and exhibited the best cycling performance for a KIB cathode material to date. A combination of electrochemical profiles, ex situ X-ray diffraction, and first-principles calculations was used to understand the overall potassium storage mechanism of P3-K 0.69 CrO 2 . Based on a reversible phase transition, P3-K 0.69 CrO 2 delivers a high discharge capacity of 100 mA h g À1 and exhibits extremely high cycling stability with B65% retention over 1000 cycles at a 1C rate. Moreover, the K-ion hopping into the P3-K 0.69 CrO 2 structure was extremely rapid, resulting in great power capability of up to a 10C rate with a capacity retention of B65% (vs. the capacity at 0.1C).

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C/NVMP allowed high electrochemical performance supported by the replace V by the Mn promoted the easier electron transfer through lower band gap energy than Mn-free NVP and carbon coating increase the electric conductivity up to 2 × 10−3 s cm−1, which led to superior electrode performance.

Novel Nb5+-doped titanium phosphate is developed and used as both the cathode and anode to realize superior sodium-ion storage.

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