Modulating composite polymer electrolyte by lithium closo-borohydride achieves highly stable solid-state battery at 25°C

Abstract

Rational composite design is highly important for the development of high-performance composite polymer electrolytes (CPEs) for solid-state lithium (Li) metal batteries. In this work, Li closo-borohydride, Li 2 B 12 H 12 , is introduced to poly(vinylidene fluoride)-Li-bis-(trifluoromethanesulfonyl) imide (PVDF-LiTFSI) with a bound N-methyl pyrrolidone plasticizer to form a novel CPE. This CPE shows superb Li + conduction properties, as evidenced by its conductivity of 1.43 × 10 −4 S cm −1 and Li + transference number of 0.34 at 25°C. Density functional theory calculations reveal that Li 2 B 12 H 12 , which features electron-deficient multicenter bonds, can facilitate the dissociation of LiTFSI and enhance the immobilization of TFSI to improve the Li + conduction properties of the CPE. Moreover, the fabricated CPE exhibits excellent electrochemical, thermal, and mechanical stability. The addition of Li 2 B 12 H 12 can help form a protective layer at the anode/ electrolyte interface, thereby preventing unwanted reactions. The above benefits of the fabricated CPE contribute to the high compatibility of the electrode. Symmetric Li cells can be stably cycled at 0.2 mA cm −2 for over 1200 h, and Li||LiFePO 4 cells can deliver a reversible specific capacity of 140 mA h g −1 after 200 cycles at 1 C at 25°C with a capacity retention of 98%.

Complex Metal Borohydrides: From Laboratory Oddities to Prime Candidates in Energy Storage Applications

“…Recent trends in improving ionic conductivity have explored complexes with weaker coordinating ligands/counteranions, as is the case for CaB 12 H 12 [ 277 ]. Despite their low electrochemical stability, borohydrides give rise to rich speciation: nido- (typical tetrahydroborate BH 4 − ), planar- (B 6 H 6 6− ), and closo (B 10 H 10 2− ; B 12 H 12 2− ), making their alkali (Li + , Na + , K + ) and alkali-earth (Mg 2+ , Ca 2+ ) salts particularly appealing in ion conduction applications [ 278 , 279 , 280 , 281 ]. The ionic conductivity trend correlates well with the size of the hydroborate species ( Figure 11 ).…”

Enhanced Electrochemical Performance of the Li2B12H12-Li2B10H10-LiBH4 Electrolyte

“…Closo -borates, such as Li 2 B 12 H 12 and Li 2 B 10 H 10 , were observed as typical intermediates during the hydrogen sorption reaction of LiBH 4 , and show great chemical and thermal stability. − Regarding the low ionic conductivity of 10 –8 S cm –1 at RT, , various approaches have been developed to improve the conduction properties, e.g., ball milling, , the creation of polymer-based electrolytes, , interface engineering, and building anion-mixed composite . In our previous work, a composite of Li 2 B 12 H 12 -5Li 2 B 10 H 10 shows the enhanced ionic conductivity of 10 –5 S cm –1 at RT, attributing to a formation of hydrogen-deficient γ-Li 2 B 10 H 10– x . , …”

Less Is More: High-Performance All-Solid-State Electrode Enabled by Multifunctional MXene

“…All-solid-state lithium-ion batteries (ASSLIBs) exhibit commercial advantages over conventional lithium-ion batteries with liquid electrolyte. − To date, previous efforts have been devoted to increasing the ionic conductivity of various solid electrolytes, − in which the Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 solid electrolyte with an ionic conductivity of 25 mS cm –1 even exceeds the commercial liquid electrolyte . Thus, recent attention has been shifted to the development of electrodes.…”