Side Reactions/Changes in Lithium-Ion Batteries: Mechanisms and Strategies for Creating Safer and Better Batteries.

Lithium-ion batteries (LIBs), in which lithium ions function as charge carriers, are considered the most competitive energy storage devices due to their high energy and power density. However, battery materials, especially with high capacity undergo side reactions and changes that result in capacity decay and safety issues. A deep understanding of the reactions that cause changes in the battery's internal components and the mechanisms of those reactions is needed to build safer and better batteries. This review focuses on the processes of battery failures, with voltage and temperature as the underlying factors. Voltage-induced failures result from anode interfacial reactions, current collector corrosion, cathode interfacial reactions, overcharge, and over-discharge, while temperature-induced failure mechanisms include SEI decomposition, separator damage, and interfacial reactions between electrodes and electrolytes. The review also presents protective strategies for controlling these reactions. As a result, the reader is offered a comprehensive overview of the safety features and failure mechanisms of various LIB components.

Preparation and Electrochemical Properties of LiNi2/3Co1/6Mn1/6O2 Cathode Material for Lithium-Ion Batteries.

The cathode material LiNi2/3Co1/6Mn1/6O2 with excellent electrochemical performance was prepared successfully by a rheological phase method. The materials obtained were characterized by X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscopy and charge-discharge tests. The results showed that both calcination temperatures and atmosphere are very important factors affecting the structure and electrochemical performance of LiNi2/3Co1/6Mn1/6O2 material. The sample calcinated at 800 °C under O2 atmosphere displayed well-crystallized particle morphology, a highly ordered layered structure with low defects, and excellent electrochemical performance. In the voltage range of 2.8-4.3 V, it delivered capacity of 188.9 mAh g-1 at 0.2 C and 130.4 mAh g-1 at 5 C, respectively. The capacity retention also reached 93.9% after 50 cycles at 0.5 C. All the results suggest that LiNi2/3Co1/6Mn1/6O2 is a promising cathode material for lithium-ion batteries.

Enhanced Structural Stability and Electrochemical Performance of LiNi0.6Co0.2Mn0.2O2 Cathode Materials by Ga Doping.

Structural instability during cycling is an important factor affecting the electrochemical performance of nickel-rich ternary cathode materials for Li-ion batteries. In this work, enhanced structural stability and electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode materials are achieved by Ga doping. Compared with the pristine electrode, Li[Ni0.6Co0.2Mn0.2]0.98Ga0.02O2 electrode exhibits remarkably improved electrochemical performance and thermal safety. At 0.5C rate, the discharge capacity increases from 169.3 mAh g-1 to 177 mAh g-1, and the capacity retention also rises from 82.8% to 89.8% after 50 cycles. In the charged state of 4.3 V, its exothermic temperature increases from 245.13 °C to more than 271.24 °C, and the total exothermic heat decreases from 561.7 to 225.6 J·g-1. Both AC impedance spectroscopy and in situ XRD analysis confirmed that Ga doping can improve the stability of the electrode/electrolyte interface structure and bulk structure during cycling, which helps to improve the electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode material.

Binder-Free Electrode based on Electrospun-Fiber for Li Ion Batteries via a Simple Rolling Formation.

With the demand for higher energy density and smaller size lithium-ion batteries (LIBs), the development of high specific capacity active materials and the reduction of the usage of inactive materials are the main directions. Herein, a universal method is developed for binder-free electrodes for excellent stable LIBs by rolling the electrospun membrane directly onto the commercial current collector. The rolling process only makes the fiber web denser without changing the fiber structure, and the fiber web still maintains a porous structure. This strategy significantly improves the structural stability of the membrane compared to the direct carbonized electrospun membrane. Moreover, this method is suitable for a variety of polymerizable adhesive polymers, and each polymer can be composited with different polymers, inorganic salts, etc. The electrode prepared by this method can be stably cycled for more than 2000 cycles at a current density of 2500 mA g-1. This study provides a cost-effective and versatile strategy to design the LIB electrode with high energy density and stability for experimental research and practical application.

Molecular Sieve-Modified Separator for High-Performance Lithium-Ion Batteries.

Lithium-ion batteries (LIBs) are currently the most important energy storage system. Separators in the battery play a critical role in terms of the rate capability, cycle life, and safe operation. However, commercial separators exhibit poor electrolyte wettability and limited safety. It is also extremely important to eliminate the hazardous small molecules (e.g., H2O and HF) inside the battery to enhance the service life. Herein, a functionalized poly(vinylidene fluoride-co-hexafluoropropylene)@polyacrylonitrile (PVDF-HFP@PAN) separator modified by 4-Å molecular sieves (MS) was fabricated by hydrothermal method for LIBs. MS@PVDF-HFP@PAN separator exhibits high thermal stability and carbonate electrolyte wettability. In addition, it can lower the moisture value in the battery system to 13 ppm, which significantly improves the electrolyte quality. When the current density increased from 0.2 to 5 C, the discharging capacity of the cell with MS@PVDF-HFP@PAN declines from 177.6 to 143.2 mAh g-1, demonstrating an excellent capacity retention of 80.6%. The discharge capacity retention of NMC622 half-cell with MS@PVDF-HFP@PAN after 100 cycles is 98.6% of its initial discharge capacity, which is higher than that of a cell with the Celgard 2400 separator (91.9%).

Binder-Free Electrodes and Their Application for Li-Ion Batteries.

Lithium-ion batteries (LIB) as energy supply and storage systems have been widely used in electronics, electric vehicles, and utility grids. However, there is an increasing demand to enhance the energy density of LIB. Therefore, the development of new electrode materials with high energy density becomes significant. Although many novel materials have been discovered, issues remain as (1) the weak interaction and interface problem between the binder and the active material (metal oxide, Si, Li, S, etc.), (2) large volume change, (3) low ion/electron conductivity, and (4) self-aggregation of active materials during charge and discharge processes. Currently, the binder-free electrode serves as a promising candidate to address the issues above. Firstly, the interface problem of the binder and active materials can be solved by fixing the active material directly to the conductive substrate. Secondly, the large volume expansion of active materials can be accommodated by the porosity of the binder-free electrode. Thirdly, the ion and electron conductivity can be enhanced by the close contact between the conductive substrate and the active material. Therefore, the binder-free electrode generally exhibits excellent electrochemical performances. The traditional manufacture process contains electrochemically inactive binders and conductive materials, which reduces the specific capacity and energy density of the active materials. When the binder and the conductive material are eliminated, the energy density of the battery can be largely improved. This review presents the preparation, application, and outlook of binder-free electrodes. First, different conductive substrates are introduced, which serve as carriers for the active materials. It is followed by the binder-free electrode fabrication method from the perspectives of chemistry, physics, and electricity. Subsequently, the application of the binder-free electrode in the field of the flexible battery is presented. Finally, the outlook in terms of these processing methods and the applications are provided.