SI20397A - Procecure of preparation of carbon anode for lithium ionic batteries - Google Patents

Abstract

According to the procedure, a polyelectrolite solution suitable to create a hairy structure on the surface of carbon particles is prepared by dissolving 0.1 g to 10 g of polylectrolite chosen among proteins, cellulose derivatives, gums or their mixtures, in 1 litre of deionized water during moderate stirring at the temperature of 30 up to 100 degrees Celsius. 1 up to 10 g of carbon particles containing graphite layers of dimensions from 1 up to 50 micrometres and specific surface of 2 up to 50 m2/g are mixed into 1 litre of thus prepared solution warmed to about room temperature with pH modified to 7 up to 9. The obtained solution is left at rest for 2 to 30 minutes, filtered through a glass frit, the black cake transferred on a copper foil, and further processed in a usual way to a lithium ionic battery anode. According to the new procedure, the use of classic binders is avoided and carbon anodes with very good characteristics for the application to lithium ionic batteries are obtained.

Description

CHEMICAL INSTITUTE

Carbon anode preparation process for lithium ion batteries

1. Technical field of the invention

The present invention is in the field of chemical technology, specifically chemical sources of electricity. It relates to a new carbon anode preparation process, and to a carbon anode prepared in this way, designed for carbon (anode) / non-aqueous liquid electrolyte / transition element (cathode) lithium ion batteries.

2. State of the art

In the subclass of lithium ion batteries, which reach a current density of 1 pAcrri ² to 1 mAcm ' ² , the anode is usually made of carbon powder, the particles of which have typical dimensions of 1-50 pm. Carbon dust may have different origins, e.g. coke, carbon black, natural or artificial graffiti, etc. (J. R. Dahn, A. K. Sleigh, H. Shi, J. N. Reimers, Electrochimica Acta, 38 (1993) 1179-1191; (2) N. Takami, A. Satoh, M. Hara, T. Ohsaki, J. Electrochem. Soc., 142 (1995) 371-378; (3) TD Tran, J. H. Feikert, X. Song, K. Kinoshita, J. Electrochem. Soc., 142 (1995) 3297-3302). It is only relevant that it contains graphene layers, among which lithium ions are embedded (intercalated) (N. Imanishi, Y. Takeda, O. Yamamoto, in; Lithium Ion Batteries, Fundamentals and Performance, ed. M. VVakihara, O. Yamamoto , Kodansha, Tokyo, and Wiley-VCH, VVeinheim, 1998, pp. 98-126).

The principle of classical anode construction is as follows: the carbon powder suspension is mixed with a suspension of Teflon-based binder (PTFE) or polyvinylidenedifluoride (PVDF) and the final mixture is applied to a flow collector (copper, aluminum, graphite pad, etc.). The application is dried for several hours in an inert atmosphere at a temperature of about 100-140 ° C. ((1) TD Tran, J. H. Feikert, X. Song, K. Kinoshita, J. Electrochem. Soc., 142 (1995) 3297-3302; (2) N. Imanishi, Y. Takeda, O. Yamamoto, in: Lithium Ion Batteries, Fundamentals and Performance, edited by M. VVakihara, O. Yamamoto, Kodansha, Tokyo and Wiley-VCH, VVeinheim, 1998, pp. 98-126; (3) I. Tamura, M. Nagasima, Y. Ikezavva , and T. Takamura, Denki Kagaku, 60 (1992) 926).

Classic anode preparation for lithium ion batteries:

An electrochemically active anode material is usually a carbon powder based on coke, carbon black, graphite, pyrolysed polymers, carbon fibers or a mixture of these materials ((1) (2) N. Takami, A. Satoh, M. Hara, T. Ohsaki, J. Electrochem. Soc., 142 (1995) 371-378; (3) TD Tran, J. H. Feikert, X. Song, K. Kinoshita, J. Electrochem. Soc., 142 (1995) 3297-3302; (4) N Imanishi, Y. Takeda, O. Yamamoto, in: Lithium Ion Batteries, Fundamentals and Performance, eds. M. VVakihara, O. Yamamoto, Kodansha, Tokyo and Wiley-VCH, VVeinheim, 1998, pp. 98-126).

These materials are obtained by temperature treatment of the starting compounds at temperatures from 1000 ° C to 3000 ° C (JR Dahn, AK Sleigh, H. Shi, JN Reimers, Electrochimica Acta, 38 (1993) 1179-1191). Typical dimensions of carbon particles are 1-50 pm and their surface area is 2-50 m ² g ' ¹ . The powder is dispersed either in ethanol, methanol, acetone and the like. The dispersions add 5-10 wt. % PTFE or PVDF ((1) TD Tran, J. H. Feikert, X. Song, K. Kinoshita, J. Electrochem. Soc., 142 (1995) 3297-3302; (2) N. Imanishi, Y. Takeda, O Yamamoto, in: Lithium Ion Batteries, Fundamentals and Performance, edited by M. VVakihara, O. Yamamoto, Kodansha, Tokyo, and Wiley-VCH, VVeinheim, 1998, pp. 98-126; (3) I. Tamura, M. Nagasima, Y. Ikezavva, and T. Takamura, Denki Kagaku, 60 (1992) 926), in dispersion form or in powder form. The resulting dispersion is mixed well and applied to copper foil or graphite. The prepared electrode is then compressed in a press at a pressure of 500-2000 kPa. The final coating thickness ranges from 50-200 pm. The electrode was dried in vacuo for 10-14 h at a temperature of 100-140 ° C.

Adsorption of polyelectrolytes on particles:

Adsorption of polyelectrolytes (such as gelatin) is studied and exploited in the food industry (AG Ward, A. Courts, in The Science and Technology of Gelatin, Academic Press, London, 1977), photography (CE Mees, CE Kenneth, in The Theory of Photographic Process «, Macmillan, New York, 1966), Electrochemistry (GM Brown, GA Hope, J. Electroanal. Chem., 397 (1995) 293), Biology, Medicine, etc. Polyelectrolytes are used as stabilizers in both suspensions ((1) TJ Maternaghan, OB Banghan, RH Ottevvill, J. Photogr. Sci. 28 (1980); (2) VV Rodin, V. Izmailova, Polym. Sci., 272 (1994 ) 433), as in emulsions (HJ Muller, H. Hermel, Colloid Polym. Sci, 272 (1994) 433). In the first case, the stabilization is achieved by a steric barrier represented by polyelectrolyte molecules (hairy structure) after adsorption onto the substrate, and the emulsions become stable due to changes in the interlayer properties.

3. Technical problem

Typical problems of the procedures described above and the anodes prepared therefrom are:

a) During the first intercalation (the first charge of the battery), a considerable proportion, namely 20-40%, of the lithium ions is chemically reacted with the electrolyte, and the products are released in the form of a passive film on the surface of carbon particles ((1). M.Jean, A. Tranchant Soc., 143 (1996) 391-394, Reactivity of lithium intercalated into petroleum shocks in carbonate electrolytes;

(2) K. Kanamura, S. Toriyama, S. Shiraishi, and Z. Takehara, J. Electrochem. Soc., 142 (1995) 1383-1389; (3) D. Aurbach, A. Zaban, Y. EinEli, I.Veissman, O. Chusid, B. Markovsky, M. Levi, E. Levi, A. Schechter, and E. Granot, 8 ^th Int. Meet. Lithium Batteries, Nagoya, Japan, 1996, Extended Abstracts, p.77-80; (4) W. Xing, J. R. Dahn, J. Electrochemical Soc., 144 (1997) 1195-1201). Passive film formation is an irreversible process, so lithium consumed in this process cannot be used for subsequent discharges and recharges.

b) Since the content of the binder is only about 5-10% by weight, it is difficult to achieve an optimal bonding of carbon particles when preparing the anode. Due to large volume changes (30 - 200%) (JO Besenhard, M. Winter, J. Power Sources, 54 (1995) 228, during intercalation and deintercalation, individual carbon particles gradually lose physical and thus electrical contact with other particles in the This is one of the main causes of degradation of lithium batteries during cycling.

c) PTFE and PVDF are electrical insulators, so their presence in the anode greatly impairs local conductivity.

d) PTFE and PVDF are electrochemically inactive materials. Their presence means a direct reduction in the energy density of lithium batteries.

4. Description of the solution to the problem with implementation examples

We propose a new carbon anode fabrication process that avoids the use of classic binders. Instead, the surface of the carbon particles is treated with polyelectrolyte prior to making the anode. The use of polyelectrolytes in the preparation of anodes for lithium ion batteries has not yet been described in the literature.

The new process significantly reduces the technical problems listed in points a) to d) and produces carbon anodes, which have very good characteristics for use in lithium ion batteries.

The carbon particles intended to be used as an electrochemically active anode material are exposed to a polyelectrolyte solution. Polyelectrolyte is adsorbed onto the surface of each carbon particle and modifies its physical and chemical properties. Modification of the surface of carbon particles is the essence of the invention and leads to the following unexpected, advantageous features of the process and product: Irreversible loss of lithium due to passivation is reduced to a maximum of 15%.

A) The adsorbed polyelectrolyte serves simultaneously as a binder between the carbon particles, so no PVDF or PFTE supplementation is required.

B) The percentage by weight of polyelectrolyte in the anode material does not exceed 1%. This makes the energy density of the anode material higher than using conventional binders.

4.1. Preparation of the polyelectrolyte solution

The solution was prepared by dissolving a water-soluble polyelectrolyte in deionized water. Polyelectrolytes have been used to form a hairy structure at the boundary between the particle and the electrolyte (for example, proteins, cellulose derivatives, rubbers, etc.). The hairy structure means that, after adsorption, the tails or loops of the polyelectrolyte protrude from the surface of the particle into the interior of the solution.

Prior to adsorption, the previously prepared polyelectrolyte solution was modified by changing the pH of the solution or by adding an appropriate ionic surfactant. This changed the charge density on the polyelectrolyte to obtain maximum adsorption.

4.2. Treatment of carbon particles in a polyelectrolyte solution

The polyelectrolyte modified according to 4.1 gave surface treatment of the carbon particles, which were subsequently used as the electrochemically active anode material. A known amount of carbon particles was added to the appropriate amount of modified polyelectrolyte solution with stirring. After 2-30 minutes, the treated particles were filtered off using a nuance. The resulting cake was used in the preparation of the anode.

4.3. Anode preparation from surface-treated carbon particles

The particles with adsorbed polyelectrolyte are filtered out of solution and the material obtained is applied to a copper foil. The application is pressurized at 100-5000 kPa and dried for several hours in a vacuum or inert atmosphere. The final coating thickness ranges from 50 - 200 pm. The dried electrode is transferred to a dry chamber where electrochemical tests are performed.

The process of preparing a carbon anode for lithium ion batteries according to the present invention is carried out by

a) prepare a solution of polyelectrolyte suitable for forming a hair structure on the surface of carbon particles by dissolving 0.1 to 10 g of polyelectrolyte selected from proteins, cellulose derivatives, gums, or mixtures thereof, in 1 I of deionized water with moderate stirring at a temperature of 30 up to 100 ° C,

b) in 1 liter of the above solution obtained, heated to approximately room temperature and modified to pH 7 to 9, mixing 1 to 10 g grafenske layer containing carbon particles with a size of 1 to 50 pm and a specific surface area of 2 to 50 m ² g ^'1 , leave for 2 to 30 minutes, filter through a drizzle, and

c) Apply the black cake from the coil onto the copper foil and further process it into the anode for the lithium ion batteries in the usual way.

Gelatin or gum arabic is preferably used as polyelectrolyte.

It is preferably stirred at about 200 rpm.

Graphite is preferably used as carbon particles.

Preferably, the pH is modified by the addition of acid or base to achieve a minimum charge on the macromolecule.

A further object of the invention is a carbon anode for lithium ion batteries made according to any one of claims 1 to 5.

Embodiment A: Preparation of a gelatin solution

0.01 - 1% gelatin solution no. 48722 from Fluk. The solution was prepared by dissolving 0.1-10 g of gelatin in 1 liter of deionized water at 30-100 ° C with moderate stirring with a magnetic stirrer of approx. 200 rpm. Before use, it was always tempered to room temperature.

Prior to adsorption, the previously prepared gelatin solution was modified with an appropriate amount of 0.1 M NaOH to obtain a pH between 7 and 9.

Embodiment B: Preparation of a gum arabic solution

0.01 - 1% solution of gum arabica spraygum irx no. 28830 by Coloides Naturels International, France. The solution was prepared by dissolving 0.1-10 g of arabic gum in 1 liter of deionized water at 30-100 ° C with moderate stirring with a magnetic stirrer of approx. 200 rpm. Before use, we always tempered it to room temperature.

Example C; Treatment of carbon particles in polyelectrolyte solution

The gelatin or gum arabic modified according to 4.1 gave surface treatment of the carbon particles, which were subsequently used as electrochemically active anode material. To 100 ml of modified polyelectrolyte was added 1 - 10 g of Timrex SFG44 while stirring. After 2-30 minutes, the treated SFG44 particles were filtered off by suction. The resulting cake was used in the preparation of the anode.

Embodiment D: Preparation of anode from surface-treated carbon particles

The particles with adsorbed polyelectrolyte were filtered out of solution and the material obtained was applied to a copper foil. The application was pressurized at 1000 kPa and dried under vacuum at 100 ° C for 10 h. The final application thickness was about 50 pm. The dried electrode was transferred to a dry chamber where electrochemical tests were performed.

The invention is explained by the accompanying Figures 1 - 4.

Figure 1 shows the first filling / emptying of the anode made of Timrex SFG44 graphite treated with Fluka gelatin no. 48722.

Figure 2 shows the first filling / emptying of the anode made of Timrex SFG44 graphite using 5 wt.% TEFLON (Aldrich 44, 509-6) as a binder. Figure 3 shows the dependence of the reversible capacity on the number of cycles for the gelatin-treated anode of SFP44 graphite.

Figure 4 shows the dependence of reversible capacity on the number of cycles for anode made of SFP44 graphite and 5% TEFLON.

Claims (7)

PATENT APPLICATIONS 1. A process for preparing a carbon anode for lithium ion batteries, characterized in that a) prepare a solution of polyelectrolyte suitable for forming a hair structure on the surface of carbon particles by dissolving 0.1 to 10 g of polyelectrolyte selected from proteins, cellulose derivatives, gums, or mixtures thereof, in 1 liter of deionized water with moderate stirring at a temperature of 30 up to 100 ° C, b) in 1 liter of the above solution, warmed to about room temperature and modified to pH 7 to 9, mix 1 to 10 g of graphene layer containing carbon particles with a dimension of 1 to 50 pm and a specific surface area of 2 to 50 m ² g ' ¹ , leave for 2 to 30 minutes, filter through a drizzle, and c) The black cake is applied to the copper foil and further processed in a conventional manner into the anode for lithium ion batteries. Process according to claim 1a, characterized in that gelatin is used as the polyelectrolyte. Process according to claim 1a, characterized in that gum arabica is used as polyelectrolyte. Process according to claim 1a, characterized in that it is stirred at about 200 rpm. Process according to claim 1b, characterized in that graphite is used as carbon particles. A process according to claim 1 b, characterized in that the pH is modified by the addition of acid or base to achieve a minimum charge on the macromolecule. 7. Carbon anode for lithium ion batteries, characterized in that it is made according to any one of claims 1 to 5.