Search

A new concept is developed using locally an enriched PAA binder to enhance the structural stability of the electrode.

This work proposes to directly use transition metal (cobalt) powder as the precursor for the synthesis of LiCoO2, solving the problem of structural instability and rapid capacity decay caused by order–disorder phase transitions without any modification.

A new concept of electrode processing with tiny amounts of multi-functional microporous PIM additives was established as an alternative to binder-containing and binder-free electrodes, leading to enhanced electrochemical performance.

Lithium secondary batteries (LSBs) have witnessed explosive growth in the last decade. A wide operating temperature window is crucial for practical applications. A new concept is developed to expand the temperature window between −20 °C and 150 °C, where a competitive decomposition process between the electrolyte and solvent is manipulated with adiponitrile (ADN) over a wide temperature range. The decomposition of ethylene carbonate (EC) solvent and anions of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium oxalyldifluoroborate (LiODFB) is regulated with ADN via a temperature-dependent lithium solvation mechanism. As a result, a SEI layer with a rich inorganic component is formed at elevated temperatures, leading to improved performance in lithium titanate (LTO)/Li, lithium iron phosphate (LFP)/Li, and LiNi0.5Co0.2Mn0.3O2 (NCM523)/Li batteries over a wide temperature range. It enables a coulombic efficiency (CE) of 97.39% at 100 °C and more than 100 hours of cycling of Li/Li batteries at 150 °C, as well as stable cycling of LFP/Li batteries in the temperature range between 120 °C and −20 °C. Stable cycling performance is demonstrated with the LTO/Li batteries over a wider temperature range from −40 °C to 150 °C. High-temperature electrochemical stability is exhibited at 5C, with a capacity retention ratio of 87.94% at 120 °C and 99.93% at 100 °C after 1000 cycles.

In this work, we extracted 95% of the electrochemically available Li from LiNi0.8Co0.15Al0.05O2 (NCA) by galvanostatically charging the NCA/MCMB full cell to 4.7 V. Joint powder X-ray and neutron diffraction (XRD & ND) studies were undertaken for NCA at highly charged states at the first cycle, and discharged states at different cycles. The results indicate that the bulk structure of NCA maintains the O3 structure up to the extraction of 0.90 Li per formula unit. In addition, we found that the transition metal layer becomes more disordered along the c-axis than along the a- and b-axes upon charging. This anisotropic disorder starts to develop no later than 4.3 V on charge and continues to grow until the end of charge. As Li is re-inserted during discharge, the structure that resembles the pristine NCA is recovered. The irreversible loss of Li and the migration of Ni to the Li layer have been quantified by the joint XRD and ND refinement and the results were further verified by solid state 7Li NMR and magnetic measurements. Our work clearly demonstrates that the NCA bulk retains a robust, single phase O3 structure throughout the wide delithiation range (up to 0.9 Li per formula unit of NCA) and is suitable for higher energy density usage with proper modifications.

The Li-rich layered oxides are attractive electrode materials due to their high reversible specific capacity (>250 mA h g−1); however, the origin of their abnormal capacity is still ambiguous. In order to elucidate this curious anomaly, we compare the lattice oxygen oxidation states among the Li-rich layered oxide Li1.14Ni0.136Co0.136Mn0.544O2, Li2MnO3 and LiNi0.5Co0.2Mn0.3O2, the two components in Li-rich layered oxides, and the most common layered oxide LiCoO2 before and after initial charge–discharge. For simplicity, we employ chemical treatments of NO2BF4 and LiI acetonitrile solutions to simulate the electrochemical delithiation and lithiation processes. X-ray photoelectron spectroscopy (XPS) studies reveal that part of lattice oxygen in Li1.14Ni0.136Co0.136Mn0.544O2 and Li2MnO3 undergoes a reversible redox process (possibly O2− ↔ O22−), while this does not occur in LiNi0.5Co0.2Mn0.3O2 and LiCoO2. This indicates that the extra capacity of Li-rich layered oxides can be attributed to the reversible redox processes of oxygen in the Li2MnO3 component. Thermogravimetric analysis (TGA) further suggests that the formed O22− species in the delithiated Li1.14Ni0.136Co0.136Mn0.544O2 can decompose into O2 at about 210 °C. This phenomenon demonstrates a competitive relationship between extra capacity and thermal stability, which presents a big challenge for the practical applications of these materials.

A composite membrane with an ultra-thin ion exchangeable layer is specially designed as a separator in lithium ion batteries with manganese-based cathode materials. The composite membrane features a Mn2+ capture function which originates from the ion exchanging process, especially at high temperature, and is proven to help to alleviate the capacity decay of lithium ion batteries effectively. The enhanced thermal stability, improved wettability and higher lithium ion transference number of the composite membrane further suggest its promising application in lithium ion batteries.

To develop a kind of gel polymer electrolyte with high ion conductivity and good mechanical strength and thermal stability, a polyimide (PI) matrix-enhanced cross-linked gel separator is designed and fabricated by a simple dip-coating and heat treatment method. The PI nonwoven substrate provides high-temperature thermal stability for the gel separator and the crosslinked gel part yields enhanced affinity with the liquid electrolyte. Besides, the cross-linked polymer network could solve the issue of long-term durability of the composite separator in batteries. The gel separator shows better cyclability and rate capability than the traditional PP separator, implying a promising potential application in high-power, high-safety lithium ion batteries. The preparation process is compatible with the traditional manufacturing process of nonwoven membranes, and can be easily converted into continuous production on the industrial scale.