This paper investigates the mechanism of Li insertion into interphase Ni3Sn in Ni-Sn alloy for the anode of lithium ion battery by means of the first-principles plane-wave pseudopotential.Compared with other phases,it is found that the Ni3Sn has larger relative expansion ratio and lower electrochemical potential,with its specific plateaus voltage around 0.3 eV when lithium atoms are filled in all octahedral interstitial sites,and the relative expansion ratio increasing dramatically when the lithiated phase transits from octahedral interstitial sites to tetrahedral interstitial sites.So this phase is a devastating phase for whole alloy electrode materials.
The mechanism of lithium intercalation/deintercalation for phase Al 0.8 Ni 3 Sn 0.2 as anode material used in lithium ion battery was studied carefully based on the first-principle plane wave pseudo-potential method.The calculated results indicated that Sn-Ni-Al alloy had high theoretical capacity when used as anode material,however,there was high initial irreversible capacity loss because of the large volume expansion.Therefore the technological parameters during preparing the Sn-Ni-Al anode should be controlled strictly to make the content of Al 0.8 Ni 3 Sn 0.2 phase as low as possible and to make the anode consist of promising Sn-Ni and Al-Ni phases.For comparison,an experiment based on magnetron sputtering was done.The result showed that the calculation is in good agreement with the experiment.We found that the first-principle investigation method is of far-reaching significance in synthesising new commercial anode materials with high capacity and good cycle performance.
Based on density functional theory(DFT)of the first-principle for cathode materials of lithium ion battery,the electronic structures of(Li1-xMex)FePO4(Me=Na and Be,x=0-0.40)are calculated by plane wave pseudo-potential method using Cambridge serial total energy package(CASTEP)program.The calculated results show that Li-site doping can improve the electronic conductivity enormously.Doping with Na has a noticeable effect on improving its electrical conductivity.However,serious structural distortion will occur when its doping density is beyond 0.25.In view of this,the best density of doping Na is less than 0.25.Doping with Be has an inconspicuous effect on increasing its electrical conductivity and has good cyclical stability,but it cannot achieve as good results as when it is doped with Na.Therefore we cannot find a middle ground between the two proposals.Considering cost and environmental protection,it is ideal to choose Na.So this method gives a reasonable prediction to the improvement of electronic conductivity through Li-site doping in LiFePO4 material.
In this work, based on First-principle plane wave pseudo-potential method, we have carried out an in-depth study on the possible dead lithium phase of Sn-Zn alloy as anode materials for lithium ion batteries. Through investigation, we found that the phases LixSn4Zn4(x = 2, 4, 6, 8) contributed to re-versible capacity, while the phases LixSn4Zn8-(x-4)(x = 4.74, 7.72) led to capacity loss due to high forma-tion energy, namely, they were the dead lithium phases during the charge/discharge process. And we come up with a new idea that stable lithium alloy phase with high lithiation formation energy (dead lithium phase) can also result in high loss of active lithium ion, besides the traditional expression that the formation of solid electrolyte interface film leads to high capacity loss.
