A Review on Regulating Li⁺Solvation Structures in Carbonate Electrolytes for Lithium Metal Batteries

Abstract

urgent need to exploit "'beyond LIBs"' that can meet this demand. [6][7][8][9][10] For the anode side, the lightweight (0.534 g cm −3 ), low electrochemical redox potential (−3.04 V vs standard hydrogen electrode), and high theoretical capacity (3860 mAh g −1 ) of lithium make it an attractive candidate for the anode as an alternative to graphite. [1,3,[11][12][13][14][15] For the cathode side, in addition to exploring materials with a high capacity such as sulfur or oxygen, which bring additional problems caused by new materials, increasing the cut-off voltage is the most effective way to boost the energy density. [3,4,6] Therefore, lithium metal batteries (LMBs) coupled with a high-voltage cathode are highly expected to be the nextgeneration battery systems.However, the development of electrolytes has always lagged far behind electrodes and enormous attention is expected to the development of electrolytes compatible with both the cathodes and anodes. Various electrolyte recipes have demonstrated great performance and among them, carbonate-based and ether-based electrolytes are the most used electrolytes. Despite that much higher Coulombic efficiency could be realized in ether-based electrolytes due to the formation of an elastic interface that helps withstand large volume changes of lithium during cycling, [16] the cut-off voltages of the full cells are usually no more than 4.6 V even in high concentration electrolytes (HCEs) and localized high concentration electrolytes (LHCEs) because of the limited intrinsic electrochemical window of ethers, hindering their use in high-voltage battery systems. [6,[17][18][19][20][21][22] Moreover, the flash points of ethers are relatively low and gas generation occurs in ether-based electrolytes at a high voltage of ≈4.6 V even in a LHCE, [23,24] making it unsuitable for very high voltage operation. Therefore, carbonate electrolytes with good oxidative stability and high flash points that have long been used in commercial LIBs are the most cost-effective and suitable to be adopted in high-voltage LMBs. [25] However, conventional ethylene carbonate (EC)-based electrolytes are not stable against the lithium metal anode, forming a low-quality interface on it that leads to the uncontrolled growth of lithium, which aggravates the consumption of the electrolyte and eventually leads to battery failure. [6,7,16] These EC-based electrolytes also undergo a series of side reactions with Ni-rich cathodes, including nucleophilic and dehydrogenation reactions, and ring-opening. [4,6] The decomposition of lithium hexafluorophosphate (LiPF 6 ), the mainstream salt, is another critical issue of carbonate electrolytes because it Lithium metal batteries (LMBs) are considered promising candidates for nextgeneration battery systems due to their high energy density. However, commercialized carbonate electrolytes cannot be used in LMBs due to their poor compatibility with lithium metal anodes. While increasing cut-off voltage is an effective way to boost the energy density of LMBs, conventional et...

Theory of Cation Solvation and Ionic Association in Non-Aqueous Solvent Mixtures

“…Lithium-ion batteries (LIBs) have transformed our everyday lives through myriad portable electronic devices [1][2][3][4][5][6][7][8]. Although current LIBs are tremendously successful, further development is necessary to meet safety and performance requirements for widespread use of electric vehicles and grid-level energy storage of renewable energy [4][5][6][7][8].…”

“…Lithium-ion batteries (LIBs) have transformed our everyday lives through myriad portable electronic devices [1][2][3][4][5][6][7][8]. Although current LIBs are tremendously successful, further development is necessary to meet safety and performance requirements for widespread use of electric vehicles and grid-level energy storage of renewable energy [4][5][6][7][8]. Thus, much of electrochemical energy storage research is focused on improving the materials beyond commerical LIBs, including high voltage and high capacity cathode materials [9], silicon anodes [10], lithium metal anodes [11][12][13], and even nonlithium based battery chemistries [14][15][16].…”

“…Thus, much of electrochemical energy storage research is focused on improving the materials beyond commerical LIBs, including high voltage and high capacity cathode materials [9], silicon anodes [10], lithium metal anodes [11][12][13], and even nonlithium based battery chemistries [14][15][16]. A requirement of any next-generation battery chemistry is an electrolyte that can operate safely, efficiently and reversibly over the course of the battery's lifetime [1][2][3][4][5][6][7][8].…”

“…One of the primary design concepts in electrolyte engineering is balancing desired, often seemingly conflicting, physicochemical properties, such as low viscosity and high conductivity, with interfacial properties, such as low charge transfer resistance and electrode passivation [4]. Commercial LIBs accomplish this design concept, to some extent, with blends of linear carbonates, such as dimethyl carbonate (DMC) for low viscosity, and cyclic carbonates, such as ethylene carbonate (EC) to passivate carbonaceous anodes [1][2][3][4][5][6][7][8]. Although carbonate blends provide a serviceable solution, electrolyte design for LIBs is far from optimized [4][5][6][7][8].…”

“…Commercial LIBs accomplish this design concept, to some extent, with blends of linear carbonates, such as dimethyl carbonate (DMC) for low viscosity, and cyclic carbonates, such as ethylene carbonate (EC) to passivate carbonaceous anodes [1][2][3][4][5][6][7][8]. Although carbonate blends provide a serviceable solution, electrolyte design for LIBs is far from optimized [4][5][6][7][8].…”