Solid-state Li Metal Batteries Research Articles

Stabilizing Solid Electrolyte-Anode Interface in Li-Metal Batteries by Boron Nitride-Based Nanocomposite Coating

Summary Solid-state Li-metal batteries are promising to improve both safety and energy density compared to conventional Li-ion batteries. However, various high-performance and low-cost solid electrolytes are incompatible with Li, which is indispensable for enhancing energy density. Here, we utilize a chemically inert and mechanically robust boron nitride (BN) film as the interfacial protection to preclude the reduction of Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte by Li, which is validated by in situ transmission electron microscopy. When combined with ∼1–2 μm PEO polymer electrolyte at the Li/BN interface, Li/Li symmetric cells show a cycle life of over 500 h at 0.3 mA·cm−2. In contrast, the same configuration with bare LATP dies after 81 h. The LiFePO4/LATP/BN/PEO/Li solid-state batteries show high capacity retention of 96.6% after 500 cycles. This study offers a general strategy to protect solid electrolytes that are unstable against Li and opens possibilities for adopting them in solid-state Li-metal batteries.

An effective LiBO2 coating to ameliorate the cathode/electrolyte interfacial issues of LiNi0.6Co0.2Mn0.2O2 in solid-state Li batteries

Solid-state batteries provide a safe and high energy density solution to next-generation energy storage devices. However, unsatisfactory power capability and cycling stability raised from lithium diffusion resistance and catalytic reaction at the electrode/electrolyte interface critically restrict their development. In this study, these interfacial issues are ameliorated by LiBO2 coating to achieve the successful implementation of nickel-rich LiNi0.6Co0.2Mn0.2O2 in poly(ether-acrylate) based solid-state batteries. The continuous coating acts not only as a physical barrier hindering the decomposition of polymer electrolyte but also as a buffer layer promoting lithium diffusion across the space charge layer owing to its electronic insulativity and ionic conductivity. In consequence, the LiBO2 coated nickel-rich cathode delivers superior cycling stability with a capacity retention of 84.3% during 150 cycles at 0.5C, remarkably improved lithium diffusion kinetics with an order of magnitude increase in apparent diffusion coefficient and prominent power performance with 97 mA h g−1 at 2C. The effectiveness of inserting such functional interlayer emphasizes the essentiality of interfacial chemistry in building high-performance solid-state Li metal batteries.

Tuning the interface by a soldering method for high performance garnet-type solid-state Li metal battery

Garnet-type solid electrolytes are promising lithium (Li) ion conductors for all-solid-state batteries. However, their poor compatibilities towards Li metal due to their inherently lithiophobic properties severely hinder their practical application in garnet-based solid-state Li metal batteries (SSLBs). Here, we demonstrated a soldering method to modify the surface of garnet ceramic by forming a thin artificial sulfur layer, which results in a homogeneous and stable Li/solid electrolyte interface. This artificial interface effectively enhances the compatibility between the garnet-type solid electrolyte and the Li metal anode. Consequently, the interfacial resistance of sulfur-coated garnet electrolyte is significantly reduced from 1750 Ω cm2 to 160 Ω cm2 based on the electrochemical impedance spectroscopy (EIS) measurements on Li symmetric cells. Besides, the symmetric cell exhibits an excellent lifetime of more than 1100 h at a steady state of voltage hysteresis, which indicates a stable and dendrite-free garnet/Li metal interface. The fabricated Li|garnet|LiCoO2 SSLB using this novel interfacial treatment delivers a high specific capacity of 126 mAh g−1 and good cycling stability.

The Cathode Composition, A Key Player in the Success of Li-Metal Solid-State Batteries

Polymer–ceramic composite electrolytes are major contenders for applications in commercial Li-metal solid-state batteries. However, the cycling performance and energy density of such batteries are ...

Extended Electrochemical Window of Solid Electrolytes via Heterogeneous Multilayered Structure for High-Voltage Lithium Metal Batteries.

In response to the call for safer high-energy-density storage systems, high-voltage solid-state Li metal batteries have attracted extensive attention. Therefore, solid electrolytes are required to be stable against both Li anode and high-voltage cathodes; nevertheless, the requirements still cannot be completely satisfied. Herein, a heterogeneous multilayered solid electrolyte (HMSE) is proposed to broaden electrochemical window of solid electrolytes to 0-5 V, through different electrode/electrolyte interfaces to overcome the interfacial instability problems. Oxidation-resistance poly(acrylonitrile) (PAN) is in contact with the cathode, while reduction tolerant polyethylene glycol diacrylate contacts with Li metal anode. A Janus and flexible PAN@Li1.4 Al0.4 Ge1.6 (PO4 )3 (80 wt%) composite electrolyte is designed as intermediate layer to inhibit dendrite penetration and ensure compact interface. Paired with LiNi0.6 Co0.2 Mn0.2 O2 and LiNi0.8 Co0.1 Mn0.1 O2 cathodes, which are rarely used in solid-state batteries, the solid-state Li metal batteries with HMSE exhibit excellent electrochemical performance including high capacity and long cycle life. Besides, the Li||Li symmetric batteries maintain a stable polarization less than 40 mV for more than 1000 h under 2 mA cm-2 and effective inhibition of dendrite formation. This study offers a promising approach to extend the applications of solid electrolytes for high-voltage solid-state Li metal batteries.

Chemically exfoliated boron nitride nanosheets form robust interfacial layers for stable solid-state Li metal batteries.

Two-dimensional (2D) boron nitride nanosheets (BNNSs) were chemically exfoliated from bulk boron nitride and coated onto the surface of a poly(ethylene oxide) (PEO)-based electrolyte through a dry-pressing transfer process. The fabricated BNNSs coating formed a robust interfacial layer to improve the chemical and mechanical stability of the PEO-based electrolyte, leading to the enhanced performance of solid-state Li metal batteries.

A branched cellulose-reinforced composite polymer electrolyte with upgraded ionic conductivity for anode stabilized solid-state Li metal batteries

Branched cellulose filler is used to reinforce the PEO based polymer electrolyte, resulting in the upgraded ionic conductivity and anode stability for solid-state Li metal batteries.

Fluorinated solid electrolyte interphase enables highly reversible solid-state Li metal battery.

Solid-state electrolytes (SSEs) are receiving great interest because their high mechanical strength and transference number could potentially suppress Li dendrites and their high electrochemical stability allows the use of high-voltage cathodes, which enhances the energy density and safety of batteries. However, the much lower critical current density and easier Li dendrite propagation in SSEs than in nonaqueous liquid electrolytes hindered their possible applications. Herein, we successfully suppressed Li dendrite growth in SSEs by in situ forming an LiF-rich solid electrolyte interphase (SEI) between the SSEs and the Li metal. The LiF-rich SEI successfully suppresses the penetration of Li dendrites into SSEs, while the low electronic conductivity and the intrinsic electrochemical stability of LiF block side reactions between the SSEs and Li. The LiF-rich SEI enhances the room temperature critical current density of Li3PS4 to a record-high value of >2 mA cm-2. Moreover, the Li plating/stripping Coulombic efficiency was escalated from 88% of pristine Li3PS4 to more than 98% for LiF-coated Li3PS4. In situ formation of electronic insulating LiF-rich SEI provides an effective way to prevent Li dendrites in the SSEs, constituting a substantial leap toward the practical applications of next-generation high-energy solid-state Li metal batteries.

Interface Engineering for Garnet-Based Solid-State Lithium-Metal Batteries: Materials, Structures, and Characterization.

Lithium-metal batteries are considered one of the most promising energy-storage systems owing to their high energy density, but their practical applications have long been hindered by significant safety concerns and poor cycle stability. Solid-state electrolytes (SSEs) are expected to improve not only the safety but also the energy density of Li-metal batteries. The key challenge for solid-state Li-metal batteries lies in the low ionic conductivity of the SSEs and moreover the interface contact between the electrode and SSE. To achieve feasible solid-state Li-metal batteries, it is imperative that the ionic conductivity is improved, especially at the electrode-SSE interface. Herein, recent advances in interface engineering for solid-state Li-metal batteries are reported, mainly focusing on garnet-type SSEs. Various materials to modify the cathode-garnet and Li-garnet interfaces by intermediate layers, alloys, and polymer electrolytes are analyzed. Structural innovations for SSEs including composite electrolytes and multilayer SSE frameworks are reviewed, along with advanced characterization approaches to probe the interfaces, which will provide further insights for garnet-based solid-state batteries. Future challenges and the great promise of garnet-based Li-metal batteries are discussed to close.

Salt-Based Organic-Inorganic Nanocomposites: Towards A Stable Lithium Metal/Li10 GeP2 S12 Solid Electrolyte Interface.

Solid-state Li metal battery technology is attractive, owing to the high energy density, long lifespans, and better safety. A key obstacle in this technology is the unstable Li/solid-state electrolyte (SSE) interface involving electrolyte reduction by Li. Herein we report a novel approach based on the use of a nanocomposite consisting of organic elastomeric salts (LiO-(CH2 O)n -Li) and inorganic nanoparticle salts (LiF, -NSO2 -Li, Li2 O), which serve as an interphase to protect Li10 GeP2 S12 (LGPS), a highly conductive but reducible SSE. The nanocomposite is formed in situ on Li via the electrochemical decomposition of a liquid electrolyte, thus having excellent chemical and electrochemical stability, affinity for Li and LGPS, and limited interfacial resistance. XPS depth profiling and SEM show that the nanocomposite effectively restrained the reduction of LGPS. Stable Li electrodeposition over 3000 h and a 200 cycle life for a full cell were achieved.

Resolving the Amorphous Structure of Lithium Phosphorus Oxynitride (Lipon)

Lithium phosphorus oxynitride,also known as Lipon, solid-state electrolytes are at the center of the search for solid-state Li metal batteries. Key to the performance of Lipon is a combination of high Li content, amorphous character, and the incorporation of N into the structure. Despite the material's importance, our work presents the first study to fully resolve the structure of Lipon using a combination of ab initio molecular dynamics, density functional theory, neutron scattering, and infrared spectroscopy. The modeled and experimental results have exceptional agreement in both neutron pair distribution function and infrared spectroscopy. Building on this synergy, the structural models show that N forms both bridges between two phosphate units and nonbridging apical N. We further show that as the Li content is increased the ratio of bridging to apical N shifts from being predominantly bridging at Li contents around 2.5:1 Li:P to only apical N at higher Li contents of 3.38:1 Li:P. This crossover from bridging to apical N appears to directly correlate withand explain both the increase in ionic conductivity with the incorporation of N and the ionic conductivity trends found in the literature.

Solid polymer electrolyte soft interface layer with 3D lithium anode for all-solid-state lithium batteries

Garnet electrolyte-based lithium (Li) metal batteries, which employ garnet-type Li7La3Zr2O12 (LLZO) as electrolyte and Li metal as anode, are regarded as a promising candidate for high-energy batteries. However, Li dendrites formation as well as poor solid-solid contact between the electrolyte and electrodes result in high interfacial resistance, large polarizations, and low Coulombic efficiency. Herein, we demonstrated that solid polymer electrolyte (SPE) soft interface layer deposited on garnet electrolyte (Ta-doped LLZO (LLZTO)) surface along with 3D Li metal anode can address these obstacles. In this architecture, SPE layer was deposited on garnet electrolyte surface to endow connected interface between the electrolyte and electrodes and thus settled the interface contact issue. 3D Li metal anode can accomplish dendrite-suppression by increasing Li ions deposition sites to lower the effective current density and render a uniform Li nucleation with 3D frameworks. With this ingenious arrangement, the solid-state 3D Li︱SPE-LLZTO-SPE︱3D Li symmetrical cell exhibits a stable voltage profile over 700 h and solid-state LiFePO4︱SPE-LLZTO-SPE︱3D Li full cell also shows an extremely superior cyclability and high Coulombic efficiency even at 90 °C. This work provides an alternative option for manufacturing safe and stable solid-state Li metal batteries.

3D lithium metal anodes hosted in asymmetric garnet frameworks toward high energy density batteries

Solid-state electrolytes (SSEs) have been widely studied to enable applications of high-energy Li metal anodes in batteries with high safety and stable performance. However, integration of SSEs into batteries is hindered by the infinite volume change of Li metal anodes upon cycling, the unstable resistance between Li and SSE, and low battery energy densities. To address these challenges, we developed a porous-dense bilayer structured garnet SSE as a 3D ionic framework for Li metal. The framework consists of one porous layer as a volume-stable host of Li metal with a large contact area, and one dense layer as a solid-state separator preventing short-circuits. The flatness of the dense layer enables simple battery manufacturing by laying a pre-made cathode on top of the bilayer framework. The thicknesses of the porous and dense layers are well controlled at 50 and 20 µm, respectively, to improve the battery energy density. Based on the bilayer garnet framework and highly loaded Li(Ni0.5Mn0.3Co0.2)O2 (NMC) cathodes (32 mg/cm2), we developed solid-state Li-NMC batteries with energy densities (329 W h/kg and 972 W h/L) significantly higher than all of the state-of-art garnet-based Li metal batteries. The bilayer framework design provides a promising strategy towards solid-state Li metal batteries with high energy densities because of its well-optimized thickness, stable cycling performance, and feasibility to be integrated with high-energy cathodes.

Intrinsic Improvement of LLZO Solid-State Electrolyte to Suppress Li Dendrite Growth

After the unexpected discovery of similar metal dendrite issues in dense ceramic electrolytes as in conventional liquid ones, the key factors governing the lithium dendrite growth e.g. in Li7La3Zr2O12 are still not fully understood. Possible factors include lithium ion diffusion kinetics at grain boundaries, influenced by microstructure [1, 2] and density [3], as well as inhomogeneous contact between LLZ solid electrolyte and Li electrodes, leading to high contact resistance. Multiple strategies can be employed to reduce the contact resistance: first, the surface can be treated in order to remove LiOH/Li2CO3-contamination [4], second, the effective contact area can be increased [5], third, surface defects can be reduced [6], and finally, the surface can be coated to increase the wettability [7-9]. To elucidate the interdependence of the various possibilities, the present work focuses on the effect of doping, microstructure, surface properties and density of the Li6.6La3Zr1.6Ta0.4O12 solid state electrolyte on its electrochemical performance, especially the resistance to dendrite penetration. Al-doped and Al-free LLZ:Ta precursor powders with larger (≈5 μm) and nano-sized particles were synthesized via solid-state synthesis and solution-assisted solid-state synthesis, respectively. LLZ:Ta pellets with high density (>99% of the theoretical density), high conductivity (8∙10-4 S/cm ) and various grain sizes were obtained for both precursor powders by hot pressing. The grain size dependence of mechanical properties (fracture toughness, micro hardness, Young’s modulus), ionic conductivity, cycling stability, stability in contact with humid air was investigated. The conductivity was separated into grain and grain boundary contributions. Activation energies of conductivity for the samples with larger and smaller grains were determined. Lower interfacial resistances and better cycling behaviour was found for the specimens with smaller grains and attributed to surface quality and mechanical properties of the material. 1. Sakamoto, J.; Rangasamy, E.; Kim, H.; Kim, Y.; Wolfenstine, J. Synthesis of nano-scale fast ion conducting cubic Li 7 La 3 Zr 2 O 12 . Nanotechnology, 2013, 24(42), 424005.2. Cheng, L.; Chen, W.; Kunz, M.; Persson, K.; Tamura, N.; Chen, G.; Doeff, M. Effect of surface microstructure on electrochemical performance of garnet solid electrolytes. ACS Appl Mater Interfaces, 2015, 7(3), 2073-2081.3. Ren, Y.; Shen, Y.; Lin, Y.; Nan, C.-W. Direct observation of lithium dendrites inside garnet-type lithium-ion solid electrolyte. Electrochemistry Communications, 2015, 57, 27-30.4. Sharafi, A.; Kazyak, E.; Davis, A. L.; Yu, S.; Thompson, T.; Siegel, D. J.; Dasgupta, N. P.; Sakamoto, J. Surface Chemistry Mechanism of Ultra-Low Interfacial Resistance in the Solid-State Electrolyte Li 7 La 3 Zr 2 O 12 . Chemistry of Materials, 2017.5. Basappa, R.H.; Ito, T.; Yamada, H. Contact between garnet-type solid electrolyte and lithium metal anode: influence on charge transfer resistance and short circuit prevention. Journal of The Electrochemical Society, 2017, 164(4), A666-A671.6. Porz, L.; Swamy, T.; Sheldon, B. W.; Rettenwander, D.; Frömling, T.; Thaman, H. L.; Berendts, S.; Uecker, R.; Carter, W. C.; Chiang, Y.-M. Mechanism of Lithium Metal Penetration through Inorganic Solid Electrolytes. Advanced Energy Materials, 2017, 1701003.7. Tsai, C. L.; Roddatis, V.; Chandran, C. V.; Ma, Q.; Uhlenbruck, S.; Bram, M.; Heitjans, P.; Guillon, O. Li 7 La 3 Zr 2 O 12 Interface Modification for Li Dendrite Prevention. ACS Appl Mater Interfaces, 2016, 8(16), 10617-10626.8. Wang, C.; Gong, Y.; Liu, B.; Fu, K.; Yao, Y.; Hitz, E.; Li, Y.; Dai, J.; Xu, S.; Luo, W.; Wachsman, E. D.; Hu, L. Conformal, Nanoscale ZnO Surface Modification of Garnet-Based Solid-State Electrolyte for Lithium Metal Anodes. Nano Lett, 2017, 17(1), 565-571.9. Han, X.; Gong, Y.; Fu, K. K.; He, X.; Hitz, G. T.; Dai, J.; Pearse, A.; Liu, B.; Wang, H.; Rubloff, G.; Mo, Y.; Thangadurai, V.; Wachsman, E. D.; Hu, L. Negating interfacial impedance in garnet-based solid-state Li metal batteries. Nat Mater, 2017. 16(5), 572-579.

Interface engineering in solid state Li metal batteries by quasi-2D hybrid perovskites

Solid-state lithium batteries (SSLBs) composed of garnet-type solid electrolytes have been intensively investigated with rapid progress, but the battery capacity does not meet the commercialization requirements yet.

Will the competitive future of solid state Li metal batteries rely on a ceramic or a composite electrolyte?

The industrial development of Li metal solid state batteries will be boosted not only by providing highly Li+ conductive electrolyte materials, but also by demonstrating their technical viability in the actual device.

Solid-State Lithium Metal Batteries Promoted by Nanotechnology: Progress and Prospects

Driven by an increasing demand on storage devices with higher energy outputs and better safety, solid-state lithium metal batteries have shown their potential to replace the traditional liquid-based Li-ion batteries and power the future storage market. In this Perspective, we will show our views on improving this emerging battery system by nanoscience. Discussions will be placed, from both scientific and engineering points of view, on the fundamentals and problems of the battery and its key components. The corresponding “nano” strategies will also be addressed, as well as recent progress in related fields including materials synthesis, battery design, and characterization techniques. With these efforts, we want to provide insights on rational design of the solid-state Li metal battery for optimized performance.

Iron oxyfluorides as lithium-free cathode materials for solid-state Li metal batteries

High energy density storage systems can be achieved by utilizing a lithium metal anode in solid-state Li secondary batteries.

Reshaping Lithium Plating/Stripping Behavior via Bifunctional Polymer Electrolyte for Room-Temperature Solid Li Metal Batteries.

High-energy rechargeable Li metal batteries are hindered by dendrite growth due to the use of a liquid electrolyte. Solid polymer electrolytes, as promising candidates to solve the above issue, are expected to own high Li ion conductivity without sacrificing mechanical strength, which is still a big challenge to realize. In this study, a bifunctional solid polymer electrolyte exactly having these two merits is proposed with an interpenetrating network of poly(ether-acrylate) (ipn-PEA) and realized via photopolymerization of ion-conductive poly(ethylene oxide) and branched acrylate. The ipn-PEA electrolyte with facile processing capability integrates high mechanical strength (ca. 12 GPa) with high room-temperature ionic conductance (0.22 mS cm-1), and significantly promotes uniform Li plating/stripping. Li metal full cells assembled with ipn-PEA electrolyte and cathodes within 4.5 V vs Li+/Li operate effectively at a rate of 5 C and cycle stably at a rate of 1 C at room temperature. Because of its fabrication simplicity and compelling characteristics, the bifunctional ipn-PEA electrolyte reshapes the feasibility of room-temperature solid-state Li metal batteries.

Lithium Metal-Copper Vanadium Oxide Battery with a Block Copolymer Electrolyte

Lithium (Li) batteries comprising multivalent positive active materials such as copper vanadium oxide have high theoretical capacity. These batteries with a conventional liquid electrolyte exhibit limited cycle life because of copper dissolution into the electrolyte. We report here on the characterization of solid-state Li metal batteries with a positive electrode based on α-Cu6.9V6O18.9 (α-CuVO3). We replaced the liquid electrolyte by a nanostructured solid block copolymer electrolyte comprising of a mixture of polystyrene-b-poly(ethylene oxide) (SEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. In situ X-ray diffraction was used to follow the Li insertion/de-insertion mechanism into the α-CuVO3 host material and its reversibility. In situ X-ray scattering revealed that the multistep electrochemical reactions involved are similar in the presence of liquid or solid electrolyte. The capacity fade of the solid-state batteries is less rapid than that of α-CuVO3–Li metal batteries with a conventional liquid electrolyte. Hard X-ray microtomography revealed that upon cycling, voids and Cu-rich agglomerates were formed at the interface between the Li metal and the SEO electrolyte. The void volume and the volume occupied by the Cu-rich agglomerates were independent of C-rate and cycle number.