Conductivity and applications of Li-biphenyl-1,2-dimethoxyethane solution for lithium ion batteries

The total conductivity of Li-biphenyl-1,2-dimethoxyethane solution(Li_xBp(DME)_(9.65), Bp = biphenyl, DME = 1,2-dimethoxyethane, x = 0.25, 0.50, 1.00, 1.50, 2.00) is measured by impedance spectroscopy at a temperature range from 0℃ to 40℃. The Li_(1.50)Bp(DME)_(9.65) has the highest total conductivity 10.7 m S/cm. The conductivity obeys Arrhenius law with the activation energy(E_(a(x=0.50))= 0.014 eV, E_(a(x=1.00))= 0.046 eV). The ionic conductivity and electronic conductivity of Li_xBp(DME)_(9.65) solutions are investigated at 20℃ using the isothermal transient ionic current(ITIC) technique with an ion-blocking stainless steal electrode. The ionic conductivity and electronic conductivity of Li_(1.00)Bp(DME)_(9.65) are measured as 4.5 mS/cm and 6.6 mS/cm, respectively. The Li_(1.00)Bp(DME)_(9.65) solution is tested as an anode material of half liquid lithium ion battery due to the coexistence of electronic conductivity and ionic conductivity. The lithium iron phosphate(LFP) and Li_(1.5)Al_(0.5)Ti_(1.5)(PO_4)_3(LATP) are chosen to be the counter electrode and electrolyte, respectively. The assembled cell is cycled in the voltage range of 2.2 V-3.75 V at a current density of 50 mA/g. The potential of Li_(1.00)Bp(DME)_(9.65) solution is about 0.3 V vs. Li~+/Li, which indicates the solution has a strong reducibility. The Li_(1.00)Bp(DME)_(9.65) solution is also used to prelithiate the anode material with low first efficiency, such as hard carbon, soft carbon and silicon.     

Size effect of Si particles on the electrochemical performances of Si/C composite anodes

A series of Si/C composites were fabricated based on pitch and Si powders with particle sizes of 30, 100, 500, and3000 nm. The size effects of the Si particles in the Si/C composites were investigated for lithium-ion battery anodes. The nanoscale Si and Si/C composites exhibited good capacity retentions. Scanning electron microscopy showed that exterior and interior cracks emerging owing to volume expansion as well as parasitic reactions with the electrolyte could well explain the performance failure.     

Gas treatment protection of metallic lithium anode

The effects of different coating layers on lithium metal anode formed by reacting with different controlled atmospheres(argon,CO_2–O_2(2:1),N_2,and CO_2–O_2–N_2(2:1:3))have been investigated.The obtained XRD,second ion mass spectroscopy(SIMS),and scanning probe microscope(SPM)results demonstrate the formation of coating layers composed of Li_2CO_3,Li_3N,and the mixture of them on lithium tablets,respectively.The Li/Li symmetrical cell and Li/S cell are assembled to prove the advantages of the protected lithium tablet on electrochemical performance.The comparison of SEM and SIMS characterizations before/after cycles clarifies that an SEI-like composition formed on the lithium tablets could modulate the interfacial stabilization between the lithium foil and the ether electrolyte.     

Li-ion batteries: Phase transition

Progress in the research on phase transitions during Li+extraction/insertion processes in typical battery materials is summarized as examples to illustrate the significance of understanding phase transition phenomena in Li-ion batteries.Physical phenomena such as phase transitions(and resultant phase diagrams) are often observed in Li-ion battery research and already play an important role in promoting Li-ion battery technology. For example, the phase transitions during Li+insertion/extraction are highly relevant to the thermodynamics and kinetics of Li-ion batteries, and even physical characteristics such as specific energy, power density, volume variation, and safety-related properties.     

高容量金属镓薄膜和粉体作为锂离子电池负极材料的自修复行为研究

锂离子电池合金类负极材料比如Si, Sn, 因其理论容量远高于目前商业化石墨负极材料受到了广泛的关注. 然而, 受限于这类材料的循环稳定性, 距离其产业化仍然有一定的距离, 主要是由于其在电化学充放电过程中锂离子的嵌入和脱出产生巨大的应力而导致出现的不可修复的裂纹. 利用金属镓低熔点的物理特性, 在其熔点之上研究其脱嵌锂过程中的自修复能力. 对制备出金属镓薄膜电极研究发现, 25次充放电后, 因为固体电解质(SEI)的持续生成, 有效自修复区域降低为34 μm, 自修复区域随着循环次数的增加逐渐降低. 同时通过简单的液相分散方法制备出金属镓粉末电极, 金属镓粉末大小为3.43 μm, 尺寸小于有效自修复区域, 电化学分析显示该金属镓粉末电极前25次循环能够实现高的可逆容量和稳定的循环性能, 25次循环后的金属镓粉末电极的SEM分析显示裂纹平均尺寸大小为1 μm, 说明金属镓在液体电解液体系中的自修复能力有限. 金属镓有望用于非液态电解质体系中的裂纹修复, 比如对全固态电池中金属锂粉化的修复.