JP5851801B2 - Lithium secondary battery - Google Patents

Description

  The present invention relates to a lithium secondary battery having a high capacity and excellent safety.

  In recent years, with the development of portable electronic devices such as mobile phones and notebook computers, and the practical application of electric vehicles, secondary batteries and capacitors used as power sources for these devices are required to have higher performance and higher stability. ing. In particular, a lithium secondary battery is attracting attention as a battery having a high energy density, and various improvements are being promoted as a suitable power source for the devices.

LiCoO ₂ (lithium cobaltate) is frequently used as a positive electrode active material for current lithium secondary batteries because it is easy to manufacture and handle. However, since LiCoO ₂ is produced from Co (cobalt), which is a rare element, 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.

For example, Patent Document 1 includes Ni (nickel), Mn (manganese), Co, and other substitution elements M in a specific ratio, and the atomic ratio of the substitution element M to Ni, Mn, and Co on the particle surface is as follows. A positive electrode active material that is larger than the average atomic ratio of the substitution element M to Ni, Mn, and Co in the entire particle is disclosed. Since the positive electrode active material containing Ni as disclosed in Patent Document 1 has a larger capacity than LiCoO ₂ , it is expected that the capacity of the lithium secondary battery can be increased.

By the way, in order to increase the capacity of the lithium secondary battery, the end voltage in the charge (constant current-constant voltage charge) before use is usually set to, for example, a current lithium secondary battery using LiCoO ₂ as a positive electrode active material. It is also possible to raise the voltage to be higher than about 4.2V that is adopted. However, the higher the end-of-charge voltage of a lithium secondary battery, the greater the risk of an abnormal condition such as exposure to an excessively high temperature after charging. Improvement in performance is also required.

  Regarding the safety of lithium secondary batteries, for example, when a groove serving as a safety valve is provided on the side of an outer can serving as a battery case, and when the internal pressure rises due to gas being generated inside due to exposure of the battery to high temperature, There has been proposed a technique for preventing the battery from rupturing by cleaving the groove and discharging the gas (Patent Document 2).

JP 2006-202647 A JP 2003-297322 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lithium secondary battery having a high capacity and excellent safety at an extremely high temperature.

  The lithium secondary battery of the present invention that has achieved the above object is a lithium secondary battery in which a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator are enclosed in a hollow columnar battery case, and the positive electrode is a positive electrode active material And a positive electrode mixture layer containing a conductive auxiliary and a binder on one or both sides of a current collector, and using a lithium-containing composite oxide containing lithium and a transition metal as the positive electrode active material. At least a part of the lithium-containing composite oxide is a lithium-containing composite oxide containing nickel as a transition metal, and the molar ratio of the total nickel amount to the total lithium amount in the total positive electrode active material is 0.05 to 1. 0, and the separator has a porous film (I) mainly composed of a thermoplastic resin and a porous layer (II) mainly composed of a filler having a heat resistant temperature of 150 ° C. or more. K The side surfaces of the battery case have two wide surfaces that are opposed to each other and wider than the other surfaces in a side view, and the pressure in the battery case is greater than a threshold value on the side surfaces. In this case, the cleavage groove that is to be cleaved is provided so as to intersect with a diagonal line in a side view from the wide surface side.

  According to the present invention, it is possible to provide a lithium secondary battery having a high capacity and excellent safety at an extremely high temperature.

It is a perspective view showing typically an example of the lithium secondary battery of the present invention. It is a side view of the lithium secondary battery of FIG. It is a perspective view showing a mode that the cleavage groove of the lithium secondary battery of FIG. 1 was cleaved. It is the II sectional view taken on the line of FIG. It is a perspective view which represents typically the other example of the external appearance of the lithium secondary battery of this invention. FIG. 6 is a side view of the lithium secondary battery in FIG. 5. It is a perspective view which represents typically the other example of the external appearance of the lithium secondary battery of this invention. It is a side view of the lithium secondary battery of FIG. It is a fragmentary longitudinal cross-sectional view which represents typically an example of the lithium secondary battery of this invention. 6 is a partial longitudinal sectional view schematically showing a lithium secondary battery of Comparative Examples 2 and 4. FIG. It is a perspective view which represents typically the external appearance of the lithium secondary battery of the comparative examples 2 and 4. FIG. 10 is a side view schematically showing the appearance of a lithium secondary battery of Comparative Example 3. FIG.

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

<Positive electrode>
As the positive electrode according to the lithium secondary battery of the present invention, one having a structure having a positive electrode mixture layer containing a positive electrode active material, a binder, a conductive auxiliary agent and the like on one side or both sides of a current collector is used.

<Positive electrode active material>
The positive electrode active material according to the lithium secondary battery of the present invention is a lithium-containing composite oxide containing lithium (Li) and a transition metal, and at least a part of the lithium-containing composite oxide contains Ni as a transition metal. The lithium-containing composite oxide contains a molar ratio of the total Ni amount to the total Li amount in the total positive electrode active material of 0.05 to 1.0.

Specific examples of the lithium-containing composite oxide containing Li and a transition metal include, for example, lithium cobalt oxide such as LiCoO ₂ ; lithium manganese oxide such as LiMnO ₂ and Li ₂ MnO ₃ ; lithium such as LiNiO ₂ Nickel oxide; lithium-containing composite oxide having a spinel structure such as LiMn ₂ O ₄ and Li _4/3 Ti _5/3 O ₄ ; lithium-containing composite oxide having an olivine structure such as LiFePO ₄ ; And oxides substituted with various elements.

  The lithium-containing composite oxide containing Ni as a transition metal is one containing at least Ni as a transition metal element constituting the composite oxide, Co, Mn, titanium (Ti), chromium (Cr), Other transition metals such as iron (Fe), copper (Cu), silver (Ag), thallium (Ta), niobium (Nb), and zirconium (Zr) may be contained as constituent elements. B), transition metal elements such as phosphorus (P), zinc (Zn), aluminum (Al) calcium (Ca), strontium (Sr), barium (Ba) germanium (Ge), tin (Sn), magnesium (Mg) It may contain other elements.

The lithium-containing composite oxide containing Ni as a transition metal has a higher capacity near 3 to 4.4 V (vs. Li) than other lithium-containing composite oxides such as LiCoO _2. It is advantageous for capacity increase. Therefore, in the lithium secondary battery of the present invention, from the viewpoint of increasing the capacity, the molar ratio of the total Ni amount to the total Li amount in the total positive electrode active material is set to 0.05 or more.

However, on the other hand, the lithium-containing composite oxide containing Ni as a transition metal has high reactivity with the non-aqueous electrolyte. Therefore, a lithium secondary battery using a lithium-containing composite oxide containing Ni as a transition metal as a positive electrode active material further increases the battery temperature when placed under an excessively high temperature in a charged state. There are concerns about thermal runaway. In particular, in a lithium secondary battery using a lithium-containing composite oxide containing Ni as a transition metal as a positive electrode active material, by using a higher end voltage during charging than a battery using LiCoO ₂ , a further battery can be obtained. However, in the state where the battery is charged at a higher voltage, the risk of the thermal runaway is further increased. Therefore, in the lithium secondary battery of the present invention, safety at an excessively high temperature is enhanced by combining the positive electrode containing the specific positive electrode active material and other components described later.

The lithium secondary battery of the present invention is used after performing constant-current-constant-voltage charging with a final voltage of about 4.2 V, for example, similarly to a conventional lithium secondary battery using LiCoO ₂ as a positive electrode active material. Although it can also be applied to applications, it is more preferable to apply to a usage that is used after performing a constant current-constant voltage charging with a final voltage exceeding 4.30 V from the viewpoint of achieving higher capacity. Even if the battery is charged under conditions and placed in an excessively high temperature environment, the safety is good.

  The lithium-containing composite oxide containing Ni as a transition metal has high thermal stability and high potential state stability, and can further enhance the safety and various battery characteristics of the lithium secondary battery. It is preferable to use the lithium-containing composite oxide represented by (1).

Li _{1 + y} MO ₂ (1)
[In the general composition formula (1), −0.15 ≦ y ≦ 0.15, and M represents a group of three or more elements including at least Ni, Co, and Mn. In the element, when the proportions (mol%) of Ni, Co and Mn are a, b and c, 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 (1) representing the lithium-containing composite oxide is 100 mol%, the Ni ratio a is 25 mol from the viewpoint of improving the capacity of the lithium-containing composite oxide. % Or more, and more preferably 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 (1) representing the lithium-containing composite oxide is 100 mol%, the Ni ratio a is preferably 90 mol% or less, and 70 mol% or less. More preferably.

  Further, 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, if it is too much, it 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 (1) representing the lithium-containing composite oxide is 100 mol%, the Co ratio b is preferably 5 mol% or more and 35 mol% or less.

  In the lithium-containing composite oxide, when the total number of elements in the element group M in the general composition formula (1) is 100 mol%, the Mn ratio c is preferably 5 mol% or more and 35 mol% or less. . 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 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 set to a value close to tetravalent. The value can be stabilized, and the reversibility of charge / discharge can be further increased. Therefore, by using such a lithium-containing composite oxide, it becomes possible to configure a battery with more excellent charge / discharge cycle characteristics.

  Moreover, in the lithium-containing composite oxide, from the viewpoint of ensuring the above-described effect by using Co and Mn in combination, the total number of elements in the element group M in the general composition formula (1) is set to 100 mol%. In this case, 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 (more preferably 50 mol% or less).

  The element group M in the general composition formula (1) representing the lithium-containing composite oxide may contain elements other than Ni, Co, and Mn. For example, Ti, Cr, Fe, Cu, Zn, It may contain elements such as Al, Ge, Sn, Mg, Ag, Ta, Nb, B, P, Zr, Ca, Sr, and Ba. However, in the lithium-containing composite oxide, in order to sufficiently obtain the above-described effect by including Ni, Co and Mn, Ni, Co and when the total number of elements in the element group M is 100 mol% When the total of the ratio (mol%) of elements other than Mn is expressed by f, f is preferably 15 mol% or less, and more preferably 3 mol% or less.

  For example, in the lithium-containing composite oxide, if 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. High lithium secondary battery can be configured. 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 lithium-containing composite oxide may cause a decrease in capacity. Therefore, in the general composition formula (1) representing the 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 addition, in order to ensure the above-mentioned effect by containing Al more favorably, when the total number of elements in the element group M is 100 mol% in the general composition formula (1) representing the lithium-containing composite oxide. In addition, the Al ratio is preferably 0.02 mol% or more.

  In the 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 the thermal stability thereof can be improved, so that the safety is higher. It becomes possible to constitute a lithium secondary battery. 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 (1) representing the lithium-containing composite oxide, when 1 + y <0 and the lithium-containing composite oxide has a Li-deficient crystal structure, Mg instead of Li becomes a Li site. A lithium-containing composite oxide can be formed in a form that enters, 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 (1) representing the 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. In addition, in order to ensure the above-mentioned effect by containing Mg more satisfactorily, in the general composition formula (1) representing the lithium-containing composite oxide, when the total number of elements in the element group M is 100 mol% Furthermore, it is preferable that the Mg ratio is 0.02 mol% or more.

In the lithium-containing composite oxide, when Ti is contained in the particles, the lithium-containing composite oxide stabilizes the crystal structure by being disposed in a defect portion of the crystal such as oxygen deficiency in the LiNiO ₂ type crystal structure. The reversibility of the reaction increases, and a lithium secondary battery having more excellent charge / discharge cycle characteristics can be configured. In order to secure the above-described effect satisfactorily, in the general composition formula (1) representing the lithium-containing composite oxide, when the total number of elements in the element group M is 100 mol%, the ratio of Ti is set to 0 It is preferable to set it as 0.01 mol% or more, and it is more preferable to set it as 0.1 mol% or more. However, 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 deterioration in characteristics. Therefore, in the general composition formula (1) representing the lithium-containing composite oxide, when the total number of elements in the element group M is 100 mol%, the proportion of Ti is preferably 10 mol% or less, preferably 5 mol%. More preferably, it is more preferably 2 mol% or less.

  Further, the 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 (1). Are preferable in that the following effects can be secured.

  When the lithium-containing composite oxide contains Ge, the crystal structure of the composite oxide after Li is destabilized can improve the reversibility of the charge / discharge reaction, It becomes possible to constitute a lithium secondary battery with higher safety and more excellent 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.

Moreover, when the 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 improved. The non-aqueous electrolysis that the lithium secondary battery has can be achieved by improving the temporal stability of the coating material (positive electrode mixture-containing composition to be described later) that can reduce the active sites and form the positive electrode mixture layer. Irreversible reaction with the liquid 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 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, Irreversible reactions with moisture, 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, in a lithium-containing composite oxide containing Mn such as the lithium-containing composite oxide, the addition of B is more effective because primary particles tend to be difficult to grow.

  When Zr is contained in the lithium-containing composite oxide, the electrochemical properties of the lithium-containing composite oxide are impaired due to the presence of Zr at the grain boundaries and surfaces of the particles of the lithium-containing composite oxide. In addition, since the surface activity is suppressed, it is possible to construct a lithium secondary battery having a better shelf life and a longer life.

  When Ga is contained in the 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, and the positive electrode mixture Stability over time when a coating for forming a layer is improved, and an irreversible reaction with a non-aqueous electrolyte can be suppressed. Moreover, 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 expansion and contraction of the lattice 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 lithium-containing composite oxide, or may be segregated on the particle surface or the like.

  In the general composition formula (1) representing the lithium-containing composite oxide, when the relation between the Co ratio b and the Mn ratio c in the element group M is b> c, the lithium-containing composite oxide is used. By promoting the growth of the oxide particles, the lithium-containing composite oxide having a high packing density at the positive electrode (the positive electrode mixture layer) and a higher reversibility can be obtained. Further improvement can be expected.

  On the other hand, in the general composition formula (1) representing the 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, more thermal stability is obtained. The lithium-containing composite oxide can be made high, and further improvement in the safety of the battery using this can be expected.

The lithium-containing composite oxide having the above composition has a large true density of 4.55 to 4.95 g / cm ³ and is a material having a high volume energy density. Note that the true density of the lithium-containing composite oxide containing Mn in a certain range varies greatly depending on the composition, but the structure is stabilized and the uniformity can be improved in the narrow composition range as described above. It is considered to be a large value close to the true density of LiCoO ₂ . 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 lithium-containing composite oxide has a higher true density especially when the composition is close to the stoichiometric ratio. Specifically, in the general composition formula (1), −0.15 ≦ y ≦ 0. .15 is preferable, 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 lithium-containing composite oxide represented by the general composition formula (1) includes Li-containing compounds (such as lithium hydroxide monohydrate), Ni-containing compounds (such as nickel sulfate), and Co-containing compounds (such as cobalt sulfate). Mn-containing compounds (such as manganese sulfate) and compounds containing other elements contained in element group M (such as aluminum sulfate and magnesium sulfate) can be 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.

  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. Although there is no restriction | limiting in particular about the time of preheating, Usually, what is necessary is just to be 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.

  In the present invention, if the molar ratio of the total Ni amount to the total Li amount in the total positive electrode active material is 0.05 to 1.0, a lithium-containing composite oxide containing Ni as a transition metal as the positive electrode active material, Preferably, the lithium-containing composite oxide represented by the general composition formula (1) may be used alone, or two or more of these may be used in combination. The molar ratio of the total Ni amount to the total Li amount in the total positive electrode active material can be obtained by the following calculation formula.

ΣN _j × a _j / ΣL _j × a _j
Here, in the above formula, N _j : molar composition ratio of Ni contained in component j, a _j : mixed mass ratio of component j, L _j : molar composition ratio of Li contained in component j.

For example, as the lithium-containing composite oxide, a first component: LiNi _0.8 Co _0.1 Mn _0.1 O ₂ and a second component: LiNi _0.7 Co _0.2 Mn _0.1 O ₂ When the mass ratio is 1: 1 (that is, the mixed mass ratio is 0.5 for both the first component and the second component), it is as follows.
(0.8 × 0.5 + 0.7 × 0.5) / (1.0 × 0.5 + 1.0 × 0.5)
= 0.75

  The positive electrode active material according to the present invention is a lithium-containing composite oxide in which the molar ratio of the total Ni amount to the total Li amount in the total positive electrode active material is 0.05 or more and 1.0 or less, and Ni is included as a transition metal. The lithium-containing composite oxide represented by the general composition formula (1) is preferably contained at least.

That is, the positive electrode active material according to the present invention is a lithium-containing composite oxide containing Ni as a transition metal if the molar ratio of the total Ni amount to the total Li amount in the total positive electrode active material is 0.05 to 1.0. In addition to lithium-containing composite oxides containing Ni as a transition metal, other lithium-containing composite oxides (lithium cobalt oxides such as LiCoO ₂ described above; lithiums such as LiMnO ₂ and Li ₂ MnO ₃ may be used. Manganese oxide; lithium-containing composite oxide having a spinel structure such as LiMn ₂ O ₄ and Li _4/3 Ti _5/3 O ₄ ; lithium-containing composite oxide having an olivine structure such as LiFePO ₄ ; And oxides substituted with various elements). In this case, you may use together 1 type, or 2 or more types of lithium containing complex oxide containing Ni as a transition metal, and 1 type or 2 types or more of other lithium containing oxides.

When a lithium-containing composite oxide containing Ni as a transition metal and another lithium-containing oxide are used in combination, a particularly preferable combination example is a lithium-containing composite oxide represented by the general composition formula (1) and LiCoO _2. It is combined use with.

For example, the first component: LiNi _0.8 Co _0.1 Mn _0.1 O ₂ [lithium-containing composite oxide represented by the general composition formula (1)] and the second component: LiCoO ₂ are added in mass. When the ratio is 1: 1 (that is, the mixing mass ratio is 0.5 for both the first component and the second component), the molar ratio of the total Ni amount to the total Li amount in the total positive electrode active material is calculated using the above formula. The following is obtained using.
(0.8 × 0.5) / (1.0 × 0.5 + 1.0 × 0.5) = 0.4

  The composition analysis of the lithium-containing composite oxide used as the positive electrode active material 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. Then, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water are added in order and dissolved by heating. After cooling, the mixture is further diluted 25 times and analyzed by ICP (“ICP-757” manufactured by JARRELASH) (calibration). Line method). The composition formula of the lithium-containing composite oxide can be derived from the results obtained by this analysis.

  When a lithium-containing composite oxide containing Ni as a transition metal is used in combination with another lithium-containing composite oxide, a high capacity of a lithium secondary battery by using a lithium-containing composite oxide containing Ni as a transition metal From the viewpoint of ensuring the better effect of the conversion, the content of the lithium-containing composite oxide containing Ni as the transition metal in the total positive electrode active material is preferably 10% by mass or more, and more preferably 30% by mass or more. It is more preferable. In addition, from the viewpoint of better ensuring the safety improvement effect under excessively high temperature of the lithium secondary battery, the content of the lithium-containing composite oxide containing Ni as a transition metal in the total positive electrode active material, It is preferable to set it as 80 mass% or less, More preferably, it is 60 mass% or more.

  The average particle size of the lithium-containing composite oxide (lithium-containing composite oxide containing Ni as a transition metal or other lithium-containing composite oxide used as necessary) used in the present invention is 5 μm or more. Is preferably 10 μm or more, more preferably 25 μm or less, and even more preferably 20 μm or less. The lithium-containing composite oxide 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.

For example, a laser scattering particle size distribution meter (for example, “LA-920” manufactured by Horiba, Ltd.) is used as the average particle size of various particles (lithium-containing composite oxide, fillers related to a separator described later, and the like) referred to in this specification. The average particle diameter D measured by dispersing these particles in a medium in which the particles are not dissolved is _50% .

Furthermore, the lithium-containing composite oxide used in the present invention has a specific surface area by the BET method of 0 for ensuring reactivity with lithium ions and suppressing side reactions with non-aqueous electrolytes. 0.1 to 0.4 m ² / g is preferable. The specific surface area by the BET method of the lithium-containing composite oxide can be measured by using a specific surface area measuring device by a nitrogen adsorption method (“Macsorb HM model-1201” manufactured by Mounttech).

  The content of the positive electrode active material in the positive electrode mixture layer (the total content of all the positive electrode active materials) is preferably 60 to 95% by mass.

<Conductive aid for positive electrode mixture layer>
The conductive additive of the positive electrode mixture layer relating to the positive electrode of the lithium secondary battery of the present invention may be any one that is chemically stable in the lithium secondary battery. For example, graphite such as natural graphite (flaky graphite), artificial graphite; carbon black such as acetylene black, ketjen black (trade name), channel black, furnace black, lamp black, thermal black; carbon fiber, metal fiber, etc. Conductive fiber; metal powder such as aluminum powder; carbon fluoride; zinc oxide; conductive whisker made of potassium titanate; conductive metal oxide such as titanium oxide; organic conductive material such as polyphenylene derivative; These may be used alone or in combination of two or more. 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.

  Moreover, the positive electrode mixture layer according to the positive electrode of the lithium secondary battery of the present invention has 0.25% by mass or more of 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. It is preferable to contain in the quantity of 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, the density of the positive electrode mixture layer can be increased, and the battery can be further increased in capacity.

  In addition, when the carbon fiber and a lithium-containing composite oxide containing Ni as a transition metal are used in combination, the reaction between the positive electrode and the non-aqueous electrolyte is suppressed to suppress the swelling of the battery due to gas generation. Load characteristics and charge / discharge cycle characteristics can also be improved.

  Details of the reason why the use of the carbon fiber makes it possible to increase the density of the positive electrode mixture layer, suppress the reaction between the positive electrode and the nonaqueous electrolyte, and improve the load characteristics and charge / discharge cycle characteristics of the battery are unknown. However, regarding the densification of the positive electrode mixture layer, the carbon fibers of the size are easily dispersed well in the positive electrode mixture layer, and in particular, the surface of the lithium-containing composite oxide has a structure in which carbon fibers are coated. In addition, since many fibers having a short fiber length are included, the distance between the positive electrode active material particles is shortened, and each component in the positive electrode mixture layer can be satisfactorily filled.

  In addition, 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. 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, so that the charge / discharge cycle characteristics are also improved, and further non-aqueous electrolysis It is considered that the reactivity with the liquid is suppressed and gas generation is suppressed.

  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.

  In addition, the average fiber length and the average fiber diameter of the carbon fiber referred to in the present specification are measured with a transmission electron microscope (TEM, for example, “JEM series” manufactured by JEOL, “H-700H” manufactured by Hitachi, Ltd.), etc. Is measured from a photographed TEM image at 100 or 200 kV. When viewing the average fiber length, take a TEM image of 100 samples 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 JIS level 1 certified metal ruler, and the averages are taken as the average fiber length and average fiber diameter.

  In the positive electrode mixture layer according to the present invention, it is particularly preferable to use the above graphite 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 dispersibility of the carbon fibers in the positive electrode mixture layer becomes better, and the load characteristics and charge / discharge cycle characteristics of the lithium secondary battery can be further improved.

  In addition, when using together the said carbon fiber and graphite, when the sum total of content of the said carbon fiber and content of graphite in a positive mix layer is 100 mass%, content of graphite is 25 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 large, 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.

  In addition, when a conductive additive other than the carbon fiber and graphite (hereinafter referred to as “other conductive additive”) is used in combination with the carbon fiber as the conductive additive related to the positive electrode mixture layer, the positive electrode mixture When the total of the carbon fiber and other conductive auxiliary in the layer is 100% by mass, the content of the other conductive auxiliary is preferably 25 to 87.5% by mass.

  It is preferable that the content rate of the conductive support agent in the positive mix layer (total content rate of all the conductive support agents) is 3-20 mass%.

<Binder of positive electrode mixture layer>
As the binder of the positive electrode mixture layer relating to the positive electrode of the 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 lithium secondary battery. More specifically, for example, vinylidene fluoride-based polymers (VDF-based polymers) whose main component monomer is vinylidene fluoride (VDF), such as polyethylene, polypropylene, and polyvinylidene fluoride (PVDF), polytetrafluoroethylene ( PTFE), polyhexafluoropropylene (PHFP), styrene butadiene rubber, tetrafluoroethylene-vinylidene fluoride copolymer [P (TFE-VDF)], tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexa Fluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrif Oroethylene (PCTFE), propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), or ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl acrylate Copolymers, ethylene-methyl methacrylate copolymers, Na ion cross-linked products of these copolymers, and the like may be used, and only one of them may be used, or two or more may be used in combination.

  Among these binders, it is preferable to use P (TFE-VDF) in combination with a VDF polymer other than P (TFE-VDF).

  VDF-based polymers such as PVDF are relatively used as a binder for a positive electrode mixture layer of a lithium secondary battery, but a lithium-containing composite oxide containing Ni as a transition metal is used as a positive electrode active material. In a positive electrode, when a VDF polymer is used as a binder, a cross-linking reaction of the VDF polymer is likely to occur, and the adhesion between the positive electrode mixture layer and the current collector is excessively increased. When such a positive electrode is used and a wound electrode body is formed together with the negative electrode and the separator, defects such as cracks are likely to occur particularly in the positive electrode mixture layer on the inner peripheral side. However, when P (TFE-VDF) is used as the binder of the positive electrode mixture layer together with the VDF polymer, the adhesion between the positive electrode mixture layer and the current collector can be moderately suppressed by the action of P (TFE-VDF). And the occurrence of defects in the positive electrode mixture layer can be satisfactorily suppressed.

  If the content of the binder in the positive electrode mixture layer (when using multiple types of binders, the total content of all binders; the same applies to the binder content in the positive electrode mixture layer) is too high. Since the adhesiveness between the mixture layer and the current collector becomes too high and the above-mentioned problems are likely to occur, the content is preferably 4% by mass or less, and preferably 3% by mass or less. More preferred.

On the other hand, 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 binder in the positive electrode mixture layer, but if the amount of binder in the positive electrode mixture layer is too small, The flexibility of the mixture layer is reduced, for example, the shape of the wound electrode body using this positive electrode (particularly 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 May be damaged. Therefore, the content of the binder in the positive electrode mixture layer is preferably 1% by mass or more, rather more preferably not less than 1.4 mass%, even more favorable it is 2.5 mass% or more better not.

Moreover, when using together P (TFE-VDF) and a VDF-type polymer as a binder of a positive mix layer, when these sum is made into 100 mass%, the ratio of P (TFE-VDF) is 0.2 mass. % is preferably set to at least, more preferably 10 mass% or more and more preferably be 20 mass% or more. Thereby, even as a positive electrode mixture layer containing a lithium-containing composite oxide containing Ni as a transition metal and a VDF polymer, it is possible to moderately suppress the adhesion with the current collector.

  However, if the amount of P (TFE-VDF) in the total of P (TFE-VDF) and the VDF polymer is too large, the adhesion strength between the positive electrode mixture layer and the current collector is reduced, and the battery resistance is reduced. This may increase the battery load characteristics. Therefore, when the sum of P (TFE-VDF) and the VDF polymer in the positive electrode mixture layer is 100% by mass, the ratio of P (TFE-VDF) is preferably 30% by mass or less.

<Positive electrode mixture layer, current collector, etc.>
The positive electrode is prepared, for example, by preparing a paste-like or slurry-like positive electrode mixture-containing composition 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). (However, the binder may be dissolved in a solvent), which is applied to one or both sides of the current collector, dried, and then subjected to a calendering process as necessary. However, the manufacturing method of the positive electrode is not limited to the above method, and may be manufactured by other manufacturing methods.

Moreover, after the calendar treatment, the thickness of the positive electrode mixture layer is preferably 15 to 200 μm per one surface 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 setting it as the positive electrode which has such a high-density positive mix layer, the capacity | capacitance of a lithium secondary battery can further be improved. 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 decrease. Therefore, the density of the positive electrode mixture layer after the calendar treatment is 4 It is preferably 2 g / cm ³ or less. In addition, as a calendar process, it can roll-press with the linear pressure of about 1-30 kN / cm, for example, It can be set as the positive mix layer which has the said density by such a process.

  Further, the density of the positive electrode mixture layer in the present specification is a value measured by the following method. The electrode is cut into a predetermined area, the mass thereof is measured using an electronic balance having a minimum scale of 0.1 mg, and the mass of the positive electrode mixture layer is calculated by subtracting the mass of the current collector. On the other hand, the total thickness of the 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 calculated from the average value obtained by subtracting the thickness of the current collector from these measured values and the area. To do. Then, the density of the positive electrode mixture layer is calculated by dividing the mass of the positive electrode mixture layer by the volume.

  As the current collector for the positive electrode, the same one used for the positive electrode of a conventionally known lithium secondary battery can be used. For example, an aluminum foil having a thickness of 10 to 30 μm is preferable.

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

  Examples of the negative electrode active material include graphitic carbon materials [natural graphite such as flaky graphite; graphitized carbon such as pyrolytic carbons, mesophase carbon microbeads (MCMB) and carbon fibers at 2800 ° C. or higher. Artificial graphite; etc.], pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, metals that can be alloyed with lithium (Si, Sn, etc.) ) Or alloys thereof, oxides, and the like, and one or more of them can be used.

Among the negative electrode active materials described above, in order to increase the capacity of a lithium secondary battery, in particular, a material containing Si and O as constituent elements (provided that the atomic ratio x of O to Si is 0.5 ≦ x ≦ The material is preferably referred to as “SiO _x ” hereinafter.

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. Since SiO _x has poor conductivity, when it is used as a negative electrode active material, from the viewpoint of securing good battery characteristics, a conductive material (conductive aid) is used, and SiO _x and conductive material in the negative electrode are used. Therefore, it is necessary to form a good conductive network by mixing and dispersing with each other. 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.

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 a state where SiO _x and the carbon material are dispersed inside the granulated body, a better conductive network can be formed. Therefore, in a lithium secondary battery having a negative electrode containing SiO _x as a negative electrode active material, a heavy load Battery characteristics such as 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. Fibrous or coil-like carbon materials are preferable in that they easily form a conductive network and have 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 even if SiO _x particles expand and contract. This is preferable in that it has a property of easily maintaining contact with the particles.

When using SiO _x as the negative electrode active material, it is preferably used in combination as a graphitic carbon material also negative active material as described later, this graphitic carbon material, according to the complex of the SiO _x and the carbon material a carbon It can also be used as a material. Graphite carbon material, like carbon black, has high electrical conductivity and high liquid retention, and even when SiO _x particles expand and contract, they easily maintain contact with the particles. Therefore, it can be preferably used for forming a complex with SiO _x .

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. Fibrous carbon material can follow the expansion and contraction of SiO _x with the charging and discharging of the battery due to the high shape is thin threadlike flexibility, also because bulk density is large, many and SiO _x particles It is because it can have a junction. 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 also be formed on the surface of the SiO _x particles by, for example, a vapor phase method.

The specific resistance value of SiO _x is usually 10 ³ to 10 ⁷ kΩcm, while 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.

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 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.

Incidentally, the SiO _x, in the case of manufacturing a granulated body with small carbon material resistivity value than SiO _x is adding the carbon material in the dispersion liquid of SiO _x are dispersed in a dispersion medium, the dispersion by using a liquid, by a similar method to the case of composite of SiO _x may be a composite particle (granule). 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 less the remaining impurities, 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.

  An isotropic pitch can be used as the pitch, and a phenol resin, a furan resin, a 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 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 processing temperature, the less the remaining impurities, 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 .

When SiO _x (preferably a composite of SiO _x and a carbon material) is used for the negative electrode active material, it is preferable to use a graphitic carbon material in combination. SiO _x has a higher capacity than a carbon material that is widely used as a negative electrode active material for lithium secondary batteries. On the other hand, the volume change due to charging / discharging of the battery is large, so that the negative electrode has a high SiO _x content. In a lithium secondary battery using a negative electrode having a mixture layer, the negative electrode (negative electrode mixture layer) undergoes a large volume change due to repeated charging and discharging, resulting in a decrease in capacity (that is, charge / discharge cycle characteristics are reduced). There is a fear. Graphite carbon material is widely used as a negative electrode active material for lithium secondary batteries, and has a relatively large capacity, while its volume change accompanying charging / discharging of the battery is smaller than that of SiO _x . Therefore, by using SiO _x and a graphitic carbon material in combination with the negative electrode active material, it is possible to suppress the battery capacity improvement effect from decreasing as the amount of SiO _x used decreases as much as possible. Since the deterioration of the charge / discharge cycle characteristics can be satisfactorily suppressed, a lithium secondary battery having higher capacity and excellent charge / discharge cycle characteristics can be obtained.

Examples of the graphitic carbon material used as the negative electrode active material together with the SiO _x include natural graphite such as scale-like graphite; graphitizable carbon such as pyrolytic carbons, mesophase carbon microbeads (MCMB), and carbon fibers. And artificial graphite graphitized at 2800 ° C. or higher.

When using a composite of SiO _x and a carbon material and a graphitic carbon material in combination with the negative electrode active material, from the viewpoint of favorably securing the effect of increasing the capacity by using SiO _x , The content of the composite of SiO _x and carbon material in is preferably 0.01% by mass or more, more preferably 1% by mass or more, and more preferably 3% by mass or more. Further, from the viewpoint of better avoiding the problem due to the volume change of SiO _x due to charge / discharge, the content of the composite of SiO _x and the carbon material in the entire negative electrode active material is 20% by mass or less. Preferably, it is 15 mass% or less.

  The negative electrode active material content in the negative electrode mixture layer (total content of all negative electrode active materials) is preferably 80 to 99% by mass.

<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.

  The binder content (total content of all binders) in the negative electrode mixture layer is preferably 1 to 20% by mass.

<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 lithium secondary battery. For example, carbon black (thermal black, furnace black, channel black, ketjen black, acetylene black, etc. ), Carbon fiber, metal powder (copper, nickel, aluminum, silver, etc.), metal fiber, polyphenylene derivative (as described in JP-A-59-20971), or one or more materials thereof Can do. Among these, carbon black is preferably used, and ketjen black and acetylene black are more preferable.

The particle size of the carbon material used as the conductive aid is, for example, the average particle size measured by the same method as the method for obtaining the average fiber length described above or a laser scattering particle size distribution meter (for example, “LA- 920 "), the average particle diameter (D _50% ) measured by dispersing these fine particles in a medium is preferably 0.01 μm or more, more preferably 0.02 μm or more, It is preferably 10 μm or less, and more preferably 5 μm or less.

  When a conductive material is contained in the negative electrode mixture layer as a conductive additive, it is preferable to use the negative electrode active material and the binder in a range that satisfies the above preferred values.

<Negative electrode mixture layer, current collector, etc.>
For the negative electrode, for example, a negative electrode active material and a binder, and a paste-like or slurry-like negative electrode mixture-containing composition in which the conductive auxiliary agent used as necessary is dispersed in a solvent such as NMP or water are prepared. (However, the binder may be dissolved in a solvent), which is applied to one or both sides of the current collector, dried, and then subjected to a calendering process as necessary. However, the manufacturing method of the negative electrode is not limited to the above method, and may be manufactured by other manufacturing methods. The thickness of the negative electrode mixture layer is preferably, for example, 10 to 100 μm per one side of the current collector.

  As the current collector 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.

<Non-aqueous electrolyte>
For the nonaqueous electrolyte solution according to the lithium secondary battery of the present invention, for example, a solution in which a lithium salt is dissolved in an organic solvent can be used.

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 (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] and the like can be used. .

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

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, 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 conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate.

  Moreover, it is preferable that the non-aqueous electrolyte used for the lithium secondary battery of this invention contains vinylene carbonate (VC). In a lithium secondary battery using a non-aqueous electrolyte containing VC, a film derived from VC is formed on the surface of the negative electrode, and this film forms a non-aqueous electrolysis by a reaction between the negative electrode and the non-aqueous electrolyte associated with charge / discharge of the battery. Since the deterioration of the liquid is suppressed, the charge / discharge cycle characteristics can be improved. In the case of a lithium secondary battery using a carbon material such as a graphitic carbon material as the negative electrode active material, the effect of improving the charge / discharge cycle characteristics by VC is particularly significant.

  Content of VC in non-aqueous electrolyte used for lithium secondary battery (non-aqueous electrolyte used in assembling the battery. The same shall apply hereinafter in the description of the content of various components related to the non-aqueous electrolyte) The rate is preferably 1% by mass or more, and more preferably 1.5% by mass or more. However, if the amount of VC in the non-aqueous electrolyte is too large, excessive gas is generated during film formation, which may cause the battery case to swell. Therefore, the content of VC in the non-aqueous electrolyte used for the lithium secondary battery is preferably 10% by mass or less, and more preferably 5% by mass or less.

  Moreover, it is preferable that the non-aqueous electrolyte used for the lithium secondary battery of this invention contains the phosphono acetate compound represented by following General formula (2).

In the general formula (2), R ^{1 to} R ³ each independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group, or an alkynyl group that may be substituted with a halogen atom, and n is 0 to 6 Indicates an integer.

  Non-aqueous electrolytes used for lithium batteries include, for example, VC, fluoroethylene carbonate, anhydrous acid for the purpose of improving battery charge / discharge cycle characteristics, suppressing high-temperature blistering, and preventing overcharge. , Sulfonic acid ester, dinitrile, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, t-butylbenzene, succinonitrile, and other additives (including these derivatives) are suitable. It is a common practice to select and add appropriate ones.

When a lithium composite oxide containing nickel as a transition metal 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, so that the reactivity between Ni in a highly charged state and the solvent or additive of the nonaqueous electrolyte solution is high, and it is considered that it is likely to become an active site. As a result, excessive reaction between the Ni active sites and the solvent or additive of the non-aqueous electrolyte generates excessive gas and causes battery swelling, and reaction products accumulate at the Ni interface, resulting in increased battery resistance. Or the capacity recovery rate after high-temperature storage may be significantly reduced.

  As a countermeasure against such a problem, it is conceivable to construct a lithium secondary battery using a conventionally known non-aqueous electrolyte to which additives such as 1,3-propane sultone and succinonitrile are added. Since these additives can act on the active sites of Ni in the battery and suppress the above-mentioned excess reaction, this can improve the high-temperature storage property of the battery and suppress the swelling of the battery.

  However, on the other hand, in a lithium secondary battery configured using a non-aqueous electrolyte containing the conventional additive as described above, the charge / discharge cycle characteristics may be deteriorated. This is because conventional additives such as 1,3-propane sultone and succinonitrile react with other than the active site of the positive electrode active material even when the addition amount in the non-aqueous electrolyte is small, and the reaction product is deposited. As a result, it is considered that the capacity is reduced and the resistance is increased.

  On the other hand, when the non-aqueous electrolyte containing the phosphonoacetate compound represented by the general formula (2) is used, the high temperature does not cause deterioration of the charge / discharge cycle characteristics of the lithium secondary battery. The storability can be improved and swelling of the battery can be suppressed. The reason for this is not clear, but it is presumed that the phosphonoacetate compound mainly covers the active sites of Ni accompanying gas generation by reacting with the non-aqueous electrolyte.

Further, 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 formed by the phosphonoacetate compound has high thermal stability, so that the battery is stored under high temperature storage. Is also difficult to disassemble, and is thought to suppress the increase in battery resistance. The reason why such an effect can be obtained is not clear, but such an effect is particularly remarkable when SiO _x is used as the negative electrode active material.

Specific examples of the phosphonoacetate compound represented by the general formula (2) include the following compounds.
[Compound wherein n = 0 in the general formula (2)]
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, etc. butyl bis (2,2,2-trifluoroethyl) phosphonoacetate formate.

[Compound wherein n = 1 in the general formula (2)]
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 , Propylbis (2,2,2-trifluoroethyl) phosphonoacetate, butylbis (2,2,2-trifluoroethyl) phosphonoacetate, allyldimethylphosphonoacetate, allyldiethylphosphonoacetate, 2-propynyldimethyl Such as phosphonoacetate.

[Compound wherein n = 2 in the general formula (2)]
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 wherein n = 3 in the general formula (2)]
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 phosphonoacetates exemplified above, triethylphosphonoacetate (TEPA) is particularly preferred.

  The content ratio of the phosphonoacetate compound represented by the general formula (2) in the non-aqueous electrolyte used for the lithium secondary battery is a viewpoint of ensuring the above-described effect by the phosphonoacetate compound more favorably. Therefore, it is preferably 0.5% by mass or more, and more preferably 1% by mass or more. However, if the amount of the phosphonoacetate compound in the non-aqueous electrolyte is too large, the reaction occurs at other than the active site of the positive electrode active material, as in the case of using the conventional additive as described above. There is a risk of causing an increase in the internal resistance of the battery. Therefore, the content of the phosphonoacetate compound represented by the general formula (2) in the nonaqueous electrolytic solution used for the lithium secondary battery is preferably 5% by mass or less, and preferably 3% by mass or less. More preferably.

  Moreover, it is preferable that the non-aqueous electrolyte used for the lithium secondary battery of the present invention contains a halogen-substituted cyclic carbonate.

  As the halogen-substituted cyclic carbonate, a compound represented by the following general formula (3) can be used.

In the general formula (3), R ⁴ , R ⁵ , R ⁶ and R ⁷ represent hydrogen, a halogen element or an alkyl group having 1 to 10 carbon atoms, and a part or all of the hydrogen of the alkyl group is halogen. may be substituted with an ^element, at least one of R ^4, R 5, ^{R 6} and ^{R 7} are ^halogen, R ^4, R 5, ^{R 6} and ^{R 7} have different respective 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.

The halogen-substituted cyclic carbonate has a function of forming a film on the negative electrode in the lithium secondary battery. For example, in a lithium secondary battery using SiO _x as a negative electrode active material, highly active Si is exposed due to grinding of SiO _x particles caused by volume change accompanying charging and discharging, which decomposes the non-aqueous electrolyte. Therefore, there is a problem that the charge / discharge cycle characteristics are likely to deteriorate. However, in a lithium secondary battery using a non-aqueous electrolyte containing a halogen-substituted cyclic carbonate, even if SiO _x particles are pulverized and a new surface is generated due to a volume change associated with charge and discharge, a halogen-substituted cyclic A film that satisfactorily covers this new surface can be formed by carbonate, and the reaction between the negative electrode active material and the non-aqueous electrolyte can be suppressed to a high degree, so that charge / discharge cycle characteristics can be improved. Therefore, when SiO _x is used as the negative electrode active material, it is more preferable to use a nonaqueous electrolytic solution containing a halogen-substituted cyclic carbonate.

  As the cyclic carbonate substituted with a halogen element, 4-fluoro-1,3-dioxolan-2-one (FEC) is particularly preferable.

The content of the halogen-substituted cyclic carbonate in the non-aqueous electrolyte used in the lithium secondary battery is preferably 1% by mass or more from the viewpoint of better securing the above-described effect due to its use. More preferably, it is 5% by mass or more. However, if the amount of the halogen-substituted cyclic carbonate in the non-aqueous electrolyte is too large, particularly when SiO _x is used as the negative electrode active material, the activity of SiO _x may be reduced. Therefore, the content of the halogen-substituted cyclic carbonate in the nonaqueous electrolytic solution used for the lithium secondary battery is preferably 5% by mass or less, and more preferably 3% by mass or less.

  The non-aqueous electrolyte used in the lithium secondary battery of the present invention includes the aforementioned fluoroethylene carbonate, acid anhydride, sulfonate ester, dinitrile, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluoro Additives (including these derivatives) such as benzene and t-butylbenzene may be appropriately added depending on the desired battery characteristics.

  In addition, the non-aqueous electrolyte may be used in a lithium secondary battery in a state where it is gelled by adding a gelling agent such as a known polymer (so-called gel electrolyte state).

<Separator>
The separator according to the lithium secondary battery of the present invention is a laminate having a porous layer (I) mainly composed of a thermoplastic resin and a porous layer (II) mainly composed of a filler having a heat resistant temperature of 150 ° C. or higher. Use a type separator. As will be described in detail later, the separator has both shutdown characteristics and heat resistance (heat shrinkage resistance). In particular, a lithium-containing composite oxide containing Ni, which is concerned about safety at an excessively high temperature, is used as a positive electrode. It can contribute to the safety improvement of the lithium secondary battery which has been used as a substance and has been increased in capacity by being charged to a voltage exceeding 4.30V.

  In this specification, “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) related to the separator is mainly for ensuring a shutdown function, and the lithium secondary battery reaches or exceeds the melting point of the thermoplastic resin that is the main component of the porous layer (I). When it does, the thermoplastic resin which concerns on porous layer (I) fuse | melts, plugs the void | hole of a separator, and the shutdown which suppresses advancing of an electrochemical reaction arises.

  The thermoplastic resin that is the main component of the porous layer (I) is a resin having a melting point, that is, a melting temperature of 140 ° C. or less measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121. More specifically, for example, PE is mentioned. Moreover, as a form of the porous layer (I), a dispersion containing PE particles is applied to a base material such as a microporous film or a nonwoven fabric that is usually used as a separator for a lithium secondary battery, and is dried. And sheet-like materials such as those obtained by the above. Here, among the total volume of the constituent components of the porous layer (I) [the total volume excluding the pores. The same applies to the volume content of the constituent components of the porous layer (I) and the porous layer (II) relating to the separator. ], The volume content of the thermoplastic resin as a main component 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 PE microporous film, the volume content of the thermoplastic resin is 100% by volume.

  The porous layer (II) according to the 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, and the heat resistant temperature is 150 ° C. The function is ensured by the above filler. That is, when the battery becomes hot, even if the porous layer (I) shrinks, the porous layer (II) that does not easily shrink can cause the positive and negative electrodes directly when the separator is thermally contracted. It is possible to prevent a short circuit due to the contact of. 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.

  The filler related to the porous layer (II) has a heat-resistant temperature of 150 ° C. or higher, is stable with respect to the non-aqueous electrolyte of the battery, and is electrochemically stable that is not easily oxidized or reduced in the battery operating voltage range. As long as it is fine, inorganic particles or organic particles may be used, but fine particles are preferable from the viewpoint of dispersion and the like, and inorganic oxide particles, more specifically, 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 accurately control the porosity of the porous layer (II). It becomes. In addition, the filler whose heat-resistant temperature is 150 degreeC or more may use the thing of the said illustration individually by 1 type, and may use 2 or more types together, for example.

  The shape of the filler having a heat resistant temperature of 150 ° C. or higher according to the porous layer (II) is not particularly limited, and may be substantially spherical (including true spherical), substantially elliptical (including elliptical), plate-like, etc. Various shapes can be used.

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

  In the porous layer (II), since the filler having a heat resistant temperature of 150 ° C. or higher is mainly contained, the filler having a heat resistant temperature of 150 ° C. or higher in the total volume of the constituent components of the porous layer (II) The volume content is 50% by volume or more, preferably 70% by volume or more, more preferably 80% by volume or more, and still more preferably 90% by volume or more. By setting the filler in the porous layer (II) to a high content as described above, even when the lithium secondary battery becomes high temperature, it is possible to satisfactorily suppress the thermal shrinkage 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.

  In addition, since it is preferable to contain an organic binder in porous layer (II) so that it may mention later, the volume in the whole volume of the structural component of porous layer (II) of the filler whose heat-resistant temperature is 150 degreeC or more The content is preferably 99.5% by volume or less.

  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 more 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. Examples of organic binders include ethylene-vinyl acetate copolymers (EVA, those having a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylic acid copolymers such as ethylene-ethyl acrylate copolymers, and 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-based rubber, and SBR are preferable. Specific examples of such highly flexible organic binders include Mitsui DuPont Polychemical's “Evaflex Series (EVA)”, Nihon Unicar's EVA, Mitsui DuPont Polychemical's “Evaflex-EAA Series (Ethylene). -Acrylic acid copolymer) ", Nippon Unicar EEA, Daikin Industries" DAI-EL Latex Series (Fluororubber) ", JSR" TRD-2001 (SBR) ", Nippon Zeon" BM-400B " (SBR) ".

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

  The separator is, for example, a porous layer (II) -forming composition (such as a liquid composition such as a slurry) containing a filler having a heat-resistant temperature of 150 ° C. or higher. It can be produced by applying it to the surface of a sheet-like material such as a porous film and drying it to a predetermined temperature to form the porous layer (II).

  The composition for forming the porous layer (II) contains a filler having a heat resistant temperature of 150 ° C. or higher, and an organic binder as required, and these are dispersed in a solvent (including a dispersion medium; the same applies hereinafter). Is. The organic binder can be dissolved in a solvent. The solvent used in the composition for forming the porous layer (II) may be any one that can uniformly disperse the filler having a heat resistant temperature of 150 ° C. or higher and can uniformly dissolve or disperse the organic binder. Common organic solvents such as aromatic hydrocarbons such as toluene, furans such as tetrahydrofuran, and ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. In addition, 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) preferably has a solid content containing, for example, a filler or an organic binder having a heat resistant temperature of 150 ° C. or higher, for example, 10 to 80% by mass.

  In the 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, a configuration in which the porous layer (I) is disposed on both sides of the porous layer (II) or a configuration in which the porous layer (II) is disposed on both sides of the porous layer (I) may be employed. However, increasing the number of layers may increase the thickness of the separator, leading to an increase in internal resistance of the battery and a decrease in energy density, so it is not preferable to increase the number of layers. The total number of layers of the layer (I) and the porous layer (II) is preferably 5 or less.

  The thickness of the separator is preferably 10 to 30 μm, for example.

  In addition, the thickness of the porous layer (II) in the separator [when the separator has a plurality of porous layers (II), the total thickness] allows the porous layer (II) to exhibit the above-described functions more effectively. From the viewpoint, it is preferably 3 μm or more. 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, the thickness of the porous layer (I) in the separator [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 further preferably 14 μm or less.

  The porosity of the separator as a whole is preferably 30% or more in a dried state in order to secure a liquid retention amount of the non-aqueous electrolyte and 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 equation (4).

P = {1- (m / t) / (Σa _i · ρ _i )} × 100 (4)
Here, in the above formula, a _i : ratio of component i when the total mass is 1, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of the separator (g / cm ² ), t: thickness of separator (cm).

Moreover, in said Formula (4), m is the mass per unit area (g / cm < ² >) of porous layer (I), t is the thickness (cm) of porous layer (I), and _ai is porous The porosity of the porous layer (I): P (%) can also be obtained by using the equation (4) by setting the ratio of the component i when the mass of the entire porous layer (I) is 1. it can. The porosity of the porous layer (I) determined by this method is preferably 30 to 70%.

Further, in the case of the laminated separator, in the formula (4), 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), and a _i is the ratio of the component i when the mass of the entire porous layer (II) is 1, so that the porosity of the porous layer (II) using the formula (4): P (%) can also be obtained. 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. By setting the separator to the above configuration, the puncture strength can be set to the above value.

  The puncture 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 semispherical 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 making a hole in the separator 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 measurement values of 5 times, and this is made into the piercing strength of a separator.

<Electrode body>
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 lithium secondary battery of the invention.

  In the laminated electrode body and the wound electrode body, it is preferable to arrange the separator so that the porous layer (II) of the separator faces at least the positive electrode. In this case, since the porous layer (II) having a heat resistance temperature of 150 ° C. or more as a main component and more excellent in oxidation resistance faces the positive electrode, the oxidation of the separator by the positive electrode can be suppressed more favorably. In addition, the storage characteristics and charge / discharge cycle characteristics of the battery at high temperatures can be improved. In addition, when a non-aqueous electrolyte containing an additive such as VC or cyclohexylbenzene is used, there is a possibility that a film is formed on the positive electrode side to clog the pores of the separator, resulting in deterioration of battery characteristics. Therefore, an effect of suppressing pore clogging can be expected by making the relatively porous porous layer (II) face the positive electrode.

  On the other hand, when one surface of the separator is the porous layer (I), it is preferable that the porous layer (I) faces the negative electrode, so that, for example, the porous layer (I ) Is suppressed from being absorbed by the electrode mixture layer, and can be efficiently used to close the pores of the separator.

<Battery case>
In FIG. 1, the perspective view which represents typically the external appearance of an example of the lithium secondary battery of this invention is shown. A lithium secondary battery 1 shown in FIG. 1 has a columnar battery case 10 that is hollow and contains a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, and the like.

  The battery case 10 includes an outer can 11 and a lid 20, and the outer can 11 has a bottomed cylindrical shape (square tube shape), and the lid 20 is covered on the opening end portion thereof. It is integrated with the lid 20 by welding. The outer can 11 and the lid 20 are made of, for example, an aluminum alloy.

  A terminal 21 made of stainless steel or the like protrudes from the lid 20, and an insulating packing 22 made of PP or the like is interposed between the terminal 21 and the lid 20. The terminal 21 is connected to, for example, a negative electrode in the battery case 10. In this case, the terminal 21 functions as a negative electrode terminal, and the outer can 11 and the lid 20 function as a positive electrode terminal. However, depending on the material of the battery case 10, the terminal 21 may be connected to the positive electrode in the battery case 10 to function as a positive electrode terminal, and the outer can 11 and the lid 20 may function as a negative electrode terminal. Further, the lid 20 is provided with a non-aqueous electrolyte injection port, which is sealed with a sealing member 23 after the non-aqueous electrolyte is injected into the battery case 10.

  The side surface portion of the battery case 10, that is, the side surface portion of the outer can 11 has two wide surfaces 111 and 111 that are opposed to each other and wider than the other surfaces (surfaces 112 and 112 in the drawing). doing. At least one of the wide surfaces 111 and 111 (in FIG. 1, the wide surface 111 at the front in the drawing) is provided with a cleavage groove 12 for cleavage when the pressure in the battery case 10 becomes greater than a threshold value. ing.

  FIG. 2 shows a side view of the battery case 10 of the lithium secondary battery shown in FIG. 1 as viewed from the wide surface 111 side. As shown in FIG. 2, the cleavage groove 12 is provided so as to intersect with a diagonal line (indicated by a one-dot chain line in the figure) in a side view from the wide surface 111 side. The diagonal line is drawn from the end of the battery case 10 when the side surface of the battery case 10 is viewed from the side of the wide surface 11 as viewed in a side view as a two-dimensional shape.

  As shown in FIGS. 1 and 2, the battery case according to the lithium secondary battery of the present invention has two wide surfaces facing each other on the side surface thereof, and the side surface portion of the battery case has The cleavage groove that is to be cleaved when the pressure in the battery case becomes larger than a threshold value is provided so as to intersect a diagonal line in a side view from the wide surface side.

  In conventional lithium secondary batteries, a lid is usually provided with a cleavage vent, and when the internal pressure rises due to the battery being placed at an excessively high temperature, the cleavage vent is cleaved to discharge the internal gas to the outside. In addition, safety is ensured by reducing the internal pressure to prevent battery rupture. However, a lithium secondary battery that uses a lithium-containing composite oxide containing Ni as a positive electrode active material and is charged to a voltage exceeding 4.30 V to increase the capacity is used at an excessively high temperature. If placed, the lithium-containing composite oxide has high reactivity, so that there is a concern that the internal pressure of the battery suddenly increases and the battery bursts before operating the cleavage vent provided on the lid.

  FIG. 3 is a perspective view showing a state of the lithium secondary battery of FIG. 1 when the battery internal pressure is increased, and FIG. 4 is a cross-sectional view taken along line II of FIG. As shown in FIGS. 3 and 4, when the internal pressure of the lithium secondary battery 1 rises and swells, the cleavage groove 12 is cleaved, and a gap 13 is formed at the cleavage portion. Is discharged.

  As shown in FIG. 3, when the internal pressure of the lithium secondary battery suddenly increases and the battery case expands, the vicinity of the portion corresponding to the diagonal line in the side view from the wide surface side of the side surface portion of the battery case is A ridge line (L in the figure) is formed, and a particularly large stress is applied to the side wall of the side surface along the ridge line L. Therefore, in the lithium secondary battery of the present invention, the internal pressure of the battery increased sharply by providing a cleavage groove so as to intersect the diagonal line, which is a portion where particularly large stress is applied when swelling occurs due to rapid internal pressure. In this case, the threshold for cleavage is lowered as much as possible to increase the operating speed of the cleavage groove, thereby improving the safety.

  FIG. 5 is a perspective view schematically showing another example of the lithium secondary battery of the present invention, and FIG. 6 is a side view of the lithium secondary battery of FIG. The lithium secondary battery shown in FIGS. 5 and 6 is an example in which a linear cleavage groove is formed in the side surface portion of the battery case 10.

  7 is a perspective view schematically showing another example of the lithium secondary battery of the present invention, and FIG. 8 is a side view of the lithium secondary battery of FIG. The lithium secondary battery shown in FIGS. 7 and 8 is an example in which a curved cleavage groove is formed in the side surface portion of the battery case 10.

  Thus, there is no restriction | limiting in particular about the shape of the cleavage groove formed in the side part of the battery case in the lithium secondary battery of this invention. For example, it may be linear as shown in FIGS. 5 and 6, or may be curved as shown in FIGS. Further, as shown in FIGS. 1 to 3, in a side view, an inwardly curved portion that curves in a projecting manner toward the inside of the side surface of the battery case 10, and a projecting shape toward the outside of the side surface of the battery case 10. It may be a cleavage groove having a shape constituting a cleavage line having a curved outward curved portion. In the case of the cleavage groove 12 shown in FIGS. 1 to 3, when the pressure in the battery case 10 becomes larger than the threshold value, the cleavage groove 12 is cleaved along the cleavage line.

  Among these, it is preferable that the opening groove has a curved shape, such as a shape as shown in FIGS. 1 to 3 or a shape as shown in FIGS. When the cleaving groove is curved, the entire length of the groove can be made longer in a narrow area than when the cleaving groove is straight, so that the area of the opening can be increased at the time of cleaving. The gas can be discharged to the outside more efficiently.

  As shown in FIGS. 1 to 3, the lithium secondary battery has an inwardly curved portion that curves in a projecting manner toward the inside of the side surface of the battery case and a laterally outward side of the battery case in a side view. It is further preferable to have a cleavage groove having a shape constituting a cleavage line having an outward curved portion that curves in a projecting manner. Since the tear line constituted by the tear groove has the inwardly curved portion and the outwardly curved portion, it is difficult for the tear groove to be broken by an impact applied to the battery case. In other words, when the cleavage groove is a straight line, if an external impact is applied from the direction of the straight line extension, there is a possibility that the cleavage groove may be cleaved at once. However, with the above-described configuration, the cleavage is caused by an external impact from a specific direction. It can suppress more favorably that this occurs. Therefore, with this configuration, it is possible to better prevent the cleavage groove from being cleaved by the impact applied to the battery case and the electrolyte inside the battery from leaking out.

  In addition, as described above, by forming the tear line by combining the inwardly curved part and the outwardly curved part, when the cleavage groove is cleaved along this tear line, the protrusion formed by the inwardly curved part And a protrusion formed by the outward bending portion protrude toward the outside of the battery. Thereby, the opening formed by the cleavage of the cleavage groove can be enlarged, and the gas inside the battery can be discharged from the cleavage portion to the outside more efficiently. In addition, in this configuration, since the protrusion formed by the cleavage of the cleavage groove is positioned outside the battery, it is better prevented that a short circuit occurs between the inside of the battery and the battery case at the cleavage part. You can also

  In the case of the cleavage groove having the shape constituting the cleavage line having the inward bending portion and the outward bending portion, as shown in FIGS. 1 to 3, the inward bending portion and the outward bending portion are alternately positioned. More preferably, it is formed on the wide surface of the side surface portion of the battery case so as to constitute a cleavage line.

  By alternately providing the inward bending portion and the outward bending portion, when the cleavage groove is torn apart, the protrusion formed by the inward bending portion and the protrusion formed by the outward bending portion are alternated. Since the battery protrudes outward, the opening formed by the cleavage of the cleavage groove can be made larger. Therefore, the gas inside the battery and the like can be discharged from the cleavage portion to the outside more efficiently. In addition, by alternately providing the inward bending portion and the outward bending portion, the protrusion formed by each bending portion protrudes more reliably toward the outside of the battery, so that the protrusion enters the inside of the battery. It is possible to more reliably prevent a short circuit from occurring.

  In the case of a cleavage groove in which an inward bending portion and an outward bending portion constitute a cleavage line alternately positioned, a cleavage line is formed by combining the inward bending portion and the outward bending portion one by one. More preferably, it is formed on the side surface of the battery case. By doing so, the cleavage groove can be more easily cleaved when the battery case swells, and a large opening can be easily formed by the cleavage of the cleavage groove.

  In the case of a cleavage groove having a shape constituting a cleavage line having the inward bending portion and the outward bending portion, as shown in FIG. 2, the connecting portion between the inward bending portion and the outward bending portion is: More preferably, the battery case is provided at a position corresponding to a diagonal line in a side view of the wide surface of the side surface portion of the battery case.

  As described above, in a side view of the wide surface of the side surface portion of the battery case, a portion corresponding to a diagonal line is highly likely to become a ridge line when the battery case bulges. Therefore, as shown in FIG. 3, when the connection portion between the inward bending portion and the outward bending portion is formed at a location corresponding to the diagonal line, when the battery case 10 swells, the connection portion Cleavage proceeds to the inwardly curved part and the outwardly curved part, whereby the entire cleavage groove 12 is cleaved. Then, by the cleavage of the cleavage groove 12, tongue portions 123 and 124 having shapes corresponding to the shapes of the inwardly curved portion and the outwardly curved portion are formed (semicircular tongue portions in the drawing).

  At this time, as shown in FIG. 4, the side wall of the battery case (side wall 11 a of the outer can) is in a state where the tongues 123 and 124 are floated with respect to other parts by the cleavage of the cleavage groove 12, and the gap 13 is formed. Is done. In other words, when the battery case side wall (side wall 11a of the outer can) is cut by the cleavage of the cleavage groove 12, a portion on the ridge line L that is pulled to the corner of the battery case is pulled outward. Thus, the tongues 123 and 124 are lifted with respect to other portions of the side wall 11a (indicated by white arrows in FIG. 4). Therefore, since the opening area of the cleavage portion can be increased, the gas inside the battery can be discharged to the outside more efficiently.

  The shape of the cleavage groove, as viewed from the side, includes an inwardly curved portion that protrudes in a projecting manner toward the inside of the side surface of the battery case, and an outwardly curved portion that curves in a projecting manner toward the outside of the side surface of the battery case. More specifically, in the case of a shape that forms a cleavage line, the inner curved portion 121 and the outer curved portion 122 have a semicircular shape having substantially the same size, as shown in FIG. Can do. In the case of the opening groove of this shape, the shape of the tongues 123 and 124 formed by cleaving as the battery internal pressure increases is semicircular as shown in FIG.

  Moreover, it is preferable that the cleavage groove is formed so that the depth of the portion located on the diagonal line in the side view from the wide surface side of the battery case side surface portion is deeper than the other portions. As described above, the vicinity of the diagonal line is highly likely to become a ridge line when the battery case swells, so by setting the depth of the cleavage groove as described above, it is positioned on the ridge line of the cleavage groove. The part to be cut can be easily cleaved. In this case, the depth of the cleavage groove may be continuously inclined and changed, and there may be a step between a deep portion and a shallow portion.

  Furthermore, the shape of the cleavage groove is, as viewed from the side, an inwardly curved portion that curves in a projecting manner toward the inside of the side surface of the battery case, and an outwardly curved portion that curves in a projecting manner toward the outside of the side surface of the battery case. It is also preferable that the cleavage groove is constituted by a plurality of groove portions that are separated from each other and are arranged side by side so as to form the cleavage line. In this case, it is possible to more reliably prevent the cleavage groove from breaking when the battery receives an impact such as dropping. And when an electronic case swells, after a several groove part is cleaved, since a battery case is cleaved so that these groove parts may be connected, it becomes possible to make it cleave easily by the said cleavage line.

  The cleavage groove can be formed when press-molding an outer can that constitutes the battery case. Thereby, since work hardening arises in the peripheral part of a cleavage groove by press work, the intensity | strength of the peripheral part of a cleavage groove can be raised. Therefore, even when an impact due to dropping or the like is applied to the lithium secondary battery, it is possible to suppress the cleavage of the cleavage groove due to the impact.

  The shape of the battery case (the shape of the outer can) may be a shape (for example, a shape that is a hexahedron) between the wide surface in the side surface and the other surface (for example, a shape that is a hexahedron). As shown in FIG. 6, the space between the wide surface and the other surface is curved (for example, the portion corresponding to the other surface of the lid and the bottom surface, which is the upper surface portion, has an arc shape, etc. The shape may be a curved surface).

  In addition, when the shape of the battery case is curved between the wide surface and the other surface in the side surface portion, particularly when the other surface is curved, even if the battery case swells, compared to the hexahedron battery case The tensile force at the portion between the wide surface and the other surface is small. In this case, the force applied to the cleavage groove is reduced, but in the lithium secondary battery of the present invention, when the battery case is swollen, a portion where a particularly large stress is applied (that is, crossing the diagonal line in the side view from the wide surface side of the side portion). Since the cleavage groove is provided at the location where the cleavage occurs, the opening area when the cleavage occurs can be increased, and the gas in the battery can be discharged efficiently.

  The lithium secondary battery of the present invention can be used for 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. However, the following examples do not limit the present invention.

<Synthesis of lithium-containing composite oxide A containing Ni>
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 kept at 50 ° C., and a sodium hydroxide aqueous solution having a concentration of 6.4 mol / dm ³ is dropped at the same time so that the pH of the reaction solution is maintained around 12. Further, 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. Lithium-containing composite oxide A was synthesized by firing for a period of time.

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

About the said lithium containing complex oxide A, the composition analysis was performed as follows using ICP method. First, 0.2 g of the lithium-containing composite oxide A 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 and analyzed by ICP (“ICP-757” manufactured by JARRELASH) (calibration). Line method). From the obtained results, the composition of the lithium-containing composite oxide A was derived and found to be a composition represented by Li _1.02 Ni _0.6 Co _0.2 Mn _0.2 O ₂ .

<Synthesis of lithium-containing composite oxide B containing Ni>
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 also dropped at the same time so that the pH of the reaction solution is maintained near 12. In order to react under an inert 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. Lithium-containing composite oxide B was synthesized by firing for a period of time. The obtained lithium-containing composite oxide B was pulverized into a powder in a mortar and then stored in a desiccator.

For the lithium-containing composite oxide B, where the composition analysis was performed by a calibration curve method using the ICP method described above, the results obtained have been derived composition of the lithium-containing complex oxide B, Li _1.02 It was found that the composition was represented by Ni _0.895 Co _0.05 Mn _0.05 Ti _0.005 O ₂ .

<Synthesis of lithium-containing composite oxide C containing Ni>
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, lithium-containing composite oxide C was synthesized in the same manner as lithium-containing composite oxide A. The composition analysis of the lithium-containing composite oxide was performed by the calibration curve method using the ICP method described above, and the composition of the lithium-containing composite oxide C was derived from the obtained results. Li _1.02 Ni It was found that the composition was represented by _0.3 Co _0.3 Mn _0.3 O ₂ .

Example 1
<Preparation of positive electrode>
The lithium-containing composite oxide A and other lithium-containing composite oxide LiCoO ₂ were weighed to a mass ratio shown in Table 1, and mixed using a Henschel mixer for 30 minutes to obtain a mixture. 100 parts by mass of the obtained mixture (positive electrode active material), 20 parts by mass of a solution in which PVDF and P (TFE-VDF) as binders were dissolved in NMP, and an average fiber having an average fiber length of 100 nm as a conductive additive A 1.04 part by mass carbon fiber having a 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 to prepare a positive electrode mixture-containing paste. did. Note that the amount of PVDF and P (TFE-VDF) NMP solution used is such that the amount of dissolved PVDF and P (TFE-VDF) is a mixture of the lithium-containing composite oxide A and LiCoO ₂ and PVDF. And P (TFE-VDF) and the conductive auxiliary agent (ie, the total amount of the positive electrode mixture layer) in 100% by mass, the amounts were 2.34% by mass and 0.26% by mass, respectively. That is, in the positive electrode, the total amount of the binder in the positive electrode mixture layer is 2.6 mass%, and the ratio of P (TFE-VDF) in the total 100 mass% of P (TFE-VDF) and PVDF is 10 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. In addition, the density of the positive mix layer measured by the above-mentioned method was 3.80 g / cm < ³ >.

<Production of negative electrode>
A composite in which the surface of SiO having an average particle diameter of 8 μm is coated with a carbon material (the amount of the carbon material in the composite is 10 mass%, hereinafter referred to as “SiO / carbon material composite”), and the average particle diameter is Negative electrode active material obtained by mixing graphite having a size of 16 μm in an amount such that the amount of the SiO / carbon material composite is 3.0 mass%: 1 mass adjusted to 98 mass parts and a viscosity of 1500 to 5000 mPa · s. % Concentration CMC aqueous solution: 100 parts by mass and SBR: 1.0 part by mass using 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 did.

  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>
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 to 5 kg of boehmite secondary aggregates having an average particle size of 3 μm. A dispersion was prepared by crushing for 10 hours with a ball mill at 40 times / min. 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.

  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 a lithium secondary battery (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. As a non-aqueous electrolyte, in a solvent in which ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed at a volume ratio = 1: 1: 1, LiPF ₆ was dissolved to a concentration of 1.1 mol / l. A solution was prepared by adding FEC in an amount of 2.0% by mass, VC in an amount of 1.0% by mass, and further adding TEPA in an amount of 1.0% by mass. It poured into the outer can.

  After injecting the non-aqueous electrolyte, the outer can was sealed to produce a lithium secondary battery having the structure shown in FIG. 9 with the appearance shown in FIGS.

  Here, the lithium secondary battery will be described with reference to FIGS. 1, 2, and 9. The lithium secondary battery is formed from the side of the side surface of the battery case 10 (the outer can 11) from the wide surface 111 side. A cleavage groove 12 is provided so as to intersect with a diagonal line in a side view. The cleavage groove 12 includes an inwardly curved portion 121 that protrudes in a projecting manner toward the inner side surface of the battery case 10 and an outwardly curved portion 122 that curves in a projecting manner toward the outer side surface of the battery case 10. The inwardly curved portion 121 and the outwardly curved portion 122 have a semicircular shape having substantially the same size, and constitute a substantially S-shaped tear line having one by one. . And the connection part of the inward bending part 121 and the outward bending part 122 is installed so that it may become a location equivalent to the diagonal in the side view from the wide surface 111 side of the side part of the battery case 10 (exterior can 11). Has been. In addition, the cleavage groove 12 was formed such that the depth of the portion located on the diagonal line in the side view from the wide surface 111 side of the side surface portion of the battery case 10 (exterior can 11) was deeper than the other portions.

  Further, as shown in FIG. 9, in the lithium secondary battery, the positive electrode 31 and the negative electrode 32 are spirally wound through the separator 33 as described above, and then pressed so as to become flat. The wound electrode body 30 is housed in a rectangular tube-shaped outer can 11 together with a non-aqueous electrolyte. However, in FIG. 1, in order to avoid complication, a metal foil, a non-aqueous electrolyte, or the like as a current collector used for manufacturing the positive electrode 31 and the negative electrode 32 is not illustrated. Also, the separator layers are not shown separately. Furthermore, the inner peripheral side portion of the wound electrode body is not cross-sectional.

  The outer can 11 is made of an aluminum alloy, and constitutes a battery case together with the lid 20. The outer can 11 also serves as a positive electrode terminal. And the insulator 40 which consists of PE sheets is arrange | positioned at the bottom part of the armored can 11, and it connects to each one end of the positive electrode 31 and the negative electrode 32 from the flat wound electrode body 30 which consists of the positive electrode 31, the negative electrode 32, and the separator 33. The positive electrode lead body 51 and the negative electrode lead body 52 thus drawn are drawn out. A stainless steel terminal 21 is attached to an aluminum alloy lid (sealing lid plate) 20 that seals the opening of the outer can 11 via a PP insulating packing 22. A stainless steel lead plate 25 is attached via an insulator 24.

  And this cover 20 is inserted in the opening part of the armored can 11, and the opening part of the armored can 11 is sealed by welding the junction part of both, and the inside of a battery is sealed. Further, in the battery of FIG. 9, the lid 20 is provided with a non-aqueous electrolyte inlet, and the sealing member 23 is inserted into the non-aqueous electrolyte inlet, for example, by laser welding or the like. Sealing of the battery is ensured by welding sealing.

  In the battery of Example 1, the outer can 11 and the lid body 20 function as a positive electrode terminal by directly welding the positive electrode lead body 51 to the lid body 20, and the negative electrode lead body 52 is welded to the lead plate 25. By connecting the negative electrode lead body 52 and the terminal 21 through the lead plate 25, the terminal 21 functions as a negative electrode terminal.

Examples 2-5, 8-10
Table 2 shows the positive electrode produced in the same manner as in Example 1 except that the mixing ratio of the lithium-containing composite oxide A and LiCoO ₂ in the positive electrode active material was changed as shown in Table 1, and the amount of TEPA added. A lithium secondary battery was produced in the same manner as in Example 1 except that the non-aqueous electrolyte prepared in the same manner as in Example 1 was used except that the above was changed.

Example 6
Except that the lithium-containing composite oxide B was used in place of the lithium-containing composite oxide A, the positive electrode produced in the same manner as in Example 1 and the amount of TEPA added were changed as shown in Table 2. A lithium secondary battery was produced in the same manner as in Example 1 except that the non-aqueous electrolyte prepared in the same manner as in Example 1 was used.

Example 7
A positive electrode was produced in the same manner as in Example 1 except that the positive electrode active material was changed to only the lithium-containing composite oxide C, and a lithium secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used. .

Examples 11 and 12
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that the amount of TEPA added was changed as shown in Table 2. A lithium secondary solution was prepared in the same manner as in Example 1 except that this non-aqueous electrolyte was used. A battery was produced.

Example 13
A negative electrode was produced in the same manner as in Example 1 except that the negative electrode active material was changed to only graphite having an average particle size of 16 μm, and a lithium secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used. did.

Comparative Example 1
A positive electrode was produced in the same manner as in Example 1 except that the positive electrode active material was changed to only LiCoO ₂ , and a lithium secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 2
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the amount of TEPA added was changed as shown in Table 2 .

A partial longitudinal sectional view and an external perspective view schematically showing the lithium secondary battery of Comparative Example 2 are shown in FIGS. 10 and 11, respectively. As shown in FIGS. 10 and 11, except that the outer can 11 in which the cleavage groove is not formed in the side surface portion, the lid body 20 in which the cleavage vent 26 is formed, and the non-aqueous electrolyte described above are used. A lithium secondary battery 102 was produced in the same manner as in Example 5 .

Comparative Example 3
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the amount of TEPA added was changed as shown in Table 2 .

A side view schematically showing the lithium secondary battery of Comparative Example 3 is shown in FIG. As shown in FIG. 12, the outer can 11 in which a cleavage groove 12 is formed in a portion shown in the drawing of the wide surface 111 (a portion not intersecting with a diagonal line in a side view on the wide surface 111 side), and the non-aqueous electrolysis described above A lithium secondary battery 103 was produced in the same manner as in Example 5 except that the liquid was used.

Comparative Example 4
A lithium secondary battery was produced in the same manner as in Comparative Example 1 except that a battery case (an outer can and a lid) having the same configuration as in Comparative Example 2 was used.

  Each of the lithium secondary batteries of Examples and Comparative Examples was evaluated as follows.

<Battery capacity>
About each battery of an Example and a comparative example, it charges until it reaches 4.4V with a constant current of 1C at the normal temperature (25 ° C.) after the first charge / discharge, and then charges with a constant voltage of 4.4V-constant-constant Voltage charge (total charge time: 2.5 hours) was performed, and then 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 1, the discharge capacity measured in each Example and Comparative Example is shown as a relative value (%) divided by the discharge capacity of Example 1. In addition, about the battery of the comparative example 4, the battery capacity was measured on the same conditions as the above except having changed the end voltage at the time of charge to 4.2V.

<Battery swelling>
About each battery of an Example and a comparative example, it charged on the same conditions as the measurement of battery capacity after initial charge / discharge. After charging, measured in advance thickness T ₁ of the battery outer can, then, stored for 24 hours in a constant temperature bath set at 85 ° C. the cells, taken out from the thermostatic bath, after 3 hours standing at ambient temperature, to measure the thickness T ₂ of the battery outer can again. The battery outer can thickness referred to in this test means the thickness between the wide surfaces of the side surfaces of the outer can. The thickness of the battery outer can was measured in units of 1/100 mm using a vernier caliper (for example, Mitutoyo Corp .; CD-15CX) with the central portion of the wide surface as the measurement target.

The battery swelling was evaluated from the rate of change to the outer can thickness T ₁ and T ₂ before and after storage relative to the outer can thickness T ₁ before storage at 85 ° C. That is, the battery swelling (%) was obtained by the following formula.
Battery swelling (%) = 100 × (T ₂ −T ₁ ) / (T ₁ )

<Capacity recovery rate after high temperature storage>
About each battery of an Example and a comparative example, it charged on the same conditions as the measurement of battery capacity after initial charge / discharge. After charging, 0.5 C constant current discharge (discharge end voltage: 3.0 V, hereinafter, the same discharge end voltage) was performed, and the obtained discharge capacity (mAh) was set to 0.5 C capacity before the storage test. Thereafter, the battery was stored in a thermostat set at 85 ° C. for 24 hours, taken out from the thermostat, and allowed to stand at room temperature for 3 hours, followed by 0.5 C constant current discharge. After charging the battery under the same conditions as described above, the discharge capacity (mAh) obtained by performing a constant current discharge of 0.5 C was taken as the 0.5 C capacity after the storage test. From these results, the capacity recovery rate at 0.5 C after the storage test with respect to the 0.5 C capacity before the storage test was determined by the following formula.
Capacity recovery rate (%)
= 100 × {(0.5 C capacity after storage test) / (0.5 C capacity before storage test)}

<Charge / discharge cycle characteristics>
About each battery of an Example and a comparative example, after initial charge / discharge, charging / discharging is repeated by making a series of operation of charge and discharge of the same conditions as measurement of battery capacity into 1 cycle. The number of cycles when the discharge capacity was 80% was examined.

<Evaluation of composition in positive electrode active material after charge / discharge cycle>
For each battery that was evaluated for charge / discharge cycle characteristics, the battery was further charged / discharged until the discharge capacity reached 50% of the discharge capacity obtained in the first cycle, and then the lithium secondary battery was disassembled and taken out. After washing with dimethyl carbonate and drying, the composition was analyzed by the above-described calibration curve method using ICP, and the composition of the positive electrode active material in the positive electrode mixture layer was derived from the obtained results, The molar ratio of the total Ni amount to the total Li amount in the total positive electrode active material was calculated.

<150 ° C heating test>
About each battery of an Example and a comparative example, the charge of the same conditions as the measurement of battery capacity was performed after the first charge / discharge. Each battery after charging is placed in a thermostatic chamber, heated from 30 ° C. to 150 ° C. at a rate of 1 ° C. per minute, heated, and then held at 150 ° C. for 30 minutes. The surface temperature was measured. A battery having a surface temperature of 170 ° C. or lower was evaluated as “◯ (good safety)”, and a battery having a surface temperature exceeding 170 ° C. (a battery that caused thermal runaway) was evaluated as “× (poor safety). ")."

  Table 1 shows the configuration of the positive electrodes of the lithium secondary batteries of Examples and Comparative Examples, and Table 2 shows the configuration of the negative electrode, the configuration of the non-aqueous electrolyte (addition amount of triethylphosphonoacetate), and the configuration of the cleavage groove. Each evaluation result is shown in Table 3, respectively. The “Ni / Li ratio” in Table 1 means the molar ratio of the total Ni amount to the total Li amount in the total positive electrode active material. Further, “1” in the column of “Cleavage groove” in Table 2 indicates that a cleavage groove is provided at a location intersecting with a diagonal line in the side view of the wide surface of the battery case side surface, and “2” indicates that the battery case side surface. In the side view of the wide surface of the part, a cleavage groove was provided at a location that does not intersect with the diagonal line, and `` × '' indicates that a cleavage groove was not formed in the side surface of the battery case and a cleavage vent was provided in the lid. , Each mean.

As is apparent from Tables 1 to 3, Examples 1 to 13 in which the molar ratio of the total amount of Ni to the total amount of Li in the total positive electrode active material was appropriate, and cleavage grooves were formed at appropriate locations in the battery case. The lithium secondary battery, for example, uses only LiCoO _{2 as} the positive electrode active material, has a higher capacity than the battery of Comparative Example 4 charged at the same end voltage as the conventional lithium secondary battery, and 150 ° C. During the heating test, the cleaving groove operates satisfactorily, so that thermal runaway is suppressed, the increase in surface temperature is suppressed, and the safety at an excessively high temperature is excellent.

  On the other hand, the battery of Comparative Example 1 in which the Ni / Li ratio in all the positive electrode active materials is inappropriate has inferior capacity. In addition, the batteries of Comparative Examples 2 and 3 in which the formation of the cleavage vent and the cleavage groove in the battery case are not suitable, the surface of the surface caused by the thermal runaway due to the cleavage vent and the cleavage groove not being fully activated during the 150 ° C. heating test. The temperature is rising.

As described above, the battery of Comparative Example 4 uses only LiCoO _{2 as} the positive electrode active material, and is charged at the end voltage equivalent to that of the conventional lithium secondary battery, and has a cleavage vent in the lid. Therefore, the cleavage vent did not work during the 150 ° C heating test, but the cathode active material does not contain Ni and has a low final voltage during charging, and has both shutdown characteristics and heat shrinkage Because of the use of a separator, thermal runaway was suppressed.

  In addition, the lithium secondary batteries of Examples 1 to 10 and 13 use a nonaqueous electrolytic solution containing a suitable amount of the phosphonoacetate compound represented by the general formula (2). Compared to the lithium secondary batteries of Examples 11 and 12 using a non-aqueous electrolyte that is not suitable, the capacity recovery rate after storage at 85 ° C. is high, battery swelling is suppressed, and the storage characteristics are excellent. The number of cycles when the capacity reaches 80% is large, and the charge / discharge cycle characteristics are also excellent.

DESCRIPTION OF SYMBOLS 1 Lithium secondary battery 10 Battery case 11 Outer can 111 Wide surface of battery case (outer can) side part 12 Cleavage groove 121 Inwardly curved part 122 Outerly curved part 20 Lid

Claims (10)

A lithium secondary battery in which a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator are sealed in a hollow columnar battery case,
The positive electrode has a positive electrode mixture layer containing a positive electrode active material, a conductive additive and a binder on one side or both sides of a current collector,
A lithium-containing composite oxide containing lithium and a transition metal is used as the positive electrode active material, and at least a part of the lithium-containing composite oxide is a lithium-containing composite oxide containing nickel as a transition metal. The molar ratio of the total nickel amount to the total lithium amount in the active material is 0.05 to 1.0,
The binder contains a tetrafluoroethylene-vinylidene fluoride copolymer and a vinylidene fluoride-based polymer whose main component monomer is vinylidene fluoride other than the tetrafluoroethylene-vinylidene fluoride copolymer,
The total content of the binder in the positive electrode mixture layer is 1 to 4% by mass, and the total of the tetrafluoroethylene-vinylidene fluoride copolymer and the vinylidene fluoride polymer is 100% by mass. When the ratio of the tetrafluoroethylene-vinylidene fluoride copolymer is 0.2% by mass or more,
The separator has a porous film (I) mainly composed of a thermoplastic resin, and a porous layer (II) mainly including a filler having a heat resistant temperature of 150 ° C. or higher.
The side surface portion of the battery case is opposed to each other and has two wide surfaces wider than other surfaces in a side view, and the pressure in the battery case is lower than a threshold value on the side surface portion. A lithium secondary battery, wherein a cleavage groove that cleaves when enlarged is provided so as to intersect a diagonal line in a side view from the wide surface side. The lithium secondary battery according to claim 1 , wherein the lithium-containing composite oxide containing nickel as a transition metal has a content of 10 to 80% by mass in all positive electrode active materials. At least a part of the lithium-containing composite oxide containing nickel as a transition metal has the following general composition formula (1):
Li _{1 + y} MO ₂ (1)
[In the general composition formula (1), −0.15 ≦ y ≦ 0.15, and M represents a group of three or more elements including at least Ni, Co, and Mn. In the element, when the proportions (mol%) of Ni, Co and Mn are a, b and c, respectively, 25 ≦ a ≦ 90, 5 ≦ b ≦ 35, 5 ≦ c ≦ 35 and 10 ≦ b + c ≦ 70. ]
The lithium secondary battery according to claim 1 or 2 in a lithium-containing composite oxide represented. The positive electrode mixture layer contains carbon fibers having an average fiber length of 10 to 1000 nm and an average fiber diameter of 1 to 100 nm as a conductive additive, and the content of the carbon fibers in the positive electrode mixture layer Is 0.25-1.5 mass%, The lithium secondary battery in any one of Claims 1-3 . The lithium secondary battery according to any one of claims 1-4 total content of the binder in the front Symbol positive electrode mixture layer is 2.5 mass% or more. The negative electrode includes a material containing Si and O as constituent elements (provided that the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5) and a graphitic carbon material as a negative electrode active material the mixture layer, lithium secondary battery according to any one of claims 1 to 5, those having on one or both sides of the current collector. The lithium secondary battery according to claim 6 , comprising a composite of a carbon material and a material containing Si and O as constituent elements as the negative electrode active material. The lithium secondary battery according to any one of claims 1 to 7 , wherein a nonaqueous electrolytic solution containing vinylene carbonate is used. The lithium secondary battery according to any one of claims 1 to 8 , wherein a nonaqueous electrolytic solution containing a phosphonoacetate compound represented by the following general formula (2) is used.

[In the general formula (2), R ^{1 to} R ³ each independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group or an alkynyl group which may be substituted with a halogen element; An integer of 6 is shown. ] The lithium secondary battery according to any one of claims 1 to 9 using the non-aqueous electrolyte containing halogen-substituted cyclic carbonate.

Images