Prepared And Study Of Lithium-and Manganese-rich Cathode Materials For Lithium Ion Batteries

Lithium rich materials are attractive cathode materials in lithium-ion batteries (LIBs)due to their advantageous physical properties which provide high operational voltage, hightheoretical capacity (>250mAh g-1) and good thermal stability. Unfortunately, lithium richmaterials have high irreversible capacity in initial charge/discharge progress, and theirintrinsically poor electronic conductivity and low lithium-ion diffusion which are kineticbarriers for achieving high-rate capability, furthermore, their structural transformationduring the cycles leading to the reduction of its power density, which greatly limiting theirpractical applications. Therefore, many attempts have been made to solve these problems,successful enhancement has been achieved through modification of techniques within thesynthesis routes such as the solid reaction process, co-precipitation, microwave heating,hydrothermal process, sol-gel preparation, molten salt process and ion-exchange reaction.On this basis, we further study the synthesis of the lithium rich materials by ion-exchangereaction. The main contents are as follow:1、Using Li2MnO3and NaxMnO2as the ion-exchange precursors, to react with thetransition metal ions. Then the obtained products were dried and heated with lithiumresource to synthesize the lithium rich cathode materials. Among these transition metalions (Ni, Fe, Co etc.), only Ni exchanged materials exhibited a good performance:(1)Using Li2MnO3as precursors. As the rise of temperature, the activity of ion-exchangereaction increased. When the temperature rose to100℃, the reaction came to balance. Theobtained lithium rich materials synthesized in this condition could deliver a dischargecapacity of241mAh g-1.(2) Using NaxMnO2as precursors. As the rise of the melting pointof lithium resources to synthesize lithium rich materials, the electrochemical performanceof the electrodes decreased. The materials synthesized from LiNO3showed the highestinitial charge/discharge capacity (charge:290.8mAh g-1, discharge:228.7mAh g-1) and thebest rate performance (110.8mAh g-1at5C). The materials synthesized from Li2CO3 delivered the lowest initial charge/discharge capacity (charge:252.1mAh g-1, discharge:191.4mAh g-1) and the worst rate performance (97.6mAh g-1at5C). Furthermore, thematerials synthesized in different conditions showed different performance, the materialssynthesized by molten-salt method exhibited the best performance.2、Introducing ball-milling progress to improve the electrochemical performance ofLi1.2Ni0.2Mn0.6O2synthesized from NaxMnO2. Three processes were employed, including(1) ion-exchange, simply mechanical mixing, calcination (Without-BM),(2) ion-exchange,ball milling, calcination (EX-priority),(3) ball milling, ion-exchange, calcination(BM-priority). The three as-prepared sample types exhibited different performancecharacteristics, depending on their respective preparation processes. The “Without-BM”sample exhibited a reversible capacity of240mA h g-1between2.0V and4.8V with acurrent density of0.1C (30mA g-1), having almost no capacity fading after80cycles. The“EX-priority” sample exhibited a desirable rate performance with a reversible capacity of213.4mAh g-1at1C and136.4mA h g-1at7C; however, the capacity retention was88.3%after80cycles at0.1C. The “BM-priority” sample displayed a moderate rate and cycleperformance. The differences between these samples demonstrated that the ball millingtreatment and its sequence have substantial effects on performance of materials. Theexperimental data indicated that the different performances can be attributed to thedifferent morphologies of the respective materials as well as the effect of sodium ionconcentration within the structure. Therefore, controlling the morphology of the materialand the amount of sodium ions in its structure may be advantageous for developing highquality cathode materials which can be diversified for specific applications in Li-ionbatteries.