Study On Preparation And Electrochemical Performance Of Li₂ZnTi₃O₈ Anode Materials For Lithium Ion Battery

Lithium zinc titanate（Li₂ZnTi₃O₈） with high theoretical capacity, low discharge plateau voltage and environmental friendliness, has been studied widely as an anode material for lithium-ion batteries, which make it occupy significant advantage when applied to portable electronic devices and energy storage. However, the electronic conductivity of pristine Li₂ZnTi₃O₈ is very poor, which limits its high rate performance. Based on the available reports, we prepared Li2 Zn Ti3O8 though high-temperature solid-phase, molten salt and sol-gel method. In order to enhance the electronic conductivity and improve the high rate electrochemical performance, metal ions doping and surface coating have been chosen for modification. The information of structure, morphology, surface area, particle size of pure and modified Li2 Zn Ti3O8 have been characterized via XRD, SEM, TEM, N2 adsorption, particle size distribution and Raman spectroscopy. And the electrochemical performance of prepared samples has been investigated. In addition, chitosan oligosaccharides is firstly used in lithium-ion battery and is selected as binder for improving the electrochemical properties of Li₂ZnTi₃O₈. Besides, we have assembled a new full battery LiNi0.5Mn1.5O4||Li₂ZnTi₃O₈, and its charge-discharge capacity and cycling stability at different charge and discharge rates have been investigated. The experimental results are summarized as follows.（1） With TiO2, Zn（CH3COO）2·2H2O, and Li2CO3 as the raw materials, cubic spinel Li2 Zn Ti3O8 is prepared by high-energy ball milling assisted solid state method. Li2 Zn Ag0.15Ti2.85O8 and Li2ZnTi2.9Al0.1O8 composites are obtained after doping Ag+ and Al3+, which shows excellent electrochemical performance. Furthermore, coating a nano-layer amorphous carbon or LiCoO2 on the outer surface of Li₂ZnTi₃O₈ particles can enhance the electronic conductivity, resulting in the improved high-rate electrochemical performance.（2） Li₂ZnTi₃O₈ nano particles with excellent electrochemical performance were firstly synthesized by molten salt and optimized sol-gel method. For molten salt method, the Li₂ZnTi₃O₈ was synthesized from Li2CO3, TiO2, Zn（CH3COO）2·2H2O, and the optimal ratio of molten salt was KCl: NaCl = 1:1. At 1.0, 2.0, 3.0 A g-1, the discharge capacities of as-prepared samples are 158.9, 126.1, 57.2 mAh g-1 after 100 cycles, respectively, and exhibit good cycling stability. For sol-gel method, the Li₂ZnTi₃O₈ was synthesized using C16H36O4 Ti, Li2CO3 and Zn（CH3COO）2·2H2O as reactants and citric acid as a chelating agent. The obtained Li₂ZnTi₃O₈ grains present uniform particle size and no obviously agglomeration. In addition, more holes can be formed during the particle stacking, and this would contribute to the larger contact area between active material and electrolyte, which is beneficial for Li+ intercalated/deintercalated at high rates. The discharge capacities of Li₂ZnTi₃O₈ prepared by sol-gel method are 207.4 mAh g-1 and 188.9 mAh g-1 after 100 cycles at 1.0 A g-1and 2.0 A g-1, respectively.（3） Chitosan oligosaccharides（COS） as a water-based organic compound, is firstly applied as the electrode binder for Li₂ZnTi₃O₈ electrode in lithium-ion batteries. Compared with conventional polyvinylidene fluoride（PVDF） binder, the electrochemical performance is significantly improved when COS binder is used for Li2 Zn Ti3O8 electrodes. At 0.5 A g-1 and 1.0 A g-1, the discharge capacity of 199.3 mAh g-1and 93.7 mAh g-1 can be obtained after 100 cycles for Li₂ZnTi₃O₈ with COS binder system. Moreover, 66.1 mAh g-1 can be remained after 1000 cycles for COS binder system, while the PVDF binder system delivers only 37.9 mAh g-1. In addition, the cycling stability of Li₂ZnTi₃O₈ electrode has been improved after using COS as binder. The elevated electrochemical performances of Li₂ZnTi₃O₈ electrode with COS binder system can be ascribed to the characters of COS binder, which can form strong hydrogen binds with both active materials and copper current collector by numerous hydroxyl groups, preventing the pole pieces desquamation during Li+ intercalated/deintercalated. In addition, suppressing swelling of electrode with electrolyte solution is another advantage for improving the electrochemical performance.（4） A novel Li Ni0.5Mn1.5O4||Li2Zn Ti3O8 full battery is constructed. The battery system delivers the discharge capacities of 161.4, 140.2, 117.4 mAh g-1 after 50 cycles charged at 0.2, 0.5, 1.0 A g-1 and discharged at 2.0 A g-1, respectively, which displays good rate discharge performance, make it propitious for power batteries and large energy storage devices.