Synthesis And Properties Of MnO_x Based Nanoelectrode Materials

As negative electrode material for secondary batteries,MnO_x has received extensive attention from researchers due to its high theoretical specific capacity(750+mAh g^-1),low operating voltage?<0.5 V?,abundant natural resources and non-toxicity.However,the poor conductivity and large volume expansion also limits its practical application.Therefore,the current research focus on the MnO_x-based nano-electrode materials lies in how to improve the limitations and improve the electrochemical performance.In order to improve the performance of MnO_x,the nano-grained and flaky MnO_x and MnO_x/C composites were prepared by co-precipitation,solid-phase,hydrothermal and ultrasonic method.At the same time,the effects of different process factors on the phase,morphology and electrochemical performance of the prepared product were studied.It also revealed its energy storage mechanism as a high-efficiency anode material for secondary batteries.The main conclusions are as follows:?1?The granular Mn₃O₄ was successfully prepared by low temperature co-precipitation method.The size of the Mn₃O₄ was about 100 nm and it had excellent electrochemical performance.However,it was limited by the poor conductivity of pure phase material.Therefore,Super P was introduced as the performance improvement agent.The nano-particulate Mn₃O₄/Super P composite was prepared by a simple one-step solid-phase method,and the chemical bond between Mn₃O₄ and Super P was successfully constructed to increase the reversibility of MnO to Mn₃O₄ conversion reaction.When the mass ratio of MnO₂ and Super P is 2:1,the heat treatment temperature is 500°C,and the heat treatment time is 5 h,the product has the best performance.The capacity can be reached 1340 mAh g^-1 after 100 cycles at a current density of 100 mA g^-1.?2?A two-step hydrothermal method and a heat treatment method are used to prepare a composite of carbon-coated manganese oxide and nitrogen-doped reduced graphene oxide,which can not only improve the conductivity of the oxide matrix,but also effectively relieve the volume expansion during charge-discharge process.It was explored that in the first step,the hydrothermal temperature was 120°C,added 1.2 g urea and half-coated state shows the best electrochemical performance.The discharge capacity can reached to 697.8 mAh g^-1 at the current density of 500 mA g^-1 after 120 cycles.The excellent performance is attribute to the special half-coated structure,its increases the adsorption capacity contribution of 42%and the conversion reaction capacity contribution of 48%.?3?The flaky MnO_x was prepared by ultrasonic method.The nanosheets prepared with 2 g SDS and ultrasonic for 6 h had the most complete structure and the most uniform thickness.However,due to the instability of the sheet structure,GO is introduced to stabilize its structure.As a negative electrode for lithium ion battery,the MnO_x/GO shows a capacity 905.1 mAh g^-1 after cycling70 cycles at a current density of 100 mA g^-1.For an anode of sodium ion battery,the specific capacity could reach to 102 mAh g^-1 at the current density of 1 A g^-1.