LiFePO₄ Cathod Using Foam-Type Three-Dimensional Current Collector And Its Matching Anode

Lithium iron phosphate battery is regarded as the most promising cathode material. Two-dimensional structure can not meet demands for high loading of LiFePO₄.Three-dimensional structure can provide greater contact area and reaction room which enhance the charge-discharge performance. lithium film as negative material faces poor security, poor cycle performance, and many other issues. Through study the matching anode for three-dimensional structure LiFePO₄ cathode, the charge-discharge performance and cycle performance can be increased.We focus on the electrode performance caursed by the charge step settings of three-dimensional structure LiFePO₄ and defined the constant charge current cut-off voltage 3.8V-non-constant charge system as the best settings. By studying the stability of nickel material in the electrolyte system [LiPF6/EC + DMC + EMC], the XPS test showed that the film generated on the surface had Ni³⁺ and Ni²⁺coexist. The surface may have oxygen species for the polymer, metal alcoholates, LiF, Ni2O3 and without LiPF₆ or PF5, Li₂O. When the charg voltage is above 3.8V, nickel seems to be instability. Electrodeposition of aluminum on nickel foam by the organic electrolyte is carried out . The Aluminum coating has poor adhesion. If it is rolled the aluminum coating may get off from the foam-Ni. Coating LiFePO₄ on the foam aluminum , the charge-discharge performance is not as good as coating LiFePO₄ on the foam Ni. The charge-discharge platforms are not flat. Charge platform is more than 3.6V and discharge platform is less than 3.2V.Different ratio of LiFePO₄ cathode component,different loading of LiFePO₄ and the thickness of the nickel foam are studied. The paste ratio of LiFePO₄: acetylene black: PVDF = 90:5:5 , loading LiFePO₄ at 230·g^-1 m-2 and compacted thickness to 900um are the best which get the battery capacity of 140mAh·g^-1.By openning the broken circulating battery, the main causes of battery failure from the anode lithium is determined. three types of three-dimensional structure negative: Fe3O4, MCMB and Li₄Ti₅O₁2 is studied. Fe3O4 has large capacity loss in the first cycle and its charge-discharge plateau voltage is not significant. So it can not be the matching negative in this paper. Nickel foam MCMB/LiFePO₄ has high charge-discharge platform but the cycle performance is poor. Li₄Ti₅O₁2/Li using foam nickel has charging platform at 1.60V and discharge platform at 1.52V. The first discharge capacity of up to 150 mAh·g^-1 and three-dimensional structure of Li₄Ti₅O₁2 has good rate performance. Li₄Ti₅O₁2/LiFePO₄ battery has charging platform at 1.93V and discharge platform at 1.80V. When the capacity reached 100mAh·g^-1 when the loading is 17.20mg and afer 100 cycles the capacity retention is up to 90% which ensure the three-dimensional structure of Li₄Ti₅O₁2 is expected to be the match negative.