DISPERSION AND COATING COMPOSITION CONTAINING LITHIUM METAL PHOSPHATE

Abstract

A dispersion may include 1 to 50% by weight of lithium metal phosphate of a general formula

Li.sub.1+aM.sub.2−bN.sub.c(PO.sub.4).sub.3+d,

wherein M is Ti, Zr or Hf; N is a metal other than Li and M; 0≤a≤0.6, 0≤b≤0.6, 0≤c≤0.6, 0≤d≤0.8; and 50 to 99% by weight of trialkyl phosphate. A coating composition may include such a dispersion and such dispersions can be used in lithium ion batteries.

Claims

1. A dispersion, comprising: 50 to 99 wt. of trialkyl phosphate; and 1 to 50 wt % of lithium metal phosphate of formula
Li.sub.1+aM.sub.2−bN.sub.c(PO.sub.4).sub.3+d, wherein M is Ti, Zr, or Hf, N is metal other than Li and M, 0≤a≤0.6, 0≤b≤0.6, 0≤c≤0.6, 0≤d≤0.8.

2. The dispersion of claim 1, wherein the lithium metal phosphate is in the form of aggregated primary particles.

3. The dispersion of claim 1, wherein the lithium metal phosphate is obtained by a pyrogenic process.

4. The dispersion of claim 1, wherein the lithium metal phosphate has a BET surface area in a range of from 5 to 100 m.sup.2/g.

5. The dispersion of claim 1, wherein the lithium metal phosphate has a particle size d.sub.99 of less than 1 μm, as determined by dynamic light scattering (DLS) at a temperature of 25° C. in a diluted form of the dispersion, with trialkyl phosphate, comprising 1 wt. % of the lithium metal phosphate.

6. The dispersion of claim 1, wherein the lithium metal phosphate has a tamped density in a range of from 20 to 200 g/L.

7. The dispersion of claim 1, wherein the trialkyl phosphate comprises trimethyl phosphate, triethyl phosphate, tri-n-propyl phosphate, triisopropyl phosphate, methyl diethyl phosphate, for a mixture thereof.

8. A process for manufacturing the dispersion of claim 1, the process comprising: mixing the lithium metal phosphate and the trialkyl phosphate, to obtain a resulting dispersion; and optionally grounding or milling the resulting dispersion.

9. The process of claim 8, wherein grounding or milling is carried out by an ultrasound treatment, or with a wet-jet mill, or a ball mill.

10. A wet coating composition, comprising: the dispersion of claim 1; an organic binder; and optionally, a solvent.

11. The composition of claim 10, comprising: 50 to 99 wt. % of the dispersion; 1 to 50 wt. % of the organic binder; and optionally, 1 to 50 wt. % of a solvent.

12. The composition of claim 10, wherein the organic binder comprises polyethylene oxide, polyvinylidene fluoride, polyvinylidene chloride, polytetrafluoroethylene, polyacrylonitrile, polyamide, polyimide, polyether ether ketone, polymethyl methacrylate, polytetraethylene glycol diacrylate, polyvinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride/chlorotrifluoroethylene copolymer, polysulfone, polyether sulfone, or a mixture of two or more of any of these.

13. A dry coating composition, obtained by evaporation of trialkyl phosphate and any solvents present from the wet composition of claim 10.

14. A process for an coating electrode or separator of a lithium ion battery, the process comprising: contacting the wet coating composition according to claim 10 or a dry coating composition, obtained by evaporation of trialkyl phosphate and any solvents present from the wet composition, with the electrode or separator of the lithium ion battery.

15. A lithium ion battery, comprising: the dry coating composition of claim 13.

16. The dispersion of claim 1, wherein the trialkyl phosphate comprises trimethyl phosphate.

17. The dispersion of claim 1, wherein the trialkyl phosphate comprises triisopropyl phosphate.

18. The dispersion of claim 1, wherein the trialkyl phosphate comprises methyl diethyl phosphate.

Description

EXAMPLES

Example 1: Preparation of Lithium Zirconium Phosphate

[0120] 23.75 Kilogram of a solution containing 3370 g of a commercial solution (Borchers® Deca Lithium 2), containing 2 wt % lithium in the form of lithium neodecanoate dissolved in naphtha, 15 kg of a commercial solution (Octa Solingen® Zirconium 12), containing 11.86 wt % Zr in the form of zirconium ethyl hexanoate dissolved in white spirit and 5384 g of a commercial solution (Alfa Aesar), containing 16.83 wt % phosphorous in the form of triethyl phosphate were mixed, resulting in a clear solution. This solution corresponding to a composition of LiZr.sub.2(PO.sub.4).sub.3.

[0121] An aerosol of 1.5 kg/h of this dispersion and 15 Nm.sup.3/h of air was formed via a two-component nozzle and sprayed into a tubular reaction with a burning flame. The burning gases of the flame consisted of 8.5 Nm.sup.3/h of hydrogen and 30 Nm.sup.3/h of air. Additionally, 25 Nm.sup.3/h of secondary air was used. After the reactor the reaction gases were cooled down and filtered.

[0122] The obtained lithium zirconium phosphate powder had a BET surface area of 44 m.sup.2/g, tamped density of 52 g/L and a d.sub.50 value of 76 nm, as determined by static light scattering method. XRD analysis showed, that the major phase of the product was the rhombohedral lithium zirconium phosphate.

[0123] Measuring of Dynamic Viscosity

[0124] The dynamic viscosity of the dispersions was measured with the Physica MCR 301 from Anton Paar using the rotational viscosity method and a measuring plate PP25 with the distance set to 0.5 mm.

[0125] The motor of the viscometer drives a bob inside a fixed cup. The rotational speed of the bob is preset and produces a certain motor torque that is needed to rotate the measuring bob. This torque must overcome the viscous forces of the tested substance and is therefore a measure for its viscosity. Data are measured at a shear rate of 10 s.sup.−1 and 22° C.

Example 2: Preparation of an LZP Dispersion

[0126] Lithium zirconium phosphate (LZP, 6 g) prepared in example 1 was added to triethyl phosphate (TEP, 14 g) while treating the mixture with ultrasound generated by ultrasound processor UP400S, 400 Watt, 24 kHz equipped with a Ti-sonotrode for 30 minutes. Particle size distribution was measured after dilution with TEP to obtain about 1 wt % LZP concentration using dynamic light scattering (DLS) method by means of LB-500 device (Horiba Ltd., Japan).

[0127] D.sub.50, d.sub.90 and d.sub.99 values obtained by DLS method directly after preparation of the dispersion as well as d.sub.99 values after 1 week and 4 weeks of storage of the dispersion at room temperature and the dynamic viscosity of the dispersion measured at 10 s.sup.−1 and 22° C. after production are shown in Table 1.

Example 3: Preparation of an LZP Dispersion

[0128] The ball mill equipment (Netzsch Laboratory Mill Micro Series) was pre-loaded with triethylphosphate (TEP, 315 g), the peristaltic pump was set to a rotation speed of 90 rpm and the ball mill to 1000 rpm. Lithium zirconium phosphate (LZP, 135 g) was added to TEP. The peristaltic pump was then adjusted to rotation speed of 120 rpm and the ball mill was set to a rotation speed of 2500 rpm. The dispersion was treated for 120 minutes (0.4 kWh energy was introduced). The particle size distribution was measured as in example 2. D.sub.50, d.sub.90 and d.sub.99 values obtained by DLS method directly after preparation of the dispersion as well as d.sub.99 values after 1 week and 4 weeks of storage of the dispersion at room temperature and the dynamic viscosity of the dispersion measured at 10 s.sup.−1 and 22° C. after production are shown in Table 1.

Comparative Example 1

[0129] A 30 wt % dispersion of LZP in ethanol (EtOH) was prepared identically to example 2 with the only difference that EtOH was used instead of TEP.

[0130] D.sub.50, d.sub.90 and d.sub.99 values obtained by DLS method directly after preparation of the dispersion as well as d.sub.99 values after 1 week and 4 weeks of storage of the dispersion at room temperature and the dynamic viscosity of the dispersion measured at 10 s.sup.−1 and 22° C. after production are shown in Table 1.

Comparative Example 2

[0131] A 30 wt % dispersion of LZP in iso-propanol (iPrOH) was intended to be prepared identically to example 2 with the only difference that iPrOH was used instead of TEP.

[0132] However, the dispersion became very viscous during the preparation, no particle size distribution or viscosity measurement was possible.

Comparative Example 3

[0133] A 30 wt % dispersion of LZP in dimethoxyethane (DME) was intended to be prepared identically to example 2 with the only difference that DME was used instead of TEP.

[0134] However, the dispersion became very viscous during the preparation, no particle size distribution or viscosity measurement was possible.

[0135] Comparison of examples 2-3 with comparative examples 1-3 shows that with TEP as a solvent, LZP dispersions with a considerably lower d.sub.99 particle sizes (Table 1), i.e. those substantially free of large particles >1 μm, can be obtained. Importantly, such dispersions with TEP solvent possess low viscosities and remain stable without any agglomeration of the particles after 1 and 4 weeks of storage at room temperature, conversely to the dispersion from comparative example 1 with EtOH as a solvent (Table 1).

Example 4: Preparation of a Coating Composition

[0136] Slurry A: The 30 wt % dispersion of LZP in TEP prepared in example 3 was diluted with TEP to a solid content of 20 wt. % LZP under stirring.

[0137] Slurry B: Poly(vinylidene fluoride-co-hexafluoropropylene, PVDF-HFP) organic binder with a MW of 400.000 g/mol from Sigma Aldrich, Germany was completely solved in TEP under stirring overnight at 35° C. to form a 10 wt. % solution PVDF-HFP in TEP.

[0138] Slurries A and B were mixed together to achieve the final LZP-to-binder ratio LZP:PVDF of 6:1 (The resulting coating composition was composed of 75 wt % of the dispersion of example 3, slurry A and 25% of slurry B and contained 15 wt % LZP, 2.5 wt % PVDF-HFP and 82.5 wt % TEP).

Example 5: Coating of a Copper Foil with the Coating Composition of Example 4

[0139] 5 ml of the coating composition obtained in example 4 was placed into the doctor blade device (Doctor blade: Quadruple Film Applicator, Model 360 from Erichsen, Germany with a slit of 50 μm). The coating speed was set to 0.4 m/min and the coating of a copper foil with a thickness of 18 μm (Hohsen, Japan) was started. A stable and homogenous wet film with a thickness of approx. 50 μm could be obtained on the surface of the copper foil.

[0140] This wet coating was dried at 100° C. for 2 h to obtain an LZP dry coating layer with a thickness of 5 μm. The adhesion of this layer to the copper foil was excellent.

TABLE-US-00001 TABLE 1 Dispersions of lithium zirconium phosphate in various solvents d.sub.99 d.sub.99 viscosity zirconium d.sub.50 d.sub.90 d.sub.99 (1 week) (4 weeks) (10 s.sup.−1), compound Solvent [nm] [nm] [nm] [nm] [nm] mPas Comparative LZP EtOH 132 241 1985  4918  4616  65 Example 1 Comparative LZP iPrOH — — — — — — Example 2.sup.(1) Comparative LZP DME — — — — — — Example 3.sup.(2) Example 1 LZP TEP 150 253 409 391 366  8 Example 2 LZP TEP 135 211 290 317 308 10 .sup.(1), .sup.(2)dispersion became very viscous during preparation, no particle size or viscosity were measured