How far has the research and development of solid-state battery technology progressed? Where are the areas of focus?
In response to these problems, NE Times interprets the progress of solid-state battery technology in the power battery research and development project led by the U.S. Department of Energy's Vehicle Technology Office (VTO) for readers. The U.S. Department of Energy's Office of Vehicle Technology provides support for advanced vehicle technology research and development. In fiscal year 2019, VOT's battery research and development funding was approximately US$106 million. Battery research and development projects include advanced battery cell research and development, battery material research and development, etc. Due to space limitations, part of the content will continue to be serialized thereafter. This article mainly introduces the solid-state inorganic nanofiber network polymer composite electrolyte project for lithium batteries in solid-state battery research.
Solid State Inorganic Nanofiber Network Polymer Composite Electrolytes for Lithium Batteries
Due to the unstable and flammable liquid organic electrolytes currently widely used, the safety of batteries has attracted much attention. Solid-state batteries can effectively solve the safety problem of batteries, and solid-state batteries have high mechanical strength and strong electrochemical stability, which can improve the chemical stability and thermal stability of lithium batteries.
Development of polymer-based solid-state electrolytes based on highly conductive inorganic nanofiber networks for use in lithium-ion batteries.
Integrating an inorganic nanofibrous network with high Li-ion conductivity into a polymer matrix not only provides continuous Li transport channels but also inhibits the crystallization of amorphous polymer electrolytes.
Inorganic nanofibers were prepared by electrospinning technology.
The ionic conductivity of inorganic nanofibers is improved by chemical substitution or doping.
Development of highly ionically conductive polymers by crosslinking and/or forming block copolymer structures.
The formation of lithium dendrites is suppressed by designing the composition and microstructure of the composite electrolyte.
(1) Flexible electrolyte-cathode bilayer structure with stable interface for all-solid-state lithium-sulfur batteries at room temperature.
Under the bilayer structure, Li0.33La0.557TiO3 (LLTO) nanofiber-polyoxyethylene (PEO) solid-state composite electrolyte and three-dimensional carbon nanofiber/sulfur (CNF/S) cathode were used as electrolyte and cathode. At room temperature, the decomposition potential of the LLTO/PEO composite electrolyte is about 4.5 Vvs. Li/Li+, the ionic conductivity is 2.3×10-4S·cm-1, and the content of LLTO nanofibers is 13 wt%.
The above lithium-sulfur battery was tested at room temperature without adding any liquid electrolyte. After 50 cycles, the coulombic efficiency of the battery remained at 99%. The test results are shown in the figure below.
(a) Voltage curves at room temperature with a current density of 0.5 mA cm-2 (inset: left: voltage curves of PEO and PEO/LLTO tested at 201–203 cycles; right: PEO/LLTO tested at 990–1000 cycles The voltage curve of ); (b) the cycle performance of the full cell with sulfur loading of 1.27 mg cm-2 (0.05 C (0.084 mA cm-2)); 0.05 C (0.084 mA cm-2), 0.1 C ( (c) charge-discharge curves and (d) rate capacity of full cells tested at 0.168 mA cm-2) and 0.2 C (0.335 mA cm-2)
(2) Garnet-rich composite solid electrolyte for solid-state lithium metal batteries without dendrites and high rate.
A novel composite solid electrolyte was developed, which was composed of silane-modified Li6.28La3Al0.24Zr2O12 nanofibers (s@LLAZO) and polyethylene glycol diacrylate (PEGDA). When s@LLAZO accounts for 60 wt%, the ionic conductivity of the composite electrolyte reaches 4.9×10-4S·cm-1, and the oxidative decomposition of the s@LLAZO-60PEGDA composite electrolyte starts at 5.3V.
Using this composite electrolyte, an all-solid-state battery with pure metal lithium as the negative electrode and lithium iron phosphate as the positive electrode was assembled. It exhibits excellent rate performance and cycling stability from 0.5C to 10C.
In short, the novel composite electrolyte containing s@LLAZO nanofibers opens a new avenue for the development of all-solid-state Li-ion batteries.
(3) Chemical interaction and strong interfacial ion transport capability of ceramic nanofiber-polymer composite electrolytes for all-solid-state lithium metal batteries.
A solid ceramic/polymer composite electrolyte was developed by combining the three-dimensional electrospun aluminum-doped LLTO nanofiber network in polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) as the matrix. Additionally, the LLTO nanofibers were coated with lithium phosphate before embedding the nanofibers into the polymer matrix. At room temperature, the ionic conductivity of the LLTO/Li3PO4/polymer composite electrolyte is 5.1×10-4S/cm-1, and the electrochemical stability window is 5.0 V vs Li/Li+.
Solid-state nuclear magnetic resonance (NMR) spectra revealed three pathways for lithium ion transport: (i) intrapolymer transport, (ii) intra-nanofiber transport and (iii) polymer/nanofiber interface transport.
The LiFePO4|PVDF-HFP/LLTO/Li3PO4|Li battery has a specific discharge capacity of 130.7mAh g−1 at 0.5C. After 160 cycles, the capacity retention rate is 87.8%, and the Coulombic efficiency remains above 99.4%. The discharge specific capacities at 0.1C, 0.2C, 0.5C, 1C, and 2C are 158, 147, 133, 98, and 76 mAh g−1, respectively, followed by a reversible capacity of 149 mAh g−1 when switched back to 0.1 C. 1.
(4) Solid polymer-garnet composite electrolyte with plastic crystals added.
A solid polymer electrolyte with plastic crystals was developed by adding SN plasticizer to poly(ethylene glycol methacrylate) and pentaerythritol tetraacrylate (PETA) cross-linked polymer.
The ionic conductivity of the polymer electrolyte at room temperature is 8.3×10-4S·cm-1, and the electrochemical stability window is 4.7V vs Li/Li+. After adding 20 wt.% LLAZO nanofibers, the ionic conductivity of the composite electrolyte at room temperature is 8.5×10-4S·cm-1, and the electrochemical stability window is 5.0V vs Li/Li+.
1. The LLTO ceramic nanofiber/PEO composite electrolyte was coupled with a three-dimensional flexible carbon nanofiber/sulfur (CNF/S) cathode to prepare a composite double-layer structure. The full battery with this double-layer structure showed good performance at room temperature. Electrochemical performance, Coulombic efficiency reaches more than 99%.
2. Due to the improved utilization of the fast ionic conductor (LLAZO) in the composite structure, the all-solid-state battery using the s@LLAZO-60PEGDA composite electrolyte exhibits stable cycling performance and excellent rate after 200 cycles at room temperature performance (up to 10C).
3. The LLTO nanofibers are doped with aluminum and then coated with lithium phosphate to form a continuous lithium ion conductive network, which promotes the transport of lithium ions on the LLTO nanofibers. The ionic conductivity of PVDF-HFP/LLTO/Li3PO4 reaches 5.1×10-4S/cm, and the full battery using this electrolyte and lithium metal anode has good cycle performance and rate capability. This study demonstrates that the interfacial synergy between nanoceramic fibers and polymers has a significant impact on the electrochemical performance of composite electrolytes.