Xu Zhang,Jinhua Wu,Shuqian Li,Yi Li,Xiaojie Li,Zhe Zhu,Jianlong Li
The vanadium-containing phosphate polyanion LiVPO 4 F has been attractive as a novel 4 V cathode for lithium-ion batteries. Herein, a hybrid cathode containing two active components of LiVPO 4 F and Li 3 V 2 (PO 4 ) 3 was successfully obtained by single-step solid-state reaction. The crystalline grains are coated by an amorphous carbon layer of about 8 nm thick. The composite presents reversible capacities of 102.8 and 98.2 mAh g −1 at the rates of 10C and 20C, respectively. Even at an ultrahigh rate of 100C (14.5 A g −1 ), it remains a discharge capacity of 70.1 mAh g −1 with a high average working potential of 3.5 V. After cycled 500 times at 10C, the obtained sample shows a capacity retention of 78.6%, implying outstanding cycling performance. The electrochemical impendence spectroscopy demonstrates that the hybrid cathode delivers higher lithium-ion diffusion coefficient . It is believed that the electrochemical performance is enhanced synergistically by the in-situ generated ionic conductor of Li 3 V 2 (PO 4 ) 3 . Finally, when charged and discharged at around 4.1 V, the intermediate phase of Li x VPO 4 F is clearly revealed by CV tests, which likely derives from a symmetry phase transform mechanism.
Nowadays, electrolytes for commercial batteries are mostly liquid solutions composed of solvent and salt to migrate the ions. However, solvents of the electrolyte bring several inherent limitations, either the electrochemical window, working temperature, volatility or flammability. Herein, we report polyphosphoric acid as a solvent-free protic liquid electrolyte, which excludes the demerits of solvent and exhibits unprecedented superiorities, including nonflammability, wider electrochemical stability window (>2.5 V) than aqueous electrolyte, low volatility and wide working temperature range (>400 °C). The proton conductive electrolyte enables MoO 3 /LiVPO 4 F rocking-chair battery to operate well in a wide temperature range from 0 °C to 250 °C and deliver a high power density of 4975 W kg −1 at a high temperature of 100 °C. The solvent-free electrolyte could provide a viable route for the stable and safe batteries working under harsh conditions, opening up a route towards designing wide-temperature electrolytes.
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