High-energy Li Metal Batteries Research Articles

Engineering High-Performance Li Metal Batteries through Dual-Gradient Porous Cu-CuZn Host.

Porous copper (Cu) current collectors show promise in stabilizing Li metal anodes (LMAs). However, insufficient lithiophilicity of pure Cu and limited porosity in three-dimensional (3D) porous Cu structures led to an inefficient Li-Cu composite preparation and poor electrochemical performance of Li-Cu composite anodes. Herein, we propose a porous Cu-CuZn (DG-CCZ) host for Li composite anodes to tackle these issues. This architecture features a pore size distribution and lithiophilic-lithiophobic characteristics designed in a gradient distribution from the inside to the outside of the anode structure. This dual-gradient porous Cu-CuZn exhibits exceptional capillary wettability to molten Li and provides a high porosity of up to 66.05%. This design promotes preferential Li deposition in the interior of the porous structure during battery operation, effectively inhibiting Li dendrite formation. Consequently, all cell systems achieve significantly improved cycling stability, including Li half-cells, Li-Li symmetric cells, and Li-LFP full cells. When paired synergistically with the double-coated LiFePO4 cathode, the pouch cell configured with multiple electrodes demonstrates an impressive discharge capacity of 159.3 mAh g-1 at 1C. We believe this study can inspire the design of future 3D Li anodes with enhanced Li utilization efficiency and facilitate the development of future high-energy Li metal batteries.

Deciphering fundamental mechanism of different-type diluents on manipulating interfacial chemistry toward lithium metal anode

The growth of dendrites on lithium metal anode is troublesome because it induces irreversible capacity loss and safety hazards. Formulating localized high-concentration electrolytes (LHCEs) is an alternative solution to satisfy these challenges. However, the role of diluents in tailoring interfacial chemistry remains to be explicated. Herein, we decipher the direct relationship between different-type diluents and Li-coordinated solvation at the molecular scale. Compare to hydrofluoroethers (HFE), the “active” difluoro ethylene carbonate (DFEC) delivers a pronounced interaction with Li+ and 1, 2-dimethoxyethane (DME) molecule, resulting in a compressed but more accumulated aggregates (AGGs) solvation shell, assisting in the expected chemical nature of SEI with defluorination of DFEC. Consequently, DFEC-based LHCEs (D-LHCEs) realize a record-long lifespan over 3000 h with dendrite-free at 1 mA cm−2 and outstanding dendrite tolerance even under 3 mA cm−2 in symmetric cells. The assembled full cells with D-LHCEs outperform a superior capacity retention of ∼86.83 % with average CE of ∼99.42 % after 500 cycles at 0.5C and the remarkable cycling performance even under harsh conditions (including pouch cells or with controlled N/P of 1.8) in 4.45 V-level Li||LiCoO2 cells. This work highlights the decisive role of diluents in pursuing high-efficiency electrolytes for high-energy Li metal batteries.

Compositionally Sequenced Interfacial Layers for High-Energy Li-Metal Batteries.

Electrolyte additives with multiple functions enable the interfacial engineering of Li-metal batteries (LMBs). Owing to their unique reduction behavior, additives exhibit a high potential for electrode surface modification that increases the reversibility of Li-metal anodes by enabling the development of a hierarchical solid electrolyte interphase (SEI). This study confirms that an adequately designed SEI facilitates the homogeneous supply of Li+, nonlocalized Li deposition, and low electrolyte degradation in LMBs while enduring the volume fluctuation of Li-metal anodes on cycling. An in-depth analysis of interfacial engineering mechanisms reveals that multilayered SEI structures comprising mechanically robust LiF-rich species, electron-rich P-O species, and elastic polymeric species enabled the stable charge and discharge of LMBs. The polymeric outer SEI layer in the as-fabricated multilayered SEI could accommodate the volume fluctuation of Li-metal anodes, significantly enhancing the cycling stability Li||LiNi0.8Co0.1Mn0.1O2 full cells with an electrolyte amount of 3.6gAh-1 and an areal capacity of 3.2mAhcm-2. Therefore, this study confirms the ability of interfacial layers formed by electrolyte additives and fluorinated solvents to advance the performance of LMBs and can open new frontiers in the fabrication of high-performance LMBs through electrolyte-formulation engineering.

Active Diluent-Anion Synergy Strategy Regulating Nonflammable Electrolytes for High-Efficiency Li Metal Batteries.

High-energy Li metal batteries (LMBs) consisting of Li metal anodes and high-voltage cathodes are promising candidates of the next generation energy-storage systems owing to their ultrahigh energy density. However, it is still challenging to develop high-voltage nonflammable electrolytes with superior anode and cathode compatibility for LMBs. Here, we propose an active diluent-anion synergy strategy to achieve outstanding compatibility with Li metal anodes and high-voltage cathodes by using 1,2-difluorobenzene (DFB) with high activity for yielding LiF as an active diluent to regulate nonflammable dimethylacetamide (DMAC)-based localized high concentration electrolyte (LHCE-DFB). DFB and bis(fluorosulfonyl)imide (FSI- ) anion cooperate to construct robust LiF-rich solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI), which effectively stabilize DMAC from intrinsic reactions with Li metal anode and enhance the interfacial stability of the Li metal anodes and LiNi0.8 Co0.1 Mn0.1 O2 (NCM811) cathodes. LHCE-DFB enables ultrahigh Coulombic efficiency (98.7 %), dendrite-free, extremely stable and long-term cycling of Li metal anodes in Li || Cu cells and Li || Li cells. The fabricated NCM811 || Li cells with LHCE-DFB display remarkably enhanced long-term cycling stability and excellent rate capability. This work provides a promising active diluent-anion synergy strategy for designing high-voltage electrolytes for high-energy batteries.

Hybrid ionic/electronic interphase enabling uniform nucleation and fast diffusion kinetics for stable lithium metal anode

Lithium (Li) dendrite issue, which is usually caused by inhomogeneous Li nucleation and fragile solid electrolyte interphase (SEI), impedes the further development of high-energy Li metal batteries. However, the integrated construction of a high-stable SEI layer that can regulate uniform nucleation and facilitate fast Li-ion diffusion kinetics for Li metal anode still falls short. Herein, we designed an artificial SEI with hybrid ionic/electronic interphase to regulate Li deposition by in-situ constructing metal Co clusters embedded in LiF matrix. The generated Co and LiF both enable fast Li-ion diffusion kinetics, meanwhile, the lithiophilic properties of Co clusters can serve as Li-ion nucleation sites, thereby contributing to uniform Li nucleation and non-dendritic growth. As a result, a dendrite-free Li deposition with a low overpotential (16.1 mV) is achieved, which enables an extended lifespan over 750 h under strict conditions. The full cells with high-mass-loading LiFePO4 (11.5 mg/cm2) as cathodes exhibit a remarkable rate capacity of 84.1 mAh/g at 5 C and an improved cycling performance with a capacity retention of 96.4% after undergoing 180 cycles.

Lithium Morphology Evolution through Crosslinked Poly(ethylene oxide) Solid Polymer Electrolyte

Solid-state, lithium metal batteries are promising candidates for developing the safe, energy-dense devices needed to transition to an electrified economy. However, lithium is highly reactive, making it thermodynamically unstable when in contact with many electrolyte materials. Achieving uniform Li plating and stripping during cycling is the key for enabling high energy Li metal batteries. The lithium stripping and plating mechanism is complicated as it can be affected by the cathode, electrolyte and lithium anode, and the resulting solid electrolyte interphase (SEI). In particular, the mechanism is not well understood in solid polymer electrolytes.In this work, we investigate lithium morphology evolution through a solid polymer electrolyte at different stages of battery cycling. Crosslinked poly(ethylene oxide) (xPEO) solid polymer electrolyte is used as a model electrolyte and full cells using single crystal LiNi0.6Mn0.2Co0.2O2 (NMC622) cathode, dry xPEO electrolyte and lithium from two commercial sources are assembled. Our results show that different lithium sources lead to different Coulombic efficiencies and capacity fade rate of the full cells assembled. The lithium morphology evolution at different stages of cycling is examined using scanning electron microscopy and the lithium plating/stripping mechanism are compared between these two commercial lithium anodes. Furthermore, the lithium morphology is compared to a gel polymer composite electrolyte with the same host polymer (xPEO). The dry solid polymer produces a smoother morphology than the gel polymer composite electrolyte without pit formation. A better understanding of the roles of each of these components (pristine Li surface chemistry, microstructure, dry vs gel polymer electrolyte) is essential to control for uniform lithium stripping and plating.

Electrodeposition-guided pre-passivation of Li-metal anode to enable long stable cycling of practical Li-metal batteries

Ultrathin, large-area Li metal anodes (LMAs) are essential for high-energy Li-metal batteries (LMBs). However, most commercially manufactured LMAs (M-Li11M-Li: Manufactured Li) form a native passivation layer (NPL22NPL: Native passivation layer) during manufacturing. Intrinsically non-uniform NPL can initiate sporadic Li dendrite growth and the chemical/structural deterioration of LMAs. This study presents an electrochemical pre-passivation method to build an electrolyte-derived native layer (ENL33ENL: Electrolyte-derived native layer) using electrodeposited Li (ED-Li44ED-Li: Electrodeposited Li). Using localized high-concentration electrolytes and post-calendering, ED-Li can build a Li2CO3-less, fluorinated ENL and decrease the surface roughness. Herein, ED-Li facilitates Li nucleation during earlier Li plating owing to the electrolyte-compatible ENL, and alleviates pitting during subsequent Li stripping, thereby mitigating LMA swelling. ED-Li improves the cycling stability of Li||NMC622 cells to outperform M-Li, which is further validated using different electrolytes under practical conditions, demonstrating its potential for use as the starting LMA in post-treatment approaches, such as protective layer coating and electrolyte-driven passivation.

Electrochemically Dealloyed 3D Porous Copper Nanostructure as Anode Current Collector of Li-Metal Batteries.

The commercialization of high-energy Li-metal batteries is impeded by Li dendrites formed during electrochemical cycling and the safety hazards it causes. Here, a novel porous copper current collector that can effectively mitigate the dendritic growth of Li is reported. This porous Cu foil is fabricated via a simple two-step electrochemical process, where Cu-Zn alloy is electrodeposited on commercial copper foil and then Zn is electrochemically dissolved to form a 3D porous structure of Cu. The 3D porous Cu layers on average have a thickness of ≈14 um and porosity of ≈72%. This current collector can effectively suppress Li dendrites in cells cycled with a high areal capacity of 10 mAhcm-2 and under a high current density of 10mAcm-2 . This electrochemical fabrication method is facile and scalable for mass production. Results of advanced in situ synchrotron X-ray diffraction reveal the phase evolution of the electrochemical deposition and dealloying processes.

Tuning the Li+ Solvation Structure by a “Bulky Coordinating” Strategy Enables Nonflammable Electrolyte for Ultrahigh Voltage Lithium Metal Batteries

In battery electrolyte design principles, tuning Li+ solvation structure is an effective way to connect electrolyte chemistry with interfacial chemistry. Although recent proposed solvation tuning strategies are able to improve battery cyclability, a comprehensive strategy for electrolyte design remains imperative. Here, we report a solvation tuning strategy by utilizing molecular steric effect to create a "bulky coordinating" structure. Based on this strategy, the designed electrolyte generates an inorganic-rich solid electrolyte interphase (SEI) and cathode-electrolyte interphase (CEI), leading to excellent compatibility with both Li metal anodes and high-voltage cathodes. Under an ultrahigh voltage of 4.6 V, Li/NMC811 full-cells (N/P = 2.0) hold an 84.1% capacity retention over 150 cycles and industrial Li/NMC811 pouch cells realize an energy density of 495 Wh kg-1. This study provides innovative insights into Li+ solvation tuning for electrolyte engineering and offers a promising path toward developing high-energy Li metal batteries.

Enhanced and evenly-distributed Li+ transport in well-aligned nanochannels enables stable lithium metal anode

The high theoretical capacity of lithium (Li) has sparkled its intensive research as the anode for Li batteries. However, the dendritic growth due to the uneven Li deposition causes premature cell failure and dramatically restricts the application of Li anode. Herein, inspired by the pore sizes effects of anodized aluminum oxide (AAO) membranes on Li+ transport performance, 20 nm aperture membrane (AAO-20) with enhanced Li+ transport can achieve higher Li+ concentration near the deposition substrate, possibly preventing rapid Li+ depletion compared to other aperture sizes. Subsequently, smaller Li nucleation overpotential and larger exchange current density in AAO-20 reveal the enhanced kinetics at deposition interface, which is derived from the enhanced Li+ transport in nanochannels, leading to a superior Li deposition. With AAO-20 which can stabilize Li anode, Li-Cu, Li-Li, and Li-LiFePO4 cells demonstrate high Coulombic efficiency, superior cycling stability, and excellent capacity retention, respectively. Such findings can be helpful for the development of high-energy Li metal batteries.

(Invited) How Does One Enable High Energy Li Metal Batteries a Case Study with Lipon

The next generation of high energy batteries using Li metal as an anode and utilizing a solid electrolyte requires good interfacial stability, reasonable ionic conductivity, and most importantly the ability to eliminate dendrites.i While most solid-state electrolytes suffer from both interfacial instability and Li penetration resulting in cell shorting,ii,iii The solid electrolyte Lipon has a remarkable ability to suppress dendrites, and enable solid state batteries that can cycle for more than 1000 cycles and support current densities as high as 10 mA/cm2.iii,iv Recent efforts have started to illuminate the origin of Lipon’s ability to enable high-energy solid-state Li metal batteries. This presentation will highlight the unique structure of Lipon and Lipon like materials, the interfacial structure of Lipon with Li metal, and the mechanics that enable high quality performance in Lipon based solid-state batteries.v,vi,vii Finally, the presentation will connect these findings from Lipon to outline key underlying principles that answer the question, how do we enable high energy Li metal batteries? Acknowledgements: Work for this presentation was funded by ARPA-E under contract #DE-AR0000775, and the US Department of Energy Office of Energy Efficiency and Renewable Energy for the Vehicle Technologies Office’s US-German Cooperation on Energy Storage: Interfaces and Interphases In Rechargeable Li-metal based Batteries Program and the Battery Materials Research Program under program managers Tien Duong and Simon Thompson. P. Albertus et al., “Challenges for and pathways toward Li-metal-based all-solid-state batteries”, ACS Energy Letters, 6, 4, 1399-1404, Mar. 2021.Fudong Han, Andrew S Westover, Jie Yue, Xiulin Fan, Fei Wang, Miaofang Chi, Donovan N Leonard, Nancy J Dudney, Howard Wang, Chunsheng Wang, “High electronic conductivity as the origin of lithium dendrite formation within solid electrolytes”, Nature Energy, 1, Jan. 2019. Andrew S Westover, Nancy J Dudney, Robert L Sacci, Sergiy Kalnaus, “Deposition and Confinement of Li Metal along an Artificial Lipon–Lipon Interface”, ACS Energy Letters, 4, 651-655, Feb. 2019.Juchuan Li, Cheng Ma, Miaofang Chi, Chengdu Liang, and Nancy J. Dudney. "Solid electrolyte: the key for high‐voltage lithium batteries." Advanced Energy Materials5, 4, 1401408, 2015. Andrew S Westover* Valentina Lacivita,* , Andrew Kercher, Nathan D Phillip, Guang Yang, Gabriel Veith, Gerbrand Ceder, Nancy J Dudney, “Resolving the amorphous structure of lithium phosphorus oxynitride (Lipon)”, Journal of the American Chemical Society 140 (35), 11029-11038, July 2018. Andrew S Westover, Robert L Sacci, Nancy Dudney, “Electroanalytical measurement of interphase formation at a Li metal–solid electrolyte interface”, ACS Energy Letters, 5, 12, 3860-3867, Nov. 2020.Sergiy Kalnaus, Andrew S Westover, Mordechai Kornbluth, Erik Herbert, Nancy J Dudney, “Resistance to fracture in the glassy solid electrolyte Lipon”, Journal of Materials Research, 36, 4, 787-796, Feb. 2021.

Nonflammable, robust and flexible electrolytes enabled by phosphate coupled polymer–polymer for Li-metal batteries

Liquid organic electrolytes commonly employed in commercial Li-ion batteries suffer from safety issues such as flammability and explosions. Replacing liquid electrolytes with nonflammable electrolytes has become increasingly attractive in the development of safe, high-energy Li-metal batteries (LMBs). In this work, nonflammable, robust, and flexible composite polymer–polymer electrolytes (PPEs) were successfully fabricated by flame-retardant solution casting with polyimide (PI) and polyvinylidene fluoride (PVDF). The optimized nonflammable PPEs (e.g., PPE-50) demonstrate not only good mechanical properties (i.e., a high tensile strength of 29.6 MPa with an elongation at break of 87.2%), but also high Li salts dissolubility, the former of which ensures the suppression of Li dendrites, while the latter further improves the ionic conductivity (∼1.86 × 10−4 S cm−1 at 30 °C). The resulting symmetric cells (Li|PPE-50|Li) offer excellent Li stripping and plating stability for 1000 h at 0.5 mA cm−2/0.25 mAh cm−2 and 600 h at 2.0 mA cm−2/1.0 mAh cm−2. In addition, the LiFePO4|PPE-50|Li half cells show high cycling performance (e.g., a reversible discharge capacity of 135.9 mAh g−1 after 300 cycles at 1C) and rate capability (e.g., 117.2 mAh g−1 at 4C). The PPE-50 is also compatible with a high-voltage cathode (e.g., LiNi0.5Mn0.3Co0.2O2), and the resulting batteries demonstrate long-term cycling stability with a high cut-off voltage of 4.5 V vs. Li/Li+. Because of the incorporation of a mechanically robust and thermally stable PI, a polar PVDF, and flame-retardant trimethyl phosphate (TMP) within PPEs, as well as the coordination between Li salts and TMP, and the interaction between Li salts and polymers (especially between Li bis(oxalato)borate) and PI, as well as the bis(oxalato)borate anion and PI), PPEs show great potential for practical and high-energy LMBs without safety concerns.

Understanding the anchoring effect on Li plating with Indium Tin oxide layer functionalized hosts for Li metal anodes

Li dendrites caused by nonuniform Li plating and locally concentrated ion/electron flux would give rise to poor cycling performance and safety issues of short-circuit and so on. Herein, a functional nanolayer consisting of Indium Tin oxide (ITO) nanoparticles on 3D Cu foam was fabricated as case study to understand the mechanism of metal oxides on anchoring Li metal spots and how initial Li nucleation influences the following dendrites growth. Based on the experimental and theoretical results, it is demonstrated that not only the pristine metal oxides have higher binding energy with Li atom, but also in situ formed alloy phase during alloying process performs a great importance on homogeneous nucleation, thus leading to ordered ion/electron distribution and fast kinetics. Therefore, excellent wettability and even self-propagation behavior between ITO-Cu foam and molten Li are achieved, meanwhile the half cells with ITO-Cu foam electrodes exhibit an ultralow nucleation overpotential of 2 mV under 0.5 mA cm−2. When the designed ITO-Cu foam@Li anodes is matched with LFP (LiFePO4) cathodes, the constructed full cells can empower superior cycling stability for over 1000 cycles at 5C (3.4 mA cm−2), and remarkable specific capacity (149 mAh g−1) and capacity retention (80% for 250 cycles) even with ultrahigh mass loading (15.3 mg cm−2), which provides an avenue to regulate Li deposition/dissolution for high energy Li metal batteries.

Anion–Diluent Pairing for Stable High-Energy Li Metal Batteries

Anion–Diluent Pairing for Stable High-Energy Li Metal Batteries

Natural protein as novel additive of a commercial electrolyte for Long-Cycling lithium metal batteries

Suffering from critical instability of lithium (Li) anode, the most commercial electrolytes, carbonate-ester electrolytes, have been restrictedly used in high-energy Li metal batteries (LMBs) despite of their broad implementation in lithium-ion batteries. Here, abundant, natural corn protein, zein, is exploited as a novel additive to stabilize Li anode and effectively prolong the cycling life of LMBs based on carbonate-ester electrolyte. It is discovered that the denatured zein is involved in the formation of solid electrolyte interphase (SEI), guides Li+ deposition and repairs the cracked SEI. In specific, the zein-rich SEI benefits the anion immobilization, enabling uniform Li+ deposition to diminish dendrite growth; the preferential zein-Li reaction effectively repairs the cracked SEI, protecting Li from parasite reactions. The resulting symmetrical Li cell exhibits a prolonged cycling life to over 350 h from <200 h for pristine cell at 1 mA cm−2withacapacityof1mAhcm−2. Paired with LiFePO4 cathode, zein additive markedly improves the electrochemical performance including a higher capacity of 130.1 mAh g−1 and a higher capacity retention of ∼ 80 % after 200 cycles at 1 C. This study demonstrates a natural protein to be an effective additive for the most commercial electrolytes for advancing performance of LMBs.

High-entropy metal oxide containing hybrid electrolyte for long-life Li-metal batteries

AbstractSolid-state electrolytes are responsible for transporting lithium (Li) ions between electrodes in solid-state batteries and are essential for high-safety and high-energy Li-metal batteries. Developing novel solid-state electrolytes with high ionic conductivity and good interfacial contact is an urgent need. Here, to this end, a solid-state hybrid electrolyte is developed by mixing high-entropy Li-containing metal oxide (Lix(Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)1−xO, HEOLi) matrix and poly(ethylene oxide)–Li salt binder and casting on polytetrafluoroethylene (PTFE) substrate. By virtue of the low Li-ion migration energy barrier of the HEOLi (0.36 eV) and the strong interaction between the oxygen vacancies of the HEOLi and the Li salt anions, a biphasic transport of Li ions in both inorganic and polymeric phases of the hybrid electrolyte is achieved, yielding a high ionic conductivity of 3 × 10−4 S cm−1 at 30°C. The Li/Li symmetric cells with the hybrid electrolyte show a low overpotential of 45 mV and a long cycle life of more than 2500 h. Furthermore, coupled with the LiFePO4 cathodes and metallic Li anodes, solid-state full cells with the hybrid electrolyte deliver a high capacity of 150 mAh g−1, stable cycle performance and high safety. Consequently, hybrid electrolytes based on high-entropy metal oxides have broad application prospects in solid-state electrochemical energy storage and are expected to achieve Li-metal batteries with high-safety, high-energy density and long life.

Modulating the lithiophilicity at electrode/electrolyte interface for high-energy Li-metal batteries

Lithium-metal anodes show significant promise for the construction of high-energy rechargeable batteries due to their high theoretical capacity (3860 mAh g-1) and low redox potential (-3.04 V vs. a standard hydrogen electrode). When Li metal is used with conventional liquid and solid electrolytes, the poor lithiophilicity of the electrolyte results in an unfavorable parasitic reaction and uneven distribution of Li+ flux at the electrode/electrolyte interface. These issues result in limited cycle life and dendrite problems associated with the Li-metal anode that can lead to rapid performance fade, failure and even safety risks of the battery. The lithiophilicity at the anode/electrolyte interface is important for the stable and safe operation of rechargeable Li-metal batteries. In this review, several factors that affect the lithiophilicity of electrolytes are discussed, including surface energy, roughness and chemical interactions. The existing problems and the strategies for improving the lithiophilicity of different electrolytes are also discussed. This review helps to shed light on the understanding of interfacial chemistry vs. Li metal of various electrolytes and guide interfacial engineering towards the practical realization of high-energy rechargeable batteries.

Lithium Fluoride in Electrolyte for Stable and Safe Lithium-Metal Batteries.

Electrolyte engineering via fluorinated additives is promising to improve cycling stability and safety of high-energy Li-metal batteries. Here, an electrolyte is reported in a porous lithium fluoride (LiF) strategy to enable efficient carbonate electrolyte engineering for stable and safe Li-metal batteries. Unlike traditionally engineered electrolytes, the prepared electrolyte in the porous LiF nanobox exhibits nonflammability and high electrochemical performance owing to strong interactions between the electrolyte solvent molecules and numerous exposed active LiF (111) crystal planes. Via cryogenic transmission electron microscopy and X-ray photoelectron spectroscopy depth analysis, it is revealed that the electrolyte in active porous LiF nanobox involves the formation of a high-fluorine-content (>30%) solid electrolyte interphase layer, which enables very stable Li-metal anode cycling over one thousand cycles under high current density (4 mA cm-2 ). More importantly, employing the porous LiF nanobox engineered electrolyte, a Li || LiNi0.8 Co0.1 Mn0.1 O2 pouch cell is achieved with a specific energy of 380 Wh kg-1 for stable cycling over 80 cycles, representing the excellent performance of the Li-metal pouch cell using practical carbonate electrolyte. This study provides a new electrolyte engineering strategy for stable and safe Li-metal batteries.

Self-Healing Commodity Polymer Electrolytes for Reliable Li Metal Batteries

As countries worldwide pledge to decarbonize their economy, the global demand for batteries is rapidly increasing, urging the development of high-specific-energy (> 500 Wh/kg at cell level) and low-cost (< 100$/kWh at pack level) batteries.1 The safety and durability of these devices are of primary importance. Polymer electrolytes are safer than traditional liquid electrolytes, and further benefit from highly tunable structures.2 Thus, polymers can be designed to achieve desired properties, including the ability of self-healing from damages, which can greatly extend battery lifetime. While the synthesis of self-healing polymers often requires specifically designed monomers or other polymerization components, it was recently shown that commodity copolymers, based on methyl methacrylate (MMA) and n-butyl acrylate (nBA) or their derivatives, display self-healing behavior.3 The autonomous self-repair of these copolymers with certain compositions is governed by interchain van der Waals forces.Herein, this finding was exploited to prepare self-healing polymer electrolytes that ensured long-term performance of high-energy Li metal batteries. The electrolytes were based on polyethylene oxide (PEO), P(MMA-co-nBA) copolymers and Li bis(trifluoromethanesulfonyl)imide (TFSI) salt. Various structures and compositions were explored, including polymer blends and block copolymers made by atom transfer radical polymerization (ATRP) using a functionalized PEO-macroinitiator (Figure 1). The effect of polymer morphology, architecture, weight fraction of PEO and LiTFSI on electrolyte conductivity, thermal and electrochemical stability, Li transference number, mechanical strength and self-healing ability was analyzed.By recovering ionic conductivity and mechanical strength upon cracks, self-healing electrolytes can suppress the growth of dendrites that hinders the utilization of Li metal anodes.4 Moreover, the viscoelastic nature of these polymers contribute to the creation of conformal interfaces on Li metal.2 Therefore, the optimized commodity self-healing polymer electrolytes were tested in Li metal batteries, demonstrating the ability of the electrolytes to enable long-term stable cycling. In addition, tests were conducted to prove the self-repair of the electrolyte upon damaging the device.

Electrolyte interface design for regulating Li dendrite growth in rechargeable Li-metal batteries: A theoretical study

Lithium metal (Li) is an ideal anode for designing high-energy Li metal batteries (LMBs) due to its high specific capacity (3860 mAh g−1) and lowest electrochemical potential. However, the practical use of Li is currently impeded by uncontrollable dendritic growth during repeated Li plating and stripping, causing serious safety hazards such as electrical short circuits. To regulate Li growth behavior, various solid electrolyte interfaces (SEIs) have been explored. Despite intensive efforts, further understanding of the dendritic growth mechanism is still required. In this respect, herein, we clarify the origin and growth mechanism of Li dendrites by evaluating the critical role of an artificial SEI using a finite element method. Based on our theoretical study, we suggest that the relatively low ionic conductivity of the SEI layer is responsible for facilitating the growth of Li dendrites and the growth can be effectively suppressed by employing an artificial SEI with a higher ionic conductivity. The high-conductivity artificial SEI regulates local current distributions, directly affecting the growth of Li dendrites as determined by measuring the current density, exchange current density, and geometry. Our findings provide new insight into the design of artificial SEIs for improving the cycling performance of advanced LMBs.