BINDER FOR LITHIUM ION BATTERIES, AND ELECTRODE AND SEPARATOR USING SAME

Abstract

Provided is a nonaqueous binder for electrodes or separators, which is used in a lithium ion battery that has excellent cycle life characteristics at high temperatures. A nonaqueous binder for electrodes or separators of lithium ion batteries, which is obtained by complexing cellulose nanofibers and a thermoplastic fluororesin, and which is characterized in that the cellulose nanofibers have a fiber size (diameter) of from 0.002 m to 1 m (inclusive), a fiber length of from 0.5 m to 10 mm (inclusive), and an aspect ratio ((fiber length of cellulose nanofibers)/(fiber diameter of cellulose nanofibers)) of from 2 to 100,000 (inclusive).

Claims

1. A composite nonaqueous binder of a cellulose nanofiber and a thermoplastic fluororesin for an electrode or a separator of a lithium ion battery, wherein the cellulose nanofiber is a cellulose having a fiber diameter (diameter) of 0.002 m or more and 1 m or less, a fiber length of 0.5 m or more and 10 mm or less, and an aspect ratio (fiber length of the cellulose nanofiber/fiber diameter of the cellulose nanofiber) of 2 or more and 100,000 or less.

2. The binder according to claim 1, wherein, when the total amount of solid contents of the cellulose nanofiber and the thermoplastic fluororesin is taken as 100 mass %, the cellulose nanofiber is contained in an amount of 5 mass % or more and 80 mass % or less, and the thermoplastic fluororesin is contained in an amount of 20 mass % or more and 95 mass % or less.

3. The binder according to claim 1, wherein the cellulose nanofiber comprises a cellulose nanofiber subjected to polybasic acid semi-esterification treatment to replace some of hydroxyl groups with carboxyl groups.

4. The binder according to claim 1, wherein the cellulose nanofiber comprises a cellulose nanofiber subjected to ethylene oxide addition treatment or propylene oxide addition treatment.

5. The binder according to claim 1, wherein the thermoplastic fluororesin comprises a polyvinylidene fluoride or a vinylidene fluoride copolymer.

6. The binder according to claim 1, wherein the thermoplastic fluororesin is dissolved in N-methyl-2-pyrrolidone, and the cellulose nanofibers are dispersed in N-methyl-2-pyrrolidone, wherein when a total mass of the cellulose nanofibers, the thermoplastic fluororesin, and the N-methyl-2-pyrrolidone in the binder is taken as 100 mass %, a total amount of solid contents of the cellulose nanofibers and the thermoplastic fluororesin is 3 mass % or more and 30 mass % or less.

7. An electrode comprising the binder according to claim 1.

8. The electrode according to claim 7, comprising a polymer gel comprising a lithium hexafluorophosphate, a cyclic carbonate, and a chain carbonate, wherein the polymer gel is a composite cellulose nanofiber.

9. The electrode according to claim 7 comprising a Li-containing active substance.

10. A separator comprising the binder according to claim 1.

11. The separator according to claim 10, comprising a polymer gel comprising a lithium hexafluorophosphate, a cyclic carbonate, and a chain carbonate, wherein the polymer gel is a composite cellulose nanofiber.

12. A lithium ion battery comprising the electrode according claim 7, wherein the electrode is integrated with a separator in the battery, and wherein the electrode is bonded and integrated with the separator through the binder contained in the electrode.

13. A lithium ion battery comprising the separator according to claim 10, wherein the separator is integrated with an electrode in the battery, and wherein the separator is bonded and integrated with the electrode through the binder contained in the separator.

14. An electrical device comprising at least one of the battery according to claim 12 and/or the battery according to claim 13.

15. A method of producing a liquid comprising cellulose nanofibers dispersed in N-methyl-2-pyrrolidone, the method comprising: a step (B) in which when a total amount of cellulose nanofibers, a liquid medium having hydroxyl groups, and N-methyl-2-pyrrolidone is taken as 100 mass %, the cellulose nanofibers-dispersed liquid medium is mixed with N-methyl-2-pyrrolidone so as to make the amount of solid content of the cellulose nanofibers to be 0.1 mass % or more and 20 mass % or less, thereby obtaining a liquid comprising the cellulose nanofibers, the liquid medium, and the N-methyl-2-pyrrolidone; and a step (C) of increasing a concentration of N-methyl-2-pyrrolidone by evaporating the liquid medium while stirring the liquid comprising the cellulose nanofibers, the liquid medium, and the N-methyl-2-pyrrolidone.

16. The method of producing the liquid comprising the cellulose nanofibers dispersed in N-methyl-2-pyrrolidone according to claim 15, wherein the step (C) comprises a step of increasing the concentration of N-methyl-2-pyrrolidone by evaporating the liquid medium through heating at 25 C. or higher and 150 C. or lower under a pressure of 10 hPa or more and 900 hPa or less.

17. The method of producing the liquid comprising the cellulose nanofibers dispersed in N-methyl-2-pyrrolidone according to claim 15, further comprising, before the step (B), a step (A) of preparing polybasic acid semi-esterified cellulose by mixing cellulose with a polybasic acid anhydride at a temperature of 80 C. or higher and 150 C. or lower by a pressure kneader or an extrusion kneader having one or more screws, and semi-esterifying some of hydroxyl groups of the cellulose with the polybasic acid anhydride to introduce carboxyl groups.

18. The method of producing the liquid comprising the cellulose nanofibers dispersed in a N-methyl-2-pyrrolidone according to claim 15 one of claims 15 to 17, further comprising, after the step (C), a step (D) of irradiating the liquid comprising the cellulose nanofibers dispersed in N-methyl-2-pyrrolidone with an ultrasonic wave having a frequency of 10 kHz or more and 200 kHz or less and an amplitude of 1 m or more and 200 m or less.

19. A method of producing a binder for a lithium ion battery, the binder being a liquid in which a thermoplastic fluororesin is dissolved in N-methyl-2-pyrrolidone and cellulose nanofibers are dispersed, the method comprising a step (E) of mixing the cellulose nanofibers with the thermoplastic fluororesin so that the amount of the cellulose nanofibers is 5 mass % or more and 80 mass % or less and the amount of the thermoplastic fluororesin is 20 mass % or more and 95 mass % or less when the total amount of solid contents of the cellulose nanofibers and the thermoplastic fluororesin is taken as 100 mass %, and dissolving the thermoplastic fluororesin in N-methyl-2-pyrrolidone.

20. A method of producing a lithium ion battery comprising the electrode according to claim 7 for at least one of a positive electrode and a negative electrode, the method comprising a step (F) of sealing a stacked or wound electrode group with a separator interposed between the positive electrode and the negative electrode in a battery case together with an electrolytic solution containing lithium hexafluorophosphate and aprotic carbonates, thereafter heating the battery case to raise the temperature thereof to 50 C. or higher and 120 C. or lower, applying a pressure from outside of the battery case perpendicularly to an extension direction of the electrode, thereby integrating the separator with the electrode comprising a composite binder of a cellulose nanofiber and a thermoplastic fluororesin.

21. A method of producing a lithium ion battery comprising the separator according to claim 10, the method comprising a step (F) of sealing a stacked or wound electrode group with a separator interposed between a positive electrode and a negative electrode in a battery case together with an electrolytic solution containing lithium hexafluorophosphate and aprotic carbonates, thereafter heating the battery case to raise the temperature thereof to 50 C. or higher and 120 C. or lower, applying a pressure from outside of the battery case perpendicularly to an extension direction of the electrode, thereby integrating the separator with the electrode comprising a composite binder of a cellulose nanofiber and a thermoplastic fluororesin.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0147] FIG. 1 is a graph showing a comparison between batteries (Example 1, Example 2, Reference Example 1) that include an electrode containing a binder material A as an electrode binder in Examples, and a battery (Comparative Example 1) which that includes an electrode containing only a binder material G as an electrode binder.

[0148] FIG. 2 is a graph showing a comparison between batteries (Examples 3 to 5, and Reference Example 2) that include an electrode containing a binder material B as an electrode binder in Examples, and a battery (Comparative Example 1), which includes an electrode containing only a binder material G as an electrode binder.

[0149] FIG. 3 is a graph showing a comparison between batteries (Examples 6 to 8, and Reference Example 3) that include an electrode containing a binder material C as an electrode binder in Examples, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0150] FIG. 4 is a graph showing a comparison between batteries (Examples 9 to 11) that include an electrode containing a binder material D as an electrode binder in Examples, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0151] FIG. 5 is a graph showing a comparison between batteries (Examples 12 to 14) that include an electrode containing a binder material E as an electrode binder in Examples, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0152] FIG. 6 is a graph showing a comparison between batteries (Reference Examples 4 to 6) that include an electrode containing a binder material F as an electrode binder in Examples, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0153] FIG. 7 is a graph showing a comparison between batteries (Example 1, Example 2, Reference Example 1) that include an electrode containing a binder material A as an electrode binder in Examples, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0154] FIG. 8 is a graph showing a comparison between batteries (Examples 3 to 5, and Reference Example 2) that include an electrode containing a binder material B as an electrode binder in Examples, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0155] FIG. 9 is a graph showing a comparison between batteries (Examples 6 to 8, and Reference Example 3) that include an electrode containing a binder material C as an electrode binder in Examples, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0156] FIG. 10 is a graph showing a comparison between batteries (Examples 9 to 11) that include an electrode containing a binder material Das an electrode binder in Examples, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0157] FIG. 11 is a graph showing a comparison between batteries (Example 14) that includes an electrode containing a binder material E as an electrode binder in Examples, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0158] FIG. 12 is a graph showing a comparison between batteries (Reference Examples 4 to 6) that include an electrode containing a binder material F as an electrode binder in Examples, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0159] FIG. 13 is a graph showing a comparison between batteries (Example 15, Example 16, and Reference Example 7) that include an electrode containing a binder material A as an electrode binder in Examples, and a battery (Comparative Example 2) that includes an electrode containing only a binder material G as an electrode binder.

[0160] FIG. 14 is a graph showing a comparison between batteries (Example 15, Example 16, and Reference Example 7) that include an electrode containing a binder material A as an electrode binder in Examples, and a battery (Comparative Example 2) that includes an electrode containing only a binder material G as an electrode binder.

[0161] FIG. 15 shows the results of checking gelation resistance (gelation resistance tests 1 and 2) of the binders in Examples.

[0162] FIG. 16 is a graph showing a comparison between batteries (Examples 17 to 20) including test separators 1 to 4 and a battery (Comparative Example 3) including an uncoated separator.

DESCRIPTION OF EMBODIMENTS

[0163] Hereinafter, the present invention will be specifically described based on Examples, but the following Examples do not limit the present invention.

[1. Production of Materials of Composite Binder]

[0164] Table 1 shows materials (binder materials A to G) for producing the composite binder. The binder material A. is a liquid in which untreated cellulose nanofibers are dispersed in NMP. The method of producing the binder material A includes: adding an equal to or higher volume of NMP to a liquid in which the untreated cellulose nanofibers were dispersed in water (solid content ratio: 5 mass %); evaporating water while stiffing by a rotary evaporator (200 hPa, 70 C. to 90 C., 160 rpm); and then irradiating ultrasonic waves (frequency 38 kHz, 1 minute) to the obtained liquid to produce the binder material A. Since the binder material A easily aggregated or precipitated when the solid content ratio was more than 7 mass %, the solid content ratio was set to 4.4 mass %. The liquid in which untreated cellulose nanofibers are dispersed in water was prepared by adding a commercially available crystalline cellulose powder (manufactured by Asahi Kasei Chemicals Co., Ltd, registered trademark: CEOLUS FD-101, average particle size: 50 m, and bulk density: 0.3 g/cc) to make the amount of the cellulose to be 4 mass % based on the total amount of an aqueous dispersion liquid, and placing the mixture in a stone-mill type defibration treatment device to pass 10 times between stone mills.

[0165] The binder material B is a liquid in which cellulose nanofibers subjected to semi-esterification treatment are dispersed in NMP. The method of producing the binder material B is the same as that of the binder material A except that a liquid (solid content ratio: 5 mass %) in which the cellulose nanofibers subjected to the semi-esterification treatment are dispersed in water is used. Since the binder material B easily aggregated or precipitated when the solid content ratio was more than 10 mass %, the solid content ratio was set to 4.1 mass %. The liquid in which the cellulose nanofibers subjected to the semi-esterification treatment were dispersed in water was prepared by blending a commercially available untreated crystalline cellulose powder (manufactured by Asahi Kasei Chemicals Co., Ltd, registered trademark: CEOLUS FD-101, average particle size: 50 m, and bulk density: 0.3 g/cc) and succinic anhydride in a ratio of 86.5 to 13.5, performing a reaction treatment in a container heated at 130 C., followed by adding the obtained product to to make the amount of the cellulose to be 4 wt % based on a total amount of an aqueous dispersion liquid, and placing the mixture in stone-mill type defibration treatment device to pass 10 times between stone mills.

[0166] The binder material C is a liquid in which cellulose nanofibers that are obtained by performing the semi-esterification treatment on the cellulose and then performing secondary propylene oxide addition are dispersed in NMP. The method of producing the binder material C is the same as that of the binder material B except that a liquid (solid content ratio: 5 mass %) in which the cellulose nanofibers that are obtained by performing the semi-esterification treatment on the cellulose and then performing secondary propylene oxide addition are dispersed in water is used. Since the binder material C easily aggregated or precipitated when the solid content ratio was more than 10 mass %, the solid content ratio was set to 3.3 mass %. The liquid in which the cellulose nanofibers subjected to addition treatment of propylene oxide were dispersed in water was prepared by blending a commercially available untreated crystalline cellulose powder (manufactured by Asahi Kasei Chemicals Co., Ltd, registered trademark: CEOLUS FD-101, average particle size: 50 and bulk density: 0.3 g/cc) and succinic anhydride in a ratio of 86.5 to 13.5, performing a reaction treatment in a container heated at 130 C., followed by further adding propylene oxide to reach 4.5 wt % based on the weight of cellulose and performing reaction treatment at 140 C., further, adding the obtained product to to make the amount of cellulose to be 4 wt % based on a total amount of an aqueous dispersion liquid, and placing the mixture in a stone-mill type defibration treatment device to pass 10 times between stone mills.

[0167] The binder material D is a liquid in which cellulose nanofibers containing lignin obtained from hardwoods are dispersed in NMP. The method of producing the binder material D is the same as that of the binder material A except that a liquid in which the cellulose nanofibers containing lignin obtained from hardwoods are dispersed in water is used. Since the binder material D easily aggregated or precipitated when the solid content ratio was more than 2 mass %, the solid content ratio was set to 1.5 mass %. The liquid in which the cellulose nanofibers containing lignin obtained from hardwoods are dispersed in water was prepared by adding cellulose to reach 4 wt % based on a total amount of an aqueous dispersion liquid, placing the mixture in a stone-mill type defibration treatment device to pass 10 times between stone mills.

[0168] The binder material E is a liquid in which cellulose nanofibers containing lignin obtained from conifers are dispersed in NMP. The method of producing the binder material F is the same as that of the binder material A except that the cellulose nanofibers generated from conifers are used. Since the binder material E easily aggregated or precipitated when the solid content ratio was more than 2 mass %, the solid content ratio was set to 1.3 mass %. The liquid in which the cellulose nanofibers containing lignin obtained from conifers are dispersed in water was prepared by adding cellulose to reach 4 wt % based on a total amount of an aqueous dispersion liquid, placing the mixture in a stone-mill type defibration treatment device to pass 10 times between stone mills.

[0169] [0077]

[0170] A binder material F is a liquid in which nanoclay (smecton SAN manufactured by Kunimine Industries Co., Ltd. 4% dispersion liquid viscosity: 4000 mPas) is dispersed in NMP. Since foaming of the binder material F was severe when the solid content ratio was more than 4 mass %, the solid content ratio was set to 1.9 mass %. The method of producing the binder material F includes: adding an equal to or higher volume of NMP to a liquid in which the nanoclay is dispersed in water (solid content ratio: 4 mass %); evaporating water while stirring by a rotary evaporator (200 hPa, 70 C. to 90 C., 160 rpm); and then irradiating ultrasonic waves (frequency 38 kHz, 1 minute) to the obtained liquid to produce the binder material F. A binder material G was a liquid in which PVdF was dissolved in NMP, and was prepared by mixing NMP with PVdF (weight average molecular weight: 280,000) by a self-orbital mixer (manufactured by Thinky Corporation, 2000 rpm, and 30 minutes). The binder material G had a solid content ratio of 12 mass %.

TABLE-US-00001 TABLE 1 Binder Materials Kind of binder material Binder material A Cellulose nanofibers (untreated) Binder material B Cellulose nanofibers (SA treated) Binder material C Cellulose nanofibers (PO addition after SA treatment) Binder material D Cellulose nanofibers (hardwood) Binder material E Cellulose nanofibers (conifer) Binder material F Nanoclav Binder material G PVdF

TABLE-US-00002 TABLE 2 Aspect ratio Fiber Fiber (fiber Binder Dispersion diameter length length/fiber Materials material (nm) (m) diameter) Lignin Binder Untreated 50 to 1 to 5 to None material A 200 1000 100000 Binder SA treatment 50 to 1 to 5 to None material B 200 1000 100000 Binder PO addition 50 to 1 to 5 to None material C treatment after 200 1000 100000 SA treatment Binder Hardwood 700 to 1 to 0.8 to Present material D 1200 4000 5700 Binder Conifer 700 to 1 to 0.8 to Present material E 1200 4000 5700

[2. Production of Binder]

[0171] Composite binders were prepared from the binder materials A to G, which contains NMP as a solvent of binders, by a self-orbital mixer (manufactured by Thinky Corporation, Neritaro, 2000 rpm, and 30 minutes), to make the electrode binder have a predetermined solid composition as shown in the following Table 3.

TABLE-US-00003 TABLE 3 Mixing ratio of cellulose nanofibers and PVdF Composition ratio of binder material (solid content mass ratio) Electrode Binder Binder Binder Binder Binder Binder Binder binder material A material B material C material D material E material F material G Binder 1 2.5 75 Binder 2 50 50 Binder 3 75 25 Binder 4 100 Binder 5 25 75 Binder 6 50 50 Binder 7 75 25 Binder 8 100 Binder 9 25 75 Binder 10 50 50 Binder 11 75 25 Binder 12 100 Binder 13 25 75 Binder 14 50 50 Binder 15 75 25 Binder 16 100 Binder 17 25 75 Binder 18 50 50 Binder 19 75 25 Binder 20 100 Binder 2.1 25 75 Binder 22 50 50 Binder 23 75 25 Binder 24 100 Binder 25 100

[3. Production of Slurry and Electrode]

<Study on Aggregation and Sedimentation of the Slurry>

[0172] This is a test of studying properties related to aggregation and sedimentation of a slurry.

[0173] An NCA electrode slurry was obtained by blending NCA (LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2) as an active substance, acetylene black as a conductive aid, and a predetermined electrode binder shown in Table 4 to make a solid content ratio of 94 mass %:2 mass %:4 mass %, and kneading) 0 and slurrying by a self-orbital mixer (manufactured by Think' Corporation, Neritaro, 2000 rpm, and 15 minutes),

[0174] As shown in Table 4, an aggregation state, a sedimentation state, and a foaming state of a slurry were observed, and then an aluminum current collector having a thickness of 20 m was coated with the slurry by a doctor blade to observe coatability of the slurry.

[0175] As is clear from Table 4, it can be seen that preferred is a slurry in which cellulose nanofibers contained in a binder are the cellulose nanofibers subjected to the polybasic acid semi-esterification (SA) treatment or the cellulose nanofibers further subjected to the propylene oxide addition treatment as a secondary treatment, compared with a slurry in which cellulose nanofibers contained in a binder are untreated cellulose nanofibers. In addition, it can be seen that as a general trend, the aggregation property tends to be improved with an increase in the content of PVdF, and coatability approaches to that of a slurry only containing PVdF.

TABLE-US-00004 TABLE 4 Composition of electrode binder Binding Slurry (mass ratio of solid content) Aggregation Sedimentation Foaming Fluidity Coatability property Slurry 1 Untreated = 100 D C B C D C Slurry 2 Untreated/PVdF = 75/25 D B A B C B Slurry 3 Untreated/PVdF = 50/50 C B A B B B Slurry 4 Untreated/PVdF = 25/75 B B A B B B Slurry 5 SA treated = 100 B B B A A B Slurry 6 SA treated/PVdF = 75/25 A A A A A A Slurry 7 SA treated/PVdF = 50/50 A A A A A A Slurry 8 SA treated/PVdF = 25/75 A A A A A A Slurry 9 SAPO addition = 100 B B B A B B Slurry 10 SAPO addition/PVdF = 75/25 A A A A B A Slurry 11 SAPO addition/PVdF = 50/50 A A A A A A Slurry 12 SAPO addition/PVdF = 25/75 A A A B A A Slurry 13 Hardwood = 100 D D B B D B Slurry 14 Hardwood/PVdF = 75/25 D C A B D A Slurry 15 Hardwood/PVdF = 50/50 D B A B D A Slurry 16 Hardwood/PVdF = 25/75 C B A B C A Slurry 17 Conifer = 100 D D B B D B Slurry 18 Conifer/PVdF = 75/25 D C A B D A Slurry 19 Conifer/PVdF = 50/50 D B A B D A Slurry 20 Conifer/PVdF = 25/75 C B A B C A Slurry 21 Nanoclay = 100 A A D A D D Slurry 22 Nanoclay/PVdF = 75/25 A A B A D D Slurry 23 Nanoclay/PVdF = 50/50 A A B B D C Slurry 24 Nanoclay/PVdF = 25/75 A A B B C C Slurry 25 PVdF = 100 A A A D A C Aggregation: A completely no aggregation, B hard to aggregate, C easy to aggregate, D aggregate immediately Sedimentation: A completely no precipitation, B hard to precipitate, C easy to precipitate, D precipitate immediately Foaming: A completely no foam, B slightly foam, D contain a lot of small bubbles Fluidity: A very good, B good, D no fluidity (gelation) Coatability: A very good, B good, C has small uneven pasts, D has large uneven pasts Binding property: A very good, B good, D easy to peel off from a current collector

<Production of NCA Electrode>

[0176] Test electrodes 1 to 25 were produced by applying slurries (slurries 1 to 25) shown in Table 4 onto aluminum foils each haying a thickness of 20 m by an applicator, performing temporary drying at 80 C., then rolling by a roll press, and drying under reduced pressure (160 C., 12 hours). The capacity density of each NCA positive electrode was 2.1 mAh/cm.sup.2. However, since a solid content of a slurry was too small for the test electrode 13, the test electrode 17, and the test electrode 21, an electrode having a capacity density more than 1 mAh/cm.sup.2 could not be produced. From this result, it can be seen that the solid content ratio of the binder material is preferably 2 mass % or more.

<Production of NCM523 Electrode:>

[0177] Test electrodes 26 to 29 were produced by applying slurries, which were obtained by blending NCM (LiNi.sub.0.5Co.sub.0.2Mn.sub.0.3O.sub.2) as an active substance, acetylene black as a conductive aid, and a predetermined electrode binder shown in Table 5 to make a solid content ratio of 94 mass %:2 mass %:4 mass %, and kneading and slurrying by a self-orbital mixer (manufactured by Thinky Corporation, Neritaro, 2000 rpm, and 15 minutes), to aluminum foils each having a thickness of 20 m by an applicator, performing temporary drying at 30 C., then rolling by a roll press, and drying under reduced pressure (160 C., 12 hours). Each NCM523 positive electrode has the capacity density of was 2.5 mAh/cm.sup.2.

TABLE-US-00005 TABLE 5 Composition of electrode binder Test electrode (mass ratio of solid content) Test electrode 26 Untreated = 100 Test electrode 27 Untreated/PVdF = 75/25 Test electrode 28 Untreated/PVdF = 50/50 Test electrode 29 PVdF = 100

[4. Production of NCA/Si Full Battery]

[0178] NCA/Si full batteries in Examples 1 to 14, Reference Examples 1 to 6 and Comparative Example 1 are test batteries including test electrodes shown in Table 6. As the test batteries, a CR 2032 type coin cell was produced with an NCA electrode (test electrode) as a positive electrode, a Si electrode as a negative electrode, a glass non-woven fabric (GA-100) as a separator, and 1 mol/L of LiPF.sub.6 (EC:DEC=50:50 vol %, +VC1 mass %) as an electrolytic solution.

[0179] The Si electrode was produced by blending Si, PVdF (weight average molecular weight: 280,000) and acetylene to reach a solid content ratio of 94 mass %:2mass %:4 mass %, kneading and slurrying by a self-orbital mixer (manufactured by Thinky Corporation, Neritaro, 2000 rpm, and 15 minutes), coating the slurry to a stainless steel foil having a thickness of 8 m, temporarily drying at 100 C., then applying an alkali metal silicate aqueous solution (A.sub.2O.sub.nSiO.sub.2; n=3.2, A=Li, Na, K) thereto by a gravure coater, and drying under reduced pressure (150 C., 12. hours). The Si electrode had a capacity density of 4.5 mAh/cm.sup.2. The reason why the Si electrode was coated with the alkali metal silicate aqueous solution was to extend the life of the Si electrode, as described in Patent Literature 7, and it was applied to improve high-temperature durability so that the test battery was not limited by the characteristics of the Si negative electrode.

[0180] In the present invention, the term full battery means a battery evaluated without containing metal lithium as a counter electrode, and the term half battery means a battery containing metal lithium as a counter electrode.

TABLE-US-00006 TABLE 6 Composition of electrode binder Test battery Test electrode (mass ratio of solid content) Reference Test electrode 1 Untreated = 100 Example 1 Example 1 Test electrode 2 Untreated/PVdF = 75/25 Example 2 Test electrode 4 Untreated/PVdF = 25/75 Reference Test electrode 5 SA treated = 100 Example 2 Example 3 Test electrode 6 SA treated/PVdF = 75/25 Example 4 Test electrode 7 SA treated/PVdF = 50/50 Example 5 Test electrode 8 SA treated/PVdF = 25/75 Reference Test electrode 9 SAPO addition = 100 Example 3 Example 6 Test electrode 10 SAPO addition/PVdF = 75/25 Example 7 Test electrode 11 SAPO addition/PVdF = 50/50 Example 8 Test electrode 12 SAPO addition/PVdF = 25/75 Example 9 Test electrode 14 Hardwood/PVdF = 75/25 Example 10 Test electrode 15 Hardwood/PVdF = 50/50 Example 11 Test electrode 16 Hardwood/PVdF = 25/75 Example 12 Test electrode 18 Conifer/PVdF = 75/25 Example 13 Test electrode 19 Conifer/PVdF = 50/50 Example 14 Test electrode 20 Conifer/PVdF = 25/75 Reference Test electrode 22 Nanoclay/PVdF = 75/25 Example 4 Reference Test electrode 23 Nanoclay/PVdF = 50/50 Example 5 Reference Test electrode 24 Nanoclay/PVdF = 25/75 Example 6 Comparative Test electrode 25 PVdF = 100 Example 1

<Cycle Life Characteristic in an Environment of Temperature at 60 C.>

[0181] This is a test of evaluating cycle-life characteristics of test batteries in Examples 1 to 14, Reference Examples 1 to 6, and Comparative Example 1 in an environment of temperature at 60 C.

[0182] In a charge/discharge test, under conditions of an ambient temperature of 60 C. and a cut-off potential of 4.25 V to 2.7 V, one cycle of charge/discharge was performed at rates of 0.1 C-rate, 0.2 C-rate, 0.5 C-rate, and 1 C-rate, and then charge/discharge was repeated at 3 C-rate.

[0183] Note that the term charge/discharge rate refers to an index based on the fact that a cell having a capacity of a nominal capacity value is discharged at a constant current, and a current value at which complete discharge occurs in one hour is defined as 1 C-rate, for example, a current value at which complete discharge occurs in five hours is defined as 0.2 C-rate, and a current value at which complete discharge occurs in 10 hours is defined as 0.1 C-rate.

[0184] FIG. 1 is a graph showing a comparison between batteries (Example 1, Example 2, Reference Example 1) that include an electrode containing a binder material A as an electrode binder, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0185] FIG. 2 is a graph showing a comparison between batteries (Examples 3 to 5, and Reference Example 2) that include an electrode containing a binder material B as an electrode binder, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0186] FIG. 3 is a graph showing a comparison between batteries (Examples 6 to 8, and Reference Example 3) that include an electrode containing a binder material C as an electrode binder, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0187] FIG. 4 is a graph showing a comparison between batteries (Examples 9 to 11) that include an electrode containing a binder material D as an electrode binder, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0188] FIG. 5 is a graph showing a comparison between batteries (Examples 12 to 14) that include an electrode containing a binder material E as an electrode binder, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0189] FIG. 6 is a graph showing a comparison between batteries (Reference Examples 4 to 6) that include an electrode containing a binder material F as an electrode binder, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0190] As is clear from FIGS. 1 to 6, it can be seen that batteries (Examples 1 to 14) containing any one of the binder materials A to E in electrode binders clearly exhibit improved cycle-life characteristics as compared with a battery (Comparative Example 1) containing only the binder material G as an electrode binder. In contrast, even with the same nano-order particles, batteries (Reference Examples 4 to 6) containing the binder material F in electrode binders did not have an effect of improving the life-span, but rather the performance deteriorated. From these results, it could be seen that the electrode binder containing cellulose nanofibers had an effect of improving cycle-life characteristics of a battery at a high temperature.

<Cycle Life Characteristic in an Environment of a Temperature at 80 C.>

[0191] This is a test of evaluating cycle-life characteristics of test batteries in Examples 1 to 14, Reference Examples 1 to 6, and Comparative Example 1 in an environment of a temperature at 80 C.

[0192] In a charge/discharge test, under conditions of an ambient temperature of 80 C. and a cut-off potential of 4.25 V to 2.7 V, one cycle of charge/discharge was performed at rates of 0.1 C-rate, 0.2 C-rate, 0.5 C-rate, and 1 C-rate, and then charge/discharge was repeated at 3 C-rate.

[0193] FIG. 7 is a graph showing a comparison between batteries (Example 1, Example 2, and Reference Example 1) that include an electrode containing a binder material A as an electrode binder, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0194] FIG. 8 is a graph showing a comparison between batteries (Examples 3 to 5, and Reference Example 2) that include an electrode containing a binder material B as an electrode binder, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0195] FIG. 9 is a graph showing a comparison between batteries (Examples 6 to 8, and Reference Example 3) that include an electrode containing a binder material C as an electrode binder, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0196] FIG. 10 is a graph showing a comparison between batteries (Examples 9 to 11) that include an electrode containing a binder material D as an electrode binder, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0197] FIG. 11 is a graph showing a comparison between batteries (Example 14) that includes an electrode containing a binder material E as an electrode binder, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0198] FIG. 12 is a graph showing a comparison between batteries (Reference Examples 4 to 6) that include an electrode containing a binder material F as an electrode binder, and a battery (Comparative Example 1) that includes an electrode containing only a binder material G as an electrode binder.

[0199] As is clear from FIGS. 7 to 12, it can be seen that batteries (Examples 1 to 14) containing any one of the binder materials A to E in electrode binders exhibit improved cycle-life characteristics as compared with a battery (Comparative Example 1) including only the binder material G as an electrode binder. In contrast, even with the same nano-order particles, batteries (Reference Examples 4 to 6) containing the binder material F in electrode binders did not have an effect of improving life-span. From these results, it could be seen that the electrode binder containing cellulose nanofibers had an effect of improving cycle-life characteristics of a battery at a high temperature. Particularly, batteries containing any one of the binder materials A to C (Examples 1 to 8, and Reference Examples 1 to 3) in electrode binders showed a remarkable difference particularly.

[0200] In the environment of a temperature at 80 C., as the cellulose nanofibers contained in the binder of the test electrode increases, the cycle-life characteristics at a high temperature tend to be improved, but the output characteristics tend to decrease.

[5. Production of NCM523/SiO Full Battery]

[0201] The NCM 523 electrodes in Example 15. Example 16, Reference Example 7 and Comparative Example 2 are test batteries including electrode binders shown in Table 7. As the test batteries, a CR 2032 type coin cell was produced with an NCM523 electrode (test electrode) as a positive electrode, a SiO electrode as a negative electrode, a polyolefin microporous film as a separator (PP/PE/PP), and 1 mol/L of LiPF.sub.6 (EC:DEC=50:50 vol %) as an electrolyte solution.

[0202] The SiO electrode was produced by blending SiO, PVA (polymerization degree 2800), acetylene black, and VGCF to reach a solid content ratio of 94 mass %:10 mass %:4 mass %:1 mass %, kneading and slurrying by a self-orbital mixer (manufactured by Thinky Corporation, Neritaro, 2000 rpm, and 15 minutes), applying the slurry to a copper foil having a thickness of 40 m, temporarily drying at 80 C., and then drying under reduced pressure (160 C., 12 hours). The SiO electrode has a capacity density of 3.2 mAh/cm.sup.2. As the SiO electrode, before assembling the full battery, a half battery was produced in advance with metallic lithium as a counter electrode, and after canceling the irreversible capacity, the SiO electrode obtained by disassembling the half battery was used.

TABLE-US-00007 TABLE 7 Composition of electrode binder Test battery Test electrode (mass ratio of solid content) Reference Test electrode 26 Untreated = 100 Example 7 Example 15 Test electrode 27 Untreated/PVdF = 75/25 Example 16 Test electrode 28 Untreated/PVdF = 50/50 Comparative Test electrode 29 PVdF = 100 Example 2
<Cycle Life Characteristic in an Environment of a Temperature at30 C.>

[0203] This is a test of evaluating cycle-life characteristics of test batteries in Example 15, Example 16, Reference Example 7, and Comparative Example 2 in an environment of a temperature at 30 C.

[0204] In a charge/discharge test, charge/discharge was repeated at 0.2 C-rate under conditions of an ambient temperature of 30 C. and cutoff potential 4.3 V to 2.5 V.

[0205] FIG. 13 is a graph showing a comparison between batteries (Example 15, Example 16, Reference Example 7) that include an electrode containing a binder material A as an electrode binder, and a battery (Comparative Example 2) that includes an electrode containing only a binder material G as an electrode binder.

[0206] As is clear from FIG. 13, in the environment of a temperature at 30 C., there is no significant difference in cycle-life characteristics.

<Cycle Life Characteristic in an Environment of a Temperature at 60 C.>

[0207] This is a test of evaluating cycle-life characteristics of test batteries in Example 15, Example 16, Reference Example 7, and Comparative Example 2 in an environment of a temperature at 60 C.

[0208] In a charge/discharge test, charge/discharge was repeated at 0.2 C-rate wider conditions of an ambient temperature of 60 C. and cutoff potential 4.3 V to 2.5 V.

[0209] FIG. 14 is a graph showing a comparison between batteries (Example 15, Example 16, Reference Example 7) that include an electrode containing a binder material A as an electrode binder, and a battery (Comparative Example 2) that includes an electrode containing only a binder material G as an electrode binder.

[0210] As is clear from FIG. 14, in the environment of a temperature at 60 C., the cycle-life characteristics are improved by containing the binder material A. Particularly, regarding a ratio of the binder material A and the binder material G, the effect increases as the amount of the binder material A increases.

[6. Examination of Gelation Resistance]

[0211] This is a test of examining whether a binder gels by strong alkalinity.

[0212] (Gelation Resistance Test 1)

[0213] In the gelation resistance test 1, 2 mass % of lithium hydroxide (LiOH) was added to Binder 4, and the mixture was stirred by a self-orbital mixer (manufactured by Thinky Corporation, Neritaro, 2000 rpm, 15 minutes) and then was allowed to stand for 12 hours in an environment of a temperature at 25 C.

[0214] (Gelation Resistance Test 2)

[0215] In the gelation resistance test 2, 2 mass % of lithium hydroxide was added to Binder 25, and the mixture was stirred by a self-orbital mixer (manufactured by Thinky Corporation, Neritaro, 2000 rpm, 15 minutes) and then was allowed to stand for 12 hours in an environment having a temperature of 25 C.

[0216] FIG. 15 shows the results of examining the gelation resistance of hinders. As is clear from FIG. 15. in the gelation resistance test 2, the color changes immediately after the addition of LiOH, whereas the color does not change even if the binder is left for 12 hours in the gelation resistance test 1. In addition, in the gelation resistance test 2, PVdF gelled and changed to a gum-like substance after standing for 12 hours, whereas fluidity of the binder was not lost in the gelation resistance test 1.

[7. Production of Surface Coated Separator]

[0217] Test separators 1 to 4 were produced by kneading and slurrying Binder 5 and alumina (particle diameter 200 nm) by a self-orbital mixer (manufactured by Thinky Corporation, Neritaro, 2000 rpm, and 30 minutes) to make predetermined solid content compositions shown in Table 8, applying the slurry to one surface of a polypropylene (PP) microporous film having a thickness of 16 m, and temporarily drying at 70 C., and then drying under reduced pressure (80 C. and 24 hours). The thickness of each of the surface coating layers of the test separators 1 to 4 was 4 m. As a Comparative Example, an uncoated PP microporous film was taken as the test separator 5.

[0218] The test batteries in Example 17, Example 18, Example 19, Example 20, and Comparative Example 3 are test batteries including separators 1 to 5 shown in Table 8. The test batteries (NCM111/graphite full battery) were produced by assembling CR2032 type coin cells with an NCM111 electrode as a positive electrode, a graphite electrode as a negative electrode, the test separators 1 to 5 as separators, and 1 mol/L of LiPF.sub.6 (EC: DEC=50:50 vol %) as an electrolyte solution, and placing the coin cells in an environment of a temperature at 80 C. for one hour. The coating layer of the separator was provided on the positive electrode side.

[0219] The NCM111 electrode was produced by blending NCM111, PVdF (weight average molecular weight: 280,000), and acetylene black to reach a solid content ratio of 91 mass %:5 mass %:4 mass %, kneading and slurrying by a self-orbital mixer (manufactured by Thinky Corporation, Neritaro, 2000 rpm, and 15 minutes), applying the slurry by to an aluminum foil having a thickness of 15 m, temporarily drying at 80 C., and then drying under reduced pressure (160 C., 12 hours). The one side of the NCM111 electrode had a capacity density of 2.5 mAh/cm.sup.2.

[0220] The graphite electrode was produced by blending graphite, SBR, carboxymethyl cellulose (CMC), acetylene black, and VGCF to reach a solid content ratio of 93.5 mass %: 2.5 mass %:1.5 mass %:2 mass %:0.5 mass %, kneading and slurrying by a self-orbital mixer (manufactured by Thinky Corporation, Neritaro. 2000 rpm, and 15 minutes), applying the slurry to a copper foil having a thickness of 10 temporarily drying at 80 C., and then drying under reduced pressure (160 C., 12 hours). The one side of the graphite electrode had a capacity density of 3.0 mAh/cm.sup.2. In this test, the graphite electrode does not cancel the irreversible capacity.

TABLE-US-00008 TABLE 8 Composition of surface coat layer of separator Test battety Test separator (mass ratio of solid content) Example 17 Test separator 1 Binder 5 = 100 Example 18 Test separator 2 Binder 5/Al.sub.2O.sub.3 = 60/40 Example 19 Test separator 3 Binder 5/Al.sub.2O.sub.3 = 40/60 Example 20 Test separator 4 Binder 5/Al.sub.2O.sub.3 = 20/80 Comparative Test separator 5 Uncoated Example 3

<Cycle Life Characteristic in an Environment of a Temperature at 60 C.>

[0221] This is a test of evaluating cycle-life characteristics of test batteries in Examples 17 to 20, and Comparative Example 3 in an environment of a temperature at 60 C.

[0222] In a charge/discharge test, under conditions of an ambient temperature of 60 C. and a cut-off potential of 4.3V to 2.5V, two cycles of charge/discharge were performed at 0.1 C-rate, then three cycles of charge/discharge were performed at 0.2 C-rate, and then charge/discharge was repeated at 1 C-rate.

[0223] FIG. 16 is a graph showing a comparison between batteries (Examples 17 to 20) including test separators 1 to 4 and a battery (Comparative Example 3) using an uncoated separator.

[0224] As is clear from FIG. 16, the cycle-life characteristics are improved by providing a coating layer on a surface of a separator. Particularly, when Al.sub.2O.sub.3 was contained, the effect is increased.

<Nail Penetration Safety>

[0225] A test for the safety of a battery (Example 21) using a surface coated separator was conducted. In addition, a battery (Comparative Example 4) including an uncoated separator as a comparison was produced and was subjected to a similar test.

[0226] A test method is according to a nail penetration test in which a nail is inserted into a laminated battery and smoke or ignition of the laminated battery is examined. Example 21 was performed in the same manner as example 20 except that in the test, a laminated battery of 1.2 Ah is used, which is obtained by stacking a plurality of graphite negative electrodes (capacity density of both sides is 6 mAh/cm.sup.2), separators, and NCM 111 positive electrodes (capacity density of both sides is 5 mAh/cm.sup.2) in an aluminum laminated casing, and sealing an electrolytic solution together in the casing. Comparative Example 4 was performed in the same manner as Comparative Example 3.

[0227] In the nail penetration test, the battery was charged up to 4.2 V at 0.1 C-rate, then an iron nail ( 3 mm, round shape) was pierced into a center of the battery until it penetrates the battery at a speed of 1 mm/sec in an environment of a temperature at 25 C., and battery voltage, temperature of the nail, and temperature of the casing were measured.

[0228] When the nail penetration was performed on the battery (Comparative Example 4) including an uncoated separator, the voltage of the battery dropped to 0 V and a large amount of smoke was generated. This is because the separator meltdown due to the heat generated when a short circuit occurs inside the battery, leading to a complete short circuit.

[0229] In contrast, when nail penetration was performed on a battery (Example 21) including a separator on which a ceramic layer including Binder 5 and Al.sub.2O.sub.3 was formed on a surface thereof, a voltage of 3 V or more was maintained, no smoke was generated, the temperature of the casing and the nail was 50 C. or lower, and heat generation due to a short circuit hardly occurs. This is because the separator does not meltdown even if heat is generated when a short circuit occurs inside the battery, and a complete short circuit does not occur.

[0230] Although the preferred Examples of the present invention have been described above with reference to the drawings, various additions, modifications, and deletions may be made without departing from the spirit of the present invention. For example, the ratio of cellulose nanofibers and a thermoplastic fluororesin is not limited to the numerical values of the above embodiment. In the above Example, as the thermoplastic fluororesin, PVdF may be a polymer or a copolymer, or a copolymer and further the weight average molecular weight is not limited to 280,000. Cellulose nanofibers, containing anionic groups such as carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, and sulfate groups are also within the scope of the present invention. In addition, the active substance is not limited to NCA or NCM523 and may be any materials capable of reversibly occluding and releasing Li ions. Accordingly, such substances are also within the scope of the present invention.