Aqueous slurry for battery electrodes

Abstract

A slurry or paste for the manufacture of electrodes for secondary batteries such as lithium ion containing electrochemical cells. The slurry comprises a water-based binder with CMC, SBR and PVDF as binder materials.

Claims

1. A method for the manufacture of an electrode for an electrochemical cell, comprising the steps of: preparing a slurry comprising mixing one of polyacrylic acid or carboxymethyl cellulose, in an aqueous solution, with styrene-butadiene rubber as binder in an aqueous solution, polyvinylidene fluoride, and carbon black and at least one selected from the group comprising graphite, titanate, and lithium metal oxides wherein the total amount of binder in the slurry is about 10% by weight; and coating or laminating the slurry on a current collector.

2. The method of claim 1, wherein preparing the slurry comprises dispersing latex in the aqueous solution for stabilizing the aqueous solution.

3. The method of claim 1, further comprising the step of adding a non-aqueous electrolyte.

4. The method of claim 1, further comprising drying the slurry.

5. The method of claim 1, wherein the concentration of each one of the polyvinylidene fluoride; the polyacrylic acid or the carboxymethyl cellulose; and the styrene-butadiene rubber is about 0.5% to about 10% by weight.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The present invention as defined by the claims will now be described with respect to detailed examples and with reference to the attached figures in which:

(2) FIG. 1 shows cycle life characteristics for electrochemical cells containing Li—NCO cathodes and graphite anode prepared with water-based binder mixture; and

(3) FIG. 2 shows a discharge rate capability behaviour of the Li—NCO/Graphite electrochemical cell of FIG. 1.

DETAILED DESCRIPTION

(4) An electrochemical cell according to the present disclosure can be prepared by standard methods known to a person skilled in the art. It is common knowledge to a person skilled in the art to use slurries for manufacturing positive or negative electrodes i.e. cathodes or anodes. The slurry may be coated onto a current collector. The current collector can be a metal foil and can comprise materials such as copper or aluminium, but other current collectors can be used with the present invention.

(5) A slurry according to the present disclosure is prepared by mixing a binder with an active electrode material in an aqueous solution. Further components may be added.

(6) The binder comprises a composition of carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR) as binder and polyvinylidene fluoride (PVDF) as lamination agent. No other binder materials are used. Alternatively or in addition to CMC, polyacrylic acid (PAA) may be used to reduce the PH of the slurry. The total amount of binder in the slurry can be about 0.5% to about 30% by weight. Good results have been obtained with a total amount of binder in the slurry of about 10% by weight. The binder can be mixed in an aqueous solution made from de-ionized water. Latex at a concentration of about 0.5-10% may be added to stabilize the aqueous PVDF dispersion.

(7) The slurry comprises an active electrode material and other components such as carbon black and optionally further additives.

(8) Example for anode active electrode material may be graphite. Examples for a cathode active electrode material comprises LFP, LNCM, LCO, Li—NCA, LMO or other metal oxides and their blends.

Example 1

Anode Electrode Slurry

(9) A graphite electrode slurry may comprise 2% CMC or PAA, 5% SBR, 3% PVDF, 2% carbon black and 88% graphite. The above components may be mixed to a slurry in an aqueous solution. The aqueous solution may be deionised water. Latex may be added to the solution in order to maintain the PVDF in a stable dispersion. The materials used are commercially available. No other materials are used. The water contents depends on active materials, binder and other conductive materials and their concentration used in the slurry.

Example 2

Cathode Electrode Slurry

(10) A cathode electrode slurry may be mixed by using 4% CMC or PAA, 6% SBR, 3% PVDF, 6% carbon black and 88% by weight of LFP or another metal oxide. Latex may be added to the solution in order to maintain the PVDF in a stable dispersion. The Li—NCO presented in this draft is prepared using PVDF as Binder and acetone as a solvent. Nevertheless, the Li—NCO electrodes can be prepared using: NMP, water, acetone, DMAC or other organic solvents.

(11) The above slurries have been coated on an anode current collector and onto a cathode count collector, respectively. The current collector can be made from any known material such as for example aluminium or copper and can be in form of a foil. The cathode and the anode produced in this way were inserted in an electrochemical cell, separated by a separator.

(12) Electrochemical cells produced in such a manner have been tested for their cycle life characteristics and for their discharge rate capability behaviour depending on the temperature.

(13) FIG. 1 shows cycle life characteristics for electrochemical cells containing Li—NCO cathodes and graphite anodes prepared with a water-based binder mixture. The slurry is prepared using PVDF as a binder and acetone as a solvent. The capacity retention in constant over at least two hundred charging and recharging cycles indicating a good cycle life of electrochemical cells based on water-based slurries.

(14) FIG. 2 shows a discharge rate capability behaviour of Li—NCO/graphite cells. The graphite electrodes were prepared with the water-based binder mixture of example 1. The results indicate that there are no differences in using water-based slurries compared to slurries based on organic solvents or other slurries. The use of the water-based slurries therefore allows to reduce or avoid the use of organic solvents in the slurries facilitating the manufacture of the slurries.

(15) It should be noted that organic solvent free slurries can be prepared. However, a certain concentration of organic solvents can be used in some applications of the present disclosure. The organic solvent is, however, not necessary for dissolving the binder material and the binder can be used in the aqueous solution.

(16) While the above description of a detailed example has been given for illustrative purposes only, other active electrode materials can be used with, CMC, SBR and PVDF as binder materials in an aqueous solution. A person skilled in the art will optimize the concentrations of CMC, SBR and PVDF depending on the active electrode material used and on the desired properties of the slurry.