JP5809946B2 - Lithium secondary battery positive electrode active material coating material, lithium secondary battery positive electrode active material, lithium secondary battery, and methods for producing the same - Google Patents

Description

  The present invention relates to a covering material for a positive electrode active material for a lithium secondary battery, a positive electrode active material for a lithium secondary battery, a lithium secondary battery, and a method for producing them.

  Lithium rechargeable batteries have high energy density and take advantage of their characteristics, and are widely used in notebook computers and mobile phones. In recent years, interest in electric vehicles has increased from the viewpoint of preventing global warming due to an increase in carbon dioxide, and the application of lithium secondary batteries as a power source has been studied.

  Although it is a lithium secondary battery having such excellent characteristics, there are also problems. One of these is improved safety. In particular, improving the safety of the battery during high temperature storage is an important issue.

  When the lithium secondary battery is stored at a high temperature, the electrolytic solution is decomposed and gas is generated inside the battery. When gas is generated, the battery can swells and the safety of the battery decreases. Since this problem becomes prominent in a square battery, countermeasures are required. Also, a decrease in battery capacity becomes a problem. Patent Document 1 reports a study of improving the battery performance by adding propane sultone to the battery.

JP 2003-86249 A

  When propane sultone is added to the battery as in Patent Document 1, there is an effect of suppressing gas generation, but since propane sultone is decomposed at the negative electrode, the battery performance may be lowered. Therefore, there is an urgent need to develop a coating material and a coating method that have an effect of suppressing gas generation during high-temperature storage and that can suppress a decrease in battery performance.

  An object of the present invention is to improve battery performance and suppress gas generation during high temperature storage.

The features of the present invention are as follows, for example.
(1) A coating material for a positive electrode active material for a lithium secondary battery, comprising a polymer represented by the following (formula 1).

In (Formula 1), n is 1 or more and 10 or less.
x is the number of repeating units including a sulfonyl group.
(2) polymer is below a lithium secondary battery positive electrode active material for a coating material is a copolymer represented by (Equation 2).

In (Formula 2), n is 1 or more and 10 or less.
p is 2 or more.
X is any of ether (—O—), imine (—NH—), lactone (—COO—), lactam (—CONH—), olefin (—CH═CH—), and sulfide (—S—). is there.
x is the number of repeating units including a sulfonyl group.
y is the number of repeating units including X.
(3 ) The coating material for a lithium secondary battery positive electrode active material, wherein the copolymer is a copolymer represented by the following (formula 3).

In (Formula 3), n is 1-10.
q is 2 or more.
x is the number of repeating units including a sulfonyl group.
y is the number of repeating units including X.
(4) A lithium secondary battery positive electrode active material including the above-described coating material for a lithium secondary battery positive electrode active material, the lithium secondary battery positive electrode active material formed on the surface of the lithium secondary battery positive electrode active material.
(5) A lithium secondary battery including the above-described lithium secondary battery positive electrode active material, wherein the polymer is 0.001 wt% or more and 10 wt% or less with respect to the lithium secondary battery positive electrode active material. Secondary battery.
(6) A lithium secondary battery in which the shape of the battery is square.
(7) A method for producing a coating material for a positive electrode active material for a lithium secondary battery, comprising: a step of forming a polymer by ring-opening polymerization of a cyclic sultone; Method.
(8) A method for producing a positive electrode active material for a lithium secondary battery as described above, comprising the following steps.
(A) Step of adding and stirring a polymer dissolved in a solvent to the positive electrode active material of the lithium secondary battery (B) Step of removing the solvent after the step (A)

  According to the present invention, it is possible to suppress suppression of gas generation during storage at high temperature and suppression of deterioration of battery performance. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is sectional drawing of a laminate-type lithium ion battery. It is a perspective view which shows a square-type lithium ion battery. It is AA sectional drawing of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible. In all the drawings for explaining the present invention, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

The polymer used as the coating material in the embodiment of the present invention is a polymer having a sulfonyl group (—SO ₃ —) in the molecule. Specifically, it is a ring-opening polymer of cyclic sultone. By covering the positive electrode active material with a polymer having an SO ₃ group in the main chain of the polymer, gas generation can be suppressed during high-temperature storage. Moreover, said polymer can suppress the fall of the battery performance at the time of high temperature storage.
A polymer is selectively formed on the surface of the positive electrode active material and is not decomposed by the negative electrode. In this case, the polymer is not present or hardly present in the negative electrode. However, there is a possibility that the polymer peels off from the positive electrode active material due to aging and penetrates into the negative electrode.

  The cyclic sultone is a cyclic compound represented by (Formula 4).

  As R in (Formula 4), H or an alkyl group is preferable, and H is particularly preferable from the viewpoint of the characteristics of the coating material. N in (Formula 4) is preferably 1 or more and 10 or less. Specific examples of cyclic sultone include 1,1-methane sultone, 1,2-ethane sultone, 1,3-propane sultone, 1,4-butane sultone, 1,5-pentane sultone, 1,7-hexane sultone, 2 , 4-butane sultone, 2,5-pentane sultone, and the like. From the viewpoint of characteristics as a coating material, 1,3-propane sultone, 1,4-butane sultone, and 1,5-pentane sultone are preferable, and 1,3-propane sultone is particularly preferable.

The polymer of the cyclic compound represented by (Formula 4) is represented by the following (Formula 1). N in (Formula 1) is preferably 1 or more and 10 or less. X in (Formula 1) is the number of repeating units including a sulfonyl group (—SO ₃ —).

The polymer can be synthesized by adding a polymerization initiator to cyclic sultone, which is a ring-opening polymerization method. The polymerization initiator is not particularly limited as long as it functions as a polymerization initiator, but amines, alkali compounds, SnCl ₄ , BF ₃ , BF ₅ , Zn, oxides of alkaline earth metals, organometallic compounds, etc. are used. It is done. In the polymerization initiator, amines are preferably used. As the amines, trimethylamine and triethylamine are preferably used from the viewpoint of synthesis.

  Moreover, the polymer of this invention can also use the polymer copolymerized with 1 type individual or 2 or more types of other cyclic monomers. As the cyclic monomer to be copolymerized, the functional group X of (Formula 5) contains one or more of O, S, and N. Specifically, ether (—O—), imine (—NH -), Lactone (-COO-), lactam (-CONH-), olefin (-CH = CH-), and those represented by sulfide (-S-). N in (Formula 5) is preferably 1 or more and 10 or less.

  X is preferably ether or lactone. By selecting these, ion exchange at the positive electrode interface becomes smooth, and it is possible to provide a coating material that does not deteriorate the battery performance. R in (Formula 5) is H or an alkyl group.

  When X is ether, n is 3 or more and 5 or less, and 7 is preferably used. When X is a lactone, n is preferably 4, 6, or 7. By selecting n, the ring-opening polymerization reaction proceeds smoothly, and the target polymer can be synthesized in a high yield.

  Specific examples of the copolymerized polymer include compounds represented by the following (formula 2) and (formula 3).

In (Formula 2), n is 1 or more and 10 or less. p is 2 or more. X is any of ether (—O—), imine (—NH—), lactone (—COO—), lactam (—CONH—), olefin (—CH═CH—), and sulfide (—S—). is there. x is the number of repeating units including a sulfonyl group. y is the number of repeating units including X.

In (Formula 3), n is 1-10. q is 2 or more. x is the number of repeating units including a sulfonyl group. y is the number of repeating units including X.

  Moreover, the polymer concerning embodiment of this invention can use the polymer copolymerized by 1 type individually or 2 or more types of acrylic monomers by anionic polymerization.

  The method for coating the positive electrode active material is not particularly limited as long as the positive electrode active material is coated with a polymer. (1) A method in which a polymer previously dissolved in a solvent is added to the positive electrode active material and the solvent is removed after stirring (2) A method of adding a polymer to the electrode slurry can be mentioned.

  In the method (1), the solvent is not particularly limited as long as the polymer dissolves, but water, alcohols such as methanol and ethanol, acetone, methyl ethyl ketone, N-methylpyrrolidone and the like are preferably used from the viewpoint of cost. . In the method (1), a spray drying method can be used at the time of coating.

  The coating amount of the polymer is 0.001 wt% to 10 wt% with respect to the positive electrode active material. Preferably, it is 0.01 wt% to 1 wt%, and particularly preferably 0.05 wt% to 0.3 wt%. If the coating amount of the polymer is too small, the effect of suppressing gas generation during high-temperature storage is lowered, and if the coating amount is large, the battery performance is lowered.

The positive electrode in the present invention is not limited as long as it can occlude and release lithium ions. For example, LiCoO ₂ , LiNiO ₂ , LiMn _1/3 Ni _{1 /} represented by a general formula of LiMO ₂ (M is a transition metal). ₃ Co _1/3 O ₂ , LiMn _0.4 Ni _0.4 Co _0.2 O ₂ oxide having a layered structure, and part of M is Al, Mg, Mn, Fe, Co, Cu, Zn, Al, Ti An oxide substituted with at least one metal element selected from the group consisting of Ge, W, and Zr. Further, oxides of Mn having a spinel crystal structure such as LiMn ₂ O ₄ and Li _{1 + x} Mn _2−x O ₄ can be given. Further, LiFePO ₄ having an olivine structure, LiMnPO ₄ , and a part of them are at least one selected from the group consisting of Al, Mg, Mn, Fe, Co, Cu, Zn, Al, Ti, Ge, W, and Zr. You may use the oxide substituted with the metal element more than the seed | species.

  The negative electrode active material in the present invention is a graphitized material obtained from natural graphite, petroleum coke, coal pitch coke, etc., heat-treated at a high temperature of 2500 ° C. or higher, mesophase carbon or amorphous carbon, carbon fiber, lithium, and the like. A metal to be alloyed or a material having a metal supported on the surface of carbon particles is used. For example, a metal or alloy selected from lithium, silver, aluminum, tin, silicon, indium, gallium, and magnesium. Further, the metal or the oxide of the metal can be used as a negative electrode active material. Furthermore, lithium titanate can also be used.

  The electrolytic solution in the present invention is a solution in which a supporting electrolyte is dissolved in a nonaqueous solvent. The nonaqueous solvent is not particularly limited as long as it can dissolve the supporting electrolyte, but the following are preferable. It is an organic solvent such as diethyl carbonate, dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate, propylene carbonate, γ-butyl lactone, tetrohydrofuran, dimethoxyethane, etc., and these can be used alone or in combination. In addition, a compound having an unsaturated double bond in the molecule such as vinylene carbonate or an aromatic compound such as cyclohexylbenzene or biphenyl may be added to the electrolytic solution. Further, an organic compound containing a hetero element such as sulfur or nitrogen in the molecule may be added.

The supporting electrolyte in the present invention is not particularly limited as long as it is soluble in a non-aqueous solvent, but the following are preferable. That is, LiPF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₆ SO ₂ ) ₂ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiI, LiBr, LiSCN, Li ₂ B ₁₀ Cl ₁₀ , LiCF ₃ CO ₂ or the like, and one kind or a mixture of two or more kinds can be used.

  The separator in the present invention may be made of a polymer such as polyolefin, polyamide, polyester, or a glass cloth using fibrous glass fiber, and any material can be used as long as it does not adversely affect the lithium battery. However, polyolefin is preferably used.

  Examples of the polyolefin include polyethylene, polypropylene, and the like, and these films can be used in an overlapping manner.

  Moreover, the air permeability (sec / 100 mL) of the separator is 10 or more and 1000 or less, preferably 50 or more and 800 or less, and particularly preferably 90 or more and 700 or less.

  The shape of the battery is not particularly limited as long as it avoids contact with the outside, and examples thereof include a cylindrical shape and a rectangular shape. When the gas is generated inside the battery, the battery swells more remarkably than the cylindrical battery. Therefore, the effect of the present invention is remarkably exhibited in the square battery.

〔Example〕
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples. The results of this example are summarized in Table 1.

<Polymer synthesis method>
The monomer was placed in a reaction vessel, and 3 wt% of triethylamine as a polymerization initiator was added to the monomer. Thereafter, the reaction vessel was sealed and heated at 60 ° C. for 6 hours to obtain a polymer. The synthesized polymer was washed with hexane, filtered and dried.

<Coating method of positive electrode active material>
The polymer was dissolved in N-methylpyrrolidone. The positive electrode active material was added to the solution and stirred for 1 hour. After stirring, N-methylpyrrolidone was distilled off. Thereafter, the positive electrode active material was sieved.

<Method for producing positive electrode>
A positive electrode active material, a conductive agent (SP270: graphite manufactured by Nippon Graphite Co., Ltd.), and a binder (polyvinylidene fluoride KF1120: Kureha Chemical Industry Co., Ltd.) were mixed at a ratio of 85: 10: 10% by weight, and N-methyl-2-pyrrolidone was mixed. The mixture was charged and mixed to prepare a slurry solution. The slurry was applied to a 20 μm thick aluminum foil by a doctor blade method and dried. The mixture application amount was 200 g / m ² . Then, it pressed and cut | judged the electrode to the magnitude | size of 10 cm < ² >, and produced the positive electrode.

<Method for producing negative electrode>
Graphite was mixed at a ratio of 90: 10% by weight and charged into N-methyl-2-pyrrolidone to prepare a slurry solution. The slurry was applied to a copper foil having a thickness of 20 μm by a doctor blade method and dried. The mixture was pressed so that the bulk density was 1.0 g / cm ³ , and the electrode was cut to a size of 10 cm ² to prepare a negative electrode.

<Production method of laminated battery>
FIG. 1 is a cross-sectional view showing a laminate-type lithium ion battery of this example. The lithium ion battery shown in FIG. 2 has a structure in which a positive electrode 1 and a negative electrode 2 are stacked with a separator 3 interposed therebetween and sealed together with a non-aqueous electrolyte solution with a package 4. The positive electrode 1 includes a positive electrode current collector 1a and a positive electrode mixture layer 1b, and the negative electrode 2 includes a negative electrode current collector 2a and a negative electrode mixture layer 2b. The positive electrode current collector 1 a is connected to the positive electrode terminal 5, and the negative electrode current collector 2 a is connected to the negative electrode terminal 6.

  A separator 3 made of polyolefin was inserted between the positive electrode 1 and the negative electrode 2 to form an electrode group. Thereto, an electrolytic solution was injected. Thereafter, the battery was sealed with an aluminum laminate to produce a battery. Then, the battery was initialized by repeating charging / discharging 3 cycles.

<Battery evaluation method>
1. Evaluation Method of Laminate Battery 1.1 Initial Capacity of Laminate Battery The battery was charged at a current density of 0.1 mA / cm ² up to a preset upper limit voltage. The discharge was performed at a current density of 0.1 mA / cm ² up to a preset lower limit voltage. The upper limit voltage was 4.2V and the lower limit voltage was 2.5V. The discharge capacity obtained in the first cycle was taken as the initial capacity of the battery.
1.2 High temperature storage test The laminated battery was charged to 4.2V. Then, it put into the 85 degreeC thermostat and preserve | saved for 24 hours. After storing for 24 hours, the battery was taken out, the battery was cooled to room temperature, the generated gas was collected with a syringe, and the amount of gas was measured.

2. Square battery evaluation A square battery was prepared in the same manner as the laminate battery. The size of the square battery was 43 mm in length, 34 mm in width, and 4.6 mm in thickness.

  FIG. 2 is a perspective view showing a prismatic lithium ion battery. In FIG. 2, a battery 110 is obtained by enclosing a flat wound electrode body in a rectangular outer can 112 together with a non-aqueous electrolyte. A terminal 115 is provided through an insulator 114 at the center of the cover plate 113.

  FIG. 3 is a cross-sectional view taken along the line AA of FIG. In FIG. 3, the positive electrode 116 and the negative electrode 118 are wound so as to sandwich the separator 117, thereby forming a flat wound electrode body 119. An insulator 120 is provided at the bottom of the outer can 112 so that the positive electrode 116 and the negative electrode 118 are not short-circuited.

  The positive electrode 116 is connected to the lid plate 113 via the positive electrode lead body 121. On the other hand, the negative electrode 118 is connected to the terminal 115 via the negative electrode lead body 122 and the lead plate 124. An insulator 123 is sandwiched so that the lead plate 124 and the lid plate 113 do not directly contact each other.

  First, the battery capacity was measured. The battery capacity was defined as the capacity when discharged at 0.2 CA with respect to the design capacity of the battery. Next, rate characteristics were evaluated. The rate characteristics were defined by dividing the capacity obtained when discharging at 1.0 CA by the capacity obtained at 0.2 CA.

  Then, the storage test of the square battery was performed. In the storage test, after charging the battery to 4.2 V, it was placed in a constant temperature bath at 85 ° C. and stored for 24 hours. Then, after cooling to room temperature, the thickness of the battery was measured. The thickness of the battery was measured at the center point of the battery, and the swelling of the battery was defined by the amount of change in the thickness of the battery before and after heating.

Reference example 1

To the reaction vessel was added 1,3-propane sultone (12.2 g) and triethylamine (0.37 g). Thereafter, the reaction vessel was heated at 60 ° C. for 6 hours to synthesize polymer A. 10 mg of the purified polymer A was dissolved in 100 g of N-methylpyrrolidone (NMP). Thereafter, 10 g of LiCoO ₂ was added and stirred, and then NMP was distilled off to coat the positive electrode active material. In this reference example, the polymer concentration of the polymer with respect to the positive electrode active material was 0.1 wt%.

  An electrode was prepared using the coated positive electrode active material, and then a laminated battery was prepared. The capacity of the battery was 32 mAh. Moreover, the high temperature storage test was done and the amount of gas generation was measured. As a result, the gas generation amount was 0.058 mL.

  Next, a square battery was fabricated using the coated positive electrode active material. The battery capacity was 820 mAh, and the rate characteristic was 93%. Further, the battery capacity after the heating test was 762 mAh, and the swelling of the battery was 1.14 mm.

Reference example 2

In Reference Example 1, the same study was conducted except that the amount of polymer A added was 5 mg. In this reference example, the polymer concentration of the polymer with respect to the positive electrode active material was 0.05 wt%.

  The capacity of the laminated battery was 32 mAh. Moreover, the high temperature storage test was done and the amount of gas generation was measured. As a result, the gas generation amount was 0.078 mL.

  Next, a square battery was fabricated using the coated positive electrode active material. The battery capacity was 820 mAh, and the rate characteristic was 95%. Further, the battery capacity after the heating test was 735 mAh, and the swelling of the battery was 1.30 mm.

Reference example 3

In Reference Example 1, the same study was conducted except that the amount of polymer A added was 30 mg. In this reference example, the polymer concentration of the polymer with respect to the positive electrode active material was 0.3 wt%.

  The capacity of the laminated battery was 32 mAh. Moreover, the high temperature storage test was done and the amount of gas generation was measured. As a result, the amount of gas generated was 0.070 mL.

  Next, a square battery was fabricated using the coated positive electrode active material. The battery capacity was 820 mAh, and the rate characteristic was 90%. Moreover, the battery capacity after the heating test was 740 mAh, and the swelling of the battery was 1.29 mm.

To the reaction vessel, 1,3-propane sultone (9.5 g), triethylamine (0.37 g), and methyl ethyl ketone as a reaction solvent were added. Thereafter, the reaction solution was cooled to −78 ° C. with dry ice. After cooling, gaseous ethylene oxide was added to the reaction vessel and then returned to room temperature. After stirring the reaction solution, the reaction vessel was gradually heated to 50 ° C. After 6 hours, the produced polymer was taken out, washed with hexane and purified to synthesize polymer B. ^When analyzed by ¹ H-NMR, the ratio of 1,3-propane sultone to ethylene oxide in the polymer was 78:22 (mol ratio).

Thereafter, an electrode was produced by coating LiCoO ₂ in the same manner as in Reference Example 1 except that polymer B was used instead of polymer A, and then a laminated battery was produced. The capacity of the battery was 32 mAh. Moreover, the high temperature storage test was done and the amount of gas generation was measured. As a result, the gas generation amount was 0.068 mL.

  Next, a square battery was fabricated using the coated positive electrode active material. The battery capacity was 820 mAh, and the rate characteristic was 95%. Further, the battery capacity after the heating test was 741 mAh, and the swelling of the battery was 1.29 mm.

To the reaction vessel, 1,3-propane sultone (2.0 g), triethylamine (0.37 g), and methyl ethyl ketone as a reaction solvent were added. Thereafter, the reaction solution was cooled to −78 ° C. with dry ice. After cooling, gaseous ethylene oxide was added to the reaction vessel and then returned to room temperature. After stirring the reaction solution, the reaction vessel was gradually heated to 50 ° C. After 6 hours, the produced polymer was taken out, washed with hexane and purified to synthesize polymer C. ^When analyzed by ¹ H-NMR, the ratio of 1,3-propane sultone to ethylene oxide in the polymer was 16:84 (mol ratio).

Thereafter, as in Reference Example 1, LiCoO ₂ was coated to produce an electrode, and then a laminated battery was produced. The capacity of the battery was 32 mAh. Moreover, the high temperature storage test was done and the amount of gas generation was measured. As a result, the gas generation amount was 0.081 mL.

  Next, a square battery was fabricated using the coated positive electrode active material. The battery capacity was 820 mAh, and the rate characteristic was 96%. Further, the battery capacity after the heating test was 731 mAh, and the swelling of the battery was 1.30 mm.

In a reaction vessel, β-propiolactone (1.8 g) is added to (9.2 g) to 1,3-propane sultone, triethylamine (0.37 g) is further added, and the mixture is heated at 60 ° C. for 6 hours to polymer D. Was synthesized. After washing with hexane and purification, it was analyzed by ¹ H-NMR. As a result, the ratio of 1,3-propane sultone and β-propiolactone in the polymer was 75:25 (mol ratio).

Thereafter, as in Reference Example 1, LiCoO ₂ was coated to produce an electrode, and then a laminated battery was produced. The capacity of the battery was 32 mAh. Moreover, the high temperature storage test was done and the amount of gas generation was measured. As a result, the amount of gas generated was 0.070 mL.

  Next, a square battery was fabricated using the coated positive electrode active material. The battery capacity was 820 mAh, and the rate characteristic was 96%. Further, the battery capacity after the heating test was 735 mAh, and the swelling of the battery was 1.30 mm.

Reference example 4

In Reference Example 1, evaluation was performed in the same manner as in Reference Example 1 except that LiMn ₂ O ₄ was used instead of LiCoO _{2 as} the positive electrode active material. The capacity of the battery was 23 mAh. Moreover, the high temperature storage test was done and the amount of gas generation was measured. As a result, the gas generation amount was 0.109 mL.

  Next, a square battery was fabricated using the coated positive electrode active material. The battery capacity was 650 mAh, and the rate characteristic was 95%. Moreover, the battery capacity after the heating test was 510 mAh, and the swelling of the battery was 1.40 mm.

Reference Example 5

In Reference Example 1, evaluation was performed in the same manner as Reference Example 1 except that LiNiO ₂ was used instead of LiCoO _{2 as} the positive electrode active material. The capacity of the battery was 37 mAh. Moreover, the high temperature storage test was done and the amount of gas generation was measured. As a result, the gas generation amount was 0.160 mL.

  Next, a square battery was fabricated using the coated positive electrode active material. The battery capacity was 950 mAh and the rate characteristic was 90%. Further, the battery capacity after the heating test was 790 mAh, and the swelling of the battery was 1.50 mm.

[Comparative Example 1]
In Example 1, it examined like Example 1 except not adding a polymer to a positive electrode active material. The capacity of the laminate type battery was 32 mAh. Moreover, the high temperature storage test was done and the amount of gas generation was measured. As a result, the gas generation amount was 0.102 mL.

  Next, a square battery was prototyped. The battery capacity was 820 mAh, and the rate characteristic was 90%. Moreover, the battery capacity after the heating test was 570 mAh, and the swelling of the battery was 1.40 mm.

[Comparative Example 2]
In Comparative Example 1, the positive electrode active material was examined in the same manner as in Comparative Example 1 except that LiMn ₂ O ₄ was used instead of LiCoO ₂ . The capacity of the laminate type battery was 25 mAh, and the gas generation amount was 0.200 mL.

  Next, a square battery was prototyped. The battery capacity was 650 mAh and the rate characteristic was 94%. In addition, the battery capacity after the heating test was 422 mAh, and the swelling of the battery was 1.66 mm.

[Comparative Example 3]
In Comparative Example 1, examination was performed in the same manner as in Comparative Example 1 except that LiNiO ₂ was used as the positive electrode active material instead of LiCoO ₂ . The capacity of the laminated battery was 37 mAh, and the amount of gas generated was 0.292 mL.

  Next, a square battery was prototyped. The battery capacity was 950 mAh, and the rate characteristic was 89%. Moreover, the battery capacity after the heating test was 660 mAh, and the swelling of the battery was 2.21 mm.

[Comparative Example 4]
In Example 1, an electrolyte solution in which 1 wt% of 1,3-propane sultone was added to the electrolyte solution was used, and an electrode to which no polymer was added was used as the positive electrode to produce a laminated battery. The capacity of the laminated battery was 32 mAh. Moreover, the high temperature storage test was done and the amount of gas generation was measured. As a result, the gas generation amount was 0.082 mL.

  Next, a square battery was prototyped. The battery capacity was 820 mAh, and the rate characteristic was 85%. Moreover, the battery capacity after the heating test was 680 mAh, and the swelling of the battery was 1.30 mm.

Claims (7)

The covering material for lithium secondary battery positive electrode active materials containing the copolymer shown by the following (Formula 2).
In (Formula 2), n is 1 or more and 10 or less.
p is 2 or more.
X is any of ether (—O—) , imine (—NH—) , lactone (—COO—) , lactam (—CONH—) , olefin (—CH═CH—) , and sulfide (—S—). is there.
x is the number of repeating units including a sulfonyl group.
y is the number of repeating units including X. The covering material for lithium secondary battery positive electrode active materials containing the copolymer shown by the following (Formula 3).
In (Formula 3), n is 1-10.
q is 2 or more.
x is the number of repeating units including a sulfonyl group.
y is the number of repeating units including X.   The lithium secondary battery positive electrode active material in which the coating material for lithium secondary battery positive electrode active materials of Claim 1 or 2 is formed in the surface. A lithium secondary battery comprising the lithium secondary battery positive electrode active material according to claim 3,
The lithium secondary battery in which the copolymer is 0.001 wt% or more and 10 wt% or less with respect to the positive electrode active material for the lithium secondary battery. In claim 4,
A lithium secondary battery having a square battery shape. It is a manufacturing method of the covering material for lithium secondary battery positive electrode active materials of Claim 1 or 2, Comprising:
The manufacturing method of the coating material for lithium secondary battery positive electrode active materials including the process in which the said copolymer is formed by ring-opening polymerization of cyclic sultone. It is a manufacturing method of the lithium secondary battery positive electrode active material of Claim 3,
The manufacturing method of the lithium secondary battery positive electrode active material including the following processes.
(1) A step of adding and stirring a polymer dissolved in a solvent to the positive electrode active material of the lithium secondary battery (2) A step of removing the solvent after the step (1)