Scientists at the University of Oxford have used smart processing protocols to produce a composite cathode with outstanding performance.

To balance the higher capacity of a metallic lithium anode (which would enable significant increases in energy density), a thick composite cathode is required. Maintaining intimate interfacial contact and electrochemical stability between the cathode material and solid electrolyte is essential. Lithium nickel manganese cobalt oxide (NMC) is a high-energy density class of cathode materials used in lithium-ion cells with liquid electrolytes. However, when used in all-solid-state cells, discharge capacities for polycrystalline NMC are often low and cells are cycled at impractical stack pressures. Rapid capacity loss is observed due to pulverisation and loss of contact with the solid electrolyte.

The research, published in ACS Applied Materials and Interfaces, shows that cold-pressed single crystal NMC composites could deliver discharge capacities >205 mA h g-1 even when cycled at a stack pressure approximately 1 MPa or less. Key to the performance was the optimised fabrication route, and careful matching of NMC and SE powder sizes and fractions. Single crystal NMC was also shown to be more robust and less likely to crack during processing and cycling. A near-practical discharge capacity at a high areal capacity of 8.7 mA h cm−2 was obtained using a low and asymmetric anode/cathode cycling pressure of only 2.5 MPa/0.2 MPa.

Image: Scanning electron micrograph of LiNbO3-coated single crystal-NMC particles

Case study published December 2022.