It is demonstrated that a novel eutectic solution including 1,3,5‐trioxane (TXE) and succinonitrile (SN) can be converted into solid‐state polymer electrolyte (SPE) via in situ polymerization triggered by lithium difluoro(oxalato)borate (LiDFOB). It is worth noting that all the precursors (LiDFOB, TXE, and SN) of this novel SPE are totally solid and nonvolatile at room temperature, where, LiDFOB works as a lithium salt and an initiator simultaneously to avoid the introduction of impurity. It is noted that such SPE presents a considerable ionic conductivity of 1.14 × 10 ⁻⁴ S cm ⁻¹ and a sufficiently wide electrochemical window of 4.5 V, which is significant for supporting the high‐energy lithium batteries. In addition, this dedicatedly designed in situ polymerization is powerful to build kinetically favorable polymer‐based protective layers on LiCoO ₂ cathode and Li metal anode simultaneously, guaranteeing outstanding cycling stability (capacity retention of 88% after 200 cycles) of 4.3 V LiCoO ₂ /lithium metal batteries at room temperature. More intriguingly, soft packed LiCoO ₂ /SPE/Li metal batteries can still light a blue light emitting diode (LED) under the harsh conditions of being bent, cut, and stroked by a hammer, demonstrating excellent safety characteristics.

Lithium ion batteries using liquid electrolytes often face challenges of safety issues. Polymer electrolytes can effectively solve this problem. Traditional preparation of polymer electrolytes is solution-casting method, which is complicated in practical application. Simultaneously, this ex-situ polymer electrolytes prepared by conventional method exhibits poor interfacial contact with electrodes. Fortunately, the emerging in-situ polymerization of solid state polymer electrolytes simplifies the preparation and forms an integrated interface for better interfacial compatibility in solid state lithium batteries. It is certain that solid state lithium batteries via in-situ polymerization exhibit various functionality: (1) forming integrated interface to enhance interfacial compatibility; (2) inhibiting the dissolution of transition metal ions; (3) suppressing the growth of lithium dendrites; (4) Improving the cycle performance of silicon anodes; (5) inhibiting the shuttling effect of polysulfides; (6) promoting battery performance of post-lithium batteries. Therefore, the review mainly considers and discuss the up-to-date research progress and insights on scientific issues underpinning solid state lithium batteries via in-situ polymerization strategy. Moreover, the challenges and perspectives of developing solid state lithium batteries via in-situ polymerization are discussed as well. We believe that this review will shed light on scientific and practical issues in the development of high-performance solid state lithium batteries.

Conventional liquid electrolytes based sodium metal batteries suffer from severe safety hazards owing to electrolyte leakage, inflammability and dendritic sodium deposition. Herein, we report a flame-retardant quasi-solid polymer electrolyte with poly(methyl vinyl ether-alt-maleic anhydride) (P(MVE-alt-MA)) as host, bacterial cellulose (BC) as reinforcement, and triethyl phosphate/vinylene carbonate/sodium perchlorate (TEP/VC/NaClO₄) as plasticizer for highly safe sodium metal batteries. The as-obtained quasi-solid polymer electrolyte exhibits superior flame retardancy (self-extinguish within 1 s), complete non-leakage property and wide electrochemical windows (4.4 V). More importantly, Na₃V₂(PO₄)₃/Na metal batteries using such polymer electrolyte delivers superior long-term cycling stability (84.4% capacity retention after 1000 cycles) which is significantly better than that (only 2% after 240 cycles) of liquid electrolyte. In addition, this flame-retardant quasi-solid polymer electrolyte provides favorable cycle performance (80.2% capacity retention after 70 cycles at 50 °C and 84.8% capacity retention after 50 cycles at −10 °C) for Na₃V₂(PO₄)₃/Na metal batteries. And this battery also displayed a normal charge/discharge property even at −15 °C. These fascinating cycle properties are mainly ascribed to the effective protective layers formed on Na₃V₂(PO₄)₃ cathode and sodium metal anode. More thorough investigation elucidates that such flame-retardant quasi-solid polymer electrolyte plays a multifunctional role in the advanced sodium metal batteries: (1) Being involved in the formation of a favorable cathode electrolyte interface (CEI) to inhibit the dissolution of vanadium and maintain the structure integrity of the Na₃V₂(PO₄)₃; (2) Participating in building a stable solid electrolyte interface (SEI) to suppress the growth of Na dendrites; (3) Integrating flame-retardance into polymer sodium batteries to enhance flame-resistance, eliminate electrolyte leakage, and thus improve safety of sodium batteries. Based on these results, we further assembled Na₃V₂(PO₄)₃/MoS₂ pouch cell which can withstand harsh conditions (bended or cut off a corner), confirming the obtained polymer electrolyte with superior non-leakage property. In all, these outstanding characteristics would endow this flame-retardant quasi-solid polymer electrolyte a very promising candidate for highly-safe sodium metal batteries.

We demonstrated a novel single molecule – tetrakis(4-carboxyphenyl) porphyrin (TCPP) with a large π-conjugated system as a high-performance organic anode of lithium batteries. It was found that this TCPP displayed relatively low solubility (<0.1 mg mL⁻¹) in a 1 M LiDFOB/PC electrolyte, high reversible specific capacity (ca. 1200 mA h g⁻¹ at 358 mA g⁻¹), excellent rate capability (548.4 mA h g⁻¹ at 8 A g⁻¹) and superior cycling performance (capacity retention of 89% after 2500 cycles at 6 A g⁻¹).

A strategy employing a concentrated electrolyte was proposed to boost the cycling life-span of LiCoO₂/graphite full cells at a high temperature up to 90 °C.