COMPOSITE MATERIAL

Abstract

A composite material for use as an electrode of an electrochemical cell comprises: a matrix that is provided by matrix particles that comprise an electrode active material; and a conductive fraction that is both electronically-conductive and ionically-conductive, the conductive fraction being provided by conductive particles that are distributed among the matrix particles. The conductive particles comprise either a material that is both ionically- and electronically-conductive; or a mixture of ionically-conductive particles and electronically-conductive particles, the electronically-conductive particles having a sphericity of at least 0.6. The conductive particles have a D90 value that is at least 10% of the D50 value of the matrix particles.

Claims

1. A composite material comprising: a matrix that is provided by matrix particles that comprise an electrode active material; and a conductive fraction that is both electronically-conductive and ionically-conductive, the conductive fraction being provided by conductive particles that are distributed among the matrix particles, the conductive particles comprising either: a material that is both ionically- and electronically-conductive; or a mixture of ionically-conductive particles and electronically-conductive particles, the electronically-conductive particles having a sphericity of at least 0.6; wherein the conductive particles have a D90 value that is at least 5% of the D50 value of the matrix particles.

2. A composite material according to claim 1, wherein the conductive particles are present in an amount of at least 10 vol %, preferably at least 15 vol %, more preferably at least 20 vol %.

3. A composite material according to claim 1, wherein the conductive particles are present in an amount of up to 35 vol %, preferably up to 30 vol %, more preferably up to 28 vol %.

4. A composite material according to claim 1, wherein the conductive particles have a D90 value that is at least 10% of the D50 value of the matrix particles.

5. A composite material according to claim 1, wherein the conductive particles have a D90 value that is at least 15% of the D50 value of the matrix particles, preferably at least 20%.

6. A composite material according to claim 1, wherein the conductive particles have a D90 value of at least 50 nm, preferably at least 100 nm, more preferably at least 200 nm.

7. A composite material comprising a matrix that is provided by matrix particles that comprise an electrode active material; an ionically-conductive fraction that is provided by ionically-conductive particles that are distributed among the matrix particles; and an electronically-conductive fraction that is distributed among the matrix particles; wherein the ionically-conductive particles have a D90 value that is at least 5% of the D50 value of the matrix particles.

8. A composite material according to claim 7, wherein the ionically-conductive particles have a D90 value that is at least 10% of the D50 value of the matrix particles, preferably 15%, more preferably 20%.

9. A composite material according to claim 7, wherein the electronically-conductive fraction is provided in the form of filaments or needles.

10. A composite material according to claim 7, wherein the electronically-conductive fraction is provided in the form of particles having a sphericity of at least 0.6, wherein the D50 value of the particles of the electronically-conductive phase is less than 25% of the D50 value of the particles of the ionically-conductive phase.

11. A composite material according to claim 7, wherein the ionically-conductive particles are present in a volume fraction of at least 10 vol % of the composite material.

12. A composite material according to claim 7, wherein the ionically-conductive particles are present in a volume fraction of up to 28 vol % of the composite material.

13. A composite material comprising a matrix that is provided by matrix particles that comprise an electrode active material; an ionically-conductive fraction that is provided by ionically-conductive particles that are distributed among the matrix particles; and an electronically-conductive fraction that is provided by electronically-conductive particles that are distributed among the matrix particles; wherein the electronically-conductive particles have a D90 value that is at least 5% of the D50 value of the matrix particles, preferably at least 10%.

14. A composite material according to claim 1, wherein the matrix particles have a D50 value of at least 0.1 μm, preferably at least 0.2 μm, at least 0.5 μm.

15. A composite material according to claim 1, wherein the particle size distribution of the matrix particles is such that the D90 value for the matrix particles is at least 1.5 times the D50 value, preferably at least 1.7 times the D50 value.

16. A composite material according to claim 1, wherein the composite material has a planar configuration having a thickness of at least 300 μm, preferably at least 400 μm, more preferably at least 500 μm.

17. An electrode comprising a composite material according to claim 1.

18. An electrochemical cell comprising two electrodes and a bulk electrolyte disposed therebetween, wherein at least one electrode comprises a composite material according to claim 1.

19. A method of making a composite material, the method comprising the steps of: providing a quantity of matrix particles, the matrix particles comprising an electrode active material; providing a quantity of conductive particles, the conductive particles comprising either: a material that is both ionically- and electronically-conductive; or a mixture of ionically-conductive particles and electronically-conductive particles, the electronically-conductive particles having a sphericity of at least 0.6; preparing an ink formulation comprising the matrix particles, the conductive particles, and a fluid carrier medium; and depositing the ink formulation on a substrate to provide a printed layer; wherein the conductive particles have a D90 value that is at least 5% of the D50 value of the matrix particles.

20. A method according to claim 19, wherein the conductive particles are present in an amount of at least 10 vol % relative to the solids content of the ink formulation, preferably at least 15 vol %, more preferably at least 20 vol %.

21. A method according to claim 19, wherein the conductive particles are present in an amount of up to 35 vol % relative to the solids content of the ink formulation, preferably up to 30 vol %, more preferably up to 28 vol %.

22. A method according to claim 19, wherein the conductive particles have a D90 value that is at least 10% of the D50 value of the matrix particles.

23. A method according to claim 19, wherein the conductive particles have a D90 value that is at least 15% of the D50 value of the matrix particles, preferably at least 20%.

24. A method according to claim 19, wherein the conductive particles have a D90 value of at least 50 nm, preferably at least 100 nm, more preferably at least 200 nm.

25. A method of making a composite material, the method comprising the steps of: providing a quantity of ionically-conductive particles, an amount of an electronically-conductive phase and a quantity of matrix particles, the matrix particles comprising an electrode active material; preparing an ink formulation comprising the matrix particles, the ionically-conductive particles, the electronically-conductive phase, and a fluid carrier medium; and depositing the ink formulation on a substrate to provide a printed layer; wherein the ionically-conductive particles have a D90 value that is at least 5% of the D50 value of the matrix particles.

26. A method according to claim 25, wherein the electronically-conductive phase comprises filaments or needles.

27. A method of making a composite material, the method comprising the steps of: providing a quantity of ionically-conductive particles, a quantity of electronically-conductive particles and a quantity of matrix particles, the matrix particles comprising an electrode active material; preparing an ink formulation comprising the matrix particles, the ionically-conductive particles, the electronically-conductive particles, and a fluid carrier medium; and depositing the ink formulation on a substrate to provide a printed layer; wherein the ionically-conductive particles have a D90 value that is at least 5% of the D50 value of the matrix particles.

28. A method according to claim 27, wherein the D50 value of the electronically-conductive particles is less than 25% of the D50 value of the ionically-conductive particles.

29. A method according to claim 25, wherein the ionically-conductive particles are present in an amount of at least 10 vol % relative to the solids content of the ink formulation, preferably at least 15 vol %, more preferably at least 20 vol %.

30. A method according to claim 25, wherein the ionically-conductive particles are present in an amount of up to 35 vol % relative to the solids content of the ink formulation, preferably up to 30 vol %, more preferably up to 28 vol %.

31. A method according to claim 25, wherein the ionically-conductive particles have a D90 value that is at least 10% of the D50 value of the matrix particles.

32. A method according to claim 25, wherein the ionically-conductive particles have a D90 value that is at least 15% of the D50 value of the matrix particles, preferably at least 20%.

33. A method according to claim 25, wherein the ionically-conductive particles have a D90 value of at least 50 nm, preferably at least 100 nm, more preferably at least 200 nm.

34. A method according to claim 19, wherein the matrix particles have a D50 value of at least 0.1 μm, preferably at least 0.2 μm, at least 0.5 μm.

35. A method of making a composite material, the method comprising the steps of: providing a quantity of ionically-conductive particles, a quantity of electronically-conductive particles and a quantity of matrix particles, the matrix particles comprising an electrode active material; preparing an ink formulation comprising the matrix particles, the ionically-conductive particles, the electronically-conductive particles, and a fluid carrier medium; and depositing the ink formulation on a substrate to provide a printed layer; wherein the electronically-conductive particles have a D90 value that is at least 5% of the D50 value of the matrix particles.

36. A method according to claim 35, wherein the D50 value of the particles of the ionically-conductive phase is less than 25% of the D50 value of the particles of the electronically-conductive phase.

37. A method according to claim 19, further comprising one or more of the following steps: reduction of the amount of organic compounds present in the printed layer, e.g. by drying; mechanical pressing of the printed layer; or sintering of the printed layer.

38. A method according to claim 19, further comprising the step of incorporating the composite material into an electrode.

39. A method according to claim 38, further comprising the step of incorporating the electrode into an electrochemical cell.

40. A method according to claim 39, wherein the electrochemical cell is an all solid-state electrochemical cell.

Description

DETAILED DESCRIPTION

[0201] The invention will now be described by way of example only with reference to the following Figures in which:

[0202] FIG. 1 is a graph of the electrical AC response used to determine the impedance of a composite material according to an embodiment of the second aspect of the invention;

[0203] FIG. 2 is a graph of the electrical AC response used to determine the impedance of a composite material according to a comparative example of the invention.

EXAMPLE 1

[0204] A composite material was prepared for use a cathode.

[0205] As a first step, an ink was prepared containing the solid phases listed in Table 1.

TABLE-US-00001 TABLE 1 Volume fraction of total solids Phase content (%) D50 D90 Electrode active material: 64 1 μm 3 μm LiNi.sub.xCo.sub.yMn.sub.zO.sub.2 Ionically-conductive material: 13 100 nm 512 nm Li.sub.7La.sub.3Zr.sub.1.4Ta.sub.0.6O.sub.12 Electronically-conductive 13 material: indium tin oxide Binder: lithium borate 7 N/A N/A Compositing agent 3 N/A N/A

[0206] The ink further contained binders, dispersants and solvents, as is known in the art. The solids content of the ink was 50 wt %±10%.

[0207] The composite material was printed onto a support using a screen-printing process, followed by the steps of: [0208] drying at a temperature below 150° C. to remove solvent from the ink; [0209] debinding using thermal or catalytic processes to remove heavy organic components; [0210] mechanical pressing; and [0211] sintering.

EXAMPLE 2

[0212] A further composite material was prepared for use a cathode.

[0213] The proportions and particle sizes of the electrode active, ionically-conductive and electronically-conductive components of the cathode are set out in Table 2.

[0214] The impedance of the composite material was measured using an Impedance Analyser. The impedance was measured using an AC excitation signal with an amplitude of 10 mV across a frequency range of 1 MHz to, for example, 0.1 Hz. The response at each frequency was determined using a five second integration time. Seven frequencies were measured per decade with logarithmic spacing between the upper and lower frequency limits.

[0215] The impedance results are presented in the Nyquist diagram shown in FIG. 1. In this diagram, Z″ (the imaginary part of the complex impedance) is plotted against Z′ (the real part of the complex impedance). The diagram has two portions: a first arc-shaped portion adjacent the origin of the graph and a second arc-shaped portion at higher values of Z′.

[0216] The diameter of the first arc-shaped portion is a function of the impedance of the ionic charge transfer within the composite material, while the diameter of the second arc-shaped portion is a function of the impedance of the electronic charge transfer within the composite material. The clearly-defined shapes of the two portions of the plot indicate that electronically- and ionically-conductive networks have been established within the composite material, which therefore has a finite ionic and electronic impedance and is suitable for use as an electrode.

TABLE-US-00002 TABLE 2 Mass fraction based on Volume fraction based on total content of electrode total content of electrode active, ionically-conductive active, ionically-conductive and electronically-conductive and electronically-conductive Phase materials (%) materials (%) D50 D90 Electrode active material: 70 87 11.9 μm 21.9 μm LiNiCoMnO.sub.2 Ionically-conductive material: 7.5 3.9 1 μm   5 μm Li.sub.6.4La.sub.3Zr.sub.1.4Ta.sub.0.6O.sub.12 Electronically-conductive 22.5 9.1 0.1 μm N/A material: indium tin oxide

COMPARATIVE EXAMPLE 3

[0217] Composite materials were prepared containing particles of an electrode active material (LiNiCoMnO.sub.2) and an ionically-conductive material (LICGC™ electrolyte from Ohara Inc).

[0218] The particle sizes of the two materials are set out in Table 3.

[0219] Three samples were prepared containing 16 vol %, 26 vol % and 50 vol % LICGC™ respectively. A further sample was prepared containing no LICGC™.

[0220] Impedance measurements were carried out on all the samples, using the method described in relation to Example 2, and the results are shown in FIG. 2. These show that as the content of ionically-conductive material increases from 0 vol % to 16 vol %, the impedance decreases as an ionically-conductive network starts to be formed through the composite material. An increase in the content of ionically-conductive material from 16 vol % to 26 vol % results in further development of the ionically-conductive network and a corresponding further decrease in impedance.

[0221] However, no further decrease in impedance occurs when the content of ionically-conductive material increases from 26 vol % to 50 vol %, demonstrating that when the ionically-conductive material is present in an amount of 26 vol %, a fully-formed conductive network is present and there is no benefit to increasing the content of ionically-conductive material any further.

TABLE-US-00003 TABLE 3 Material D50 D90 Electrode active material: 11.9 μm 21.9 μm LiNiCoMnO.sub.2 Ionically-conductive material  0.3 μm  0.9 μm (LICGC ™)