Thermal Synergy Effect between LiNi0.5Co0.2Mn0.3O2 and LiMn2O4 Enhances the Safety of Blended Cathode for Lithium Ion Batteries

Weakly Solvating Cyclic Ether-Based Deep Eutectic Electrolytes for Stable High-Temperature Lithium Metal Batteries

Deep eutectic electrolytes (DEE) have emerged as an innovative approach to address the instability and safety issues of lithium metal batteries at elevated temperatures. However, in practice, there is often an undesirable incompatibility between the eutectic mixture and electrodes, and also an insufficient reduction stability of DEE due to the increased Li+ concentration. Herein, we designed a new DEE by utilizing weakly solvating tetrahydropyran (THP) solvent. Due to the high reduction resistance of THP and concentrated lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), this DEE demonstrates enhanced compatibility with Li metal anode and high temperature tolerance with LiMn2O4 cathode. The Li||LiMn2O4 cell (1.6 mAh cm-2) shows a high capacity retention of 96.02 % after 600 cycles at room temperature. More importantly, this Li||LiMn2O4 cell achieves a remarkable high-temperature performance with a high capacity retention of 91.72 % after 120 cycles and low self-discharge after storage for 240 hours at a high temperature of 55 °C, which is critical for LiMn2O4 cathode. Overall, this electrolyte design provides an alternative pathway for the development of DEEs for high-temperature and high-voltage lithium metal batteries, which can also be expanded to other batteries.

Ternary Cathode Blend Electrodes for Environmentally Friendly Lithium-Ion Batteries

The combination of two active materials into one positive electrode of a lithium-ion battery is an uncomplicated and cost-effective way to combine the advantages of different active materials while reducing the disadvantages of each material. In this work, the concept of binary blends is extended to ternary compositions. The combination of three different active materials provides high versatility in designing the properties of an electrode. Therefore, the unique properties of a layered oxide, phospho-olivine, and spinel type material are mixed to design a high-energy cathode with improved environmental friendliness. Four different compositions of blend electrodes are investigated, each with individual benefits. Synergistic effects improved the rate capability, power density, thermal and chemical stability simultaneously. The blend electrode consisting of 75 % NMC, 12.5 % LMFP and LMO provides similar energy and power density as a pure NMC electrode while economizing 25 % cobalt and nickel.

La4NiLiO8-Shielded Layered Cathode Materials for Emerging High-Performance Safe Batteries

Low theoretical capacities of the commercial cathode materials (olivine: ∼170 mA h g^-1 and spinel: ∼140 mA h g^-1) dictate the need for higher energy density alternates such as nickel-rich (denotes as NCM) materials with a theoretical capacity of ∼270 mA h g^-1. However, low conductivity and the bulk degradation after direct contact with liquid electrolytes, especially at temperatures higher than 50 °C, are the biggest issues to resolve for safe use and confident commercialization of the NCM materials. In this context, we first report "La₄NiLiO₈ shields" to simultaneously boost charge conduction characteristics and circumvent the electrolytic degradation of NCM. Consequently, the La₄NiLiO₈-shielded LiNi_0.5Co_0.2Mn_0.3O₂ (LSN5) not only offers a 4.1× less charge transfer resistance and significantly higher discharge capacity (219.7 mA h g^-1) than the nonshielded NCM (187 mA h g^-1) and theoretical capacities of commercial cathode materials but also maintains more than 91.7% of capacity retention at 25 °C after 500 cycles and 84.2% at 60 °C after 200 cycles. In contrast, the nonshielded NCM cathodes can only provide 58.9 and 45.5% capacity retentions at corresponding test temperatures and performance cycles. The acquired excellent electrochemical performance and battery stability at both the ambient and high-temperature conductions infer great importance of the novel La₄NiLiO₈ shields in developing high-performance safe secondary batteries.

Thermal Runaway Triggered by Plated Lithium on the Anode after Fast Charging

Battery safety, at the foundation of fast charging, is critical to the application of lithium-ion batteries, especially for high energy density cells applied in electric vehicles. In this paper, an earlier thermal runaway of cells after fast charging application is illustrated. Under this condition, the reaction between the plated lithium and electrolyte is revealed to be the mechanism of thermal runaway triggering. The mechanism is proved by the accelerated rate calorimetry tests for partial cells, which determine the triggering reactions of thermal runaway in the anode-electrolyte thermodynamic system. The reactants in this system are analyzed by nuclear magnetic resonance and differential scanning calorimetry, proving that the vigorous exothermic reaction is induced by the interaction between the plated lithium and electrolyte. As a result, the finding of thermal runaway triggered by the plated lithium on anode surface of cells after fast charging promotes the understanding of thermal runaway mechanisms, which warns of the danger of plated lithium in the utilization of lithium-ion batteries.

Electrochemical Degradation Mechanism and Thermal Behaviors of the Stored LiNi0.5Co0.2Mn0.3O2 Cathode Materials

The degradation mechanism of the stored LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) electrode has been systematically investigated by combining physical and electrochemical tests. After stored at 55 °C and 80% relative humidity for 4 weeks, the NCM523 materials are coated with a layer of impurities containing adsorbed species, Li₂CO₃ and LiOH, resulting in both the weight gains of the materials and the electrochemical performance deterioration of the electrode. The impurities generated in air will react with the electrolyte and instantly turn into Li _xPO _yF _z and other species containing the decomposition products of electrolyte when the stored NCM523 materials are soaked into the electrolyte, causing the charge potential plateau and the impedance to ascend. For the stored NCM523 electrodes, the huge and changeable impedance deteriorates the discharge capacity in the first 10 cycles and the discharge capacity will slowly recover and stabilize within 10 cycles when charging/discharging in 0.1 or 0.2 C. The thermal stability of the stored NCM523 materials get slightly better due to the relatively lower delithiated state after charged to 4.3 V.

Synergistic Effect between LiNi0.5Co0.2Mn0.3O2 and LiFe0.15Mn0.85PO4/C on Rate and Thermal Performance for Lithium Ion Batteries

A blend cathode has been prepared by mixing both LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) of high energy density and high specific capacity and LiFe_0.15Mn_0.85PO₄/C (LFMP/C) of excellent thermal stability via a low-speed ball-milling method. The lithium ion batteries using the blend cathode with LFMP/C of optimum percent exhibit better capacity retention after 100 cycles than those using only single NCM523 or LFMP/C. Both theoretical simulation and experimental rate performances demonstrate that the electrochemical property of blend cathode materials is predictable and economical. In addition, the thermal behaviors of blend cathodes are studied by using differential scanning calorimetry analysis. The thermal stability of blend cathode materials behaves better than that of the bare NCM523 accompanied with an electrolyte. It is found that the outstanding rate and thermal performance of the blend cathode is due to the prominent synergistic effect between NCM523 and LFMP/C, and 10% LFMP/C in the blend cathode materials is the most adaptable as considering both electrochemical and thermal properties simultaneously.

Recent Progresses and Development of Advanced Atomic Layer Deposition towards High-Performance Li-Ion Batteries

Electrode materials and electrolytes play a vital role in device-level performance of rechargeable Li-ion batteries (LIBs). However, electrode structure/component degeneration and electrode-electrolyte sur-/interface evolution are identified as the most crucial obstacles in practical applications. Thanks to its congenital advantages, atomic layer deposition (ALD) methodology has attracted enormous attention in advanced LIBs. This review mainly focuses upon the up-to-date progress and development of the ALD in high-performance LIBs. The significant roles of the ALD in rational design and fabrication of multi-dimensional nanostructured electrode materials, and finely tailoring electrode-electrolyte sur-/interfaces are comprehensively highlighted. Furthermore, we clearly envision that this contribution will motivate more extensive and insightful studies in the ALD to considerably improve Li-storage behaviors. Future trends and prospects to further develop advanced ALD nanotechnology in next-generation LIBs were also presented.