JPWO2018110188A1 - Lithium ion secondary battery, its manufacturing method and lithium ion secondary battery precursor - Google Patents

Abstract

Provided are a lithium ion secondary battery having a high capacity and excellent charge / discharge cycle characteristics, a production method thereof, and a precursor for constituting the lithium ion secondary battery. The precursor of the lithium ion secondary battery of the present invention has a negative electrode mixture layer containing a negative electrode active material doped with Li ions, the negative electrode active material containing a material S containing at least Si, and Co , Mn, Mg, and element M1 (M1 is at least one selected from the group consisting of Al, Ti, Sr, Zr, Nb, Ag, and Ba). A positive electrode having a positive electrode mixture layer and a separator are provided. The lithium ion secondary battery of the present invention is characterized by comprising the precursor of the lithium ion secondary battery of the present invention and a non-aqueous electrolyte.

Description

  The present invention relates to a lithium ion secondary battery having high capacity and excellent charge / discharge cycle characteristics, a method for producing the lithium ion secondary battery, and a precursor for constituting the lithium ion secondary battery.

  Lithium-ion secondary batteries have high voltage and high capacity, so there are great expectations for their development. Under these circumstances, various materials used in lithium ion secondary batteries, such as positive electrode active materials and negative electrode active materials involved in battery reactions, non-aqueous electrolytes, and binders used in positive and negative electrodes, have been improved. ing.

  For example, Patent Document 1 proposes a positive electrode active material using lithium nickel oxide that has a high capacity and is excellent in charge / discharge cycle characteristics even when the upper limit voltage during charging is increased.

  Further, in Patent Documents 2 and 3, even when lithium nickel oxide having a large irreversible capacity (irreversible capacity) is used as the positive electrode active material, the amount of the negative electrode active material additionally added is remarkably reduced. In order to further increase the capacity of the secondary battery, a secondary battery using at least one selected from silicon, silicon oxide, and silicon alloy as a negative electrode active material has been proposed.

  The negative electrode active material as described in Patent Documents 2 and 3 is a material that can accommodate more Li (lithium) than graphite, which has been conventionally used as a negative electrode active material for lithium ion secondary batteries. However, in a battery configured using such a high-capacity negative electrode material, generally, out of Li released from the positive electrode by charging, it is taken into the high-capacity negative electrode material and remains without being released at the next discharge. The ratio of things is large, and the problem that the capacity that the battery originally has cannot be drawn out easily tends to occur.

  In order to reduce the irreversible capacity of such a battery, the negative electrode (the negative electrode active material in the negative electrode mixture layer) can be doped (pre-doped) with Li ions, and can be moved back and forth between the positive electrode and the negative electrode during charge / discharge of the battery. Techniques for increasing the proportion of Li are also being studied. As a technique for pre-doping Li ions into such a negative electrode, in addition to means for pre-doping Li ions into the negative electrode in the battery (hereinafter sometimes referred to as “in-system pre-doping”), it is described in Patent Documents 4 and 5. Thus, means for assembling a battery using a negative electrode pre-doped with Li ions in advance (hereinafter, pre-doping of Li ions into the negative electrode by such means may be referred to as “outside pre-doping”) has also been proposed.

JP 2016-24879 A JP 2010-15986 A Japanese Patent Laid-Open No. 2006-100054 JP-A-11-283670 JP 2008-91191 A

  However, in the above known examples, there is no mention of relatively long-term charge / discharge cycle characteristics, or only a small amount of Si is added to the negative electrode. There was room for improvement.

  The present invention has been made in view of the above circumstances, and an object thereof is to configure a lithium-ion secondary battery having a high capacity and excellent charge / discharge cycle characteristics, a manufacturing method thereof, and the lithium-ion secondary battery. It is to provide a precursor.

  The precursor of the lithium ion secondary battery of the present invention that has achieved the above object includes a negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder, and a positive electrode mixture layer containing a positive electrode active material and a binder. The negative electrode mixture layer contains at least a negative electrode active material doped with Li ions, and the negative electrode active material contains a material S containing at least Si. The positive electrode mixture layer includes a lithium-containing metal oxide (A) represented by the following general formula (1) as the positive electrode active material.

Li _a Ni _1- bcd _Cob Mn _c M ¹ _d Mg _e O ₂ (1)

In the general formula (1), M ¹ contains at least one element selected from the group consisting of Al, Ti, Sr, Zr, Nb, Ag, and Ba, and 0.9 ≦ a ≦ 1.10. 0.1 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0.1 ≦ b + c ≦ 0.9, 0.003 ≦ d ≦ 0.06, and 0 ≦ e ≦ 0.003.

  Moreover, the lithium ion secondary battery of the present invention is characterized by comprising the precursor of the lithium ion secondary battery of the present invention and a non-aqueous electrolyte.

  The lithium ion secondary battery of the present invention includes a negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder, a step of doping the negative electrode active material with Li ions, and a negative electrode obtained through the step. And a process for assembling a precursor of a lithium ion secondary battery, and a step of forming a lithium ion secondary battery using the precursor of the lithium ion secondary battery and a non-aqueous electrolyte. It can be manufactured by (1).

  Further, the lithium ion secondary battery of the present invention is obtained by the steps of producing a negative electrode having a negative electrode mixture layer using a negative electrode active material doped with Li ions at least in part and a binder, and the above steps. A step of assembling a precursor of a lithium ion secondary battery using the negative electrode and a step of forming a lithium ion secondary battery using the precursor of the lithium ion secondary battery and a non-aqueous electrolyte. It can also be produced by the production method (2) of the invention.

  ADVANTAGE OF THE INVENTION According to this invention, the precursor for comprising the lithium ion secondary battery which was high capacity | capacitance and excellent in charging / discharging cycling characteristics, its manufacturing method, and the said lithium ion secondary battery can be provided.

It is explanatory drawing of the process of doping Li ion to the negative electrode active material in the negative mix layer of a negative electrode by the roll-to-roll method. It is a longitudinal cross-sectional view which represents typically an example of the lithium ion secondary battery of this invention.

  The lithium ion secondary battery of the present invention includes a negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder, a positive electrode having a positive electrode mixture layer containing a positive electrode active material and a binder, a separator, and a non-aqueous electrolyte solution. It is housed in the exterior body. The negative electrode contains at least a negative electrode active material doped with Li ions, and the negative electrode active material contains a material S containing at least Si, and the positive electrode has a positive electrode active material, What has a positive mix layer containing the lithium containing metal oxide (A) represented by the said General formula (1) is used.

  A positive electrode according to a lithium ion secondary battery has a positive electrode mixture layer containing a positive electrode active material and a binder. For example, the positive electrode mixture layer has a structure in which the positive electrode mixture layer is formed on one side or both sides of a current collector. is doing.

  For the positive electrode, the lithium-containing metal oxide (A) represented by the general formula (1) is used as the positive electrode active material. The lithium-containing metal oxide represented by the general formula (1) exhibits excellent reversibility even when a battery using the lithium-containing metal oxide is used in a method of charging at a high voltage of, for example, 4.3 V or higher. Therefore, the lithium ion secondary battery of the present invention is based on the lithium-containing metal oxide (A) even if the upper limit voltage for charging is increased to 4.3 V or higher, which is higher than the conventional 4.2 V, even if the capacity is increased. Combined with the above-mentioned action and the action of Li ion pre-doping in the negative electrode (details will be described later), excellent charge / discharge cycle characteristics [particularly charge / discharge cycle characteristics at high temperature (about 40 to 60 ° C.)] It can be demonstrated. Moreover, the lithium ion secondary battery of this invention can also suppress the battery swelling after a charging / discharging cycle by the effect | action of a lithium containing metal oxide (A).

Lithium-containing metal oxide (A) is, Ni, Co, when set to 1 all elements of Mn and the element ^{M 1,} the ratio c of the ratio b and Mn of Co, respectively, 0.1 ≦ b ≦ 0 .5, 0 ≦ c ≦ 0.5, and 0.1 ≦ b + c ≦ 0.9, Co is present or Co and Mn are present in the crystal lattice. Thereby, when the phase transition of the lithium-containing metal oxide (A) occurs due to the elimination and insertion of Li, the irreversible reaction due to the structural change is alleviated by the action of Co and Mn. The reversibility of the layered crystal structure of the lithium-containing metal oxide (A) represented is improved.

  In the lithium-containing metal oxide (A), Co is a component that contributes to improvement of charge / discharge cycle characteristics at high temperatures, particularly during charging with an upper limit voltage of 4.3 V or higher. In the general formula (1), the amount b of Co is 0.1 or more, preferably 0.12 or more, from the viewpoint of ensuring the above-described effects satisfactorily. However, if the amount of Co in the lithium-containing metal oxide (A) is too large, the amount of other elements decreases, and the effects of these cannot be ensured satisfactorily, so Co in the general formula (1) The amount b is 0.5 or less.

  Furthermore, the lithium-containing metal oxide (A) does not need to contain Mn, but when it is contained, the amount c of Mn in the general formula (1) from the viewpoint of ensuring the above-mentioned effect satisfactorily. Is preferably 0.005 or more. However, if the amount of Mn in the lithium-containing metal oxide (A) is too large, the amount of other elements decreases and the effects of these cannot be ensured satisfactorily. Therefore, Mn in the general formula (1) The amount b is 0.5 or less, preferably 0.2 or less, and more preferably 0.15 or less.

Further, the lithium-containing metal oxide (A) as the element ^{M 1, Al, Ti, Sr} , Zr, Nb, contains at least one element selected from the group consisting of Ag and Ba, of Also by containing an element, the stability can be improved and a positive electrode capable of constituting a battery having high charge / discharge cycle characteristics and high safety can be obtained. Among these, Al is preferable because it easily exhibits the above-described effects and has high versatility. Such effect element ^{M 1} from the viewpoint of satisfactorily ensuring the amount d of the element ^{M 1} in the general formula (1) is 0.003 or more, preferably 0.01 or more. However, if the amount of the element M ^{1 in} the lithium-containing metal oxide (A) is too large, the amount of other elements decreases, and the effects of these cannot be secured satisfactorily. Therefore, the general formula (1) The amount d of the element M ¹ in is 0.06 or less, and preferably 0.04 or less.

  Furthermore, the lithium-containing metal oxide (A) contains Ni. When Ni is present in the crystal lattice of the lithium-containing metal oxide (A), Li is easily removed and inserted during charge / discharge of the battery, and the capacity of the lithium-containing metal oxide (A) can be increased. it can.

In the general formula (1) representing the lithium-containing metal oxide (A), the amount of Ni is “1-bcd” using the amount b of Co, the amount c of Mn, and the amount d of the element M ^1. Specifically, the amount of Ni “1-bcd” is preferably 0.69 or more, and preferably 0.897 or less.

  Further, the lithium-containing metal oxide (A) may contain Mg, but since Mg has a stronger action than other metal elements to cause a decrease in capacity of the lithium-containing metal oxide (A), the amount thereof is It is preferable to limit. Specifically, in the general formula (1) representing the lithium-containing metal oxide (A), the amount e of Mg is 0.003 or less, and preferably 0.002 or less. Moreover, since the lithium-containing metal oxide (A) may not contain Mg, the lower limit of the amount e of Mg in the general formula (1) is zero.

  When the lithium-containing metal oxide (A) has a composition close to the stoichiometric ratio, it is possible to increase the true density and the reversibility and to obtain a higher capacity material. Therefore, in the general formula (1) representing the lithium-containing metal oxide (A), the amount of Li a is 0.9 or more and 1.10 or less, and thus the true value of the lithium-containing metal oxide (A). Density and reversibility can be increased.

  The lithium-containing metal oxide (A) present in the positive electrode mixture layer preferably contains particles having a primary particle size of 0.5 μm or more. Specifically, the proportion of the particles is 100 in total. It is preferable that it is 50 mass% or more in mass%, It is more preferable that it is 70 mass% or more, It is especially preferable that it is 100 mass%. By using the lithium-containing metal oxide (A) containing the particles having a relatively large primary particle size in the above-mentioned amount, the charge / discharge cycle characteristics of the battery at a high temperature can be further improved. The lithium-containing metal oxide (A) may be in a primary particle state as long as it contains particles having a primary particle diameter of 0.5 μm or more in the above-mentioned amount, and secondary particles in which primary particles are aggregated. The primary particle and the secondary particle may be mixed.

  However, if the primary particle diameter of the lithium-containing metal oxide (A) is too large, the load characteristics are deteriorated and the capacity may be reduced. Therefore, particles contained in the lithium-containing metal oxide (A) (primary Among the particles, the maximum value of the particle diameter (maximum value of the primary particle diameter) is preferably 5 μm.

  The primary particle diameter of the lithium-containing metal oxide (A) referred to in the present specification is a value measured by the following method (a).

(A) Method for measuring primary particle diameter of lithium-containing metal oxide (A) present in positive electrode mixture layer Scanning electron equipped with EDX device for cross section of positive electrode (positive electrode mixture layer) processed by ion milling Using a microscope, mapping is performed with an EDX apparatus under the condition of an observation magnification of 500 times, and the particles having a high Ni concentration are further identified as lithium-containing metal oxide (A) by elemental analysis. And about the particle | grains of the lithium containing metal oxide (A) which exists in the visual field, when enlarging on the conditions of 5000 times magnification, the short diameter of a primary particle (the part orthogonal to the part used as the largest diameter in a primary particle) The primary particle diameter is obtained by measuring the length of (diameter). Here, the ratio of the particles having a primary particle diameter of 0.5 μm or more in the lithium-containing metal oxide (A) is that of the particles of 0.5 μm or more of the lithium-containing metal oxide (A) measured by the above-described method. The number is obtained by dividing the number by the total number of primary particles in the field of view, and the maximum primary particle diameter is the largest primary particle diameter among them. In the examples described later, an “S-3400N scanning electron microscope” manufactured by Hitachi High-Technologies Corporation was used as the scanning electron microscope, the acceleration voltage during mapping was 15 kV, and the lithium-containing metal oxide ( The primary particle size of the lithium-containing metal oxide (A) in the positive electrode mixture layer was determined by setting the acceleration voltage during observation at a magnification of 5000 times of the particles of A) to 2 kV.

  Contains a lithium-containing metal oxide (A) containing 50% by mass or more of particles having a primary particle size of 0.5 μm or more, and further includes a lithium-containing metal oxide (A) in which the maximum primary particle size satisfies the preferred value. The positive electrode material mixture layer includes a lithium-containing metal oxide (A) containing 50% by mass or more of particles having a primary particle size of 0.5 μm or more measured by the method (b) below, It can form by using the lithium containing metal oxide (A) in which the maximum value of the primary particle diameter measured by the method satisfies the above preferred value.

(B) Method for measuring primary particle diameter of lithium-containing metal oxide (A) used for forming positive electrode mixture layer Lithium-containing metal oxide (A) powder is pulverized to primary particles, and laser diffraction is performed. By measuring the particle size distribution using a scattering particle size distribution analyzer, the proportion of particles having a primary particle size of 0.5 μm or more in the lithium-containing metal oxide (A) used for forming the positive electrode mixture layer, And the maximum primary particle diameter of the lithium-containing metal oxide (A) is determined. In Examples described later, “Microtrack HRA” manufactured by Nikkiso Co., Ltd. is used as a laser diffraction / scattering particle size distribution measuring device, and the number of times the powder of the lithium-containing metal oxide (A) is crushed reduces errors. In order to do this, it was set to 20 times.

The lithium-containing metal oxide (A) includes a Li-containing compound (such as lithium hydroxide), a Ni-containing compound (such as nickel sulfate), a Co-containing compound (such as cobalt sulfate), a Mn-containing compound (such as manganese sulfate), and the element M ^1. And a compound containing Mg (oxide, hydroxide, sulfate, etc.) can be mixed, and this raw material mixture can be fired.

Incidentally, the synthesized lithium-containing metal oxide (A) at a higher purity, Ni, Co, Mn, complex compound containing a plurality of elements selected from the elements M ¹ and Mg (hydroxides, such as an oxide) And other raw material compounds (such as Li-containing compounds) are preferably mixed and the raw material mixture is fired.

  The firing conditions of the raw material mixture for synthesizing the lithium-containing metal oxide (A) can be, for example, 800 to 1050 ° C. for 1 to 24 hours, but once lower than the firing temperature (for example, 250 to It is preferable to carry out preliminary heating by heating to 850 ° C. and holding at that temperature, and then proceed to the reaction by raising the temperature to the firing temperature. Although there is no restriction | limiting in particular about the time of preheating, Usually, what is necessary is just 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.

  For the positive electrode related to the lithium ion secondary battery, only the lithium-containing metal oxide (A) may be used as the positive electrode active material, and the lithium-containing metal oxide (A) and another positive electrode active material are used in combination. Also good. However, from the viewpoint of ensuring the above-described effects due to the use of the lithium-containing metal oxide (A), when the total amount of the positive electrode active material contained in the positive electrode mixture layer is 100% by mass, the lithium-containing metal oxide ( The content of A) is preferably 5% by mass or more, and more preferably 10% by mass or more.

In the positive electrode, the positive electrode active material used in combination with the lithium-containing metal oxide (A) includes lithium cobalt oxides such as LiCoO ₂ ; lithium manganese oxides such as LiMnO ₂ and Li ₂ MnO ₃ ; Excluding those represented by the formula (1) and those represented by the general formula (1) and those having an Ni content equal to or higher than that]; LiMn ₂ O ₄ , Li _4/3 Ti _5/3 O Examples include lithium-containing composite oxides having a spinel structure such as ₄ ; lithium-containing metal oxides having an olivine structure such as LiFePO ₄ ; oxides having the above-described oxide as a basic composition and substituted with various elements.

  When lithium cobalt oxide is used as the positive electrode active material used in combination with the lithium-containing metal oxide (A), as the lithium cobalt oxide, for example, a lithium-containing metal oxide (B) represented by the following general formula (2) Is mentioned. The lithium-containing metal oxide (B) has good charge / discharge cycle characteristics under a high voltage where the upper limit voltage is 4.3 V or higher. Therefore, when using together lithium-containing metal oxide (A) and another positive electrode active material, it is desirable to use lithium-containing metal oxide (B) as said other positive electrode active material.

^{_{Li f Co 1-g-h}} M 2 g M 3 h O 2 (2)

In the general formula (2), M ² is at least one element selected from the group consisting of Al, Mg, and Er, and M ³ is Zr, Ti, Ni, Mn, Na, Bi, Ca, F , P, Sr, W, Ba, Mo, V, Sn, Ta, Nb and at least one element selected from the group consisting of Zn, 0.9 ≦ f ≦ 1.10, 0.010 ≦ g ≦ 0.1, 0 ≦ h ≦ 0.05, g + h ≦ 0.12.

In the lithium-containing metal oxide (B), an element M ² Al, Mg and Er are hot during charging to suppress the elution of Co due to the charge and discharge of the battery, especially the upper limit voltage 4.3V or more It is a component that contributes to improving the charge / discharge cycle characteristics below. Lithium-containing metal oxide (B) is, Al as the element M ^2, it is sufficient only to contain at least one of Mg and Er, may contain plural kinds.

The effect of the by elements ^{M 2} from the viewpoint of satisfactorily ensuring the amount g of elements ^{M 2} in the formula (2) is preferably 0.010 or more, and more preferably 0.014 or more . However, if the amount of the element M ^{2 in} the lithium-containing metal oxide (B) is too large, the amount of other elements decreases, and the effects of these cannot be secured satisfactorily. Therefore, the general formula (2) The amount g of the element M ² in is preferably 0.1 or less, and more preferably 0.05 or less.

Further, the lithium-containing metal oxide (B), as the element ^{M 3, Zr, Ti, Ni} , Mn, Na, Bi, Ca, F, P, Sr, W, Ba, Mo, V, Sn, Ta, At least one element selected from the group consisting of Nb and Zn may also be included. These elements M ³ also contributes to the charge-discharge cycle characteristics improve at a high temperature, particularly in the time of charging to the upper limit voltage or 4.3 V.

However, if the amount of the element M ^{3 in} the lithium-containing metal oxide (B) is too large, the amount of other elements decreases, and the effects of these cannot be secured satisfactorily. Therefore, the general formula (2) The amount h of the element M ³ in is preferably 0.05 or less, and more preferably 0.01 or less. Note that the lithium-containing metal oxide (B) may not contain the element M ³ , but in the case of containing these, from the viewpoint of better securing the above-described effect by the element M ³ , The amount h of the element M ³ in the general formula (2) is preferably 0.0005 or more.

Further, in the lithium-containing metal oxide (B), since Co is a component that contributes to an increase in capacity, the amount of element M ² or element M ³ is limited so that a sufficient amount of Co can be contained. From the viewpoint of maintaining a large capacity of the metal oxide (B), the total g + h of the amount g of the element M ² and the amount h of the element M ³ in the general formula (2) is preferably 0.12 or less.

  Similarly to the lithium-containing metal oxide (A), the lithium-containing metal oxide (B) increases the true density and reversibility, particularly when the composition is close to the stoichiometric ratio, thereby making a higher-capacity material. It becomes possible. Therefore, in the general formula (2) representing the lithium-containing metal oxide (B), the amount f of Li is preferably 0.9 or more and 1.10 or less, whereby the lithium-containing metal oxide (B ) True density and reversibility.

Lithium-containing metal oxide (B) is, Li-containing compound (lithium hydroxide, etc.), Co-containing compound (such as cobalt sulfate), and the element M ² and the element M ³ compounds containing (oxides, hydroxides, sulfate Salt) and the like, and the raw material mixture is fired.

In order to synthesize lithium-containing metal oxide (B) with higher purity, a composite compound (hydroxide, oxide, etc.) containing a plurality of elements of Co, element M ² and element M ³ , It is preferable to mix other raw material compounds (such as Li-containing compounds) and to fire this raw material mixture.

  The firing conditions of the raw material mixture for synthesizing the lithium-containing metal oxide (B) can be, for example, 800 to 1050 ° C. for 1 to 24 hours, but once lower than the firing temperature (for example, 250 to It is preferable to carry out preliminary heating by heating to 850 ° C. and holding at that temperature, and then proceed to the reaction by raising the temperature to the firing temperature. 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.

  The content of the positive electrode active material in the positive electrode mixture layer is preferably 94 to 98% by mass.

  The positive electrode mixture layer usually contains a conductive additive. Examples of the conductive assistant include graphites such as natural graphite (flaky graphite and the like) and artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black; It is preferable to use carbon materials such as carbon fibers; conductive fibers such as metal fibers; carbon fluoride; metal powders such as aluminum; zinc oxide; conductive whiskers such as potassium titanate; Conductive metal oxides such as; organic conductive materials such as polyphenylene derivatives;

  The content of the conductive additive in the positive electrode mixture layer suppresses the lithium ion desorption speed at the positive electrode during charging, improves the balance with the lithium ion acceptance speed at the negative electrode, and charges and discharges the battery. From the viewpoint of highly suppressing the generation of lithium dendrite on the negative electrode surface and further improving the charge / discharge cycle characteristics of the battery, it is preferably 2.0% by mass or less, and 1.5% by mass or less. Is more preferable. However, if the amount of the conductive additive in the positive electrode mixture layer is too small, the conductivity in the positive electrode mixture layer may be reduced, leading to a decrease in battery capacity. The content of the auxiliary agent is preferably more than 0.5% by mass, and more preferably 1.0% by mass or more.

  The positive electrode mixture layer may further contain a filler. When the positive electrode mixture layer contains a filler, the catalytic properties of the positive electrode active material are relaxed, and elution of cobalt ions from the active material and the surface of the conductive auxiliary agent attached to the non-aqueous electrolyte and the positive electrode active material or the positive electrode active material This is because the decomposition reaction of the nonaqueous electrolytic solution can be suppressed. By these, it can suppress that the decomposition product of cobalt ion and a nonaqueous electrolyte solution precipitates in a separator and a negative electrode, and since the damage which a negative electrode and a separator receive is reduced, it suppresses deterioration of charging / discharging cycling characteristics. be able to. Furthermore, since generation | occurrence | production of gas can be suppressed by suppressing the decomposition reaction of a non-aqueous electrolyte, the swelling of the battery after a charging / discharging cycle can be suppressed.

  The filler that can be contained in the positive electrode mixture layer is preferably an inorganic filler because of its high oxidation resistance and low reactivity with the non-aqueous electrolyte, and in particular, Mg, Al, Si, Ti An oxide or hydrate containing at least one selected from the group consisting of Mn, Zr, Nb, Sn, W, Er, Ba and Sr is preferred. For example, oxides such as alumina, zirconia, and titania; hydroxide oxides such as boehmite;

  The filler content in the positive electrode mixture layer is preferably 0.1% by mass or more, and more preferably 0.3% by mass or more in order to satisfactorily exert the above-described effects. However, if the content of the filler in the positive electrode mixture layer is too high, the load characteristics deteriorate, and therefore it is preferably 3% by mass or less, and more preferably 1% by mass or less.

  The average particle size of the filler is preferably selected in the range of 0.001 to 1.5 μm because it is unsuitable whether it is too large or too small for uniform dispersion on the surface of the positive electrode active material.

  A known binder can be used as the positive electrode binder for the lithium ion secondary battery, but in general, polyvinylidene fluoride (PVDF) is used.

  By the way, the positive electrode of the lithium ion secondary battery is prepared by preparing a positive electrode mixture-containing composition such as a positive electrode active material, a slurry and a paste containing a binder and a solvent, and applying this to a current collector and drying it. It is common to be made. However, when PVDF is used as the positive electrode binder and a lithium-containing metal oxide containing nickel is used as the positive electrode active material, the positive electrode mixture-containing composition is easily gelled. Further, when a battery having a positive electrode using PVDF as a binder is charged to a voltage exceeding 4.2 V, detachment of PVDF-derived hydrofluoric acid is likely to occur, and the decomposition of the non-aqueous electrolyte may be promoted. Therefore, in the positive electrode according to the lithium ion secondary battery, the ratio of PVDF in the total binder of the positive electrode mixture layer is preferably 80% by mass or less.

  As the binder other than PVDF, a polymer that can be dissolved in the solvent of the positive electrode mixture-containing composition can be used. The binder used together with PVDF forms a film on the surface of the positive electrode active material particles in the positive electrode mixture-containing composition. This film can suppress gelation of the positive electrode mixture-containing composition. Moreover, the film formed on the surface of the positive electrode active material particles by the binder used in combination with PVDF contributes to the suppression of the decomposition reaction in the non-aqueous electrolyte during charging of the lithium ion secondary battery. Since PVDF does not necessarily need to be used as a binder for the positive electrode, the lower limit of the PVDF ratio in all the binders of the positive electrode mixture layer is 0% by mass.

  The solvent used for the positive electrode mixture-containing composition for forming the positive electrode mixture layer is preferably an organic solvent such as N-methyl-2-pyrrolidone (NMP). Therefore, the binder related to the positive electrode (binder other than PVDF) includes at least one polymer selected from the group consisting of a polymer soluble in such a solvent, specifically, acrylonitrile, acrylic acid ester, and methacrylic acid ester. Copolymer formed by two or more monomers including monomers; Hydrogenated nitrile rubber; Vinylidene fluoride-chlorotrifluoroethylene copolymer (VDF-CTFE), Vinylidene fluoride-tetrafluoroethylene copolymer (VDF) -TFE) or a fluororesin such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer (VDF-HFP-TFE); As the polymer that can be dissolved in the solvent, for example, only one of the above-described examples may be used, or two or more may be used in combination.

  The content of the binder in the positive electrode mixture layer is such that the positive electrode active material and the conductive additive in the positive electrode mixture layer can be satisfactorily bound to prevent desorption from these positive electrode mixture layers. From the viewpoint of better improving the reliability of the battery used, it is preferably 1% by mass or more. However, if the amount of the binder in the positive electrode mixture layer is too large, the amount of the positive electrode active material and the amount of the conductive auxiliary agent are decreased, and the effect of increasing the capacity may be reduced. Therefore, the binder content in the positive electrode mixture layer is preferably 1.6% by mass or less.

  In producing the positive electrode, as described above, the positive electrode active material such as the lithium-containing metal oxide (A) and the binder, and further the positive electrode mixture containing the conductive auxiliary agent are uniformly dispersed using a solvent such as NMP. A paste-like or slurry-like positive electrode mixture-containing composition is prepared (the binder may be dissolved in a solvent), this composition is applied to the surface of the positive electrode current collector and dried, and if necessary A method of adjusting the thickness and density of the positive electrode mixture layer by press treatment can be employed. However, the manufacturing method of the positive electrode is not limited to the above method, and other methods may be adopted.

  The material of the positive electrode current collector is not particularly limited as long as it is an electron conductor that is chemically stable in the battery. For example, in addition to aluminum or aluminum alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., a composite material in which a carbon layer or a titanium layer is formed on the surface of aluminum, aluminum alloy, or stainless steel can be used. . Among the positive electrode current collectors made of such materials, foils, films, etc. made of aluminum or aluminum alloys are preferable.

  The thickness of the positive electrode current collector is preferably 11 μm or less, and more preferably 10 μm or less. By making the positive electrode current collector thinner, the proportion occupied by the positive electrode current collector in the internal volume of the lithium ion secondary battery can be made as small as possible. In the lithium ion secondary battery to be used, for example, it is possible to increase the amount of nonaqueous electrolyte introduced into the interior.

  When the capacity is increased by setting the upper limit voltage of charging to 4.3 V or higher, the potential of the positive electrode in a state where the lithium ion secondary battery is charged becomes very high. Oxidative decomposition of the positive electrode and the lack of non-aqueous electrolyte in the positive electrode may cause decomposition products to accumulate on the surface layer of the positive electrode active material contained in the positive electrode, or reduce the ion conduction path between particles, These may cause deterioration of charge / discharge cycle characteristics of the battery. However, when the thin positive electrode current collector as described above is used and the amount of the non-aqueous electrolyte introduced into the lithium ion secondary battery is increased, the occurrence of the above problem is suppressed, and this problem is prevented. Since the deterioration of the charge / discharge cycle characteristics due to the occurrence can be suppressed, the charge / discharge cycle characteristics of the battery can be further enhanced.

  However, if the positive electrode current collector is too thin, strength may be insufficient and productivity of the positive electrode or battery may be impaired. Therefore, the thickness of the positive electrode current collector is preferably 6 μm or more.

  The thickness of the positive electrode mixture layer is preferably 30 to 80 μm per one side of the current collector. In the positive electrode mixture layer, the filling rate is preferably 75% or more from the viewpoint of higher capacity. However, when the filling rate of the positive electrode mixture layer is too high, the number of pores in the positive electrode mixture layer becomes too small, and the permeability of the nonaqueous electrolyte (nonaqueous electrolyte solution) into the positive electrode mixture layer decreases. Since there exists a possibility, it is preferable that the filling rate is 83% or less. The filling rate of the positive electrode mixture layer is determined by the following formula.

    Filling rate (%) = 100 × (actual density of positive electrode mixture layer / theoretical density of positive electrode mixture layer)

The “theoretical density of the positive electrode mixture layer” in the above formula for calculating the filling rate of the positive electrode mixture layer is a density (positive electrode mixture) calculated from the density and content of each component of the positive electrode mixture layer. The density obtained by assuming that there are no vacancies in the layer), and the “actual density of the positive electrode mixture layer” is measured by the following method. First, it cuts a positive electrode to a size of 1 cm × 1 cm, a thickness micrometer _{(l 1),} measuring the mass _{(m 1)} a precision balance. Next, the positive electrode material mixture layer is scraped off, and only the current collector is taken out, and the thickness (l _c ) and mass (m _c ) of the current collector are measured in the same manner as the positive electrode. From the obtained thickness and mass, the actual density (d _ca ) of the positive electrode mixture layer is determined by the following formula (the unit of thickness is cm, and the unit of mass is g).
d _ca = (m ₁ −m _c ) / (l ₁ −l _c )

  As the negative electrode active material used for the negative electrode mixture layer, carbon materials such as graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon; Si or Sn simple substance; Si or Sn-containing alloy; Si or Sn-containing oxide; As the negative electrode active material, only one of these may be used, or two or more may be used in combination.

  Among such negative electrode active materials, since the effect of the present invention becomes more remarkable, for example, 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, hereinafter, it is preferable to use this material).

Examples of the material S include materials containing Si and O as constituent elements and not containing Li as a constituent element, such as those represented by the composition formula SiO _x (0.5 ≦ x ≦ 1.5). Can be mentioned.

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, the SiO _x includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and is dispersed in the amorphous SiO ₂ . In combination with Si, the atomic ratio x may satisfy 0.5 ≦ x ≦ 1.5. 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, since x = 1, the structural formula is represented by SiO. . 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.

  The material S preferably constitutes a composite that is combined with a carbon material. For example, the surface of the material S is preferably covered with the carbon material. In general, since the material S has poor conductivity, when using it as a negative electrode active material, a conductive material (conductive aid) is used from the viewpoint of securing good battery characteristics, and the material S and the conductive material in the negative electrode are electrically conductive. It is necessary to form an excellent conductive network by making good mixing and dispersion with the conductive material. In the case of a composite in which the material S is combined with a carbon material, for example, the conductive network in the negative electrode is better than when a material obtained by simply mixing the material S and a conductive material such as a carbon material is used. Formed.

  Examples of the composite of the material S and the carbon material include a granulated body of the material S and the carbon material as well as the material S whose surface is covered with the carbon material as described above.

  As a carbon material that can be used for forming a complex with the material S, for example, low crystalline carbon, carbon nanotube, vapor grown carbon fiber, and the like are preferable.

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

  Among the carbon materials exemplified above, a fibrous carbon material is particularly preferable for use when the composite with the material S is a granulated body. The fibrous carbon material has a thin thread shape and high flexibility, so that it can follow the expansion and contraction of the material S that accompanies charging / discharging of the battery, and since the bulk density is large, This is because it can have many junctions. 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.

  In the composite of the material S and the carbon material, the ratio of the material S to the carbon material is preferably 3 parts by mass or more of the carbon material with respect to 100 parts by mass of the material S: 5 parts by mass or more. More preferably, it is more preferably 7 parts by mass or more, more preferably 20 parts by mass or less, and even more preferably 17 parts by mass or less. The reason is not clear, but when Li ions are doped, the charge / discharge cycle characteristics of the battery can be further improved by adjusting the ratio of the material S and the carbon material in the composite as described above. It becomes.

  A composite of the material S and the carbon material can be obtained, for example, by the following method.

  When the surface of the material S is coated with a carbon material to form a composite, for example, the particles of the material S and the hydrocarbon gas are heated in the gas phase, and are generated by thermal decomposition of the hydrocarbon gas. Carbon is deposited on the surface of the particles. Thus, according to the vapor deposition (CVD) method, the hydrocarbon-based gas spreads to every corner of the particle of the material S, and a thin and uniform film (carbon) containing a conductive carbon material on the particle surface. Since the material covering layer) can be formed, the conductivity of the particles of the material S can be imparted with good uniformity with a small amount of carbon material.

  In the production of the material S coated with the carbon material, the processing temperature (atmosphere temperature) of the CVD method varies depending on the type of hydrocarbon gas, but is usually 600 to 1200 ° C., and particularly 700 ° C. It is preferable that it is above, and it is still more preferable that it is 800 degreeC or more. 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, when producing a granulated body of the material S and the carbon material, a dispersion liquid in which the material S is dispersed in a dispersion medium is prepared, sprayed and dried to obtain a granulated body including a plurality of particles. Make it. 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, a granulated body of the material S and the carbon material can be produced also by a granulating method by a mechanical method using a vibration type or planetary type ball mill or rod mill.

  If the average particle size of the material S is too small, the dispersibility of the material S may be reduced and the effects of the present invention may not be sufficiently obtained, and the material S has a large volume change associated with charging / discharging of the battery. If the average particle diameter is too large, the material S is likely to collapse due to expansion / contraction (this phenomenon leads to capacity degradation of the material S), and therefore it is preferably 0.1 μm or more and 10 μm or less.

  The content of the composite in the total amount of the negative electrode active material contained in the negative electrode mixture layer is, for example, 5% by mass or more from the viewpoint of better ensuring the effect of increasing the battery capacity by using the composite. It is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 50% by mass or more. In addition, since only the said composite may be used for a negative electrode active material, the suitable upper limit of content of the said composite in the negative electrode active material whole quantity which a negative mix layer contains is 100 mass%.

  The negative electrode active material content (total content of all negative electrode active materials) in the negative electrode mixture layer is preferably 80 to 99.5% by mass.

  As the binder for the negative electrode mixture layer, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyimide, polyamide, polyamideimide, or the like can be used. However, it is preferable to use a copolymer having a unit represented by the following formula (3) and a unit represented by the following formula (4) [hereinafter referred to as “copolymer (A)”].

  In the formula (4), R is hydrogen or a methyl group, and M ′ is an alkali metal element.

  When the negative electrode active material in the negative electrode mixture layer of the negative electrode is doped with Li ions by pre-doping outside the system, the hardness of the negative electrode mixture layer usually increases and becomes brittle. Is likely to occur. In addition, even when the negative electrode mixture layer is formed using a negative electrode active material doped with Li ions by pre-doping outside the system, the negative electrode mixture layer is likely to be brittle, and the handleability during production and use of the negative electrode is reduced. There is a fear. However, the negative electrode mixture layer using the copolymer (A) as a binder has high flexibility and also improves the peel strength from the negative electrode current collector. Even if the negative electrode active material in the layer is doped with Li ions, or a negative electrode mixture layer is formed using a negative electrode active material doped with Li ions, defects in the negative electrode mixture layer are unlikely to occur, and its handleability Will improve. Therefore, when a copolymer (A) is used for the binder of a negative mix layer, productivity of a negative electrode improves more. In addition, in manufacturing the negative electrode, even when the pre-doping by the roll-to-roll method is performed, the defect portion is hardly generated. Therefore, when the negative electrode mixture layer is doped with Li ions, the negative electrode Productivity can be increased.

  Moreover, when a copolymer (A) is used for the binder of a negative mix layer, since it can suppress deterioration of the negative mix layer by repetition of charging / discharging also in a lithium ion secondary battery, charging / discharging cycling characteristics Is further improved.

  Furthermore, the load characteristic of a lithium ion secondary battery is also improved by using a copolymer (A) for the binder of a negative mix layer. This is thought to be because the negative electrode mixture layer using the copolymer (A) as a binder has a structure in which the nonaqueous electrolytic solution penetrates well inside. In addition, by using the copolymer (A) as a binder, Li deposition on the negative electrode surface, which may occur with the use of a lithium ion secondary battery, can be further suppressed.

  The copolymer (A) having the unit represented by the formula (3) and the unit represented by the formula (4) is a vinyl ester and at least one of an acrylate ester and a methacrylate ester as monomers. A copolymer obtained by polymerization can be obtained by saponification.

  Examples of the vinyl ester for obtaining the copolymer (A) include vinyl acetate, vinyl propionate, and vinyl pivalate, and one or more of them can be used. Among these vinyl esters, vinyl acetate is more preferable.

  The copolymer of vinyl ester and at least one of acrylic acid ester and methacrylic acid ester for obtaining copolymer (A) is a unit derived from monomers other than vinyl ester, acrylic acid ester and methacrylic acid ester. You may have.

  The copolymer of vinyl ester and at least one of acrylic acid ester and methacrylic acid ester is a suspension in which polymerization is performed in a state where these monomers are suspended in an aqueous solution containing a polymerization catalyst and a dispersant, for example. Polymerization can be performed by a turbid polymerization method. As the polymerization catalyst at this time, organic peroxides such as benzoyl peroxide and lauryl peroxide; azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile; and the like can be used. In addition, the dispersant used in the suspension polymerization includes water-soluble polymers (polyvinyl alcohol, poly (meth) acrylic acid or a salt thereof, polyvinyl pyrrolidone, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, etc.), inorganic compounds (Calcium phosphate, magnesium silicate, etc.) can be used.

  The temperature at which the suspension polymerization is performed may be about -20 to + 20 ° C with respect to the 10-hour half-life temperature of the polymerization catalyst, and the polymerization time may be several hours to several tens of hours.

  Saponification of a copolymer of vinyl ester with at least one of acrylic acid ester and methacrylic acid ester uses an alkali (sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.) containing an alkali metal, and is aqueous. It can be performed in a mixed solvent of an organic solvent and water. By this saponification, the unit derived from the vinyl ester becomes a unit in which a hydroxyl group is directly bonded to the main chain of the copolymer [that is, a unit represented by the above formula (3)]. The unit derived from at least one monomer is a unit in which an alkali metal salt (group) of a carboxyl group is directly bonded to the main chain of the copolymer [that is, a unit represented by the above formula (4)]. Therefore, M ′ in the formula (4) includes sodium, potassium, lithium and the like.

  Examples of the aqueous organic solvent used for saponification include lower alcohols (such as methanol and ethanol) and ketones (such as acetone and methyl ethyl ketone). The use ratio of the aqueous organic solvent and water is preferably 3/7 to 8/2 in terms of mass ratio.

  The temperature at the time of saponification should just be 20-60 degreeC, and the time in that case should just be about several hours.

  The saponified copolymer may be taken out from the reaction solution, washed, and then dried.

  The unit represented by the formula (3) of the copolymer (A) obtained through the saponification has a structure in which an unsaturated bond of vinyl alcohol is opened and polymerized, The unit represented by the above (4) is an acrylate or methacrylate (hereinafter referred to as “(meth) acrylate” collectively, and acrylic acid and methacrylic acid together as “(meth) A structure in which an unsaturated bond of “acrylic acid” is polymerized by opening. Therefore, the copolymer (A) uses vinyl alcohol or (meth) acrylate as a monomer and is not obtained by copolymerizing these, but for convenience, “vinyl alcohol and (meth) It may also be referred to as an acrylate salt [a copolymer of (meth) acrylic acid alkali metal neutralized product].

  In the copolymer (A), the composition ratio of the unit represented by the formula (3) and the unit represented by the formula (4) is the formula (3) when the total of these units is 100 mol%. Is preferably 5 mol% or more, more preferably 50 mol% or more, still more preferably 60 mol% or more, and preferably 95 mol% or less, and 90 mol%. The following is more preferable. That is, when the total of the unit represented by the formula (3) and the unit represented by the formula (4) is 100 mol%, the ratio of the unit represented by the formula (4) is 5 mol% or more. Is preferably 10 mol% or more, more preferably 95 mol% or less, more preferably 50 mol% or less, and still more preferably 40 mol% or less.

  The content of the copolymer (A) in the negative electrode mixture layer suppresses the effects of its use (the effect of enhancing the load characteristics of the battery, the falling off of the negative electrode active material, and the peeling between the negative electrode mixture layer and the current collector). From the viewpoint of ensuring a good effect), the content is preferably 2% by mass or more, and more preferably 5% by mass or more. However, if the amount of the copolymer (A) in the negative electrode mixture layer is too large, it becomes difficult to adjust the density of the negative electrode mixture layer to a value described later, and the capacity and load characteristics of the battery are reduced. There is a fear. Therefore, the content of the copolymer (A) in the negative electrode mixture layer is preferably 15% by mass or less, and more preferably 10% by mass or less.

  In the negative electrode mixture layer, together with the copolymer (A), binders used in the negative electrode mixture layer related to the negative electrode of ordinary lithium ion secondary batteries, for example, SBR, CMC, polyvinylidene fluoride (PVDF), etc. Can also be used. However, the content of the binder other than the copolymer (A) in the total amount of binder contained in the negative electrode mixture layer is preferably 50% by mass or less.

  The negative electrode mixture layer may contain a conductive additive as necessary. Examples of conductive assistants to be included in the negative electrode mixture layer include graphites such as natural graphite (scaly graphite, etc.), artificial graphite and the like; acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black and the like. -It is preferable to use carbon materials such as bon blacks; carbon fibers; and conductive fibers such as metal fibers; carbon fluorides; metal powders such as aluminum; zinc oxide; conductivity such as potassium titanate. Whiskers; conductive metal oxides such as titanium oxide; organic conductive materials such as polyphenylene derivatives; and the like can also be used. As the conductive assistant, those exemplified above may be used singly or in combination of two or more.

  When the conductive additive is contained in the negative electrode mixture layer, the content of the conductive additive in the negative electrode mixture layer is preferably 10% by mass or less.

  The negative electrode (negative electrode precursor) to be used for pre-doping outside the system in order to produce the negative electrode of the present invention by the production method (1) contains, for example, a negative electrode active material and a binder, and further, if necessary, a conductive aid. The negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) or water to prepare a paste-like or slurry-like negative electrode mixture-containing composition (however, the binder is dissolved in the solvent). Alternatively, after applying this to one or both sides of the current collector and drying, it can be produced through a step of applying a press treatment such as a calender treatment if necessary. However, the negative electrode to be used for pre-doping outside the system is not limited to those manufactured by the above method, but may be manufactured by other methods.

  Further, when producing the negative electrode of the present invention by the production method (2), for example, a negative electrode active material (at least partly uses a negative electrode active material doped with Li ions by pre-doping outside the system) and a binder, Furthermore, if necessary, a negative electrode mixture containing a conductive auxiliary agent is dispersed in a solvent such as NMP or water to prepare a paste-like or slurry-like negative electrode mixture-containing composition (however, the binder is added to the solvent). It may be dissolved), and this may be applied to one or both sides of the current collector, dried, and then subjected to a pressing process such as a calendar process if necessary.

  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.

  The thickness of the negative electrode mixture layer (in the case where the negative electrode mixture layer is provided on both sides of the current collector) is preferably 10 to 100 μm.

  The extra-system pre-doping of the negative electrode active material can be performed, for example, by the following (i) or (ii).

In-system pre-doping method (i)
A negative electrode manufactured using a negative electrode active material not doped with Li ions is used, and the negative electrode active material is doped with Li ions.

  In the extra-system pre-doping method (i), the doping of Li ions into the negative electrode active material in the negative electrode mixture layer of the negative electrode is carried out, for example, in a solvent such as tetrahydrofuran or diethyl ether with biphenyl, polycyclic aromatic compounds (anthracene, naphthalene) Etc.), and the negative electrode is immersed in a solution in which p-benzoquinone, metal Li, etc. are dissolved, and then washed and dried with a solvent [hereinafter referred to as “out-of-system pre-doping method (i-1)”. ]. The doping amount of Li ions at this time can be controlled by adjusting the amount of each component in the solution. For example, the molar ratio Li / M described later may be adjusted so as to satisfy a preferable value described later.

  Further, in the extra-system pre-doping method (i), a negative electrode (working electrode) and a lithium metal foil (counter electrode, including a lithium alloy foil) are immersed in a nonaqueous electrolytic solution, and a current is passed between them. The negative electrode active material in the negative electrode mixture layer can be doped with Li ions (hereinafter referred to as “out-of-system pre-doping method (i-2)”). As the non-aqueous electrolyte, the same non-aqueous electrolyte for lithium ion secondary batteries (described in detail later) can be used. The doping amount of Li ions at this time can be controlled by adjusting the current density per area of the negative electrode (negative electrode mixture layer) and the amount of electricity to be applied. For example, the molar ratio Li / M described later is suitable as described later. Adjust to meet the value.

  When performing the extra-system pre-doping method (i-2), the negative electrode wound around a roll is pulled out and introduced into an electrolyte bath provided with a non-aqueous electrolyte and a lithium metal electrode, and the negative electrode in the electrolyte bath It is preferable to carry out by a roll-to-roll method in which a negative electrode active material in a negative electrode mixture layer is doped with Li ions by energizing between the lithium metal electrode and the lithium metal electrode, and the subsequent negative electrode is wound into a roll shape. . If the negative electrode of the present invention is used, it is difficult for defects to occur in the negative electrode mixture layer even if it is wound into a roll after doping with Li ions. Therefore, productivity can be further improved by applying the roll-to-roll method.

  FIG. 1 shows an explanatory diagram of a step of doping Li ions into the negative electrode active material in the negative electrode mixture layer of the negative electrode by a roll-to-roll method. First, the negative electrode 2a is pulled out from the roll 20a around which the negative electrode 2a for use in doping Li ions is wound, and introduced into the electrolytic solution tank 101 for doping Li ions. The electrolyte bath 101 has a non-aqueous electrolyte (not shown) and a lithium metal electrode 102, and can be energized by a power source 103 between the negative electrode 2 a passing through the electrolyte bath 101 and the lithium metal electrode 102. It is configured as follows. When the negative electrode 2a passes through the electrolytic solution tank 101 while facing the lithium metal layer 202, the negative electrode mixture layer of the negative electrode 2a is energized between the negative electrode 2a and the lithium metal electrode 102 by the power source 103. The negative electrode active material therein is doped with Li ions.

  The negative electrode 2 after the Li-ion is doped into the negative electrode active material in the negative electrode mixture layer and passed through the electrolyte bath 101 is preferably washed and wound on a roll 20. The negative electrode 2 can be cleaned, for example, by allowing the negative electrode 2 to pass through a cleaning tank 104 filled with a cleaning organic solvent, as shown in FIG. Moreover, it is preferable that the negative electrode 2 after passing through the cleaning tank 104 is wound around the roll 20 after passing through the drying means 105 and being dried. The drying method in the drying means 105 is not particularly limited as long as the organic solvent adhering to the negative electrode 2 can be removed in the cleaning tank 104. For example, drying with warm air or an infrared heater, or in a dry inert gas Various methods such as drying through can be applied.

  In addition, the electrolytic solution tank 101 shown in FIG. 1 is lithium metal so that the negative electrode mixture layer formed on both surfaces of the negative electrode current collector can be doped with Li ions simultaneously on the negative electrode mixture layers on both surfaces. In the case of an electrolyte bath used only to dope Li ions into the negative electrode mixture layer of the negative electrode having a negative electrode mixture layer only on one side of the negative electrode current collector, although two electrodes 102 are provided. It is only necessary to provide one lithium metal electrode only at a location facing the negative electrode mixture layer.

Out-of-system pre-doping method (ii)
A negative electrode active material not doped with Li ions is directly doped with Li ions. In this case, by immersing a negative electrode active material (a negative electrode active material before Li ion doping) in place of the negative electrode in the solution in which the negative electrode described above in the description of the extra-system pre-doping method (i-1) is immersed. The negative electrode active material can be doped with Li ions.

  When this extra-system pre-doping method (ii) is adopted, a part or all of the negative electrode active material used for the production of the negative electrode is doped with Li ions by the extra-system pre-doping method (ii). Can do. The ratio of the negative electrode active material doped with Li ions by the extra-system pre-doping method (ii) in the negative electrode active material used for the production of the negative electrode and the doping amount of Li ions into the negative electrode active material are, for example, the molar ratio Li described later. Adjustment may be made so that / M satisfies a preferable value described later.

  The negative electrode active material doped with Li ions by the extra-system pre-doping method (ii) preferably has a large acceptance amount of Li ions and a large irreversible capacity. For example, Li ions are added to a material containing Si and O as constituent elements. It is desirable to dope.

  Using a negative electrode after doping Li ions into the negative electrode active material in the negative electrode mixture layer by the extra-system pre-doping method (i), a negative electrode active material doped with Li ions by the extra-system pre-doping method (ii), etc. The negative electrode obtained by forming the agent layer is cut into a required size and is used for the production of a lithium ion secondary battery. Moreover, you may form the lead body for electrically connecting with the other member in a lithium ion secondary battery according to a conventional method to a negative electrode as needed.

  In a lithium ion secondary battery, a negative electrode (a negative electrode containing a negative electrode active material doped with Li ions by pre-doping outside the system) and a positive electrode are laminated body (laminated electrode body) laminated via a separator, or this laminated body. Is further used in the form of a wound body (wound electrode body) wound in a spiral shape.

  The separator is preferably a porous film composed of polyolefin such as polyethylene, polypropylene, and ethylene-propylene copolymer; polyester such as polyethylene terephthalate and copolymer polyester; In addition, it is preferable that a separator has the property (namely, shutdown function) which the hole obstruct | occludes in 100-140 degreeC. Therefore, the separator has a melting point, that is, a thermoplastic resin having a melting temperature measured using a differential scanning calorimeter (DSC) of 100 to 140 ° C. in accordance with JIS K 7121 as a component. Preferably, it is a single layer porous film mainly composed of polyethylene or a laminated porous film comprising a porous film such as a laminated porous film in which 2 to 5 layers of polyethylene and polypropylene are laminated. Is preferred. When a resin having a melting point higher than that of polyethylene such as polyethylene and polypropylene is used by mixing or laminating, it is preferable that polyethylene is 30% by mass or more, and 50% by mass or more as the resin constituting the porous membrane. More preferred.

  As such a resin porous membrane, for example, a porous membrane composed of the above-mentioned exemplified thermoplastic resin used in a conventionally known lithium ion secondary battery or the like, that is, a solvent extraction method, a dry type Alternatively, an ion-permeable porous film manufactured by a wet stretching method or the like can be used.

  The average pore size of the separator is preferably 0.01 μm or more, more preferably 0.05 μm or more, more preferably 1 μm or less, and even more preferably 0.5 μm or less.

  As the separator, a laminated separator having 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 may be used. . The separator has both shutdown characteristics, heat resistance (heat shrinkage resistance), and high mechanical strength. Moreover, the charge / discharge cycle characteristics of the battery are further improved by using the laminated separator. The reason for this is not clear, but the high mechanical strength of the laminated separator shows high resistance to the expansion and contraction of the negative electrode accompanying the charge / discharge cycle of the battery. It is presumed that this is because the adhesion between the positive electrodes can be maintained.

  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 membrane (I) according to the separator is mainly for ensuring a shutdown function, and when the battery reaches or exceeds the melting point of the thermoplastic resin, which is the main component of the porous membrane (I), The thermoplastic resin related to the porous membrane (I) melts and closes the pores of the separator, and a shutdown that suppresses the progress of the electrochemical reaction occurs.

  The thermoplastic resin that is the main component of the porous membrane (I) is preferably a resin having a melting point of 140 ° C. or lower, and specifically includes polyethylene. In addition, as the form of the porous membrane (I), a microporous membrane usually used as a battery separator or a dispersion containing polyethylene particles is applied to a substrate such as a nonwoven fabric and dried. Examples thereof include sheet-like materials such as those obtained. Here, among the total volume of the constituent components of the porous membrane (I) [the total volume excluding the void portion. The same applies to the volume content of the constituent components of the porous membrane (I) and the porous layer (II) according to the separator. ], The volume content of the resin whose main melting point is 140 ° C. or lower is 50% by volume or more, and more preferably 70% by volume or more. For example, when the porous membrane (I) is formed of the polyethylene microporous membrane, the volume content of the resin having a melting point of 140 ° C. or lower 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 battery rises, and has a heat resistance temperature of 150 ° C. or higher. The function is secured by. That is, when the battery becomes high temperature, even if the porous membrane (I) shrinks, the porous layer (II) which does not easily shrink can cause the positive and negative electrodes directly when the separator is thermally shrunk. It is possible to prevent a short circuit due to the contact. In addition, since the heat-resistant porous layer (II) acts as a skeleton of the separator, thermal contraction of the porous membrane (I), that is, 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 difficult to be oxidized and reduced within the battery operating voltage range. Any inorganic particles or organic particles may be used as long as they are fine, 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 control the porosity of the porous layer (II) with high accuracy. 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 phrase “containing a filler having a heat resistant temperature of 150 ° C. or higher as a main component” of the porous layer (II) means that 70% by volume or more of the filler is included in the total volume of the constituent components of the porous layer (II). is doing. The amount of the filler in the porous layer (II) is preferably 80% by volume or more and more preferably 90% by volume or more in the total volume of the constituent components of the porous layer (II). By making the said filler in porous layer (II) high content as mentioned above, the thermal contraction of the whole separator can be suppressed favorably and high heat resistance can be provided.

  The porous layer (II) preferably contains an organic binder to bind the fillers or bind the porous layer (II) and the porous membrane (I). From such a viewpoint, the suitable upper limit of the amount of the filler in the porous layer (II) is, for example, 99% by volume in the total volume of the constituent components of the porous layer (II). If the amount of the filler in the porous layer (II) is less than 70% by volume, for example, it is necessary to increase the amount of the organic binder in the porous layer (II). There is a possibility that the holes of II) are filled with the organic binder and the function as a separator is lost, for example.

  As the organic binder used for the porous layer (II), the above-mentioned fillers and the porous layer (II) and the porous membrane (I) can be favorably bonded, are electrochemically stable, and are a lithium ion secondary battery. If it is stable with respect to the nonaqueous electrolyte solution for use, there is no particular limitation. Specifically, fluororesin (such as PVDF), fluororubber, SBR, CMC, hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), poly N-vinylacetamide, Cross-linked acrylic resin, polyurethane, epoxy resin and the like can be mentioned. These organic binders may be used alone or in combination of two or more.

  The laminated separator is, for example, a composition for forming a porous layer (II) containing, in the porous membrane (I), the filler, an organic binder, and the like, and a solvent (an organic solvent such as water and ketones) ( It can be manufactured by applying a slurry, paste, etc.) and then drying at a predetermined temperature to form the porous layer (II).

  The laminated separator may have one or more porous membranes (I) and porous layers (II), respectively. Specifically, the porous layer (II) is disposed only on one side of the porous membrane (I) to form the laminated separator. For example, the porous layer (II) is formed on both sides of the porous membrane (I). May be used as the laminated separator. However, if the number of layers of the multilayer separator is too large, it is not preferable because the thickness of the separator is increased, which may increase the internal resistance of the battery or decrease the energy density. Is preferably 5 layers or less.

  The thickness of the separator (the laminated separator and other separators) is preferably 6 μm or more and more preferably 10 μm or more from the viewpoint of more reliably separating the positive electrode and the negative electrode. On the other hand, if the separator is too thick, the energy density of the battery may be lowered. Therefore, the thickness is preferably 50 μm or less, and more preferably 30 μm or less.

  In addition, the thickness of the porous membrane (I) [the total thickness when a plurality of porous membranes (I) are present] is preferably 5 to 30 μm. Further, the thickness of the porous layer (II) [when there are a plurality of porous layers (II), the total thickness] is preferably 1 μm or more, more preferably 2 μm or more, and 4 μm or more. Further, it is preferably 20 μm or less, more preferably 10 μm or less, and further preferably 6 μm or less.

  The porosity of the separator (the laminated separator and other separators) is preferably 30 to 70%.

  Moreover, it is preferable that the separator (the laminated separator and other separators) has an adhesive layer on one side or both sides thereof. When the separator and the electrode are integrated by the adhesive layer of the separator when forming the laminated electrode body or the wound electrode body, even if charging / discharging is repeated in a battery using such an electrode body, Since the shape change can be suppressed, the charge / discharge cycle characteristics of the battery are further improved. In the case of a battery using a flat wound electrode body having a flat cross section, the effect of improving the charge / discharge cycle characteristics by the adhesive layer is particularly remarkable.

  It is preferable that the adhesive layer of the separator contains an adhesive resin that exhibits adhesiveness when heated. In the case of an adhesive layer containing an adhesive resin, the separator and the electrode can be integrated by undergoing a step of pressing while heating the electrode body (heating press). The minimum temperature at which the adhesiveness of the adhesive resin is expressed needs to be lower than the temperature at which shutdown occurs in the layers other than the adhesive layer in the separator. Specifically, the temperature is from 60 ° C to 120 ° C. Preferably there is. Further, when the separator is the laminated separator, the minimum temperature at which the adhesive resin exhibits adhesiveness needs to be lower than the melting point of the thermoplastic resin that is the main component of the porous membrane (I). .

  By using such an adhesive resin, deterioration of the separator can be satisfactorily suppressed when the separator and the positive electrode and / or the negative electrode are integrated by hot pressing.

  Due to the presence of the adhesive resin, the peel strength obtained when a peel test at 180 ° between the electrode (for example, the negative electrode) constituting the electrode body and the separator is carried out is preferable in the state before the hot press. Is 0.05 N / 20 mm or less, particularly preferably 0 N / 20 mm (a state having no adhesive force), and a delayed tack property of 0.2 N / 20 mm or more after being heated and pressed at a temperature of 60 to 120 ° C. It is preferable to have.

  However, if the peel strength is too strong, the electrode mixture layer (the positive electrode mixture layer and the negative electrode mixture layer) may peel from the current collector of the electrode, and the conductivity may be lowered. The peel strength by the peel test at ° is preferably 10 N / 20 mm or less after being hot-pressed at a temperature of 60 to 120 ° C.

  In addition, the peel strength at 180 ° between the electrode and the separator in the present specification is a value measured by the following method. The separator and the electrode are each cut into a size of 5 cm in length and 2 cm in width, and the cut-out separator and the electrode are overlapped. When obtaining the peel strength in the state after being hot-pressed, a test piece is prepared by hot-pressing a 2 cm × 2 cm region from one end. The end of the test piece on the side where the separator and electrode are not heated and pressed is opened, and the separator and the negative electrode are bent so that these angles are 180 °. Thereafter, using a tensile tester, both the one end side of the separator opened at 180 ° of the test piece and the one end side of the electrode are gripped and pulled at a pulling speed of 10 mm / min. Measure the strength when peeled off. In addition, the peel strength of the separator and the electrode before heating press was determined by preparing a test piece in the same manner as above except that the separator and electrode cut out as described above were stacked and pressed without heating. The peel test is performed in the same manner as described above.

  Therefore, the adhesive resin has almost no adhesiveness (stickiness) at room temperature (for example, 25 ° C), and the minimum temperature at which the adhesiveness is developed is less than the temperature at which the separator shuts down, preferably 60 ° C to 120 ° C. Those having tackiness are desirable. The temperature of the heating press when integrating the separator and the electrode is more preferably 80 ° C. or more and 100 ° C. or less at which the thermal contraction of the separator does not occur significantly, and the adhesiveness of the adhesive resin is exhibited. The minimum temperature is more preferably 80 ° C. or higher and 100 ° C. or lower.

  As the adhesive resin having a delayed tack property, a resin that has almost no fluidity at room temperature, exhibits fluidity when heated, and has a property of being adhered by pressing is preferable. A resin of a type that is solid at room temperature, melts by heating, and exhibits adhesiveness by a chemical reaction can also be used as the adhesive resin.

  The adhesive resin preferably has a softening point in the range of 60 ° C. or higher and 120 ° C. or lower with the melting point, glass transition point and the like as indices. The melting point and glass transition point of the adhesive resin can be measured, for example, by a method prescribed in JIS K 7121, and the softening point of the adhesive resin can be measured, for example, by a method prescribed in JIS K 7206.

  Specific examples of such adhesive resins include, for example, low density polyethylene (LDPE), poly-α-olefin [polypropylene (PP), polybutene-1, etc.], polyacrylate ester, ethylene-vinyl acetate copolymer. (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer (EBA), ethylene-methyl methacrylate copolymer (EMMA), ionomer resin Etc.

  Each resin, or a resin having adhesiveness at room temperature such as SBR, nitrile rubber (NBR), fluorine rubber, or ethylene-propylene rubber is used as a core, and the melting point and softening point are within a range of 60 ° C to 120 ° C. It is also possible to use a resin having a core-shell structure with a resin as a shell as an adhesive resin. In this case, various acrylic resins and polyurethane can be used for the shell. Further, as the adhesive resin, one-pack type polyurethane, epoxy resin, or the like that exhibits adhesiveness in a range of 60 ° C. or higher and 120 ° C. or lower can be used.

  As the adhesive resin, the above-exemplified resins may be used alone or in combination of two or more.

  When an adhesive layer made of an adhesive resin and containing substantially no pores is formed, there is a risk that the non-aqueous electrolyte of the battery will be difficult to contact the surface of the electrode integrated with the separator. For this reason, it is preferable that a portion where the adhesive resin exists and a portion where the adhesive resin does not exist are formed on the surface where the adhesive resin exists in the positive electrode, the negative electrode, and the separator. Specifically, for example, the location where the adhesive resin is present and the location where the adhesive resin is not present may be alternately formed in a groove shape, and the location where the adhesive resin such as a circle is not present in a plan view is not present. A plurality may be formed continuously. In these cases, the locations where the adhesive resin is present may be regularly arranged or randomly arranged.

  In addition, in the presence surface of the adhesive resin in the positive electrode, the negative electrode, and the separator, when forming the location where the adhesive resin is present and the location where the adhesive resin is not present, The area (total area) may be such that, for example, the peel strength at 180 ° after thermocompression bonding of the separator and the electrode is the above value, and depending on the type of adhesive resin used Specifically, the adhesive resin is preferably present in 10 to 60% of the surface area of the adhesive resin in plan view.

Further, in the presence of the adhesive resin, the basis weight of the adhesive resin improves the adhesion with the electrode. For example, the peel strength at 180 ° after the pressure bonding between the separator and the electrode is performed as described above. to adjust the value is preferably to 0.05 g / ^{m 2} or more, and more preferably set to 0.1 g / ^{m 2} or more. However, if the basis weight of the adhesive resin is too large in the presence of the adhesive resin, the electrode body becomes too thick, or the adhesive resin blocks the pores of the separator, and the movement of ions inside the battery is hindered. There is a risk of doing. Therefore, the existing surface of the adhesive resin, the basis weight of the adhesive resin is preferably 1 g / m ² or less, more preferably 0.5 g / m ² or less.

  The adhesive layer is composed of a porous film or a porous film (I) and a porous layer (II) using a composition for forming an adhesive layer (adhesive resin solution or emulsion) containing an adhesive resin and a solvent as a separator. ) And a step of applying to one side or both sides of the laminate.

  As the nonaqueous electrolytic solution according to the lithium ion secondary battery, for example, a solution prepared by dissolving a lithium salt in the following nonaqueous solvent can be used.

  Non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone (γ-BL ), 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO), 1,3-dioxolane, formamide, dimethylformamide (DMF), dioxolane, acetonitrile, nitromethane, Methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, Aprotic organic solvents such as diethyl ether and 1,3-propane sultone can be used singly or as a mixed solvent in which two or more are mixed.

The lithium salt according to the non-aqueous electrolyte solution, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, 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] At least one selected from the above. The concentration of these lithium salts in the non-aqueous electrolyte is preferably 0.6 to 1.8 mol / l, and more preferably 0.9 to 1.6 mol / l.

  Non-aqueous electrolytes include vinylene carbonate, vinyl ethylene carbonate, acid anhydride, sulfonic acid for the purpose of further improving the charge / discharge cycle characteristics of the battery and improving safety such as high temperature storage and overcharge prevention. Additives (including these derivatives) such as esters, dinitriles, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, and t-butylbenzene may be added as appropriate.

  Further, as the non-aqueous electrolyte, a gel (gel electrolyte) obtained by adding a known gelling agent such as a polymer can be used.

  There is no restriction | limiting in particular about the form of a lithium ion secondary battery. For example, any of a small cylindrical shape, a coin shape, a button shape, a flat shape, a square shape, a large size used for an electric vehicle, and the like may be used.

  When assembling a lithium ion secondary battery, a negative electrode containing a negative electrode active material doped with Li ions, a positive electrode and a separator are assembled into a precursor of a lithium ion secondary battery. A method of sealing the exterior body after putting the non-aqueous electrolyte in the exterior body can be employed. In the precursor of the lithium ion secondary battery, the negative electrode, the positive electrode, and the separator that are accommodated in the outer package can be prepared in advance as the electrode body. Further, as described above, doping of Li ions into the negative electrode active material contained in the negative electrode can be performed by, for example, pre-doping (i) or (ii).

  Some lithium ion secondary batteries having a negative electrode containing a negative electrode active material doped with Li ions perform Li ion doping to the negative electrode active material in the negative electrode mixture layer by in-system pre-doping. For example, by assembling a battery using an electrode (third electrode) having a Li supply source separately from the positive electrode and the negative electrode, and energizing the third electrode, the Li supply source in the negative electrode mixture layer in the battery Some negative electrode active materials are doped with Li ions. Therefore, in this type of battery, even when the doping of Li ions is completed, the third electrode in which a part of the Li supply source remains or all of it disappears remains in the battery. Since the lithium ion secondary battery is assembled using a negative electrode containing a negative electrode active material previously doped with Li ions by pre-doping outside the system, a third electrode used (or used) for doping Li ions is provided inside. I don't have it.

  In-system pre-doping is performed by facing the mixture layer after forming the negative electrode mixture layer by attaching a metal lithium foil to the negative electrode mixture layer or forming a Li vapor deposition layer on the negative electrode mixture layer. In general, a method of introducing Li ions by arranging a Li source so as to perform electrochemical contact (short circuit) is generally used. However, when Li ions are introduced while facing the surface of the mixture layer, the negative electrode mixture layer of the negative electrode closest to the Li source may not maintain the adhesive state with the negative electrode current collector and may fall off. . This is because the short-circuit current is high according to the electrochemical contact, so that the Li ion doping reaction to the negative electrode active material in the negative electrode mixture layer of the negative electrode closest to the Li source proceeds preferentially, and the Li source is the most. It is presumed that the negative electrode mixture layer of the near negative electrode receives the most Li ions and expands greatly. It is considered that the damage to the negative electrode mixture layer adversely affects various characteristics such as a charge / discharge cycle when the battery is used.

  In the lithium ion secondary battery, the negative electrode active material in the negative electrode mixture layer of the negative electrode is doped with Li ions until the voltage reaches 2.0 V at a discharge current rate of 0.1 C. When discharged, it can be grasped by the molar ratio (Li / M) between Li contained in the positive electrode active material and the metal M other than Li. In the lithium ion secondary battery, it is preferable to use a negative electrode in which the Li ion doping amount of the negative electrode active material in the negative electrode mixture layer is adjusted so that the molar ratio Li / M is 0.7 or more and 1.05 or less. The molar ratio Li / M is more preferably 0.7 or more and 0.9 or less. Incidentally, in a battery having a negative electrode in which a negative electrode active material in a negative electrode mixture layer containing a negative electrode active material containing no Li is not pre-doped (and pre-doped) with Li ions, a molar ratio of Li / M becomes smaller than the lower limit value.

  Li-ion doped into the negative electrode active material by external pre-doping so that the molar ratio Li / M in the battery is 0.7 or more and 1.05 or less, when converted into battery capacity, Same or less.

  The composition analysis of the positive electrode active material when discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V can be performed as follows using an ICP (Inductively Coupled Plasma) method. First, 0.2 g of a positive electrode active material to be measured is collected and placed in a 100 mL container. Thereafter, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were added in order and dissolved by heating. After cooling, the sample was further diluted 25 times with pure water, and calibrated using an ICP analyzer “ICP-757” manufactured by JARRELASH. The composition is analyzed by the line method. The composition amount can be derived from the obtained results. The molar ratio Li / M described in the examples described later is a value determined by this method.

  The negative electrode active material in the negative electrode mixture layer by the extra-system pre-doping has a negative electrode doped with Li ions, and the degree of doping of the Li ions is determined so that the molar ratio Li / M in the positive electrode active material is within the above range. In the case of a battery assembled using a negative electrode adjusted to be, since an appropriate amount of Li ions is doped to reduce the irreversible capacity of the negative electrode active material, for example, the generation of Li dendrite can be suppressed. It is possible to satisfactorily suppress the occurrence of a short circuit of the battery.

  The lithium ion secondary battery of the present invention can exhibit good battery characteristics even when used at a charging upper limit voltage of about 4.2 V, as in the case of a normal lithium ion secondary battery. Even if the upper limit voltage is increased to 4.3 V or more, excellent charge / discharge cycle characteristics can be exhibited. Therefore, in the lithium ion secondary battery of the present invention, the capacity can be increased by setting the upper limit voltage for charging higher than usual, and even if it is repeatedly used over a long period of time, it can stably exhibit excellent characteristics.

  In addition, it is preferable that the upper limit voltage of charge of a lithium ion secondary battery is 4.7 V or less.

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

Example 1
<Production of negative electrode>
A unit represented by the above formula (3) and a unit represented by the above formula (4), wherein R is hydrogen and M 'is potassium in the above formula (4). A copolymer (A) having a molar ratio of 6/4 to the unit represented by the formula (4) is dissolved in ion-exchanged water, and an aqueous solution having a copolymer (A) concentration of 8% by mass is obtained. Prepared. In this aqueous solution, a composite Si-1 in which the surface of SiO serving as the negative electrode active material was coated with a carbon material (average particle diameter was 5 μm, specific surface area was 8.8 m ² / g, and the amount of carbon material in the composite was SiO : 10 parts by mass with respect to 100 parts by mass) and carbon black were added and mixed by stirring to obtain a negative electrode mixture-containing paste. The composition ratio (mass ratio) of negative electrode active material: carbon black: copolymer (A) in this paste was 90: 2: 8.

The negative electrode mixture-containing paste is unwound from a roll wound with a copper foil having a thickness of 10 μm, continuously applied to one side of the copper foil and dried to form a negative electrode mixture layer on one side of the copper foil, The density of the negative electrode mixture layer was adjusted to 1.2 g / cm ³ by performing a press treatment, and then wound into a roll to obtain a negative electrode roll.

About the negative electrode pulled out from the said negative electrode roll, Li ion was doped to the negative electrode active material in a negative mix layer by the method (roll to roll method) shown in FIG. The negative electrode 2a is pulled out from the negative electrode roll 20a, LiPF ₆ is dissolved at a concentration of 1 mol / l in a non-aqueous electrolyte (a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 30:70), and vinylene carbonate: 4 mass. %, 4-fluoro-1,3-dioxolan-2-one: a solution added in an amount of 5% by mass) and the electrolyte bath 101 provided with the lithium metal electrode 102. In the electrolyte bath 101, an electric current corresponding to 500 mAh / g per mass of the negative electrode active material is obtained between the negative electrode 2a and the lithium metal electrode 102 at a current density of 0.2 mA / cm ² per area of the negative electrode. The negative electrode active material in the negative electrode mixture layer was doped with Li ions by applying an amount of electricity.

  The negative electrode 2 after Li ion doping is washed in a washing tank 104 equipped with diethyl carbonate after passing through the electrolytic solution tank 101, further dried in a drying tank 105 filled with argon gas, and then wound around a roll 20. It was.

<Preparation of positive electrode>
LiNi _0.78 Co _0.20 Al _0.02 O ₂ which is a positive electrode active material [lithium-containing metal oxide (A), particles having a primary particle diameter of 0.5 μm or more determined by the measurement method of (b) above The ratio is 50% by mass and the maximum primary particle size is 2 μm]: 96.8 parts by mass, conductive additive (carbon black): 1.5 parts by mass, alumina filler (average particle size is 0.7 μm): 0.5 parts by mass and VDF-CTFE as a binder: 1.2 parts by mass were mixed to form a positive electrode mixture. To this positive electrode mixture, NMP as a solvent was added, and “Claremix CLM0 manufactured by M Technique Co., Ltd.” was added. .8 (trade name) "was processed at a rotational speed of 10,000 min ^-1 for 30 minutes to obtain a paste-like mixture. NMP which is a solvent was further added to this mixture, and the mixture was treated at a rotational speed of 10000 min ⁻¹ for 15 minutes to prepare a positive electrode mixture-containing composition.

The positive electrode mixture-containing composition is applied to one surface of an aluminum alloy foil (thickness: 10.0 μm) as a current collector, vacuum-dried at 80 ° C. for 12 hours, and further subjected to a press treatment to collect current. A positive electrode having a positive electrode mixture layer with a thickness of 33 μm on one side of the body was produced. The density (actual density) of the positive electrode mixture layer after the press treatment determined by the above method was 3.65 g / cm ³ and the filling rate was 76.5%.

<Preparation of separator>
Modified polybutyl acrylate resin binder: 3 parts by mass, boehmite powder (average particle size: 1 μm): 97 parts by mass, and water: 100 parts by mass were mixed to prepare a slurry for forming a porous layer (II). This slurry was applied to one side of a polyethylene microporous membrane [porous layer (I)] having a thickness of 12 μm and dried. A separator in which a porous layer (II) mainly composed of boehmite was formed on one surface of the porous layer (I) was obtained. The thickness of the porous layer (II) was 3 μm.

<Assembly of coin-type lithium ion secondary battery>
The negative electrode, the positive electrode, and the separator after Li ion doping were punched out so that their diameters were 17 mm, 16 mm, and 18 mm, respectively. Punched negative electrode, a positive electrode and the separator, the nonaqueous electrolytic solution (mixed at a volumetric ratio of 30:70 of ethylene carbonate and diethyl carbonate, LiPF ₆ was dissolved at a concentration of 1 mol / l, vinylene carbonate: 4 mass%, 4-fluoro-1,3-dioxolan-2-one: 5% by mass, adiponitrile: 0.5% by mass, and 1,3-dioxane: 0.5% by mass of added solution) and battery container A coin-type lithium ion secondary battery having a diameter of 20 mm and a thickness of 1.6 mm and having a structure shown in FIG. 2 was produced.

  Here, FIG. 2 will be described. FIG. 2 is a longitudinal sectional view schematically showing the coin-type lithium ion secondary battery of Example 1. FIG. In the lithium ion secondary battery 10, the positive electrode 1 is accommodated inside a metal outer can 4, and the negative electrode 2 is disposed thereon via a separator 3. The negative electrode 2 is in contact with the inner surface of the metal sealing plate 5. In FIG. 2, the layers of the positive electrode 1, the negative electrode 2, and the separator 3 are not shown separately, but the positive electrode 1 and the negative electrode 2 are opposed to each other with the positive electrode mixture layer and the negative electrode mixture layer through the separator 3. Thus, the separator 3 is arranged so that the porous layer (II) is on the positive electrode 1 side. Further, a non-aqueous electrolyte (not shown) is injected into the lithium ion secondary battery 10.

  In the lithium ion secondary battery 10, the outer can 4 also serves as a positive electrode terminal, and the sealing plate 5 also serves as a negative electrode terminal. And the opening part of the armored can 4 presses the resin-made annular packing 6 arrange | positioned in the peripheral part of the sealing board 5 by the inward fastening of the opening edge part of the armored can 4, and the sealing plate 5 The peripheral edge and the inner peripheral surface of the opening end of the outer can 4 are pressed against each other and sealed. That is, in the coin-type lithium ion battery 10, a resin packing 6 is interposed between the positive electrode terminal (exterior can 4) and the negative electrode terminal (sealing plate 5), and is sealed by this packing 6.

(Example 2)
LiNi _0.82 Co _0.15 Al _0.03 O ₂ as a positive electrode active material [lithium-containing metal oxide (A), ratio of particles having a primary particle diameter of 0.5 μm or more determined by the measurement method of (b) Was used in the same manner as in Example 1, except that the maximum primary particle diameter was 2 μm]. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this positive electrode.

(Example 3)
LiNi _0.47 Co _0.5 Al _0.03 O ₂ as a positive electrode active material [lithium-containing metal oxide (A), ratio of particles having a primary particle diameter of 0.5 μm or more determined by the measurement method of (b) Was used in the same manner as in Example 1, except that the maximum primary particle diameter was 2 μm]. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this positive electrode.

Example 4
LiNi _0.82 Co _0.145 Al _0.03 Ba _0.005 O ₂ as the positive electrode active material [lithium-containing metal oxide (A), primary particle diameter determined by the measurement method of (b) above 0.5 μm A positive electrode was produced in the same manner as in Example 1 except that the ratio of the particles was 50% by mass and the maximum primary particle diameter was 2 μm. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this positive electrode.

(Example 5)
LiNi _0.80 Co _0.10 Mn _0.10 Nb _0.02 O ₂ as a positive electrode active material [Lithium-containing metal oxide (A), primary particle diameter determined by the measurement method of (b) above 0.5 μm A positive electrode was produced in the same manner as in Example 1 except that the ratio of the particles was 50% by mass and the maximum primary particle diameter was 2 μm. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this positive electrode.

(Example 6)
As the positive electrode active material, LiNi _0.78 Co _0.20 Al _0.02 O ₂ and LiCo _0.985 Al _0.008 Mg _0.006 Zr _0.001 O ₂ used in Example 1 [lithium-containing metal oxide] A positive electrode was produced in the same manner as in Example 1, except that the mixture with (B)] (mass ratio 80:20) was used. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this positive electrode.

(Example 7)
Artificial graphite having an average particle diameter of 22 μm: 50% by mass, and a composite Si-1 having an SiO surface coated with a carbon material (average particle diameter of 5 μm, specific surface area of 8.8 m ² / g, carbon material in the composite Was mixed with SiO: 10 parts by mass with respect to 100 parts by mass): 50% by mass for 12 hours with a V-type blender to obtain a negative electrode active material. A negative electrode mixture-containing paste was prepared in the same manner as in Example 1 except that this negative electrode active material was used, and a negative electrode roll was obtained in the same manner as in Example 1 except that this negative electrode mixture-containing paste was used. The negative electrode active material in the negative electrode mixture layer of the negative electrode according to this negative electrode roll was doped with Li ions in the same manner as in Example 1 except that the amount of electricity passed was 250 mAh / g per negative electrode active material mass. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

(Example 8)
Artificial graphite having an average particle diameter of 22 μm: 95% by mass, and composite Si-1 having an SiO surface coated with a carbon material (average particle diameter is 5 μm, specific surface area is 8.8 m ² / g, carbon material in the composite The amount of SiO was 10 parts by mass with respect to 100 parts by mass): 5% by mass for 12 hours with a V-type blender to obtain a negative electrode active material. A negative electrode mixture-containing paste was prepared in the same manner as in Example 1 except that this negative electrode active material was used, and a negative electrode roll was obtained in the same manner as in Example 1 except that this negative electrode mixture-containing paste was used. The negative electrode active material in the negative electrode mixture layer of the negative electrode related to the negative electrode roll was doped with Li ions in the same manner as in Example 1 except that the amount of electricity supplied was 50 mAh / g per mass of the negative electrode active material. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

Example 9
Scale A graphite powder: 97 parts by mass and silicon powder: 3 parts by mass were mixed by a mixing method involving compressive force and shear force to obtain a mixture A. Mixture B was prepared by mixing 100 parts by mass of this mixture A and 3 parts by mass of non-graphitic carbon material by a mixing method involving compression force and shearing force. The mixture B is heated at 1000 ° C. for 1 hour in an inert atmosphere, and then crushed, and composite particles in which silicon sandwiched between the scaly graphite particles is fixed by amorphous carbon are obtained. Obtained. A negative electrode mixture-containing paste was prepared in the same manner as in Example 1 except that this was used as the negative electrode active material, and a negative electrode roll was obtained in the same manner as in Example 1 except that this negative electrode mixture-containing paste was used. The negative electrode active material in the negative electrode mixture layer of the negative electrode related to the negative electrode roll was doped with Li ions in the same manner as in Example 1 except that the amount of electricity supplied was 100 mAh / g per mass of the negative electrode active material. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

(Example 10)
Artificial graphite with an average particle size of 22 μm: 50 mass%, Si-2 whose SiO surface is not coated with a carbon material (average particle size is 5 μm, specific surface area is 6.8 m ² / g, carbon material in the composite Was mixed with SiO: 10 parts by mass with respect to 100 parts by mass): 50% by mass for 12 hours with a V-type blender to obtain a negative electrode active material. A negative electrode mixture-containing paste was prepared in the same manner as in Example 1 except that this negative electrode active material was used, and a negative electrode roll was obtained in the same manner as in Example 1 except that this negative electrode mixture-containing paste was used. The negative electrode active material in the negative electrode mixture layer of the negative electrode according to this negative electrode roll was doped with Li ions in the same manner as in Example 1 except that the amount of electricity passed was 250 mAh / g per negative electrode active material mass. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

(Example 11)
The amount of electricity when the negative electrode is passed through the electrolyte layer is 0.2 mA / cm ² per area of the negative electrode, and an amount of electricity corresponding to 100 mAh / g per mass of the negative electrode active material is energized to negative electrode mixture layer A negative electrode after Li ion doping was obtained in the same manner as in Example 1 except that the negative electrode active material therein was doped with Li ions.

  A coin-type lithium ion secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used.

Example 12
The same procedure as in Example 1 was conducted except that the negative electrode active material in the negative electrode mixture layer of the negative electrode was doped with Li ions by applying a current corresponding to 100 mAh / g of the amount of electricity to the negative electrode active material. A negative electrode after ion doping was obtained.

  A coin-type lithium ion secondary battery was produced in the same manner as in Example 2 except that this negative electrode was used.

(Example 13)
The same procedure as in Example 1 was performed except that the negative electrode active material in the negative electrode mixture layer of the negative electrode was doped with Li ions by supplying a current corresponding to 200 mAh / g of the amount of electricity to the negative electrode active material. A negative electrode after ion doping was obtained.

  A coin-type lithium ion secondary battery was produced in the same manner as in Example 3 except that this negative electrode was used.

(Example 14)
The same procedure as in Example 1 was performed except that the negative electrode active material in the negative electrode mixture layer of the negative electrode was doped with Li ions by supplying a current corresponding to 200 mAh / g of the amount of electricity to the negative electrode active material. A negative electrode after ion doping was obtained.

  A coin-type lithium ion secondary battery was produced in the same manner as in Example 4 except that this negative electrode was used.

(Example 15)
The same procedure as in Example 1 was performed except that the negative electrode active material in the negative electrode mixture layer of the negative electrode was doped with Li ions by supplying a current corresponding to 200 mAh / g of the amount of electricity to the negative electrode active material. A negative electrode after ion doping was obtained.

  A coin-type lithium ion secondary battery was produced in the same manner as in Example 5 except that this negative electrode was used.

(Example 16)
The same procedure as in Example 1 was conducted except that the negative electrode active material in the negative electrode mixture layer of the negative electrode was doped with Li ions by supplying a current corresponding to 150 mAh / g of the amount of electricity to the negative electrode active material. A negative electrode after ion doping was obtained.

  A coin-type lithium ion secondary battery was produced in the same manner as in Example 6 except that this negative electrode was used.

(Example 17)
The same procedure as in Example 1 was conducted except that the negative electrode active material in the negative electrode mixture layer of the negative electrode according to the negative electrode roll obtained in the same manner as in Example 7 was changed to a current carrying amount of 100 mAh / g per mass of the negative electrode active material. Thus, a negative electrode after Li ion doping was obtained. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

(Example 18)
The same procedure as in Example 1 was conducted except that, in the negative electrode active material in the negative electrode mixture layer of the negative electrode related to the negative electrode roll obtained in the same manner as in Example 8, the amount of electricity was 20 mAh / g per mass of the negative electrode active material. And doped with Li ions. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

Example 19
The same procedure as in Example 1 was conducted except that, in the negative electrode active material in the negative electrode mixture layer of the negative electrode obtained in the same manner as in Example 9, the amount of electricity was 50 mAh / g per negative electrode active material mass. And doped with Li ions. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

(Example 20)
Except for the negative electrode active material in the negative electrode mixture layer of the negative electrode related to the negative electrode roll obtained in the same manner as in Example 10, the amount of electricity supplied was 20 mAh / g per mass of the negative electrode active material. And doped with Li ions. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

(Comparative Example 1)
Coin-type lithium in the same manner as in Example 1 except that the same negative electrode as prepared in Example 1 (negative electrode before doping Li ions to the negative electrode active material in the negative electrode mixture layer) was used as it was. An ion secondary battery was produced.

(Comparative Example 2)
LiNi _0.91 Co _0.03 Mn _0.02 Al _0.02 Mg _0.02 O ₂ as the positive electrode active material [the proportion of particles having a primary particle size of 0.5 μm or more determined by the measurement method of (b) above A positive electrode was produced in the same manner as in Example 1 except that 50% by mass and the maximum primary particle size was 2 μm. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this positive electrode.

(Comparative Example 3)
A negative electrode mixture-containing paste was prepared in the same manner as in Example 1 except that artificial graphite having an average particle size of 22 μm was used as the negative electrode active material, and the same procedure as in Example 1 was conducted except that this negative electrode mixture-containing paste was used. Thus, a negative electrode roll was obtained. The negative electrode active material in the negative electrode mixture layer of the negative electrode related to the negative electrode roll was doped with Li ions in the same manner as in Example 1 except that the amount of electricity passed was 30 mAh / g per mass of the negative electrode active material. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

(Comparative Example 4)
The same negative electrode as prepared in Example 1 (negative electrode before doping Li ions into the negative electrode mixture layer) was punched out so as to have a diameter of 17 mm. A metal Li foil (thickness: 50 μm) corresponding to an amount of electricity of 500 mAh / g per mass of the negative electrode active material was attached to the center of the negative electrode. A coin-type lithium ion secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used.

(Comparative Example 5)
The amount of electricity when the negative electrode is passed through the electrolyte layer is 0.2 mA / cm ² per area of the negative electrode, and an amount of electricity corresponding to 100 mAh / g per mass of the negative electrode active material is energized to negative electrode mixture layer A negative electrode after Li ion doping was obtained in the same manner as in Example 1 except that the negative electrode active material therein was doped with Li ions.

  A coin-type lithium ion secondary battery was produced in the same manner as in Comparative Example 2 except that this negative electrode was used.

(Comparative Example 6)
Except for the negative electrode active material in the negative electrode mixture layer of the negative electrode relating to the negative electrode roll obtained in the same manner as in Comparative Example 3, the amount of electricity was 10 mAh / g per negative electrode active material mass, and the same as in Example 1. And doped with Li ions. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

  Regarding the charge / discharge cycle characteristics of the examples and comparative examples, the following discharge capacity measurement and charge / discharge cycle characteristics evaluation were performed.

<Discharge capacity measurement>
Five lithium ion secondary batteries of Examples and Comparative Examples were each charged with a constant current of up to 4.4 V at a current value of 0.5 C, and subsequently reached a current value of 0.02 C at a constant voltage of 4.4 V. Charged until Then, it discharged to 2.0V with the constant current of 0.2C, calculated | required the initial discharge capacity, and made this into the discharge capacity of each battery.

<Charge / discharge cycle characteristics evaluation>
After the initial discharge capacity measurement, the lithium ion secondary batteries (5 each) were charged at a constant current of up to 4.4V at a current value of 0.5C, and subsequently the current value was set at 0.02C at a constant voltage of 4.4V. Charged until it reached. Then, it discharged to 2.0V with the constant current of 0.2C, and calculated | required the initial discharge capacity. Next, each battery was charged with a constant current up to 4.4 V at a current value of 1 C, subsequently charged with a constant voltage of 4.4 V until the current value reached 0.05 C, and then 2. with a current value of 1 C. A series of operations for discharging to 0 V was taken as one cycle, and this was repeated 500 times. And about each battery, the constant current-constant voltage charge and the constant current discharge were performed on the same conditions as the time of first time discharge capacity measurement, and the discharge capacity was calculated | required. Then, a value obtained by dividing these discharge capacities by the initial discharge capacities was expressed as a percentage to obtain a capacity maintenance ratio, and an average value of 5 pieces was calculated for each.

The structure of the lithium ion secondary battery of an Example and a comparative example is shown in Tables 1-6, and each said evaluation result is shown in Tables 7-9. The LiNi _0.91 Co _0.03 Mn _0.02 Al _0.02 Mg _0.02 O ₂ used in Comparative Example 2 and Comparative Example 5 does not satisfy the general formula (1) and contains lithium. Although not corresponding to the metal oxide (A), in Tables 1 to 3, this is described in the column of “lithium-containing metal oxide (A)”. Further, “composite particles” in the column of negative electrode active material in Tables 4 to 6 mean composite particles in which silicon sandwiched between scaly graphite particles is fixed by amorphous carbon. Furthermore, “present (in system)” in the column of Comparative Example 4 in “Non-doping presence / absence of Li ion doping in negative electrode active material” in Tables 4 to 6 means Li foil serving as a Li supply source in the battery. This means that the negative electrode active material in the negative electrode mixture layer was doped with Li ions (in-system pre-doping) in the battery. In Tables 7 to 9, the discharge capacity and the capacity retention rate at the time of charge / discharge cycle characteristics evaluation are shown as relative values when the value of the battery of Comparative Example 1 is 100.

  As shown in Tables 1 to 9, a negative electrode in which the material S is a negative electrode active material and a negative electrode mixture layer is doped with Li ions by pre-doping outside the system, and a positive electrode having a lithium-containing metal oxide (A) as a positive electrode active material The lithium ion secondary batteries of Examples 1 to 20 having a large capacity and charge / discharge cycle characteristics compared to the battery of Comparative Example 1 using a negative electrode in which the negative electrode mixture layer is not doped with Li. The capacity maintenance rate at the time of evaluation was high, and it had excellent charge / discharge cycle characteristics.

  On the other hand, the batteries of Comparative Examples 2 and 5 using a lithium-containing metal oxide with too much Ni and too little Co as the cathode active material, and the anode active material in the anode mixture layer by pre-doping in the system The battery of Comparative Example 4 having a negative electrode doped with Li ions in the battery had a lower capacity retention rate at the time of evaluation of charge / discharge cycle characteristics than the battery of the example, and was inferior in charge / discharge cycle characteristics. The batteries of Comparative Examples 3 and 6 using only graphite as the negative electrode active material had a smaller capacity than the batteries of the examples.

  Moreover, in each battery of the examples, the batteries having the same configuration except that the molar ratio Li / M is different (Example 1 and Example 11, Example 2 and Example 12, Example 3 and Example 13, Example 4 and Example 14, Example 5 and Example 15, Example 6 and Example 16, Example 7 and Example 17, Example 8 and Example 18, Example 9 and Example 19, When Example 10 and Example 20) are compared, the batteries of Examples 11 to 20 having a more preferable molar ratio Li / M have a higher capacity retention rate at the time of charge / discharge cycle characteristic evaluation, and are more charged / discharged. Cycle characteristics were excellent.

[Experimental example of a lithium ion secondary battery having a negative electrode containing a negative electrode active material doped with Li ions by an out-of-system pre-doping method (ii)]
A negative electrode was produced in the same manner as in Example 1 except that the same composite Si-1 as used in Example 1 was doped with Li ions by the extra-system pre-doping method (ii) to make the negative electrode active material. A coin-type lithium ion secondary battery could be satisfactorily produced in the same manner as in Example 1 except that this negative electrode was used without pre-doping by the extra-system pre-doping method (i). .

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

  The lithium ion secondary battery of the present invention can be applied to the same use as that of a conventionally known lithium ion secondary battery.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 2a Negative electrode before Li dope 3 Separator 4 Outer can 5 Sealing plate 6 Resin packing 10 Lithium ion secondary battery 20 Roll which wound negative electrode 2 20a Roll 101 which wound negative electrode 2a Electrolyte tank 102 Lithium metal electrode 103 Power supply 104 Cleaning tank 105 Drying means

Claims (7)

A precursor of a lithium ion secondary battery in which a negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder, a positive electrode having a positive electrode mixture layer containing a positive electrode active material and a binder, and a separator are housed in an exterior body. There,
The negative electrode mixture layer contains at least a negative electrode active material doped with Li ions,
The negative electrode active material contains a material S containing at least Si,
The positive electrode mixture layer has the following general formula (1) as the positive electrode active material.
Li _a Ni _1- bcd _Cob Mn _c M ¹ _d Mg _e O ₂ (1)
[In the general formula (1), M ¹ contains at least one element selected from the group consisting of Al, Ti, Sr, Zr, Nb, Ag, and Ba, and 0.9 ≦ a ≦ 1. 10, 0.1 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0.1 ≦ b + c ≦ 0.9, 0.003 ≦ d ≦ 0.06, and 0 ≦ e ≦ 0.003. ] The lithium ion secondary battery precursor characterized by containing the lithium containing metal oxide (A) represented by these. The precursor of the lithium ion secondary battery according to claim 1, wherein the material S contains SiO _x (where 0.5 ≦ x ≦ 1.5). The precursor of a lithium ion secondary battery according to claim 1 or 2, wherein the SiO _x forms a composite with a carbon material.   The precursor of the lithium ion secondary battery according to claim 3, wherein the content of the composite in the total amount of the negative electrode active material contained in the negative electrode mixture layer is 5% by mass or more.   A lithium ion secondary battery comprising the lithium ion secondary battery precursor according to claim 1 and a non-aqueous electrolyte. A method for manufacturing the lithium ion secondary battery according to claim 5, comprising:
A step of doping the negative electrode active material with Li ions of a negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder;
Assembling a precursor of a lithium ion secondary battery using the negative electrode obtained through the above steps;
And a step of forming a lithium ion secondary battery using the precursor of the lithium ion secondary battery and a non-aqueous electrolyte. A method for manufacturing the lithium ion secondary battery according to claim 5, comprising:
Producing a negative electrode having a negative electrode mixture layer using a negative electrode active material doped with Li ions at least partially and a binder;
Assembling a precursor of a lithium ion secondary battery using the negative electrode obtained by the step;
And a step of forming a lithium ion secondary battery using the precursor of the lithium ion secondary battery and a non-aqueous electrolyte.

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