Insight into the Key Factors in High Li+ Transference Number Composite Electrolytes for Solid Lithium Batteries

Research Progress on the Composite Methods of Composite Electrolytes for Solid-State Lithium Batteries

In the current challenging energy storage and conversion landscape, solid-state lithium metal batteries with high energy conversion efficiency, high energy density, and high safety stand out. Due to the limitations of material properties, it is difficult to achieve the ideal requirements of solid electrolytes with a single-phase electrolyte. A composite solid electrolyte is composed of two or more different materials. Composite electrolytes can simultaneously offer the advantages of multiple materials. Through different composite methods, the merits of various materials can be incorporated into the most essential part of the battery in a specific form. Currently, more and more researchers are focusing on composite methods for combining components in composite electrolytes. The ion transport capacity, interface stability, machinability, and safety of electrolytes can be significantly improved by selecting appropriate composite methods. This review summarizes the composite methods used for the components of composite electrolytes, such as filler blending, embedded framework, and multilayer bonding. It also discusses the future development trends of all-solid-state lithium batteries (ASSLBs).

Hybrid Solid Polymer Electrolytes Based on Epoxy Resins, Ionic Liquid, and Ceramic Nanoparticles for Structural Applications

Solid polymer electrolytes (SPE) and composite polymer electrolytes (CPE) serve as crucial components in all-solid-state energy storage devices. Structural batteries and supercapacitors present a promising alternative for electric vehicles, integrating structural functionality with energy storage capability. However, despite their potential, these applications are hampered by various challenges, particularly in the realm of developing new solid polymer electrolytes that require more investigation. In this study, novel solid polymer electrolytes and composite polymer electrolytes were synthesized using epoxy resin blends, ionic liquid, lithium salt, and alumina nanoparticles and subsequently characterized. Among the formulations tested, the optimal system, designated as L70P30ILE40Li1MAl2 and containing 40 wt.% of ionic liquid and 5.7 wt.% of lithium salt, exhibited exceptional mechanical properties. It displayed a remarkable storage modulus of 1.2 GPa and reached ionic conductivities of 0.085 mS/cm at 60 °C. Furthermore, a proof-of-concept supercapacitor was fabricated, demonstrating the practical application of the developed electrolyte system.

Anionic Anchoring Enhanced Quasi Solid Composite Polymer Electrolytes for High Performance Lithium Metal Battery

Herein, ZIF-8 inorganic particles with different sized reinforced poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) solid composite polymer electrolytes (PVDF-HFP/10%ZIF-8) were prepared via a facile blade-coating approach, and free-standing quasi solid-state composite electrolytes (PVDF-HFP/10%ZIF-8(0.6)/Plasticizer, abbreviated as PH/10%ZIF-8(0.6)/P), were further obtained through the introduction of plasticizer. Optimized PH/10%ZIF-8(0.6)/P exhibited a high ionic conductivity of 2.8 × 10-4 S cm-1 at 30 °C, and superior Li+ transfer number of 0.89 with an ultrathin thickness (26 µm). Therefore, PH/10%ZIF-8(0.6)/P could effectively inhibit the growth of lithium dendrites, and the assembled Li/LiFePO4 cell delivered good cycling stability with a capacity retention rate of 89.1% after 100 cycles at 0.5 C.

In Situ and Low-Cost Improvement of the Lithium Anode Interface in Garnet-Type Solid-State Electrolytes

In recent years, the development of electric vehicles and environmental concerns have made necessary improvements in the energy density and safety of lithium-ion batteries. Therefore, the development of all-solid-state lithium-ion batteries (ASSLIBs) has become imperative. One advantage of ASSLIBs is their potential for downsizing with the use of lithium metal as the anode. However, in this study, a garnet-type solid electrolyte (Li6.75La3Zr1.75Ta0.25O12) was used, which has low reactivity with lithium metal. Thus, interface modification using CaCl2 was employed to form a Li-Ca-Cl composite anode. The interfacial resistance was remarkably reduced to 7 Ω cm2, and the symmetric cell exhibited stable cycling for 1200 h at room temperature and a current density of 0.1 mA cm-2. The voltage ranged from ±15 to ±16 mV. The full cell demonstrated a high initial discharge capacity of 149.2 mA h g-1 and a Coulombic efficiency of 98.0% while maintaining a discharge capacity retention of 91.3% after 100 cycles. These findings lay a solid foundation for future commercial applications as interface modification was achieved through a simple spin-coating process using low-cost CaCl2 (0.7 USD g-1).

Synergistic Effect of the Anode Interface of Garnet-Type All-Solid-State Batteries

Next-generation lithium-ion batteries must have high energy density and safety, making the development of all-solid-state batteries imperative. One of the biggest advantages of an all-solid-state lithium-ion battery (ASSLIB) is that its alloy uses lithium metal as an anode while ignoring its flammability and other dangers. Herein, high-conductivity garnet-type Li6.75La3Zr1.75Ta0.25O12 (LLZTO) was chosen as the solid electrolyte part of an all-solid-state battery. A composite anode was formed by melting Li and MXene-MAX together, reducing the interface impedance from 566 to 55 Ω cm2. The Li-MXene|LLZTO|LFP full battery displayed a high initial discharge capacity of 163.0 mAh g-1 and a Coulombic efficiency of 97.0% and maintained 90.2% of its discharge capacity over 100 cycles, but it did not maintain a good overpotential. Therefore, the synergistic effect of Li-MXene-Pt will highly improve the performance of the full battery because of its high initial discharge capacity of 150.0 mAh g-1 and Coulombic efficiency of 95.5%, discharge capacity maintained at 93.3% over 100 cycles, and low overpotential of 0.04 V.

LLZTO Nanoparticle- and Cellulose Mesh-Coreinforced Flexible Composite Electrolyte for Stable Li Metal Batteries

Composite electrolytes have been regarded as the most prospective electrolytes for commercial application because they acquire the advantages of both polymer and inorganic electrolytes, commonly exhibiting appreciated flexibility and suitable ionic conductivity. Nevertheless, the conventional solution-casting method with toxic solvent and poor interfacial contact still hamper their commercialization process. Moreover, electrolytes with higher ionic conductivity and transference number are urgently needed for satisfying fast-charging batteries. Herein, a novel composite electrolyte (LZEC) reinforced by mechanically robust LLZTO nanoparticles and flexible cellulose mesh was fabricated by a simple and advanced in situ thermal polymerization method, with adding of highly ion-conductive liquid plasticizer. Consequently, the rationally designed LZEC composite electrolyte exhibits superior flexibility and remarkable electrochemical properties in the form of high ionic conductivity, wide electrochemical stability window, and high Li+ transference number. Importantly, the in situ synthesis method is expected to help construct an enhanced electrolyte/electrode interface inside the battery, and the LZEC composite electrolyte is capable of suppressing Li dendrite growth effectively, as evidenced by the prolonged stable cycling of the Li/Li symmetric cell. Therefore, the LFP/LZEC/Li full cell exhibits superior rate performance and long cyclic life. These attractive properties make LZEC a potential composite electrolyte for boosting the practical application of safe and long-life Li metal batteries.

Composite polymer electrolytes with ionic liquid grafted-Laponite for dendrite-free all-solid-state lithium metal batteries

Composite polymer electrolytes (CPEs) with high ionic conductivity and favorable electrolyte/electrode interfacial compatibility are promising alternatives to liquid electrolytes. However, severe parasitic reactions in the Li/electrolyte interface and the air-unstable inorganic fillers have hindered their industrial applications. Herein, surface-edge opposite charged Laponite (LAP) multilayer particles with high air stability were grafted with imidazole ionic liquid (IL-TFSI) to enhance the thermal, mechanical, and electrochemical performances of polyethylene oxide (PEO)-based CPEs. The electrostatic repulsion between multilayers of LAP-IL-TFSI enables them to be easily penetrated by PEO segments, resulting in a pronounced amorphous region in the PEO matrix. Therefore, the CPE-0.2LAP-IL-TFSI exhibits a high ionic conductivity of 1.5 × 10-3 S cm-1 and a high lithium-ion transference number of 0.53. Moreover, LAP-IL-TFSI ameliorates the chemistry of the solid electrolyte interphase, significantly suppressing the growth of lithium dendrites and extending the cycling life of symmetric Li cells to over 1000 h. As a result, the LiFePO4||CPE-0.2LAP-IL-TFSI||Li cell delivers an outstanding capacity retention of 80% after 500 cycles at 2C at 60 °C. CPE-LAP-IL-TFSI also shows good compatibility with high-voltage LiNi0.8Co0.1Mn0.1O2 cathodes.

Spontaneous In Situ Formation of Lithium Metal Nitride in the Interface of Garnet-Type Solid-State Electrolyte by Tuning of Molten Lithium

All-solid-state lithium-ion batteries (ASSLIBs) have attracted much attention owing to their high energy density and safety and are known as the most promising next-generation LIBs. The biggest advantage of ASSLIBs is that it can use lithium metal as the anode without any safety concerns. This study used a high-conductivity garnet-type solid electrolyte (Li6.75La3Zr1.75Ta0.25O12, LLZTO) and Li-Ga-N composite anode synthesized by mixing melted Li with GaN. The interfacial resistance was reduced from 589 to 21 Ω cm2, the symmetry cell was stably cycled for 1000 h at a current density of 0.1 mA cm-2 at room temperature, and the voltage range only changed from ±30 to ±40 mV. The full cell of Li-Ga-N|LLZTO|LFP exhibited a high first-cycle discharge capacity of 152.2 mAh g-1 and Coulombic efficiency of 96.5% and still maintained a discharge capacity retention of 91.2% after 100 cycles. This study also demonstrated that Li-Ga-N had been shown as two layers. Li3N shows more inclined to be closer to the LLZTO side. This method can help researchers understand what interface improvements can occur to enhance the performance of all-solid-state batteries in the future.