably 20 to 60%.

The separator preferably has high mechanical strength. For example, the puncture strength is preferably 3N or more. For example, when SiO _x having a large volume change due to charge / discharge is used as the negative electrode active material, mechanical damage is also applied to the facing separator due to expansion / contraction of the entire negative electrode by repeating charge / discharge. If the piercing strength of the separator is 3N or more, good mechanical strength is ensured, and mechanical damage to the separator can be reduced.

Examples of the separator having a puncture strength of 3N or more include the above-described laminated separator, and in particular, an inorganic filler having a heat resistant temperature of 150 ° C. or higher in the porous layer (I) mainly composed of a resin having a melting point of 140 ° C. or lower. A separator in which a porous layer (II) containing as a main component is laminated is preferable. This is considered because the mechanical strength of the inorganic filler is high, so that the mechanical strength of the entire separator can be increased by supplementing the mechanical strength of the porous layer (I).

The piercing strength can be measured by the following method. A separator is fixed on a plate having a hole with a diameter of 2 inches so as not to be wrinkled or bent, and a semicircular metal pin having a tip diameter of 1.0 mm is lowered onto a measurement sample at a speed of 120 mm / min. Measure the force when the separator is perforated 5 times. And an average value is calculated | required about the measurement of 3 times except the maximum value and the minimum value among the said 5 times of measured values, and this is made into the piercing strength of a separator.

The positive electrode, the negative electrode, and the separator are formed in the form of a laminated electrode body in which a separator is interposed between the positive electrode and the negative electrode, or a wound electrode body in which the separator is wound in a spiral shape. It can be used for the first lithium secondary battery of the invention.

In the laminated electrode body and the wound electrode body, the laminated separator, particularly the porous layer (I) mainly composed of a resin having a melting point of 140 ° C. or lower, mainly composed of an inorganic filler having a heat resistant temperature of 150 ° C. or higher. When using the separator which laminated | stacked porous layer (II) included as, it is preferable to arrange | position so that porous layer (II) may face a positive electrode at least. In this case, since the porous layer (II) that includes an inorganic filler having a heat resistant temperature of 150 ° C. or more as a main component and more excellent in oxidation resistance faces the positive electrode, oxidation of the separator by the positive electrode can be better suppressed, It is also possible to improve the storage characteristics and charge / discharge cycle characteristics of the battery at high temperatures. Further, when an additive such as VC or cyclohexylbenzene is added to the non-aqueous electrolyte, a film is formed on the positive electrode side to clog the pores of the separator, which may cause deterioration of battery characteristics. Therefore, an effect of suppressing clogging of pores can be expected by causing the relatively porous porous layer (II) to face the positive electrode.

[Battery form]
As a form of the 1st lithium secondary battery of this invention, the cylinder shape (square cylinder shape, cylindrical shape, etc.) etc. which used a steel can, an aluminum can, etc. as an exterior can are mentioned. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

The first lithium secondary battery of the present invention can be used in the same applications as various applications to which conventionally known lithium secondary batteries are applied.

Hereinafter, the present invention will be described in detail based on examples of the first embodiment. However, the following examples do not limit the present invention.

Example 1-1
<Synthesis of first lithium-containing composite oxide>
Aqueous ammonia whose pH was adjusted to about 12 by adding sodium hydroxide was placed in a reaction vessel, and while vigorously stirring, nickel sulfate, cobalt sulfate and manganese sulfate were each added to 2.4 mol / dm ^3. , 0.8 mol ^/ dm 3, a mixed aqueous solution containing a concentration of 0.8 mol / dm ^3, and aqueous ammonia 25% strength by weight, respectively, 23cm ³ / min at a rate of 6.6 cm ³ / min, The solution was added dropwise using a metering pump to synthesize a coprecipitation compound of Ni, Co, and Mn (spherical coprecipitation compound). At this time, the temperature of the reaction solution is maintained at 50 ° C., and a 6.4 mol / dm ³ concentration sodium hydroxide aqueous solution is simultaneously added so that the pH of the reaction solution is maintained around 12. In order to react under an active atmosphere, nitrogen gas was bubbled at a flow rate of 1 dm ³ / min.

The coprecipitated compound was washed with water, filtered and dried to obtain a hydroxide containing Ni, Co and Mn in a molar ratio of 6: 2: 2. 0.196 mol of this hydroxide and 0.204 mol of LiOH.H ₂ O were dispersed in ethanol to form a slurry, and then mixed with a planetary ball mill for 40 minutes and dried at room temperature to obtain a mixture. . Next, the mixture is put in an alumina crucible, heated to 600 ° C. in a dry air flow of 2 dm ³ / min, kept at that temperature for 2 hours for preheating, further heated to 900 ° C. and heated to 12 ° C. The first lithium-containing composite oxide was synthesized by firing for a period of time.

The obtained first lithium-containing composite oxide was washed with water, then heat-treated in the atmosphere (oxygen concentration of about 20% by volume) at 850 ° C. for 12 hours, and then pulverized in a mortar to obtain a powder. The first lithium-containing composite oxide after pulverization was stored in a desiccator.

About the said 1st lithium containing complex oxide, the composition analysis was performed as follows using ICP method mentioned above. First, 0.2 g of the first lithium-containing composite oxide was sampled and placed in a 100 mL container. Thereafter, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were added in order and dissolved by heating. After cooling, the mixture was further diluted 25 times with pure water, and an ICP analyzer “ICP-757” manufactured by JARRELASH was used. The composition was analyzed by a calibration curve method. From the obtained results, the composition of the first lithium-containing composite oxide was derived and found to be a composition represented by Li _1.02 Ni _0.6 Co _0.2 Mn _0.2 O _2. did. At this time, the ratio of Ni to Li in the total amount of the first lithium-containing composite oxide (molar ratio: hereinafter abbreviated as Ni / Li) is Li = 1.02, Ni = 0.6, Ni / Li = 0.59 (the third decimal place was rounded off).

<Preparation of positive electrode>
The first lithium-containing composite oxide and the second lithium-containing composite oxide LiCoO ₂ are weighed to a mass ratio of 3: 7 and mixed for 30 minutes using a Henschel mixer. Got. 100 parts by mass of the obtained mixture as a positive electrode active material, 20 parts by mass of a solution obtained by dissolving PVDF and P (TFE-VDF) as binders in N-methyl-2-pyrrolidone (NMP), and a conductive auxiliary agent A 1.04 part by mass carbon fiber having an average fiber length of 100 nm and an average fiber diameter of 10 nm and 1.04 part by mass of graphite are kneaded using a biaxial kneader, and NMP is added to adjust the viscosity. Thus, a positive electrode mixture-containing paste was prepared. The amount of the PVDF and P (TFE-VDF) NMP solution used is such that the amount of the dissolved PVDF and P (TFE-VDF) is the mixture of the first lithium-containing composite oxide and LiCoO ₂ , PVDF and , P (TFE-VDF) and the conductive auxiliary agent (ie, the total amount of the positive electrode mixture layer) in 100% by mass, amounts to 2.34% by mass and 0.26% by mass, respectively. That is, the total amount of binder in the positive electrode mixture layer is 2.6% by mass, and the ratio of P (TFE-VDF) in the total of 100% by mass of P (TFE-VDF) and PVDF is 10% by mass.

The positive electrode mixture-containing paste is intermittently applied to both sides of an aluminum foil (positive electrode current collector) having a thickness of 15 μm while adjusting the thickness, dried, and then subjected to a calendering process so that the total thickness becomes 130 μm. The thickness of the positive electrode mixture layer was adjusted, and the positive electrode was produced by cutting so as to have a width of 54.5 mm. Further, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion. Here, when the density of the positive electrode mixture layer was measured by the above-described method, it was 3.80 g / cm ³ .

<Production of negative electrode>
A composite in which the surface of SiO _x having an average particle diameter D50% of 8 μm is coated with a carbon material (the amount of the carbon material in the composite is 10 mass%) and graphite having an average particle diameter D50% of 16 μm are combined with SiO _x. Mixture in which the amount of the composite whose surface is coated with a carbon material is 3.0% by mass: 98 parts by mass, and a 1% by mass CMC aqueous solution whose viscosity is adjusted to a range of 1500 to 5000 mPa · s : 100 parts by mass and SBR: 1.0 part by mass were mixed with ion-exchanged water having a specific resistance of 2.0 × 10 ⁵ Ωcm or more as a solvent to prepare an aqueous negative electrode mixture-containing paste.

The negative electrode mixture-containing paste is intermittently applied on both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm while adjusting the thickness, dried, and then calendered so that the total thickness becomes 110 μm. The thickness of the negative electrode mixture layer was adjusted, and the negative electrode was produced by cutting so as to have a width of 55.5 mm. Further, a tab was welded to the exposed portion of the copper foil of the negative electrode to form a lead portion.

<Preparation of separator>
Add 5 kg of ion-exchanged water and 0.5 kg of a dispersant (aqueous polycarboxylic acid ammonium salt, solid content concentration 40 mass%) to 5 kg of boehmite with an average particle diameter D50% of 1 μm, and have an internal volume of 20 L and 40 turns. A dispersion was prepared by pulverizing with a ball mill for 10 hours per minute. When a part of the treated dispersion was vacuum dried at 120 ° C. and observed with a scanning electron microscope (SEM), the shape of boehmite was almost plate-like.

To 500 g of the above dispersion, 0.5 g of xanthan gum as a thickener and 17 g of a resin binder dispersion (modified polybutyl acrylate, solid content 45% by mass) as a binder are added and stirred with a three-one motor for 3 hours to form a uniform slurry. [Slurry for forming porous layer (II), solid content ratio: 50% by mass] was prepared.

PE microporous separator for lithium secondary batteries [Porous layer (I): thickness 12 μm, porosity 40%, average pore diameter 0.08 μm, PE melting point 135 ° C.] on one side corona discharge treatment (discharge amount 40 W)・ Min / m ² ), a porous layer (II) forming slurry is applied to the treated surface by a micro gravure coater, and dried to form a porous layer (II) having a thickness of 4 μm. A separator was obtained. The mass per unit area of the porous layer (II) in this separator was 5.5 g / m ² , the boehmite volume content was 95% by volume, and the porosity was 45%.

<Battery assembly>
The positive electrode and the negative electrode obtained as described above were stacked with the separator porous layer (II) facing the positive electrode, and wound in a spiral shape to produce a wound electrode body. The obtained wound electrode body was crushed into a flat shape and placed in an aluminum alloy outer can having a thickness of 5 mm, a width of 42 mm, and a height of 61 mm. In addition, LiPF ₆ was dissolved to a concentration of 1.1 mol / L in a solvent in which ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed at a volume ratio of 1: 1: 1 as a non-aqueous electrolyte. A solution was prepared by adding 2.0% by mass of FEC, 1.0% by mass of VC, and further adding triethylphosphonoacetate to a concentration of 2.0% by mass. Next, the non-aqueous electrolyte was poured into the outer can.

After injecting the non-aqueous electrolyte, the outer can was sealed, and a lithium secondary battery having the structure shown in FIGS. 1A and 1B and the appearance shown in FIG. 2 was produced. This battery includes a cleavage vent for lowering the pressure when the internal pressure rises at the top of the can.

Here, the battery shown in FIGS. 1A, 1B and 2 will be described. FIG. 1A is a plan view of the lithium secondary battery of this example, and FIG. 1B is a cross-sectional view of FIG. 1A. As shown in FIG. 1B, the positive electrode 1 and the negative electrode 2 are spirally wound through the separator 3 as described above, and then pressed so as to be flattened to form a flat wound electrode body 6. A cylindrical outer can 4 is accommodated together with the electrolytic solution. However, in FIG. 1B, in order to avoid complication, a metal foil, an electrolytic solution, or the like as a current collector used in manufacturing the positive electrode 1 and the negative electrode 2 is not illustrated. Further, each layer of the separator 3 is not shown separately.

The outer can 4 is made of an aluminum alloy and constitutes an outer casing of the battery. The outer can 4 also serves as a positive electrode terminal. And the insulator 5 which consists of PE sheets is arrange | positioned at the bottom part of the armored can 4, and it connected to each one end of the positive electrode 1 and the negative electrode 2 from the winding electrode body 6 which consists of the positive electrode 1, the negative electrode 2, and the separator 3. The positive electrode lead body 7 and the negative electrode lead body 8 are drawn out. A stainless steel terminal 11 is attached to a sealing lid plate 9 made of aluminum alloy for sealing the opening of the outer can 4 via a PP insulating packing 10, and an insulator 12 is attached to the terminal 11. A stainless steel lead plate 13 is attached via

The cover plate 9 is inserted into the opening of the outer can 4 and welded to join the opening of the outer can 4 to seal the inside of the battery. In the battery shown in FIGS. 1A and 1B, a non-aqueous electrolyte inlet 14 is provided in the lid plate 9, and a sealing member is inserted into the non-aqueous electrolyte inlet 14, for example, with a laser. The battery is hermetically sealed by welding or the like, so that the battery is sealed. Accordingly, in the batteries of FIGS. 1A, 1B and 2, the non-aqueous electrolyte inlet 14 is actually a non-aqueous electrolyte inlet and a sealing member. An electrolyte inlet 14 is shown. Further, the lid plate 9 is provided with a cleavage vent 15 as a mechanism for discharging the internal gas to the outside when the temperature of the battery rises.

In the battery of this embodiment, the outer can 4 and the lid plate 9 function as a positive electrode terminal by directly welding the positive electrode lead body 7 to the lid plate 9, and the negative electrode lead body 8 is welded to the lead plate 13. The terminal 11 functions as a negative electrode terminal by conducting the negative electrode lead body 8 and the terminal 11 through the plate 13. However, depending on the material of the outer can 4, the sign may be reversed. is there.

FIG. 2 is a perspective view of the lithium secondary battery of this example, and this FIG. 2 is shown for the purpose of showing that the battery is a square battery. 1A and 1B schematically show the battery, and only specific members are shown among the members constituting the battery. Also in FIG. 1B, the inner peripheral side portion of the wound electrode body 6 is not cross-sectional.

Example 1-2
A lithium secondary battery was produced in the same manner as in Example 1-1 except that triethylphosphonoacetate was added to the nonaqueous electrolytic solution in an amount of 0.5% by mass.

(Example 1-3)
A lithium secondary battery was produced in the same manner as in Example 1-1, except that triethylphosphonoacetate was added to the nonaqueous electrolytic solution in an amount of 10.0% by mass.

(Example 1-4)
As a non-aqueous electrolyte, LiPF ₆ was dissolved at a concentration of 1.1 mol / L in a solvent in which ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed at a volume ratio of 1: 1: 1, and FEC and VC were respectively added. Examples were used except that a solution having a concentration of 2.0% by mass and 1.0% by mass and triethyl-3-phosphonopropionate added to an amount of 2.0% by mass was used. A lithium secondary battery was produced in the same manner as in 1-1.

(Example 1-5)
98 parts by weight of graphite having an average particle diameter D50% of 16 μm: 100 parts by weight of CMC aqueous solution having a concentration of 1% by weight adjusted to a viscosity of 1500 to 5000 mPa · s: 1.0 part by weight and SBR: 1.0 part by weight Except that ion-exchanged water having a specific resistance of 2.0 × 10 ⁵ Ωcm or more was mixed as a solvent to prepare an aqueous negative electrode mixture-containing paste, and a negative electrode was produced using this negative electrode mixture-containing paste. A lithium secondary battery was produced in the same manner as in Example 1-1.

(Example 1-6)
<Synthesis of first lithium-containing composite oxide>
Aqueous ammonia whose pH was adjusted to about 12 by adding sodium hydroxide was placed in a reaction vessel, and while vigorously stirring, nickel sulfate, manganese sulfate, and cobalt sulfate were each added to 3.76 mol / dm ^3. , 0.21 mol ^/ dm 3, a mixed aqueous solution containing a concentration of 0.21 mol / dm ^3, and aqueous ammonia 25% strength by weight, respectively, 23cm ³ / min at a rate of 6.6 cm ³ / min, The mixture was added dropwise using a metering pump to synthesize a coprecipitation compound of Ni, Mn, and Co (spherical coprecipitation compound). At this time, the temperature of the reaction solution is maintained at 50 ° C., and a 6.4 mol / dm ³ concentration sodium hydroxide aqueous solution is simultaneously added so that the pH of the reaction solution is maintained around 12. In order to react under an active atmosphere, nitrogen gas was bubbled at a flow rate of 1 dm ³ / min.

The coprecipitated compound was washed with water, filtered and dried to obtain a hydroxide containing Ni, Mn and Co in a molar ratio of 90: 5: 5. 0.196 mol of this hydroxide, 0.204 mol of LiOH.H ₂ O and 0.001 mol of TiO ₂ were dispersed in ethanol to form a slurry, and then mixed for 40 minutes with a planetary ball mill. And dried to obtain a mixture. Next, the mixture is put in an alumina crucible, heated to 600 ° C. in a dry air flow of 2 dm ³ / min, held at that temperature for 2 hours for preheating, further heated to 800 ° C. and heated to 12 ° C. The first lithium-containing composite oxide was synthesized by firing for a period of time. The obtained first lithium-containing composite oxide was pulverized into a powder in a mortar and then stored in a desiccator.

This first lithium-containing composite oxide, when carried out in the same manner as the composition analysis as in Example 1-1, from the results obtained, to derive the composition of the first lithium-containing composite oxide, Li _{1 0.02} Ni _0.895 Co _0.05 Mn _0.05 Ti _0.005 O ₂ was found to be the composition. At this time, from Li: Ni = 1.02: 0.895, Ni / Li = 0.88 (the third decimal place was rounded off).

The first lithium-containing composite oxide and the second lithium-containing composite oxide LiCoO ₂ were weighed to a mass ratio of 3: 7 and mixed for 30 minutes using a Henschel mixer. A lithium secondary battery was produced in the same manner as in Example 1-1 except that the obtained mixture was used as the positive electrode active material. Here, the density of the positive electrode mixture layer measured by the same method as in Example 1-1 was 3.65 g / cm ³ .

(Example 1-7)
By adjusting the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitation compound, a hydroxide containing Ni, Co and Mn at a molar ratio of 1: 1: 1 was synthesized and used. Except for the above, a first lithium-containing composite oxide was synthesized in the same manner as in Example 1-1. This first lithium-containing composite oxide, when carried out in the same manner as the composition analysis as in Example 1-1, from the results obtained, to derive the composition of the first lithium-containing composite oxide, Li _{1 0.02} Ni _0.3 Co _0.3 Mn _0.3 O ₂ was found to be the composition. At this time, from Li: Ni = 1.02: 0.3, Ni / Li = 0.29 (the third decimal place was rounded off).

The first lithium-containing composite oxide and the second lithium-containing composite oxide LiCoO ₂ were weighed to a mass ratio of 3: 7 and mixed for 30 minutes using a Henschel mixer. A lithium secondary battery was produced in the same manner as in Example 1-1 except that the obtained mixture was used as the positive electrode active material. Here, the density of the positive electrode mixture layer measured by the same method as in Example 1-1 was 3.60 g / cm ³ .

(Example 1-8)
Example 1 except that the thickness of the positive electrode mixture layer after calendering was the same as that of Example 1-1 and the density of the positive electrode mixture layer after calendering was 3.20 g / cm ^3. A lithium secondary battery was produced in the same manner as in Example-1.

(Comparative Example 1-1)
As in Example 1-1, only LiCoO ₂ was used as the positive electrode active material and the density of the positive electrode mixture layer after calendering was adjusted to 3.80 g / cm ^3. A battery was produced.

(Comparative Example 1-2)
As a non-aqueous electrolyte, LiPF ₆ was dissolved at a concentration of 1.1 mol / L in a solvent in which ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed at a volume ratio of 1: 1: 1, and FEC and VC were respectively added. Example 1-1 and Example 1-1 were used except that a solution having a concentration of 2.0 mass% and 1.0 mass in which 1,3-propane sultone was added in an amount of 2.0 mass% was used. Similarly, a lithium secondary battery was produced.

(Comparative Example 1-3)
As a positive electrode active material, only LiCoO ₂ was used, and a lithium secondary secondary was prepared in the same manner as in Comparative Example 1-2, except that the density of the positive electrode mixture layer after calendering was adjusted to 3.80 g / cm ^3. A battery was produced.

(Comparative Example 1-4)
A lithium secondary battery was produced in the same manner as in Example 1-1 except that the concentration of triethylphosphonoacetate in the nonaqueous electrolytic solution was changed to 0.3% by mass.

(Comparative Example 1-5)
Only LiCoO ₂ was used as the positive electrode active material, the thickness of the positive electrode mixture layer after calendering was made the same as in Example 1-1, and the density of the positive electrode mixture layer after calendering was 3.20 g / cm 3. ^A lithium secondary battery was produced in the same manner as in Example 1-1 except that the adjustment was made to be 3.

Composition of the first lithium-containing composite oxide used as the positive electrode active material of the lithium secondary batteries of Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-5, and Ni / Li (molar ratio) Table 1 shows the content of the phosphonoacetate compound in the nonaqueous electrolytic solution.

Further, with respect to the lithium secondary batteries produced in Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-5, the battery capacity, battery swelling, capacity recovery rate after high-temperature storage, and charge / discharge cycles were measured by the following methods. The characteristics (capacity retention rate) were evaluated. The results are shown in Table 2 together with the density of the positive electrode mixture layer.

<Battery capacity measurement>
After the initial charge and discharge of each battery, the battery is charged at room temperature (25 ° C.) with a constant current of 1 C until it reaches 4.2 V, and then charged with a constant voltage of 4.2 V (constant current-constant voltage charging (total charging time: 2.5 hours), 0.2 C constant current discharge (discharge end voltage: 3.0 V) was performed, and the obtained discharge capacity (mAh) was defined as the battery capacity. In Table 2, the value obtained by dividing the discharge capacity measured in each Example and each Comparative Example by the discharge capacity of Example 1-1 is shown as a relative battery capacity (%) expressed as a percentage.

<Battery swelling>
Each battery was charged under the same conditions as the battery capacity measurement after the initial charge / discharge. Measured in advance thickness T ₁ of the outer can of the battery after charging, then, stored for 24 hours in a constant temperature bath set at 85 ° C. the cells, taken out from the thermostatic bath, after standing 3 hours at room temperature , to measure the thickness T ₂ of the outer can again. Here, the thickness of the outer can means the thickness between the wide side surfaces of the outer can. The thickness of the outer can was measured in units of 1/100 mm using a caliper “CD-15CX” manufactured by Mitutoyo Co., Ltd. with the central part of the wide side face as the measurement target. The battery swelling was evaluated by the battery swelling ratio (%) obtained by the following formula.

Battery swelling rate (%) = 100 × (T ₂ −T ₁ ) / (T ₁ )

<Capacity recovery rate after high temperature storage>
Each battery was charged under the same conditions as the battery capacity measurement after the initial charge / discharge. Thereafter, a constant current discharge of 0.5 C (discharge end voltage: 3.0 V, hereinafter the discharge end voltage is the same) was performed, and the obtained discharge capacity (mAh) was set to 0.5 C capacity before the storage test. Then, after charging under the same conditions as the battery capacity measurement, the battery was stored in a thermostat set at 85 ° C. for 24 hours, taken out from the thermostat and left at room temperature for 3 hours, and then a constant current discharge of 0.5 C. Went. Subsequently, after charging under the same conditions as the battery capacity measurement, 0.5 C constant current discharge was performed, and the obtained discharge capacity (mAh) was set to 0.5 C capacity after the storage test. From these results, the capacity recovery rate at 0.5 C capacity after the storage test with respect to 0.5 C capacity before the storage test was determined by the following formula.

Capacity recovery rate (%) = 100 × {(0.5C capacity after storage test) / (0.5C capacity before storage test)}

<Charge / discharge cycle characteristics>
After charging and discharging each battery for the first time, charging and discharging were repeated 500 cycles with a series of operations of charging and discharging under the same conditions as in the battery capacity measurement as one cycle, and then charging under the same conditions as in the battery capacity measurement was performed again. After that, 1C constant current discharge (discharge end voltage: 3.0V) was performed, 1C discharge capacity (mAh) was measured, and this 1C discharge capacity was divided by the 0.2C discharge capacity obtained by the battery capacity measurement. The value was expressed as a percentage and used as a capacity maintenance rate (%).

From Tables 1 and 2, the first lithium-containing composite oxide containing Li and Ni and having a molar ratio of Ni to Li in the range of 0.05 to 1.05 is used as the positive electrode active material. A lithium secondary battery using a non-aqueous electrolyte containing 0.5 to 20% by mass of a noacetate compound has a high capacity, a small battery swelling after high-temperature storage, a high capacity recovery rate, and charge / discharge. It can be seen that the cycle characteristics are also good.

Next, the present invention will be described in detail based on another example of the first embodiment. However, the following examples do not limit the present invention.

<Synthesis of first lithium-containing composite oxide A containing nickel>
Aqueous ammonia whose pH was adjusted to about 12 by adding sodium hydroxide was placed in a reaction vessel, and while vigorously stirring, nickel sulfate, cobalt sulfate and manganese sulfate were each added to 2.4 mol / dm ^3. , 0.8 mol ^/ dm 3, a mixed aqueous solution containing a concentration of 0.8 mol / dm ^3, and aqueous ammonia 25% strength by weight, respectively, 23cm ³ / min at a rate of 6.6 cm ³ / min, The solution was added dropwise using a metering pump to synthesize a coprecipitation compound of Ni, Co, and Mn (spherical coprecipitation compound). At this time, the temperature of the reaction solution is maintained at 50 ° C., and a 6.4 mol / dm ³ concentration sodium hydroxide aqueous solution is simultaneously added so that the pH of the reaction solution is maintained around 12. In order to react under an active atmosphere, nitrogen gas was bubbled at a flow rate of 1 dm ³ / min.

The coprecipitated compound was washed with water, filtered and dried to obtain a hydroxide containing Ni, Co and Mn in a molar ratio of 6: 2: 2. 0.196 mol of this hydroxide and 0.204 mol of LiOH.H ₂ O were dispersed in ethanol to form a slurry, and then mixed with a planetary ball mill for 40 minutes and dried at room temperature to obtain a mixture. . Next, the mixture is put in an alumina crucible, heated to 600 ° C. in a dry air flow of 2 dm ³ / min, kept at that temperature for 2 hours for preheating, further heated to 900 ° C. and heated to 12 ° C. The first lithium-containing composite oxide A was synthesized by firing for a period of time.

The obtained first lithium-containing composite oxide A was washed with water, then heat treated in the atmosphere (oxygen concentration about 20% by volume) at 850 ° C. for 12 hours, and then pulverized in a mortar to obtain a powder. . The first lithium-containing composite oxide A after pulverization was stored in a desiccator.

The composition analysis of the first lithium-containing composite oxide A was performed in the same manner as in Example 1-1 described above, and the composition of the first lithium-containing composite oxide A was derived from the obtained results. However, it was found that the composition was represented by Li _1.02 Ni _0.6 Co _0.2 Mn _0.2 O ₂ .

<Synthesis of first lithium-containing composite oxide B containing nickel>
Aqueous ammonia whose pH was adjusted to about 12 by adding sodium hydroxide was placed in a reaction vessel, and while vigorously stirring, nickel sulfate, manganese sulfate, and cobalt sulfate were each added to 3.76 mol / dm ^3. , 0.21 mol ^/ dm 3, a mixed aqueous solution containing a concentration of 0.21 mol / dm ^3, and aqueous ammonia 25% strength by weight, respectively, 23cm ³ / min at a rate of 6.6 cm ³ / min, The mixture was added dropwise using a metering pump to synthesize a coprecipitation compound of Ni, Mn, and Co (spherical coprecipitation compound). At this time, the temperature of the reaction solution is maintained at 50 ° C., and a sodium hydroxide aqueous solution having a concentration of 6.4 mol / dm ³ is simultaneously dropped so that the pH of the reaction solution is maintained at around 12. In order to react under an active atmosphere, nitrogen gas was bubbled at a flow rate of 1 dm ³ / min.

The coprecipitated compound was washed with water, filtered and dried to obtain a hydroxide containing Ni, Mn and Co in a molar ratio of 90: 5: 5. 0.196 mol of this hydroxide, 0.204 mol of LiOH.H ₂ O and 0.001 mol of TiO ₂ were dispersed in ethanol to form a slurry, and then mixed for 40 minutes with a planetary ball mill. And dried to obtain a mixture. Next, the mixture is put in an alumina crucible, heated to 600 ° C. in a dry air flow of 2 dm ³ / min, held at that temperature for 2 hours for preheating, further heated to 800 ° C. and heated to 12 ° C. The first lithium-containing composite oxide B was synthesized by firing for a period of time. The obtained first lithium-containing composite oxide B was pulverized into a powder in a mortar and then stored in a desiccator.

The composition analysis of the first lithium-containing composite oxide B was performed in the same manner as in Example 1-1 described above, and the composition of the first lithium-containing composite oxide B was derived from the obtained results. However, it was found that the composition was represented by Li _1.02 Ni _0.895 Co _0.05 Mn _0.05 Ti _0.005 O ₂ .

<Synthesis of nickel-containing lithium-containing composite oxide C>
By adjusting the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitation compound, a hydroxide containing Ni, Co and Mn at a molar ratio of 1: 1: 1 was synthesized and used. Except for the above, a first lithium-containing composite oxide C was synthesized in the same manner as the synthesis of the first lithium-containing composite oxide A. The composition analysis of the first lithium-containing composite oxide C was performed in the same manner as in Example 1-1 described above, and the composition of the first lithium-containing composite oxide C was derived from the obtained results. However, it was found that the composition was represented by Li _1.02 Ni _0.3 Co _0.3 Mn _0.3 O ₂ .

(Examples 2-1 to 2-5)
<Preparation of positive electrode>
The first lithium-containing composite oxide A containing nickel and LiCoO ₂ that is the second lithium-containing composite oxide are weighed to a mass ratio shown in Table 3 and mixed for 30 minutes using a Henschel mixer. To obtain a mixture. 100 parts by mass of the obtained mixture as a positive electrode active material, 20 parts by mass of a solution obtained by dissolving PVDF and P (TFE-VDF) as binders in N-methyl-2-pyrrolidone (NMP), and a conductive auxiliary agent A 1.04 part by mass carbon fiber having an average fiber length of 100 nm and an average fiber diameter of 10 nm and 1.04 part by mass of graphite are kneaded using a biaxial kneader, and NMP is added to adjust the viscosity. Thus, a positive electrode mixture-containing paste was prepared. The amount of the PVDF and P (TFE-VDF) NMP solution used is such that the amount of the dissolved PVDF and P (TFE-VDF) is the mixture of the first lithium-containing composite oxide and LiCoO ₂ , PVDF and , P (TFE-VDF) and the conductive auxiliary agent (ie, the total amount of the positive electrode mixture layer) in 100% by mass, amounts to 2.34% by mass and 0.26% by mass, respectively. That is, the total amount of binder in the positive electrode mixture layer is 2.6% by mass, and the ratio of P (TFE-VDF) in the total of 100% by mass of P (TFE-VDF) and PVDF is 10% by mass.

The positive electrode mixture-containing paste is intermittently applied to both sides of an aluminum foil (positive electrode current collector) having a thickness of 15 μm while adjusting the thickness, dried, and then subjected to a calendering process so that the total thickness becomes 130 μm. The thickness of the positive electrode mixture layer was adjusted, and the positive electrode was produced by cutting so as to have a width of 54.5 mm. Further, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion. Here, the density of the positive electrode mixture layer measured by the above-described method was 3.80 g / cm ³ .

<Production of negative electrode>
A composite in which the surface of SiO _x having an average particle diameter D50% of 8 μm is coated with a carbon material (the amount of the carbon material in the composite is 10 mass%) and graphite having an average particle diameter D50% of 16 μm are combined with SiO _x. Negative electrode active material mixed in such an amount that the amount of the composite whose surface was coated with a carbon material was 3.0% by mass: 98 parts by mass, and a 1% by mass concentration whose viscosity was adjusted in the range of 1500 to 5000 mPa · s CMC aqueous solution: 100 parts by mass and SBR: 1.0 part by mass were mixed with ion-exchanged water having a specific resistance of 2.0 × 10 ⁵ Ωcm or more as a solvent to prepare an aqueous negative electrode mixture-containing paste.

<Preparation of separator>
To 5 kg of boehmite secondary aggregate having an average particle diameter D50% of 3 μm, 5 kg of ion-exchanged water and 0.5 kg of a dispersant (aqueous polycarboxylic acid ammonium salt, solid content concentration 40% by mass) are added. Dispersion was prepared by crushing for 10 hours with a ball mill with 40 rotations / minute. When a part of the treated dispersion was vacuum dried at 120 ° C. and observed with a scanning electron microscope (SEM), the shape of boehmite was almost plate-like. The average particle size of the boehmite after the treatment was 1 μm.

<Battery assembly>
The positive electrode and the negative electrode obtained as described above were stacked with the separator porous layer (II) facing the positive electrode, and wound in a spiral shape to produce a wound electrode body. The obtained wound electrode body was crushed into a flat shape and placed in an aluminum alloy outer can having a thickness of 5 mm, a width of 42 mm, and a height of 61 mm. Further, as a non-aqueous electrolyte, LiPF ₆ was dissolved in a solvent in which ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed at a volume ratio of 1: 1: 1 to a concentration of 1.1 mol / L. A solution was prepared by adding 2.0% by mass of FEC, 1.0% by mass of VC, and further adding triethylphosphonoacetate to the concentrations shown in Table 3. Next, the non-aqueous electrolyte was poured into the outer can.

After injecting the non-aqueous electrolyte, the outer can was sealed, and a lithium secondary battery having the structure shown in FIGS. 1A and 1B and the appearance shown in FIG. 2 was produced.

(Example 2-6)
A mixture was metered in a weight ratio of 0.5: the a synthesized first lithium-containing composite oxide containing nickel B, and a LiCoO ₂ as the second lithium-containing composite oxide, 0.5 A wound electrode body was produced in the same manner as in Example 2-1, except that the positive electrode active material was used. Further, the density of the positive electrode mixture layer measured by the above-described method was 3.80 g / cm ³ . Next, a non-aqueous electrolyte similar to that used in Example 2-1 except that the concentration of triethylphosphonoacetate was 5.0% by mass was poured into the outer can, and Example 2-1 Similarly, a lithium secondary battery was produced.

(Example 2-7)
A wound electrode body was produced in the same manner as in Example 2-1, except that only the first lithium-containing composite oxide C containing nickel was used as the positive electrode active material. Further, the density of the positive electrode mixture layer measured by the above-described method was 3.80 g / cm ³ . Next, a non-aqueous electrolyte similar to that used in Example 2-1 was poured into the outer can, and a lithium secondary battery was produced in the same manner as in Example 2-1.

(Example 2-8)
What mixed and mixed the 1st lithium containing complex oxide A containing the said nickel and LiCoO2 which is a _2nd lithium containing complex oxide to the mass ratio of 0.1: 0.9. A wound electrode body was produced in the same manner as in Example 2-1, except that it was used as the positive electrode active material and only graphite having an average particle diameter D50% of 16 μm was used as the negative electrode active material. Further, the density of the positive electrode mixture layer measured by the above-described method was 3.80 g / cm ³ . Next, a non-aqueous electrolyte similar to that used in Example 2-1 was poured into the outer can except that the concentration of triethylphosphonoacetate was 0.5% by mass, and Example 2-1 Similarly, a lithium secondary battery was produced.

(Example 2-9)
A Henschel mixer was prepared by weighing the first lithium-containing composite oxide A containing nickel and the second lithium-containing composite oxide LiCoO ₂ to a mass ratio of 0.5: 0.5. Was mixed for 30 minutes to obtain a mixture. A wound electrode body was produced in the same manner as in Example 2-1, except that 100 parts by mass of the obtained mixture was used as the positive electrode active material and 2.08 parts by mass of acetylene black was used as the conductive auxiliary agent. Further, the density of the positive electrode mixture layer measured by the above-described method was 3.40 g / cm ³ . Next, a non-aqueous electrolyte similar to that used in Example 2-1 was poured into the outer can, and a lithium secondary battery was produced in the same manner as in Example 2-1.

(Example 2-10)
A Henschel mixer was prepared by weighing the first lithium-containing composite oxide A containing nickel and the second lithium-containing composite oxide LiCoO ₂ to a mass ratio of 0.5: 0.5. Was mixed for 30 minutes to obtain a mixture. Example 2-1 except that 100 parts by mass of the obtained mixture was used as the positive electrode active material, only PVDF was used as the binder, and the total amount of PVDF in the positive electrode mixture layer was adjusted to 2.6% by mass. Thus, a wound electrode body was produced. Further, the density of the positive electrode mixture layer measured by the above-described method was 3.60 g / cm ³ . Next, a non-aqueous electrolyte similar to that used in Example 2-1 was poured into the outer can, and a lithium secondary battery was produced in the same manner as in Example 2-1.

(Comparative Example 2-1)
A wound electrode body was produced in the same manner as in Example 2-1, except that only LiCoO ₂ was used as the positive electrode active material. Further, the density of the positive electrode mixture layer measured by the above-described method was 3.80 g / cm ³ . Next, a non-aqueous electrolyte similar to that used in Example 2-1 was poured into the outer can, and a lithium secondary battery was produced in the same manner as in Example 2-1.

(Comparative Example 2-2)
A lithium secondary battery was produced in the same manner as in Example 2-1, except that the concentration of triethylphosphonoacetate in the nonaqueous electrolytic solution was changed to 0.3% by mass.

(Comparative Example 2-3)
Instead of triethylphosphonoacetate, a lithium non-aqueous electrolyte was used in the same manner as in Example 2-1, except that a non-aqueous electrolyte to which 1,3-propane sultone was added in an amount of 2.0% by mass was used. A secondary battery was produced.

Composition of the positive electrode active material relating to the positive electrode used in the lithium secondary batteries of Examples 2-1 to 2-10 and Comparative Examples 2-1 to 2-3, and the total amount of the positive electrode active material calculated by the above formula (3) Table 3 shows the total molar ratio of total nickel to total lithium (hereinafter abbreviated as total Ni / Li) and the content of the phosphonoacetate compound in the nonaqueous electrolytic solution.

Further, for the lithium secondary batteries produced in Examples 2-1 to 2-10 and Comparative Examples 2-1 to 2-3, Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1- The battery capacity (relative battery capacity with respect to the battery capacity of Example 2-1), battery swelling (battery swelling ratio), and capacity recovery rate after high temperature storage were evaluated in the same manner as in No. 5. The charge / discharge cycle characteristics were evaluated as follows. The results are shown in Table 4.

<Charge / discharge cycle characteristics>
After the initial charge / discharge of each battery, charge / discharge is repeated with the series of operations of charging and discharging under the same conditions as the battery capacity measurement described above as one cycle, and the discharge capacity is 80% of the discharge capacity obtained in the first cycle. The number of cycles was determined.

About each battery which investigated the said cycle number, it repeats charging / discharging on the same conditions until it becomes 50% of discharge capacity with respect to the discharge capacity obtained in the 1st cycle, and then disassembles the lithium secondary battery. The positive electrode taken out was washed with dimethyl carbonate and dried, and then the composition was analyzed using the ICP method described above (calibration curve method). From the obtained result, the composition of the positive electrode active material was derived, The total molar ratio (total Ni / Li) of total nickel to total lithium in the total amount of the positive electrode active material was calculated from (3) and listed in Table 4.

From Tables 3 and 4, the first lithium-containing composite oxide containing Li and Ni and the second lithium-containing composite oxide are used as the positive electrode active material, and the total nickel in all lithium in the total amount of the positive electrode active material A lithium secondary battery using a non-aqueous electrolyte containing a phosphonoacetate compound in an amount of 0.05 to 1.0% and a phosphonoacetate compound of 0.5 to 20% by mass is high capacity and high It can be seen that the battery swelling after storage is small, the capacity recovery rate is high, and the charge / discharge cycle characteristics are also good.

(Embodiment 2)
The second lithium secondary battery of the present invention includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator. The negative electrode includes a current collector and a negative electrode mixture layer formed on the current collector, the negative electrode mixture layer includes a negative electrode active material, and the negative electrode active material includes silicon and A material containing oxygen as a constituent element is included. Furthermore, the non-aqueous electrolyte solution includes a halogen-substituted cyclic carbonate and a phosphonoacetate compound represented by the following general formula (1). In the non-aqueous electrolyte solution, the content of the phosphonoacetate compound Is set below the content of the halogen-substituted cyclic carbonate.

As described above, in the battery using SiO _x as the negative electrode active material, highly active Si is exposed by grinding of the SiO _x particles generated due to the volume change accompanying charging and discharging, and this decomposes the non-aqueous electrolyte. Therefore, there is a problem that the charge / discharge cycle characteristics are likely to deteriorate.

Therefore, in the second lithium secondary battery of the present invention, a non-aqueous electrolyte containing a halogen-substituted cyclic carbonate is used. The halogen-substituted cyclic carbonate can form a film that satisfactorily coats the SiO _x particles by pulverization due to the volume change associated with charge and discharge, resulting in a new surface. Therefore, the reaction between the negative electrode active material and the non-aqueous electrolyte is highly suppressed by such a film, and a lithium secondary battery excellent in charge / discharge cycle characteristics can be obtained.

However, since the halogen-substituted cyclic carbonate generates gas along with the film formation reaction on the negative electrode surface, the battery tends to swell. Therefore, in the second lithium secondary battery of the present invention, a non-aqueous electrolyte containing a phosphonoacetate compound represented by the general formula (1) is used in addition to the halogen-substituted cyclic carbonate. It was. The phosphonoacetate compound represented by the general formula (1) has an action of suppressing the occurrence of battery swelling. Therefore, by using together with the halogen-substituted cyclic carbonate, it is possible to satisfactorily suppress the occurrence of battery swelling caused by the halogen-substituted cyclic carbonate.

However, the phosphonoacetate compound represented by the general formula (1) also has an effect of impairing the charge / discharge cycle characteristics of the battery. For example, when the amount of use increases, the effect of suppressing the battery swelling is good. On the other hand, it has been found that the charge / discharge cycle characteristics are greatly deteriorated. Therefore, in the second lithium secondary battery of the present invention, the content of the halogen-substituted cyclic carbonate in the non-aqueous electrolyte and the content of the phosphonoacetate compound represented by the general formula (1) are: It is possible to effectively bring out both the action of the halogen-substituted cyclic carbonate and the action of the phosphonoacetate compound by suppressing the deterioration of charge / discharge cycle characteristics caused by the phosphonoacetate compound. Thus, it is possible to provide a lithium secondary battery that is excellent in charge / discharge cycle characteristics and can suppress the occurrence of swelling well.

[Negative electrode]
The negative electrode according to the second lithium secondary battery of the present invention has, for example, a structure in which a negative electrode mixture layer containing a negative electrode active material, a binder, and a conductive auxiliary agent if necessary is provided on one side or both sides of a current collector Can be used.

The negative electrode active material used for the negative electrode of the second lithium secondary battery of the present invention contains a material containing silicon and oxygen as constituent elements. Usually, as a material containing silicon and oxygen as constituent elements, a material represented by the general formula composition formula SiO _x and 0.5 ≦ x ≦ 1.5 in the general composition formula is used. As the material represented by the general formula composition formula SiO _x and 0.5 ≦ x ≦ 1.5, the same materials as those described in the first embodiment can be used.

Further, as the negative electrode active material, a composite of a material containing silicon and oxygen described in Embodiment 1 as constituent elements and a carbon material can be used. Furthermore, as the negative electrode active material, the material containing silicon and oxygen as constituent elements described in Embodiment 1 and the graphitic carbon material can be used in combination.

As the binder of the negative electrode mixture layer, the conductive additive, and the current collector of the negative electrode, the same materials as those described in Embodiment 1 can be used. Moreover, a negative electrode can be manufactured by the method similar to what was demonstrated in Embodiment 1, for example. Furthermore, the negative electrode mixture layer can have the same configuration as that described in the first embodiment.

[Positive electrode]
For the positive electrode according to the second lithium secondary battery of the present invention, for example, a positive electrode mixture layer containing a positive electrode active material, a binder, a conductive additive and the like is used on one side or both sides of the current collector. it can.

<Positive electrode active material>
The positive electrode active material used for the positive electrode of the second lithium secondary battery of the present invention includes a positive electrode active material used for a conventionally known lithium secondary battery, that is, a material capable of inserting and extracting lithium ions. If there is no restriction in particular. For example, a lithium-containing composite oxide can be used. Among them, the lithium-containing composite oxide containing lithium and nickel represented by the general composition formula (2) described in Embodiment 1 is preferable because of its high capacity and excellent thermal stability. Also, as the positive electrode active material, for example described in Embodiment 1, the lithium cobalt oxide such as LiCoO _{_2;} LiMnO _2, lithium manganese oxides such as _{_{Li 2 MnO 3; LiMn 2 O}} 4, Li 4/3 Ti 5 _{/ 3} O ₄ and other spinel-structure lithium-containing composite oxides; LiFePO ₄ and other olivine-structure lithium-containing composite oxides; These oxides have a basic composition, and some of the constituent elements are replaced with other elements Oxides; etc. can be used.

As the binder of the positive electrode mixture layer, the conductive additive, and the current collector of the positive electrode, the same materials as those described in Embodiment 1 can be used. Moreover, a positive electrode can be manufactured by the method similar to what was demonstrated in Embodiment 1, for example. Furthermore, the positive electrode mixture layer can have the same configuration as that described in the first embodiment.

[Non-aqueous electrolyte]
The non-aqueous electrolyte solution according to the second lithium secondary battery of the present invention uses a halogen-substituted cyclic carbonate and a phosphonoacetate compound represented by the general formula (1). In the non-aqueous electrolyte, the content of the phosphonoacetate compound is set to be equal to or less than the content of the halogen-substituted cyclic carbonate.

As the halogen-substituted cyclic carbonate and the phosphonoacetate compound represented by the general formula (1), the same compounds as those described in Embodiment 1 can be used.

The content of the halogen-substituted cyclic carbonate in the non-aqueous electrolyte is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, from the viewpoint of better ensuring the effect of its use. Is more preferable. However, if the content of the halogen-substituted cyclic carbonate in the non-aqueous electrolyte is too large, the battery swelling suppression effect may be reduced. Therefore, the content of the halogen-substituted cyclic carbonate in the nonaqueous electrolytic solution used for the battery is preferably 30% by mass or less, and more preferably 5% by mass or less.

In addition, the content of the phosphonoacetate compound represented by the general formula (1) in the nonaqueous electrolytic solution may be 0.1% by mass or more from the viewpoint of better securing the effect of its use. Preferably, it is 0.5 mass% or more. However, if the content of the phosphonoacetate compound represented by the general formula (1) in the non-aqueous electrolyte is too large, the effect of improving the charge / discharge cycle characteristics of the battery may be reduced. Therefore, the content of the phosphonoacetate compound represented by the general formula (1) in the nonaqueous electrolytic solution used for the battery is preferably 10% by mass or less, and more preferably 3% by mass or less. preferable.

In particular, when the negative electrode contains a graphite carbon material together with SiO _x as the negative electrode active material, it is preferable to use a non-aqueous electrolyte that further contains vinylene carbonate (VC). . In particular, VC effectively acts on the carbon material to improve the properties of the film formed on the negative electrode surface, so that a battery with more excellent charge / discharge cycle characteristics can be configured.

In the non-aqueous electrolyte used in the second lithium secondary battery of the present invention, the content of the phosphonoacetate compound represented by the general formula (1) is equal to or less than the content of the halogen-substituted cyclic carbonate. To do. As described above, the phosphonoacetate compound represented by the general formula (1) has a battery swelling suppression effect, but also causes deterioration in charge / discharge cycle characteristics of the battery. However, the content of the halogen-substituted cyclic carbonate in the non-aqueous electrolyte used in the battery is the same as or more than the content of the phosphonoacetate compound represented by the general formula (1). Thus, by the effect of improving the charge / discharge cycle characteristics of the battery by the halogen-substituted cyclic carbonate, the deterioration of the charge / discharge cycle characteristics caused by the volume change of SiO _x accompanying the charge / discharge of the battery is suppressed. The deterioration of the charge / discharge cycle characteristics due to the represented phosphonoacetate compound can also be satisfactorily suppressed.

For the same reason as described above, in the nonaqueous electrolytic solution used in the second lithium secondary battery of the present invention, when VC is contained, the halogen-substituted cyclic carbonate content and the VC content It is preferable to reduce the content of the phosphonoacetate compound represented by the general formula (1) rather than the total amount.

Further, when VC is contained in the non-aqueous electrolyte, the content is preferably 0.1% by mass or more, more preferably 1.0% by mass or more from the viewpoint of better securing the effect of using VC. It is more preferable that However, if the content of VC in the non-aqueous electrolyte is too large, the effect of suppressing battery swelling may be reduced. Therefore, the content of VC in the non-aqueous electrolyte used for the battery is preferably 10% by mass or less, and more preferably 4.0% by mass or less.

As the lithium salt and organic solvent used in the non-aqueous electrolyte, the same ones as described in Embodiment 1 can be used.

In addition, non-aqueous electrolytes may contain acid anhydrides, sulfonic acid esters, dinitriles, 1,3-methyl ether for the purpose of further improving charge / discharge cycle characteristics and improving safety such as high-temperature storage and overcharge resistance. Additives such as propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, t-butylbenzene, and derivatives thereof may be added as appropriate.

[Separator]
As the separator according to the second lithium secondary battery of the present invention, the same separator as described in Embodiment 1 can be used.

[Battery form]
The form of the second lithium secondary battery of the present invention can be the same as that described in the first embodiment.

Hereinafter, the present invention will be described in detail based on examples of the second embodiment. However, the following examples do not limit the present invention.

Example 3-1
<Synthesis of lithium-containing composite oxide>
Aqueous ammonia whose pH was adjusted to about 12 by adding sodium hydroxide was placed in a reaction vessel, and while vigorously stirring, nickel sulfate, cobalt sulfate and manganese sulfate were each added to 2.4 mol / dm ^3. , 0.8 mol ^/ dm 3, a mixed aqueous solution containing a concentration of 0.8 mol / dm ^3, and aqueous ammonia 25% strength by weight, respectively, 23cm ³ / min at a rate of 6.6 cm ³ / min, The solution was added dropwise using a metering pump to synthesize a coprecipitation compound of Ni, Co, and Mn (spherical coprecipitation compound). At this time, the temperature of the reaction solution is maintained at 50 ° C., and a 6.4 mol / dm ³ concentration sodium hydroxide aqueous solution is simultaneously added so that the pH of the reaction solution is maintained around 12. In order to react under an active atmosphere, nitrogen gas was bubbled at a flow rate of 1 dm ³ / min.

The coprecipitated compound was washed with water, filtered and dried to obtain a hydroxide containing Ni, Co and Mn in a molar ratio of 6: 2: 2. 0.196 mol of this hydroxide and 0.204 mol of LiOH.H ₂ O were dispersed in ethanol to form a slurry, and then mixed with a planetary ball mill for 40 minutes and dried at room temperature to obtain a mixture. . Next, the mixture is put in an alumina crucible, heated to 600 ° C. in a dry air flow of 2 dm ³ / min, kept at that temperature for 2 hours for preheating, further heated to 900 ° C. and heated to 12 ° C. The lithium-containing composite oxide was synthesized by firing for a period of time.

The obtained lithium-containing composite oxide was washed with water and then heat-treated in the atmosphere (oxygen concentration of about 20% by volume) at 850 ° C. for 12 hours, and then pulverized in a mortar to obtain a powder. The lithium-containing composite oxide after pulverization was stored in a desiccator.

When the composition of the lithium-containing composite oxide was analyzed with an atomic absorption spectrometer, it was found that the composition was represented by Li _1.02 Ni _0.6 Co _0.2 Mn _0.2 O ₂ .

<Preparation of positive electrode>
100 parts by mass of the lithium-containing composite oxide, 20 parts by mass of an NMP solution containing PVDF as a binder at a concentration of 10% by mass, 1 part by mass of artificial graphite and 1 part by mass of acetylene black as conductive assistants, A positive electrode mixture-containing paste was prepared by kneading using a shaft kneader and further adjusting the viscosity by adding NMP.

The positive electrode mixture-containing paste is intermittently applied to both sides of an aluminum foil (positive electrode current collector) having a thickness of 15 μm while adjusting the thickness, dried, and then subjected to a calendering process so that the total thickness becomes 130 μm. The thickness of the positive electrode mixture layer was adjusted, and the positive electrode was produced by cutting so as to have a width of 54.5 mm. Further, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion.

<Production of negative electrode>
A composite in which the surface of SiO _x having an average particle diameter D50% of 8 μm is coated with a carbon material (the amount of the carbon material in the composite is 10 mass%) and graphite having an average particle diameter D50% of 16 μm are combined with SiO _x. Mixture in which the amount of the composite whose surface was coated with a carbon material was mixed in an amount of 0.01% by mass: 98 parts by mass, and a CMC aqueous solution having a concentration of 1% by mass adjusted to a viscosity of 1500 to 5000 mPa · s : 1.0 part by mass and SBR: 1.0 part by mass using ion-exchanged water having a specific conductivity of 2.0 × 10 ⁵ Ω / cm or more as a solvent to prepare an aqueous negative electrode mixture-containing paste. Prepared.

<Battery assembly>
The positive electrode and the negative electrode obtained as described above were stacked with the separator porous layer (II) facing the positive electrode, and wound in a spiral shape to produce a wound electrode body. The obtained wound electrode body was crushed into a flat shape and placed in an aluminum alloy outer can having a thickness of 5 mm, a width of 42 mm, and a height of 61 mm. Further, as a non-aqueous electrolyte, LiPF ₆ was dissolved in a solvent in which ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed at a volume ratio of 1: 1: 1 so as to have a concentration of 1.1 mol / L. A solution was prepared by adding FEC, triethylphosphonoacetate, and VC to each sample so that the respective concentrations were 1.25 mass%, 1.25 mass%, and 1.75 mass%. Next, the non-aqueous electrolyte was poured into the outer can.

(Example 3-2)
Example 3-1 except that the FEC content was changed to 2.00% by mass, the triethylphosphonoacetate content was changed to 1.50% by mass, and the VC content was changed to 1.50% by mass. A non-aqueous electrolyte was prepared in the same manner as described above, and a lithium secondary battery was produced in the same manner as in Example 3-1, except that this non-aqueous electrolyte was used.

Example 3-3
Example 3-1 except that the content of FEC was changed to 2.00% by mass, the content of triethylphosphonoacetate was changed to 2.00% by mass, and the content of VC was changed to 2.50% by mass. A non-aqueous electrolyte was prepared in the same manner as described above, and a lithium secondary battery was produced in the same manner as in Example 3-1, except that this non-aqueous electrolyte was used.

(Example 3-4)
Instead of triethylphosphonoacetate, the trimethylphosphonoacetate content is 1.00% by mass, the FEC content is 1.00% by mass, and the VC content is 2.00% by mass. %, Respectively, except that the non-aqueous electrolyte was prepared in the same manner as in Example 3-1, and a lithium secondary battery was prepared in the same manner as in Example 3-1, except that this non-aqueous electrolyte was used. Was made.

(Example 3-5)
Example 3-1 except that the content of FEC was changed to 1.25% by mass, the content of triethylphosphonoacetate was changed to 0.50% by mass, and the content of VC was changed to 1.75% by mass. A non-aqueous electrolyte was prepared in the same manner as described above, and a lithium secondary battery was produced in the same manner as in Example 3-1, except that this non-aqueous electrolyte was used.

(Example 3-6)
Example 3-1 except that the FEC content was changed to 1.00% by mass, the triethylphosphonoacetate content was changed to 0.50% by mass, and the VC content was changed to 1.00% by mass. A non-aqueous electrolyte was prepared in the same manner as described above, and a lithium secondary battery was produced in the same manner as in Example 3-1, except that this non-aqueous electrolyte was used.

(Example 3-7)
Instead of FEC, the content of the cyclic carbonate represented by the general formula (4), wherein R ⁴ and R ⁵ are fluorine (F), and R ⁶ and R ⁷ are hydrogen (H) is 1.25% by mass. In the same manner as in Example 3-1, except that the content of triethylphosphonoacetate was changed to 1.25% by mass and the content of VC was changed to 1.75% by mass. A lithium secondary battery was produced in the same manner as in Example 3-1, except that an aqueous electrolyte was prepared and this nonaqueous electrolyte was used.

(Example 3-8)
Instead of FEC, the cyclic carbonate is represented by the general formula (4), R ⁴ and R ⁵ are F, and R ⁶ and R ⁷ are H. Example 3-1 except that trimethylphosphonoacetate was used instead of triethylphosphonoacetate so that the content of trimethylphosphonoacetate was 2.00% by mass and the VC content was changed to 2.00% by mass. A non-aqueous electrolyte was prepared in the same manner, and a lithium secondary battery was produced in the same manner as in Example 3-1, except that this non-aqueous electrolyte was used.

(Comparative Example 3-1)
Instead of FEC, the content of the cyclic carbonate represented by the general formula (4), wherein R ⁴ is chlorine (Cl), and R ⁵ , R ⁶ and R ⁷ are H is 1.00% by mass. The nonaqueous electrolytic solution was used in the same manner as in Example 3-1, except that the content of triethylphosphonoacetate was changed to 2.00% by mass and the content of VC was changed to 1.00% by mass. A lithium secondary battery was fabricated in the same manner as in Example 3-1, except that this nonaqueous electrolytic solution was used.

(Comparative Example 3-2)
Instead of FEC, it is used so that the content of the cyclic carbonate represented by the general formula (4), R ⁴ is Cl, and R ⁵ , R ⁶ and R ⁷ are H is 1.25% by mass, A non-aqueous electrolyte was prepared in the same manner as in Example 3-1, except that the triethylphosphonoacetate content was changed to 2.00% by mass and the VC content was changed to 1.00% by mass. A lithium secondary battery was produced in the same manner as in Example 3-1, except that this non-aqueous electrolyte was used.

(Comparative Example 3-3)
Without using trimethylphosphonoacetate, the content of the cyclic carbonate represented by the general formula (4), wherein R ⁴ and R ⁵ are F, and R ⁶ and R ⁷ are H is 1.00% by mass. A non-aqueous electrolyte was prepared in the same manner as in Example 3-8 except that the non-aqueous electrolyte was used, and a lithium secondary battery was produced in the same manner as in Example 3-1, except that this non-aqueous electrolyte was used. .

The following evaluations were made on the lithium secondary batteries produced in Examples 3-1 to 3-8 and Comparative Examples 3-1 to 3-3. These results are shown in Table 5 together with the composition of the additive added to the non-aqueous electrolyte of each battery.

<Charge / discharge cycle characteristics evaluation>
After the initial charge and discharge of each battery, constant current charging was performed until the current value of 320 mA reached 4.2 V, and then constant voltage charging was performed at 4.2 V. The total charging time for constant current charging and constant voltage charging was 3 hours. Subsequently, the battery after charging was subjected to constant current discharge until the current value of 320 mA reached 3.0 V. The above charge and discharge were regarded as one cycle, and this was repeated 200 times to obtain the discharge capacity. The value was divided by the discharge capacity at the first cycle and expressed as a percentage to obtain the capacity maintenance ratio.

<Evaluation of battery thickness change after high temperature storage>
After the initial charge / discharge of each battery, the battery was charged under the same conditions as in the charge / discharge cycle characteristic evaluation. Each battery after charging was stored for 120 hours in an environment of 60 ° C., and the change in thickness (swelling amount) of the battery before and after storage was determined. Here, the thickness of the battery means the thickness between the wide side surfaces of the outer can, as described above.

Since the conditions adopted in the evaluation of the change in the thickness of the battery after high-temperature storage are extremely severe, the change in the thickness of the battery is usually very large (the battery swells greatly). Examples 3-1 to 3-8 and Comparative Examples were compared with the lithium secondary battery of Comparative Example 3-3 using a non-aqueous electrolyte containing no phosphonoacetate compound represented by the general formula (1) In the lithium secondary batteries 3-1 and 3-2, the thickness change is suppressed by the action of the non-aqueous electrolyte containing the phosphonoacetate compound represented by the general formula (1).

However, Comparative Examples 3-1 and 3-2 using a non-aqueous electrolyte in which the relationship between the amount of the halogen-substituted cyclic carbonate and the amount of the phosphonoacetate compound represented by the general formula (1) is inappropriate In the battery of Example 3, the capacity retention rate at the time of charge / discharge cycle characteristics evaluation is low and the charge / discharge cycle characteristics are inferior. In the battery of 3-8, the capacity retention rate is high and the charge / discharge cycle characteristics are also excellent.

The present invention can be implemented in forms other than those described above without departing from the spirit of the present invention. The embodiments disclosed in the present application are merely examples, and the present invention is not limited thereto. The scope of the present invention is construed in preference to the description of the appended claims rather than the description of the above specification, and all modifications within the scope equivalent to the claims are construed in the scope of the claims. It is included.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Exterior can 5 Insulator 6 Winding electrode body 7 Positive electrode lead body 8 Negative electrode lead body 9 Lid board 10 Insulation packing 11 Terminal 12 Insulator 13 Lead board 14 Nonaqueous electrolyte injection port 15 Cleavage vent

Claims

A lithium secondary battery including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator,
The positive electrode includes a current collector and a positive electrode mixture layer formed on the current collector,
The positive electrode mixture layer includes a positive electrode active material,
The positive electrode active material includes a first lithium-containing composite oxide containing lithium and nickel,
The molar ratio of the nickel to the lithium in the total amount of the first lithium-containing composite oxide is 0.05 to 1.05;
The lithium secondary battery, wherein the non-aqueous electrolyte contains 0.5 to 20% by mass of a phosphonoacetate compound represented by the following general formula (1).

In the general formula (1), R 1 , R 2 and R 3 are each independently an alkyl group having 1 to 12 carbon atoms which may be substituted with a halogen atom, and n is an integer of 0 to 6 It is.
The first lithium-containing composite oxide is represented by a general composition formula Li 1 + y MO 2 ,
In the general composition formula, −0.15 ≦ y ≦ 0.15, and M represents an element group containing Ni, Co, and Mn,
When the ratio of the number of elements of Ni, Co, and Mn contained in the element group M to the total number of elements in the element group M is a (mol%), b (mol%), and c (mol%), respectively. The lithium secondary battery according to claim 1, represented by: 25 ≦ a ≦ 90, 5 ≦ b ≦ 35, 5 ≦ c ≦ 35, and 10 ≦ b + c ≦ 70.
2. The lithium secondary battery according to claim 1, wherein the positive electrode active material further includes a second lithium-containing composite oxide containing lithium and a transition metal.
The lithium secondary battery according to claim 3, wherein the total molar ratio of total nickel to total lithium in the total amount of the positive electrode active material is 0.05 to 1.0.
The lithium secondary battery according to claim 1, wherein a density of the positive electrode mixture layer is 3.2 g / cm 3 or more.
The lithium secondary battery according to claim 1, wherein a density of the positive electrode mixture layer is 3.6 g / cm 3 or more.
The lithium secondary battery according to claim 1, wherein the non-aqueous electrolyte further includes a halogen-substituted cyclic carbonate and vinylene carbonate.
The negative electrode includes a current collector and a negative electrode mixture layer formed on the current collector,
The negative electrode mixture layer includes a negative electrode active material,
The lithium secondary battery according to claim 1, wherein the negative electrode active material includes a material containing silicon and oxygen as constituent elements.
The negative electrode includes a current collector and a negative electrode mixture layer formed on the current collector,
The negative electrode mixture layer includes a negative electrode active material,
The lithium secondary battery according to claim 1, wherein the negative electrode active material includes a composite of a material containing silicon and oxygen as constituent elements and a carbon material.
The lithium secondary battery according to claim 8, wherein the negative electrode active material further includes a graphitic carbon material.
A lithium secondary battery including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator,
The negative electrode includes a current collector and a negative electrode mixture layer formed on the current collector,
The negative electrode mixture layer includes a negative electrode active material,
The negative electrode active material includes a material containing silicon and oxygen as constituent elements,
The non-aqueous electrolyte includes a halogen-substituted cyclic carbonate and a phosphonoacetate compound represented by the following general formula (1):
In the non-aqueous electrolyte, the content of the phosphonoacetate compound is less than or equal to the content of the halogen-substituted cyclic carbonate.

In the general formula (1), R 1 , R 2 and R 3 are each independently an alkyl group having 1 to 12 carbon atoms which may be substituted with a halogen atom, and n is an integer of 0 to 6 It is.
The material containing silicon and oxygen as constituent elements is represented by a general formula composition formula SiO x ,
The lithium secondary battery according to claim 11, wherein 0.5 ≦ x ≦ 1.5 in the general composition formula.
The lithium secondary battery according to claim 11, wherein the negative electrode active material includes a composite of a material containing silicon and oxygen as constituent elements and a carbon material.
The lithium secondary battery according to claim 11, wherein the negative electrode active material further includes a graphitic carbon material.
The lithium secondary battery according to claim 11, wherein a content of the halogen-substituted cyclic carbonate in the non-aqueous electrolyte is 0.1 to 30% by mass.
The lithium secondary battery according to claim 11, wherein the content of the phosphonoacetate compound in the non-aqueous electrolyte is 0.1 to 10% by mass.
The negative electrode active material further includes a graphitic carbon material,
The lithium secondary battery according to claim 11, wherein the non-aqueous electrolyte further includes vinylene carbonate.
The lithium secondary battery according to claim 17, wherein the content of vinylene carbonate in the non-aqueous electrolyte is 0.1 to 10% by mass.
The positive electrode includes a current collector and a positive electrode mixture layer formed on the current collector,
The positive electrode mixture layer includes a positive electrode active material,
The lithium secondary battery according to claim 11, wherein the positive electrode active material includes a lithium-containing composite oxide.
The lithium secondary battery according to claim 19, wherein the lithium-containing composite oxide includes nickel.