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Mixed silicon and carbon (Si–C) materials with high capacity are ideal candidates for the substitution of graphite or other carbon anodes in lithium-ion batteries. However, the low coulombic efficiency of the Si–C anode in the first cycle due to the formation of a solid electrolyte interphase and the consumption of active lithium have hindered its commercial applications. Here, we report using Li2S as a prelithiation material to compensate for the loss of active lithium in the first cycle and, consequently, to enhance the specific energy of lithium-ion batteries. The Si–C anode has an initial discharge specific capacity of ∼738 mA h g−1 and a charge specific capacity of ∼638 mA h g−1. The prelithiation material with a core–shell structure is prepared by mixing Li2S, Ketjenblack (KB) and poly(vinylpyrrolidone) (PVP) in anhydrous ethanol, which shows a high irreversible capacity of ∼1084 mA h g−1. The effect of the compensation of lost active lithium is verified via a LiFePO4 (Li2S)/Si–C full cell, which exhibits not only a high specific capacity but also a stable cycling performance. The specific energy of the LiFePO4 (Li2S)/Si–C full cell shows a remarkable increase compared to the LiFePO4/Si–C full cell, exhibiting ∼13.4%, ∼26.7%, ∼65.0% and ∼110.2% more specific energy after the 1st, 10th, 100th and 200th cycle, respectively.

The formation of Li dendrites is effectively inhibited by utilizing a small amount of polysulfide (1 to 2 mM Li2Sx, 2 ≤ x ≤ 8) in a conventional carbonate electrolyte to introduce a significant amount of polyethylene oxide (PEO)-like polymers into solid-electrolyte interphase (SEI) films. The polysulfide added likely acts as a catalyst rather than an additive, which is not consumed during repeated charging/discharging cycles. Thus the stability of Li-metal batteries during prolonged cycling is remarkably improved.

Detailed investigation of the influence of surface modification using a typical oxide (TiO2) on the electrochemical cycling performance of LiNi0.5Mn1.5O4 at room temperature (25 °C) and elevated temperature (55 °C) is reported. This spinel cathode material is commonly surface-modified with various metal oxides to improve its electrochemical cycling performance in lithium ion batteries. However, the underlying mechanisms of such a treatment, with respect to the surface crystal structure and chemistry evolution, have remained unclear. Bare-LiNi0.5Mn1.5O4 and TiO2-modified LiNi0.5Mn1.5O4 both show excellent cycling performance, i.e. almost no capacity retention and ∼99% coulombic efficiency for 150 cycles, at room temperature. However, at 55 °C the latter shows significantly better electrochemical cycling performance, with 93% capacity retention and ∼96% coulombic efficiency for 100 cycles, than the former with 70% capacity retention and ∼93% coulombic efficiency. Via advanced electron microscopy techniques, we observed that titanium ions migrated into the surface region of LiNi0.5Mn1.5O4 during the surface modification process at high temperature and reconstructed the (1–3 nm) surface spinel structure into a rocksalt-like structure and the subsurface (several nanometers) into a pseudo-rocksalt-like structure. The reconstruction of the surface and subsurface of the LiNi0.5Mn1.5O4 spinel cathode material mitigates not only the migration of Mn ions from the bulk into the electrolyte but also the formation of a solid state electrolyte interface, which plays a critical role in the improvement of electrochemical cycling performance at elevated temperatures.

Due to the abundance of sodium in nature, sodium-ion batteries (SIBs) have attracted widespread attention. Numerous intercalated cathode materials have already been reported, but fewer intercalated anode materials are known. Among these materials, most anodes suffer from low coulombic efficiency and the dendritic growth of sodium due to the lower sodiated voltages (below 1.0 V). To improve the safety performance of batteries, exploring new anode materials which have higher sodiated voltage above 1.0 V is very important. Herein, a series of novel intercalated anode materials, ATiOPO4 (A = NH4, K, Na), is introduced for SIBs at the first time. Preparation of NaTiOPO4 by a traditional solid-state reaction is difficult. So we first synthesized NH4TiOPO4 (NTP) by a simple hydrothermal reaction, KTiOPO4 (KTP) and NaTiOPO4 (NaTP) were each prepared by ion exchange with the respective nitrate. These samples were investigated by electrochemical discharge/charge which showed average sodiated voltages of 1.45 V (NTP), 1.4 V (KTP) and 1.5 V (NaTP); respectively. In situ XRD results indicated that a two-phase reaction mechanism accompanies electrochemical Na insertion/extraction in NaTP. These anode materials are potential candidates for developing SEI-free and high safety SIBs.

We present a new set of interatomic potentials for modelling the BaTiO3 perovskite system. The potential model is fitted using multiple parameters to a range of experimental and ab initio data including the cohesive energy and lattice parameters of BaTiO3, BaO and rutile TiO2. This procedure provides internal consistency to the potential model for studying the energetics of the defect chemistry of BaTiO3. This is tested by examining rare-earth cation doping in BaTiO3 and considering all five possible compensation schemes. Our simulations are in agreement with experiment and predict small rare-earth cations to dope exclusively on the Ti site; medium sized rare-earth cations to dope on both the Ti and Ba sites and large rare-earth cation doping exclusively on the Ba-site. For Ba-site substitution the simulations predict electron compensation to be energetically unfavourable compared to the formation of Ti vacancies.