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Over the past decades, Li-ion battery (LIB) has turned into one of the most important advances in the history of technology due to its extensive and in-depth impact on our life. Its omnipresence in all electric vehicles, consumer electronics and electric grids relies on the precisely tuned electrochemical dynamics and interactions among the electrolytes and the diversified anode and cathode chemistries therein. With consumers' demand for battery performance ever increasing, more and more stringent requirements are being imposed upon the established equilibria among these LIB components, and it became clear that the state-of-the-art electrolyte systems could no longer sustain the desired technological trajectory. Driven by such gap, researchers started to explore more unconventional electrolyte systems. From superconcentrated solvent-in-salt electrolytes to solid-state electrolytes, the current research realm of novel electrolyte systems has grown to unprecedented levels. In this review, we will avoid discussions on current state-of-the-art electrolytes but instead focus exclusively on unconventional electrolyte systems that represent new concepts. [ABSTRACT FROM AUTHOR]

An in-situ enabled lithium battery (or called a "Li-free" battery) is proposed by using Li-rich Li 2 CuO 2 additive to pre-plate Li metal onto Cu current collector. Conventional Cu foil is unsuitable for efficient Li cycling particularly due to poor adhesion of Li deposits to the Cu substrate and the dendritic deposition nature of Li metal. As a solution to this problem, a very thin Li metal layer is in-situ pre-plated onto the Cu surface and served as the primer layer for next Li cycling in the battery. Results show that the addition of Li 2 CuO 2 not only provides extra Li + ions for forming a very thin Li primer layer on the Cu current collector but also enhances rate capability of LiNi 0.80 Mn 0.10 Co 0.10 O 2 cathode, which is probably because the presence of CuO particles (one of Li 2 CuO 2 decomposition products) increases liquid electrolyte uphold in the cathode. [ABSTRACT FROM AUTHOR]

The capacity of transition metal oxide cathode for Li‐ion batteries can be further enhanced by increasing the charging potential. However, these high voltage cathodes suffer from fast capacity decay because the large volume change of cathode breaks the active materials and cathode‐electrolyte interphase (CEI), resulting in electrolyte penetration into broken active materials and continuous side reactions between cathode and electrolytes. Herein, a robust LiF‐rich CEI was formed by potentiostatic reduction of fluorinated electrolyte at a low potential of 1.7 V. By taking LiCoO2 as a model cathode, we demonstrate that the LiF‐rich CEI maintains the structural integrity and suppresses electrolyte penetration at a high cut‐off potential of 4.6 V. The LiCoO2 with LiF‐rich CEI exhibited a capacity of 198 mAh g−1 at 0.5C and an enhanced capacity retention of 63.5 % over 400 cycles as compared to the LiF‐free LiCoO2 with only 17.4 % of capacity retention. [ABSTRACT FROM AUTHOR]

The capacity of transition metal oxide cathode for Li‐ion batteries can be further enhanced by increasing the charging potential. However, these high voltage cathodes suffer from fast capacity decay because the large volume change of cathode breaks the active materials and cathode‐electrolyte interphase (CEI), resulting in electrolyte penetration into broken active materials and continuous side reactions between cathode and electrolytes. Herein, a robust LiF‐rich CEI was formed by potentiostatic reduction of fluorinated electrolyte at a low potential of 1.7 V. By taking LiCoO2 as a model cathode, we demonstrate that the LiF‐rich CEI maintains the structural integrity and suppresses electrolyte penetration at a high cut‐off potential of 4.6 V. The LiCoO2 with LiF‐rich CEI exhibited a capacity of 198 mAh g−1 at 0.5C and an enhanced capacity retention of 63.5 % over 400 cycles as compared to the LiF‐free LiCoO2 with only 17.4 % of capacity retention. [ABSTRACT FROM AUTHOR]

Lithium-ion capacitors, as a hybrid electrochemical energy storage device, realize high specific energy and power density within one device, thus attracting extensive attention. Here, hierarchically porous Li 3 VO 4 /C nanocomposite is prepared by a solvo-thermal reaction, followed with a post-annealing process. This composite has macropores at the center and mesopores in the wall, thus effectively promoting electrolyte penetration and structure stability upon cycling simultaneously. Compared to mesoporous Li 3 VO 4 , the enhanced rate capability and specific capacity of hierarchically porous Li 3 VO 4 /C indicate the synergistic effect of mesopores and macropores. Inspired by these results, this composite is coupled with mesoporous carbon (CMK-3) for lithium-ion capacitors, generating a specific energy density of 105 Wh kg −1 at a power density of 188 W kg −1 . Even if the power density increases to 9.3 kW kg −1 , the energy density still remains 62 Wh kg −1 . All these results demonstrate the promising potential of hierarchically porous Li 3 VO 4 in lithium ion capacitors. [ABSTRACT FROM AUTHOR]

A 2.9 V intrinsic safe aqueous LiNi0.5Mn1.5O4/Mo6S8 full cell delivers 80 W h kg−1 energy density with capacity decay of 0.075% per cycle (5 C). After the electrolyte pH value adjustment, almost full capacity of LiNi0.5Mn1.5O4 (125 mA h kg−1) is achieved, and 126 W h kg−1 energy density is provided for LiNi0.5Mn1.5O4/Mo6S8 cell, representing one of the highest voltage and energy density among all the aqueous batteries. [ABSTRACT FROM AUTHOR]

A new super-concentrated aqueous electrolyte is proposed by introducing a second lithium salt. The resultant ultra-high concentration of 28 m led to more effective formation of a protective interphase on the anode along with further suppression of water activities at both anode and cathode surfaces. The improved electrochemical stability allows the use of TiO2 as the anode material, and a 2.5 V aqueous Li-ion cell based on LiMn2O4 and carbon-coated TiO2 delivered the unprecedented energy density of 100 Wh kg−1 for rechargeable aqueous Li-ion cells, along with excellent cycling stability and high coulombic efficiency. It has been demonstrated that the introduction of a second salts into the 'water-in-salt' electrolyte further pushed the energy densities of aqueous Li-ion cells closer to those of the state-of-the-art Li-ion batteries. [ABSTRACT FROM AUTHOR]

A system of electrolytes using water as a solvent was successfully used to support a typical lithium-ion battery chemistry that operates at 3.7V–4.2 V using standard ultraviolet-cured acrylic-based polymers as hydrophobic barriers. The aqueous electrolyte is contained in a system of poly(ethylene glycol) acrylate polymers crosslinked to produce an electrolyte gel that has electrochemical properties similar to that of the liquid phase component. The electrolyte gels have elastic moduli in the kPa range, making them soft enough to tolerant flexing, cutting, and blunt force impacts while keeping the electrodes covered and safe from shorting. While batteries based on water-in-salt electrolyte provides intrinsic safety that is otherwise unavailable from typical non-aqueous electrolytes, acrylate-based aqueous gel electrolytes offer the potential of large-scale manufacturing owing to the relatively low volatility of the electrolyte components and the low complexity of the proposed manufacturing process. • UV-cured gel electrolytes were used to construct a 4 V lithium ion battery. • The main gel electrolyte was water-based, making the battery safe. • Gel electrolytes had conductivity ≥0.3 mS/cm. • Gel electrolytes exhibited favorable impedance characteristics. • Battery cells used graphite anodes and LiCoO 2 cathodes. [ABSTRACT FROM AUTHOR]