ABSTRACT
Lithium-ion batteries (LIBs) have been widely used in almost all types of electronic devices for decades. 1 , 2 Typical LIBs consist of a negative electrode (anode), a positive electrode (cathode), an electrolyte solution with dissociated salts, and a separator. The electrodes are isolated by a separator, through which ions can be transported. The electrolytes containing dissociated salts are a key component in LIBs, enabling ion transfer between the two electrodes and influencing the cycling performance, capacity, and safety of LIBs. Flammable and volatile organic solvents are used as electrolytes in commercial LIBs. Li metal anodes for LIBs have long been developed because of the high specific capacity (3860 mAh g−1) and low electrochemical potential (−3.04 V vs SHE) of metallic Li. 3–5 The instability of conventional organic liquid electrolytes (LEs) against Li metal results in safety concerns related to Li dendrite growth; therefore, 216graphite has replaced the Li metal as the anode in commercial LIBs. 6 , 7 , 5 The energy density of contemporary LIBs (theoretically 390 W h kg−1 and practically 100–200 W h kg−1) does not meet demands for energy storage. 5 , 2 The low-energy density of graphite anodes has slowed the further development of LIBs; thus, graphite anodes are incapable of fulfilling the growing consumer demand for advanced technologies. Moreover, the development of batteries with safer electrolytes and design, high-energy density, and enhanced battery life is urgently required. Gel and solid-state electrolytes (SSEs) have been proposed as a replacement for conventional organic LEs to overcome safety concerns. Gel polymer electrolytes (GPEs) composed of liquid plasticizers/organic solvents have been incorporated into polymer-salt systems. Because LE components remain in the GPE system, the safety concerns for LIBs cannot be completely resolved. SSEs are a promising candidate for safer high-energy density Li metal batteries because of their high mechanical strength, which is capable of preventing internal short circuits of the battery by blocking Li dendrite penetration. In this chapter, we discuss various SSE types and properties. The primary challenges associated with SSEs and efforts exerted to overcome these challenges for their commercialization are also briefly discussed. GPEs for LIBs are also discussed.
