Insight into the failure mechanism of large-scale cylindrical lithium-sulphur cells.

Li-S batteries with a sulphur loading content of 5 mg cm-2 were produced as large-scale 18 650 cylindrical cells. We have found that a key failure mode of cylindrical Li-S battery cells is the severe capacity fading during the galvanostatic charge-discharge process due to the corrosion of the electrodes, the electrolyte decomposition, and the severe polysulphide shuttling effect.

Microcracking of Ni-rich layered oxide does not occur at single crystal primary particles even abused at 4.7 V.

There is a controversial issue based on the particle cracking of the Ni-rich layered oxide cathode materials whether it occurs at the primary particles or the grain boundary. Herein, we found that the microcracking of NMC811 does not occur at single crystalline primary particles even abused at a severe upper cell voltage of 4.7 V having a lot of gas evolution since the single-crystal NMC811 has superior mechanical stability. The capacity retentions determined at 1C rate and a 100% state of charge (SOC) are 80% and 50% after 1000 cycles for single crystal and polycrystal NMC811, respectively.

Free carbonate-based molecules in the electrolyte leading to severe safety concerns of Ni-rich Li-ion batteries.

The safety of Li-ion batteries is one of the most important factors, if not the most, determining their practical applications. We have found that free carbonate-based solvent molecules in the hybrid electrolyte system can cause severe safety concerns. Mixing ionic liquids with a carbonate-based solvent as the co-solvent at a fixed salt concentration of 1 M LiPF6 can lead to free carbonate-based molecules causing poor charge storage performance and safety concerns.

Core-shell structure of LiMn2O4 cathode material reduces phase transition and Mn dissolution in Li-ion batteries.

Although the LiMn2O4 cathode can provide high nominal cell voltage, high thermal stability, low toxicity, and good safety in Li-ion batteries, it still suffers from capacity fading caused by the combination of structural transformation and transition metal dissolution. Herein, a carbon-coated LiMn2O4 cathode with core@shell structure (LMO@C) was therefore produced using a mechanofusion method. The LMO@C exhibits higher cycling stability as compared to the pristine LiMn2O4 (P-LMO) due to its high conductivity reducing impedance growth and phase transition. The carbon shell can reduce direct contact between the electrolyte and the cathode reducing side reactions and Mn dissolution. Thus, the cylindrical cell of LMO@C//graphite provides higher capacity retention after 900 cycles at 1 C. The amount of dissoluted Mn for the LMO@C is almost 2 times lower than that of the P-LMO after 200 cycles. Moreover, the LMO@C shows smaller change in lattice parameter or phase transition than P-LMO, indicating to the suppression of λ-MnO2 phase from the mixed phase of Li1-δMn2O4 + λ-MnO2 when Li-delithiation at highly charged state leading to an improved cycling reversibility. This work provides both fundamental understanding and manufacturing scale demonstration for practical 18650 Li-ion batteries.

Effect of fluoroethylene carbonate on the transport property of electrolytes towards Ni-rich Li-ion batteries with high safety.

Transport phenomena and the solvation structure of lithium ions (Li+) and hexafluorophosphate anions (PF6-) in electrolytes with different fluoroethylene carbonate (FEC) concentrations as well as the electrochemical performance and safety of Ni-rich Li-ion battery cells at the 18650 cylindrical cell level are investigated. We have found that the electrolyte with an optimized FEC concentration (25% v/v) can effectively enhance the transport property in terms of the Li+ transference number and contact ion pair (CIP) ratio leading to high performance and safety of practical 18650 cylindrical LIBs.

Insight into the effect of additives widely used in lithium-sulfur batteries.

The interaction between the reactive lithium metal surface and LiNO3 results in the formation of LixNOy clusters, which can protect the Li metal anode and suppress the shuttling effect of lithium polysulfides via the dipole-dipole interaction called the lithium bond.