Design of interfacial Li-ion transfer channels for practical improvement of a multicomponent high-voltage olivine cathode

The development of a high-voltage olivine cathode is of great interest to increase the energy density of Li-ion batteries. Focusing on the multicomponent LiFe0·4Mn0·3Co0·3PO4 (LFMCP) olivine material, in which the involvement of Co is necessary to extend the operating voltage range of the olivine materials up to 5.0 V despite having many critical issues, our research shows that the construction of Li-ion transfer channels on the particle surface is a key factor for the practical realization of the high-voltage cathode. A systematic electrochemical investigation reveals that the weakening and disappearance of the Mn activity due to the redox shift and overlap during cycling are responsible for the poor capacity delivery and capacity retention of the multicomponent LFMCP material. Surface coating of the LFMCP material with either carbon (LFMCP@C) or with a combination of carbon and LATP (LFMCP@C_LATP) helps to identify and stabilize the redox regions of the Fe, Mn, and Co components. The presence of LATP as a Li-ion conductor and an electrochemically active component on the LFMCP particle surface can induce the formation of the Li-ion concentration gradient between the core and the shell to facilitate the Li-ion diffusion during cycling. As a result, the LFMCP@C_LATP has faster Li-ion diffusion in all redox regions, more stable operating plateaus, and can therefore provide better capacity and retention than the conventional LFMCP@C. The LFMCP@C_LATP can provide a discharge capacity of 139.2 mA h g−1 with 80.5 % retention after 50 cycles, while the LFMCP@C provides a discharge capacity of 135.1 mA h g−1 with 68.4 % retention under the same cycling conditions, using a common electrolyte without the addition of any high-voltage additive.