A gel polymer electrolyte (GPE) is a liquid electrolyte (LE) entrapped by a small amount of polymer network less than several wt%, which is characterized by properties between those of liquid and solid electrolytes in terms of the ionic conductivity and physical phase. Electrolyte leakage and flammability, demerits of liquid electrolytes, can be mitigated by using GPEs in electrochemical cells. However, the contact problems between GPEs and porous electrodes are challenging because it is difficult to incorporate GPEs into the pores and voids of electrodes. Herein, the focus is on GPEs that are gelated in situ within cells instead of covering comprehensive studies of GPEs. A mixture of LE and monomer or polymer in a liquid phase is introduced into a pre‐assembled cell without electrolyte, followed by thermal gelation based on physical gelation, monomer polymerization, or polymer cross‐linking. Therefore, GPEs are formed omnipresent in cells, covering the pores of electrode material particles, and even the pores of separators. As a result, different from ex situ formed GPEs, the in situ GPEs have no electrode/electrolyte contact problems. Functional GPEs are introduced as a more advanced form of GPEs, improving lithium‐ion transference number or capturing transition metals released from electrode materials.
Formation of a glue-nanofiller layer between grains, consisting of a middle-temperature spinel-like Lix CoO2 phase, reinforces the strength of the incoherent interfacial binding between anisotropically oriented grains by enhancing the face-to-face adhesion strength. The cathode treated with the glue-layer exhibits steady cycling performance at both room-temperature and 60 °C. These results represent a step forward in advanced lithium-ion batteries via simple cathode coating.
The rapidly growing technological demand for lithium-ion batteries has prompted the development of novel cathode materials with high energy density, low cost, and improved safety. High voltage spinel, LiNi 0.5 Mn 1.5 O 4 (LNMO), is one of the most promising candidates yet to be commercialized. The two primary obstacles for this material are the inferior electronic conductivity and fast capacity degradation in full cells due to the high operating voltage. By systematically addressing these limitations, we successfully develop a thick LNMO electrode with areal capacity loadings up to 3 mAh⋅cm À 2. The optimized thick electrode is paired with a commercial graphite anode at both the coin cell and pouch cell level, achieving a full cell capacity retention as high as 72% and 78%, respectively, after 300 cycles. We attribute this superior cycling stability to careful optimizations of cell components and testing conditions, with a specific focus improving electronic conductivity and high voltage compatibility. These results suggest precise control of materials quality, electrode architecture and electrolyte optimization can soon support the development of a cobalt-free battery system based on a thick LNMO cathode (>4 mAh⋅cm 2), which will eventually meet the needs of next-generation Li-ion batteries with reduced cost, improved safety, and assured sustainability.
The charge/discharge characteristics of lithium ion batteries at low temperature (LT ¼ À20 C) are enhanced by using ethylene carbonate (EC)-based electrolytes with the help of assistant solvents of nitriles. Conventional liquid electrolytes (e.g. a mixture of EC and dimethyl carbonate (DMC), abbreviated as L ED) cannot support a satisfactory capacity at low temperature as well as at high rates even if electric vehicles require low-temperature operation. Introducing propionitrile or butyronitrile (Pn or Bn) into L ED (resulting in L EDPn or L EDBn) as a co-solvent increases significantly the high-rate capacities at À20 C. For example, L EDPn delivers 62% of the available capacity at 1 C and 46% at 3 C with a 2.7 V cutoff while the control L ED provides just 6% and 4% at the same rates. Successful operation at À20 C with nitrileassistant electrolytes results from high ionic conductivity, low viscosity and freezing point depression caused by the eutectic behavior of the carbonates (EC/DMC) and Pn. Based on the phase diagram of Pn with EC/DMC, we expect a meaningful battery operation up to À110 C, probably lower, at the eutectic composition. Broader context Lithium ion batteries for electric vehicles should provide required energy within limited spaces with guaranteed safety, delivering enough power to satisfy the requirements of electric motors, be charged within a short time period so that drivers can endure and be operated in a wide range of temperature including the cryogenic range up to À20 C and more severely À30 C. The inferior charge and discharge characteristics of LIBs at low temperatures are one of the most serious problems that should be overcome by research and development. The disability of LIBs at low-temperature operations is caused by the limited ionic transport properties of the electrolyte, sluggish Li + desolvation with slow charge transfer kinetics and phase transition of the electrolyte, leading to severe ohmic and concentration polarization. In this work, we present nitrile-assistant carbonate-based eutectic electrolytes showing signicantly enhanced charge and discharge characteristics at À20 C and high rates up to 3 C. The successful operation at À20 C with the nitrile-assistant electrolytes results from high ionic conductivity, low viscosity and freezing point depression caused by the eutectic behavior of the carbonates and nitriles.
Dye-sensitized photo-rechargeable battery (DSPB) harvests and stores dim light efficiently, realizing indoor-light-harvesting battery to operate IoT devices successfully without sun light.
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