| Lithium iron phosphate?LiFePO4?has been in an important position in lithium ion battery cathode materials due to its advantages such as good cycle performance,high theoretical specific capacity(170 mAh×g-1),and stable charging and discharging platform.At the same time,because the material itself is environmentally friendly,it is one of the earliest commercially available cathode materials.However,its low electrical conductivity(10-9 S×cm-1)and low ion diffusion rate(10-310-6 cm2×s-1)result in poor rate performance and low specific capacity.This not only directly affects the application of LiFePO4 in the huge energy market,but also limits its development in solid-state lithium-ion batteries.This paper describes the following researching on the above problems of LiFePO4.In this paper,the template material was added to hydrothermally prepare the LiFePO4 material with relatively uniform particle size and good crystallization.At current densities of 0.1 C,0.2 C,0.5 C,1 C,and 2 C,the experiments confirmed that the discharge capacity of the LiFePO4 material prepared by adding 5wt%polyvinylpyrrolidone?PVP?is 154 mAh×g-1,148 mAh×g-1,130 mAh×g-1,125 mAh×g-1,120 mAh×g-1.After 100 cycles,the coulomb efficiency can be stably maintained at 95%.In the absence of any material coating,the template is used to induce the synthesis of positive electrode materials with relatively stable electrochemical performance.Secondly,the advantages of graphene's high specific surface and high carrier mobility,and the combination of carbon materials can inhibit the growth of particles and improve the electrical conductivity of the material to a certain extent.The graphene-modified carbon-coated LiFePO4 material can be prepared with 2wt%graphene and a one-step synthesis method to prepare a material with high specific capacity and excellent rate performance.At a current density of 0.1 C,the discharge capacity of the material is167.4 mAh×g-1,which is almost close to the theoretical capacity of the material.At a current density of 10 C,the specific capacity of 90.8 mAh×g-1 can be stably exhibited.This method greatly simplifies the preparation process of the material,being cost-efficient and reliable for commercial applications.This method can also be used to prepare a positive electrode material with good activity,which is beneficial to the application of the material in solid batteries.Finally,by exploring the acid-modified Li7La3Zr2O12,a composite solid electrolyte with a high ion conductivity of 9.0×10-4S×cm-1 was prepared.The LiFePO4 solid battery obtained with the modified composite solid electrolyte has a capacity discharge of 163 mAh×g-1 at a current density of 0.2 C and a capacity retention rate of 90%after 200 cycles. |
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