High-throughput study examining the wide benefit of Li substitution in oxide cathodes for Na-ion batteries

The stability of Na-ion cathodes is crucial for the widespread adoption of these sustainable battery technologies. Air stability, a critical factor, impacts the synthesis, storage, electrochemical performance, and safety of cathode materials from laboratory research through to commercial manufacturing. Poor air stability of these cathodes leads to disastrous electrochemical performance. Despite significant advancement in understanding air stability of these materials, a comprehensive strategy to universally enhance the air stability of layered oxides remains undeveloped. Here, we use high-throughput methods to systematically study the impact of substituting Li into 24 different sodium layered oxides. The compositions include all of the currently studied structures such as P2, P3 and O3. From a structural point of view, this substitution is quite facile and generally Li integrates smoothly into the structures. Remarkably, lithium strongly enhances air stability across all 24 compositions as determined from the large set of 96 XRD patterns. The improvement in air stability is thus established as a universal benefit of lithium substitution. While a number of Li-doped samples show lower capacities than in their undoped counterparts, two Li-doped samples demonstrate both improved electrochemical performance and complete air stability under harsh aging conditions.