Cobalt-free copper-substituted Na(Ti,Mn,Ni,Cu)O₂ layered oxide cathode materials for Na-ion batteries

This work presents the results of an investigation of the structural, transport (electronic and ionic components of electrical conductivity, chemical diffusion coefficients of sodium) and electrochemical properties of P2-Na0.67Ti0.67Ni0.33-yCuyO2 (y = 0, 0.1) and P2-Na0.67Ti0.33Mn0.33Ni0.33-yCuyO2 (y = 0, 0.1, 0.2) cathode materials. Both families of compounds possess structural and electronic transport properties that change significantly upon copper substitution. Substitution with 0.1 mol of copper makes it possible to increase the electronic component of conductivity by more than one order of magnitude. A correlation between transport properties and electrochemical performance is demonstrated. The most desirable electrochemical behaviour was observed for the copper-substituted Na0.67Ti0.67Ni0.23Cu0.1O2 and Na0.67Ti0.33Mn0.33Ti0.33Ni0.23Cu0.1O2 cathode materials. The initial capacity of the former was 98 mAh g(-1) with 96% capacity retention after 60 cycles with varying current rate, while the latter was characterized by 96 mAh g(-1) with 99% capacity retention.