Study On Preparation And Electrochemical Performance Of Modified Li₄Ti₅O₁₂ Via A Co-precipitation Method

Spinel structure of lithium titanate(Li4Ti5O12) is called as a "zero strain" insertion lithium material, in the process of charging and discharging, material structure keeps stability, and exhibits better cycle performance. But its low electronic and ionic conductivity are the main factors causing the low capacity at high current rates.Different methods have been applied to enhance the electronic and ionic conductivity of Li4Ti5O12 material, such as surface coating with a conductive metal oxides, or doping with metal ions, obtained the composites with high rate capacity.1. Li4-x/3Ti5-2x/3Crx O12 hierarchical microspheres have been synthesized by a simple one-pot co-precipitation method. The result shows that Cr3+ can enhance the electronic and ionic conductivity of Li4Ti5O12. X=0.46, the Li3.85Ti4.70Cr0.46O12 electrode shows the higher initial discharge capacity of 163 m Ah g-1, a higher discharge capacity of 152.9 m Ah g-1 can be obtained after 200 cycles at 10 C, while the Li4Ti5O12 delivers the initial discharge capacity of 119 m Ah g-1, a discharge capacity of 107 m Ah g-1 can be kept after 200 cycles. In addition, the electrode exhibits high rate discharge capacity of 172 m Ah g-1 at 5 C than Li4Ti5O12 of 137 m Ah g-1.2. Li4Ti5-x Tbx O12-δ(0≤x≤0.1) composites have been synthesized via a co-precipitation method. After the XRD、XPS and electrochemical performance tests,the results show that Tb3+ is successfully doped into the Li4Ti5O12 structure. X=0.06,the Li4Ti4.94Tb0.06O12-δ electrode exhibits an outstanding electrochemical performance.Li4Ti4.94Tb0.06O12-δ sample exhibits a higher initial discharge capacity of 168.4 m Ah g-1, a higher discharge capacity of 150 m Ah g-1 can be obtained after 500 cycles at 10 C, while the Li4Ti5O12 shows the initial discharge capacity of 140 m Ah g-1, a discharge capacity of 123 m Ah g-1 can be kept after 500 cycles. Furthermore, the composite delivers a rate capacity of 166.2 m Ah g-1 at 20 C, which is much higher than pureLi4Ti5O12 of 104.1 m Ah g-1。3. Li4Ti5O12@Er2O3 hierarchical microsphere has been synthesized via a co-precipitation method. After the XRD、XPS、TEM and electrochemical performance tests, besides partial doping of Er3+ into the Li4Ti5O12 structure, Er2O3 is coated on the surface of Li4Ti5O12. When Er2O3/Li4Ti5O12 molar ratio is 0.02, the results display that the diffraction peak of Er2O3 in XRD is appeared. It exhibits a higher initial discharge capacity of 192.1 m Ah g-1, a higher discharge capacity of 154.3 m Ah g-1 can be kept after 200 cycles at 20 C, while the Li4Ti5O12 shows the initial discharge capacity of134.6 m Ah g-1, a discharge capacity of 119.9 m Ah g-1 can be kept after 200 cycles.The composite delivers a rate capacity of 180.4 m Ah g-1 at 30 C, which is much higher than pure Li4Ti5O12 material of 118.5 m Ah g-1. Er2O3 coating not only reduces polarization, but also increases Li+ diffusion rate of the material.