Universality of Benzoquinone-based Anodes toward Various Metal Cations in Aqueous Rechargeable Batteries.

The poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (denoted as PDBM) capable of reversible coordination/uncoordination with both mono- and multivalent cations in aqueous electrolytes is desired to develop safe, sustainable, and cost-effective aqueous rechargeable batteries (ARBs). However, the comprehensive mechanism between the electrochemical performance of PDBM and properties of these metal cations is unclear. Herein, we initially demonstrate the universality of PDBM to reversibly coordinate/uncoordinate with various cations (Na+, Mg2+, Ca2+, Zn2+, Al3+, etc.) with high specific capacities (>200 mA h g-1), high rate capabilities (∼20 C), and long cycling life (5000 cycles). Additionally, an unprecedented ion-coordination mechanism is presented: the monovalent cations prefer to occupy the in-plane sites with respect to the benzene rings of PDBM during the electrochemical reduced process, while the multivalent cations with the larger charge density tend to occupy the out-of-plane sites, which can use more active sites in the PDBM molecule and deliver the higher specific capacities. Meanwhile, the redox potential of PDBM decreases with the decrease in the binding energy between metal cations and PDBM molecules. The universality of PDBM to numerous cations is beneficial to design high-safety, low-cost, and long-lifespan ARBs for large-scale energy storage systems by modulating the aqueous electrolytes.

One-Step Synthesis of LiCo1-1.5xYxPO4@C Cathode Material for High-Energy Lithium-ion Batteries.

Intrinsically low ion conductivity and unstable cathode electrolyte interface are two important factors affecting the performances of LiCoPO4 cathode material. Herein, a series of LiCo1-1.5xYxPO4@C (x = 0, 0.01, 0.02, 0.03) cathode material is synthesized by a one-step method. The influence of Y substitution amount is optimized and discussed. The structure and morphology of LiCo1-1.5xYxPO4@C cathode material does not lead to obvious changes with Y substitution. However, the Li/Co antisite defect is minimized and the ionic and electronic conductivities of LiCo1-1.5xYxPO4@C cathode material are enhanced by Y substitution. The LiCo0.97Y0.02PO4@C cathode delivers a discharge capacity of 148 mAh g-1 at 0.1 C and 96 mAh g-1 at 1 C, with a capacity retention of 75% after 80 cycles at 0.1 C. Its good electrochemical performances are attributed to the following factors. (1) The uniform 5 nm carbon layer stabilizes the interface and suppresses the side reactions with the electrolyte. (2) With Y substitution, the Li/Co antisite defect is decreased and the electronic and ionic conductivity are also improved. In conclusion, our work reveals the effects of aliovalent substitution and carbon coating in LiCo1-1.5xYxPO4@C electrodes to improve their electrochemical performances, and provides a method for the further development of high voltage cathode material for high-energy lithium-ion batteries.

Garnet Li7La3Zr2O12-Based Solid-State Lithium Batteries Achieved by In Situ Thermally Polymerized Gel Polymer Electrolyte.

Garnet Li7La3Zr2O12 (LLZO) is a potential solid electrolyte for solid-state batteries (SSBs) because of its high ionic conductivity, electrochemical stability, and mechanical strength. However, large interface resistances arising from deserted cathodes and rigid garnet/electrode interfaces block its application. In order to deal with this issue, a gel polymer electrolyte (GPE) was introduced into the cathode and both sides of LLZO to achieve a solid-state battery. Especially, the provided GPE could be thermally polymerized and solidified in situ, which would integrate LLZO with both anode and cathode and dramatically simplify the battery manufacturing process. Since the interface from rigid LLZO is improved by the flexible GPE buffer, the inability of flexible GPE to inhibit lithium dendrites is compensated by the rigid LLZO in return. As a result, the interface resistances are reduced from 6880 to 473 Ω, the Li symmetric cell exhibits a flat galvanostatic charge/discharge for 400 h without lithium dendrites, and the solid-state Li|GPE@LLZO|LiCoO2 battery exerts a capacity retention of 82.6% after 100 cycles at 0.5 C at room temperature. Such an interfacial engineering approach represents a promising strategy to address solid-solid interface issues and provides a new design for SSBs with high performance.

Establish TiNb2O7@C as Fast-Charging Anode for Lithium-Ion Batteries.

Intercalation-type metal oxides are promising active anode materials for the fabrication of safer rechargeable lithium-ion batteries, as they are capable of minimizing or even eliminating Li plating at low voltages. Due to the excellent cycle performance, high specific capacity and appropriate working potential, TiNb2O7 (TNO) is considered to be the candidate of anode materials. Despite a lot of beneficial characteristics, the slow electrochemical kinetics of the TNO-based anodes limits their wide use. In this paper, TiNb2O7@C was prepared by using the self-polymerization coating characteristics of dopamine to enhance the rate-performance and cycling stability. The TNO@C-2 particles present ideal rate performance with the discharge capacity of 295.6 mA h g-1 at 0.1 C. Moreover, the TNO@C-2 anode materials exhibit initial discharge capacity of 177.4 mA h g-1, providing 91% of capacity retention after 400 cycles at 10 C. The outstanding electrochemical performance can be contributed to the carbon layer, which builds fast lithium ion paths, enhancing the electrical conductivity of TNO. All these results confirm that TNO@C is a valid methodology to enhance rate-performance and cycling stability and is a new way to provide reliable and quickly rechargeable energy storage resources.

Direct surface coating of high voltage LiCoO2 cathode with P(VDF-HFP) based gel polymer electrolyte.

For high-voltage cycling of lithium-ion batteries, a gel polymer Li-ion conductor layer, P(VDF-HFP)/LiTFSI (PHL) with high electrochemical stability has been coated on the surfaces of as-formed LiCoO2 (LCO) cathodes by a solution-casting technique at low temperature. An LCO cathode coated with around 3 µm thickness of the PHL ultrathin membrane, retains 88.4% of its original capacity (184.3 mA h g-1) after 200 cycles in the 3.0-4.6 V range with a standard carbonate electrolyte, while the non-coated one retains only 80.4% of its original capacity (171.5 mA h g-1). The reason for the better electrochemical behaviors and high-voltage cycling is related to the distinctive characteristics of the PHL coating layer that is compact, has highly-continuous surface coverage and penetrates the bulk of LCO, forming an integrated electrode. The PHL coating layer plays the role of an ion-conductive protection barrier to inhibit side reactions between the charged LCO surface and electrolyte, reduces the dissolution of cobalt ions and maintains the structural stability of LCO. Further, the PHL coated LCO cathode is well preserved, compared to the uncoated one which is severely cracked after 200 cycles at a charging cut-off voltage of 4.6 V.