Electrode composite material and non-aqueous lithium ion secondary battery

Abstract

To provide an electrode mixture capable of suppressing the decrease in charge / discharge capacity due to battery charge / discharge cycles, and a nonaqueous lithium ion secondary battery.SOLUTION: A disclosed electrode mixture is an electrode mixture that contains a first silicone-active material in which silicon-based particles are at least partially coated with a cationic polymer and a second silicone-active material in which the silicon-based particles are at least partially coated with an anionic polymer. The silicon-based particles may be Si particles.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to an electrode composite material and a non-aqueous lithium-ion secondary battery.

Background Art

[0002] Patent Document 1 discloses a composite comprising a silicon material, a carbon layer covering the silicon material, and a cationic polymer layer having a cationic polymer covering the carbon layer.

[0003] Patent Document 2 discloses a negative electrode material for a lithium storage battery, which includes a core containing silicon, and the surface of the core has an O y SiH x group (where 1 < x < 3, 1 ≦ y ≦ 3, and x > y), and the material has a positive zeta potential within the range of pH 3.5 to 9.5.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] It is required to suppress a decrease in charge-discharge capacity associated with cycles of a battery, for example, a lithium-ion battery.

[0006] An object of the present disclosure is to provide an electrode composite material and a non-aqueous lithium-ion secondary battery that can suppress a decrease in charge-discharge capacity associated with charge-discharge cycles of a battery.

Means for Solving the Problems

[0007] The present inventor has found that the above problems can be achieved by the following means: <<Aspect 1>> A first silicon-based active material in which silicon-based particles are at least partially coated with a cationic polymer, and A second silicon-based active material in which silicon-based particles are at least partially coated with an anionic polymer An electrode binder containing the same. <<Aspect 2>> The electrode binder according to Aspect 1, wherein the silicon-based particles are Si particles. <<Aspect 3>> The electrode binder according to Aspect 1 or 2, wherein the content ratio of the first silicon-based active material to the second silicon-based active material is 25:75 to 75:25. <<Aspect 4>> The electrode binder according to any one of Aspects 1 to 3, wherein the cationic polymer is at least one selected from the group consisting of poly(diallyldimethylammonium chloride), polyethyleneimine, polypyrrole, and polyaniline. <<Aspect 5>> The electrode binder according to any one of Aspects 1 to 4, wherein the anionic polymer is at least one selected from the group consisting of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, polyacrylic acid, and polystyrene sulfonic acid. <<Aspect 6>> The electrode binder according to any one of Aspects 1 to 5, wherein the first silicon-based active material has a zeta potential in water of +30.0 mV or more. <<Aspect 7>> The electrode binder according to any one of Aspects 1 to 6, wherein the second silicon-based active material has a zeta potential in water of -15.0 mV or less. <<Aspect 8>> A negative electrode body containing the electrode binder according to any one of Aspects 1 to 7. <<Aspect 9>> A non-aqueous lithium ion secondary battery in which a positive electrode body, a separator, and the negative electrode body according to Aspect 8 are sequentially housed in a battery case filled with an electrolytic solution.

Effect of the Invention

[0008] According to the present disclosure, it is possible to provide an electrode composite material and a non-aqueous lithium-ion secondary battery that can suppress a decrease in charge-discharge capacity associated with charge-discharge cycles of a battery.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments and can be implemented with various modifications within the scope of the gist of the disclosure.

[0011] 《Electrode Composite Material》 The electrode composite material of the present disclosure contains a first silicon-based active material in which silicon-based particles are at least partially coated with a cationic polymer, and a second silicon-based active material in which silicon-based particles are at least partially coated with an anionic polymer.

[0012] In a non-aqueous lithium-ion secondary battery, from the viewpoint of suppressing the formation of SEI with an electrolytic solution, it is conceivable to use a silicon-based active material in which the surface of a silicon-based negative electrode active material is coated with a cationic polymer.

[0013] However, such silicon-based active materials do not attract each other because they have the same sign of zeta potential. Therefore, mechanical degradation of the electrode body caused by the expansion and contraction of the silicon-based active material accompanying charge and discharge of the non-aqueous lithium ion secondary battery cannot be suppressed. As a result, a decrease in charge and discharge capacity accompanying the progress of charge and discharge cycles is inevitable.

[0014] In contrast, the electrode composite material of the present disclosure contains a first silicon-based active material in which silicon-based particles are at least partially coated with a cationic polymer, and a second silicon-based active material in which silicon-based particles are at least partially coated with an anionic polymer.

[0015] In the electrolytic solution, the first silicon-based active material has a positive zeta potential, while the second silicon-based active material has a negative zeta potential. Therefore, when the electrode composite material of the present disclosure is applied to the electrode body of a non-aqueous lithium ion secondary battery, the first silicon-based active material and the second silicon-based active material attract each other in the electrolytic solution, thereby suppressing mechanical degradation of the electrode body caused by the expansion and contraction of the silicon-based active material accompanying charge and discharge of the non-aqueous lithium ion secondary battery. Thereby, a decrease in charge and discharge capacity accompanying the progress of charge and discharge cycles is suppressed.

[0016] In the electrode composite material of the present disclosure, the content ratio (A:B) of the first silicon-based active material A and the second silicon-based active material B may be 25:75 to 75:25. Here, the content ratio is the ratio of the content (mass) of the first silicon-based active material to the content (mass) of the second silicon-based active material.

[0017] A:B may be 25:75, 30:70, 50:50, 70:30, or 75:25.

[0018] 〈First silicon-based active material〉 The first silicon-based active material is a first silicon-based active material in which silicon-based particles are at least partially coated with a cationic polymer.

[0019] The silicon-based particles may be, for example, Si alloy particles or Si particles. The Si alloy particles may be an alloy of Si and one or more metals selected from the group consisting of, for example, Sn, Ti, Fe, Ni, Cu, Co, and Al.

[0020] The cationic polymer may be any cationic polymer that has low reactivity with the electrolyte under the use conditions of the non-aqueous lithium-ion secondary battery and has a positive zeta potential in the electrolyte.

[0021] The cationic polymer can be at least one selected from the group including, for example, poly(diallyldimethyl chloride), polyethyleneimine, polypyrrole, and polyaniline.

[0022] The first silicon-based active material preferably has a zeta potential of +30.0 mV or more in water. Note that "in water" means pure water.

[0023] The zeta potential of the first silicon-based active material in water may be +30.0 mV or more and +60.0 mV or less. The zeta potential may be +30.0 mV or more, +33.0 mV or more, +36.0 mV or more, or +39.0 mV or more, and may be +60.0 mV or less, +50.0 mV or less, +45.0 mV or less, or +40.0 mV or less.

[0024] The "zeta potential" is also called the electrokinetic potential and means the part of the potential difference at the interface between a solid and a liquid that effectively acts on the electrokinetic phenomenon. Regarding the present invention, this zeta potential is the zeta potential measured by the laser Doppler method, which is an electrophoretic light scattering method.

[0025] 〈Second silicon-based active material〉 The second silicon-based active material is a second silicon-based active material in which the silicon-based particles are at least partially coated with an anionic polymer.

[0026] The silicon-based particles can include, for example, those described for the first silicon-based active material.

[0027] The anionic polymer may be any anionic polymer that has low reactivity with the electrolyte under the use conditions of the non-aqueous lithium ion secondary battery and has a negative zeta potential in the electrolyte.

[0028] The anionic polymer can be at least one selected from the group including poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, polyacrylic acid, and polystyrene sulfonic acid.

[0029] The second silicon-based active material preferably has a zeta potential in water of -15.0 mV or less. Here, water means pure water.

[0030] The zeta potential of the second silicon-based active material in water may be -15.0 mV or less and -30.0 mV or more. The zeta potential in water may be -15.0 mV or less, -16.0 mV or less, -17.0 mV or less, or -18.0 mV or less, and may be -30.0 mV or more, -28.0 mV or more, -25.0 mV or more, or -20.0 mV or more.

[0031] 《Negative electrode body》 The negative electrode body has a negative electrode current collector and a negative electrode active material. The negative electrode body may have a shape in which the surface of the negative electrode body, such as a layered or rod shape, is partially or entirely covered with the negative electrode active material layer. The negative electrode active material layer contains the electrode composite material of the present disclosure.

[0032] The negative electrode active material layer can contain the electrode composite material of the present disclosure, and optionally a binder, a conductive assistant, and the like.

[0033] The negative electrode active material layer may be formed, for example, by adhering and drying a slurry in which the electrode composite material of the present disclosure, an optional binder, a conductive assistant, etc. are dispersed on a base material. The base material can be composed of a material having conductivity such as metal, etc., and can also serve as the negative electrode current collector.

[0034] 〈Negative electrode current collector〉 The material used for the negative electrode current collector may be stainless steel (SUS), aluminum, copper, nickel, iron, titanium, gold, platinum, zinc, carbon, or the like. Further, as the negative electrode current collector, one in which nickel, chromium, carbon, or the like is plated or vapor-deposited on the surface of these materials may be employed. It is preferable to use copper, a copper alloy, or one in which nickel, chromium, carbon, or the like is plated or vapor-deposited on the surface of these.

[0035] The shape of the negative electrode current collector is not particularly limited, and may be, for example, rod-shaped or layered.

[0036] 〈Binder〉 Examples of the binder may include, but are not limited to, materials such as polyacrylic acid-based binders, polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), butadiene rubber (BR), styrene-butadiene rubber (SBR), or combinations thereof.

[0037] 〈Conductive assistant〉 As the conductive assistant, known ones can be used, and examples include carbon materials and metal particles. Examples of the carbon materials may include at least one selected from the group consisting of carbon blacks such as ketjen black, acetylene black, and furnace black, vapor-grown carbon fibers (VGCF), carbon nanotubes, and carbon nanofibers. Among them, from the viewpoint of electron conductivity, it may be at least one selected from the group consisting of VGCF, carbon nanotubes, and carbon nanofibers. Examples of the metal particles include particles of nickel, copper, iron, stainless steel, and the like.

[0038] "Non-aqueous Lithium Ion Secondary Battery" The non-aqueous lithium ion secondary battery of the present disclosure is a non-aqueous lithium ion secondary battery in which a positive electrode body, a separator, and the negative electrode body of the present disclosure are housed in this order in a battery case filled with an electrolytic solution.

[0039] FIG. 1 is a schematic diagram of a non-aqueous lithium ion secondary battery 1 according to the first embodiment of the present disclosure. Note that FIG. 1 is not intended to limit the non-aqueous lithium ion secondary battery of the present disclosure.

[0040] As shown in FIG. 1, the non-aqueous lithium ion secondary battery 1 according to the first embodiment of the present disclosure has a positive electrode body layer 10 having a positive electrode current collector layer 11 and a positive electrode active material layer 12 disposed on the positive electrode current collector layer 11, a separator layer 20, and a negative electrode body layer 30 having a negative electrode current collector layer 31 and a negative electrode active material layer 32 disposed on the negative electrode current collector layer 31, and can have a structure housed in an exterior body 100 filled with an electrolytic solution 40. Here, the negative electrode body layer 30 is the negative electrode body of the present disclosure. Note that FIG. 1 is not intended to limit the present disclosure.

[0041] 〈Positive Electrode Body〉 The positive electrode body has a positive electrode current collector and a positive electrode active material. The positive electrode body may have a shape in which the surface of the positive electrode body, such as a layer or rod shape, is partially or entirely covered with a layer containing the positive electrode active material, that is, the positive electrode active material layer.

[0042] The material used for the positive electrode current collector may be the material described for the negative electrode current collector. Among them, the material of the positive electrode current collector is preferably aluminum.

[0043] The shape of the positive electrode current collector layer may also be the shape described for the negative electrode current collector.

[0044] The positive electrode active material layer may contain any positive electrode active material that can be employed in a lithium ion battery.

[0045] Such a positive electrode active material may be, for example, lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), lithium manganate (LiMn2O4), LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, Li 1+x Mn 2-x-y M y O4 (M is one or more metal elements selected from Al, Mg, Co, Fe, Ni, and Zn), such as a hetero-element substituted Li-Mn spinel having a composition represented by these, but is not limited thereto.

[0046] Further, such a positive electrode active material may be, for example, a sulfur-based active material. Here, the sulfur-based active material is an active material containing at least the S element. The sulfur-based active material may or may not contain the Li element. Examples of the sulfur-based active material include elemental sulfur, lithium sulfide (Li2S), and polysulfide lithium (Li2S x , 2 ≦ x ≦ 8).

[0047] 〈Separator〉 The separator may be a layer of a porous resin, for example, a layer of polypropylene or polyethylene.

[0048] As the separator, porous polymer membranes such as a porous polyethylene membrane (PE), a porous polypropylene membrane (PP), a porous polyolefin membrane, and a porous polyvinyl chloride membrane can be used. Further, as the separator, a lithium ion conductive polymer electrolyte membrane can also be used. These separators can be used alone or in combination. From the viewpoint of increasing the battery output, it is preferable to use a three-layer coated separator in which a porous polyethylene membrane (PE) is sandwiched between two upper and lower porous polypropylene membranes (PP).

[0049] 〈Negative Electrode Body〉 The negative electrode body is the negative electrode body of the present disclosure.

[0050] 〈Electrolyte〉 The electrolyte may be a composition in which a supporting salt is contained in a non-aqueous solvent. Examples of the non-aqueous solvent include materials selected from the group consisting of organic electrolytes, fluorine-based solvents, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and combinations of two or more thereof.

[0051] As the non-aqueous solvent, a fluorine-based solvent, such as a fluorinated carbonate ester, is preferable. Specific examples of the fluorinated carbonate ester include methyl-2,2,2-trifluoroethyl carbonate (MFEC; Carbonic acid, methyl 2,2,2-trifluoroethyl ester; CAS 156783-95-8), and / or difluorodimethyl carbonate (DFDMC), and a mixture thereof in a volume ratio of 50 to 50 is particularly preferable.

[0052] Examples of the supporting salt include materials selected from the group consisting of lithium compounds (lithium salts) such as LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, and LiI, and combinations of two or more thereof. From the viewpoints of improving battery voltage and durability, LiPF6 is preferable as the supporting salt.

[0053] 〈Battery case〉 The battery case can be composed of a material inert to the non-aqueous electrolyte, such as a resin.

Examples

[0054] 《Examples 1 to 3, Comparative Example 1, and Reference Example 1》 〈Example 1〉 (Adjustment of silicon-based active material A) 1 g of Si particles were dispersed in a 1 L solution containing 0.5 wt% of poly(diallyldimethylammonium chloride) (manufactured by Sigma-Aldrich), a cationic polymer, using a homogenizer and stirred for 1 hour. The stirred solution was filtered and washed three times with 100 mL of water to remove the excess polymer. The resulting powder was further dried in vacuo at 60 °C for 24 hours to obtain silicon-based active material A.

[0055] Note that the zeta potential of silicon-based active material A in water was +39.5 mV.

[0056] (Preparation of silicon-based active material B) 1 g of Si particles were dispersed in a 1 L solution containing 0.05 wt% of PEDOT:PSS (manufactured by Sigma-Aldrich), an anionic polymer, using a homogenizer and stirred for 1 hour. The stirred solution was filtered and washed three times with 100 mL of water to remove the excess polymer. The resulting powder was further dried in vacuo at 60 °C for 24 hours to obtain silicon-based active material B.

[0057] Note that the zeta potential of silicon-based active material B in water was -19.5 mV.

[0058] (Preparation of the positive electrode body) NMP, a 5 wt% butyl butyrate solution of a PVdF-based binder, LiNi with an average particle size of 6 m as a positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3 O2, and VGCF as a conductive assistant were added to a container and stirred with a mixer (ARE-310 manufactured by Shinki Co., Ltd.) for 10 minutes. Using an applicator, it was coated on an Al foil (manufactured by Showa Denko K.K.) by the blade method and dried on a hot plate at 80 °C for 60 minutes.

[0059] (Preparation of the negative electrode body) To a screw tube bottle, water, a polyacrylic acid-based binder, silicon-based active materials A and B as the negative electrode active material, VGCF and KB as the conductive aids were added to the container, and they were stirred for 10 minutes with an Awatori Rengroutaro (ARE-310 manufactured by Shinki Co., Ltd.). Using an applicator, it was coated on a Cu foil (manufactured by Furukawa Electric Co., Ltd.) by the blade method and dried on a hot plate at 80 °C for 60 minutes.

[0060] Note that the ratio A:B of the silicon-based active materials A and B was 75:25.

[0061] (Adjustment of non-aqueous lithium-ion secondary battery) After punching out the positive electrode body and the negative electrode body to diameters of 14 mm and 16 mm respectively, they were set in a roll press machine and pressed at 20 kN / cm. Then, the positive electrode body was vacuum dried at 120 °C and the negative electrode body was vacuum dried at 60 °C for 24 hours.

[0062] The positive electrode body and the negative electrode body were transferred to a glove box. 1 ml of an electrolytic solution (1.2 M LiPF6 solution. The solvent was FEC:EC:EMC:DMC (1:2:4:3 vol%)) was dropped onto the negative electrode body, a separator (made of polypropylene) was laminated, and after dropping 1 ml of the electrolytic solution again, the positive electrode body was laminated, and a coin cell-shaped non-aqueous lithium-ion secondary battery was fabricated using an automatic coin cell caulking machine (manufactured by Hozen Co., Ltd.).

[0063] 〈Example 2〉 A non-aqueous lithium-ion secondary battery of Example 2 was fabricated in the same manner as in Example 1, except that the ratio A:B of the silicon-based active materials A and B was set to 50:50.

[0064] 〈Example 3〉 A non-aqueous lithium-ion secondary battery of Example 3 was fabricated in the same manner as in Example 1, except that the ratio A:B of the silicon-based active materials A and B was set to 25:75.

[0065] 〈Comparative Example 1〉 A non-aqueous lithium-ion secondary battery of Comparative Example 1 was fabricated in the same manner as in Example 1, except that silicon-based active material B was not used, i.e., the ratio A:B of silicon-based active materials A and B was 100:0.

[0066] <Reference Example 1> A non-aqueous lithium-ion secondary battery of Reference Example 1 was fabricated in the same manner as in Example 1, except that silicon-based active material A was not used, i.e., the ratio A:B of silicon-based active materials A and B was 0:100.

[0067] <Charge and Discharge Cycle Test> For each non-aqueous lithium-ion secondary battery of each example, after constant-current charging to 4.2 V at a 0.1C rate, when discharging to 2.5 V at a 0.1C rate, the battery capacity at that time was taken as the initial capacity, and a charge and discharge test of constant-current charging to 4.2 V at a 1C rate and then constant-current discharging at 1C was repeated 50 times, and the discharge capacity retention rate after 50 cycles with respect to the initial capacity was calculated.

[0068] <Results> The results are shown in Table 1 and FIG. 2.

[0069] [Table 1]

[0070] As shown in Table 1 and FIG. 2, in the non-aqueous lithium-ion secondary batteries of Examples 1 to 3 using silicon-based active materials A and B, the discharge capacity retention rates after 50 cycles were 79.1%, 82.5%, and 83.0% in order, respectively. On the other hand, in the non-aqueous lithium-ion secondary battery of Comparative Example 1 that did not use silicon-based active material B, the discharge capacity retention rate after 50 cycles was 77.6%. That is, the non-aqueous lithium-ion secondary batteries of Examples 1 to 3 using silicon-based active materials A and B had a higher discharge capacity retention rate after 50 cycles than the non-aqueous lithium-ion secondary battery of Comparative Example 1 that did not use silicon-based active material B.

[0071] In Reference Example 1 where silicon-based active material A was not used, the discharge capacity retention rate after 50 cycles was 81.8%.

Explanation of Symbols

[0072] 1 Non-aqueous lithium-ion secondary battery 10 Positive electrode body layer 11 Positive electrode current collector layer 12 Positive electrode active material layer 20 Separator layer 30 Negative electrode body layer 31 Negative electrode current collector layer 32 Negative electrode active material layer 40 Electrolyte

Claims

1. A first silicon-based active material in which silicon-based particles are at least partially coated with a cationic polymer, and A second silicon-based active material in which silicon-based particles are at least partially coated with an anionic polymer are contained, wherein the first silicon-based active material and the second silicon-based active material are different silicon-based active materials from each other, an electrode composite material.

2. The electrode composite material according to claim 1, wherein the silicon-based particles are Si particles.

3. The electrode composite material according to claim 1 or 2, wherein the content ratio of the first silicon-based active material and the second silicon-based active material is 25:75 to 75:

25.

4. The electrode composite material according to any one of claims 1 to 3, wherein the cationic polymer is at least one selected from the group consisting of poly(diallyldimethyl chloride), polyethyleneimine, polypyrrole, and polyaniline.

5. The electrode composite material according to any one of claims 1 to 4, wherein the anionic polymer is at least one selected from the group consisting of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, polyacrylic acid, and polystyrene sulfonic acid.

6. The electrode composite material according to any one of claims 1 to 5, wherein the first silicon-based active material has a zeta potential in water of +30.0 mV or more.

7. The electrode composite material according to any one of claims 1 to 6, wherein the second silicon-based active material has a zeta potential in water of -15.0 mV or less.

8. A negative electrode body containing the electrode composite material according to any one of claims 1 to 7.

9. A non-aqueous lithium ion secondary battery in which a positive electrode body, a separator, and the negative electrode body according to claim 8 are housed in this order in a battery case filled with an electrolytic solution.

10. The electrode composite material according to any one of claims 1 to 7, wherein the first silicon-based active material has a positive zeta potential in pure water, and the second silicon-based active material has a negative zeta potential in pure water.

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