Rechargeable Li Metal Research Articles

In Situ Formed Gel Polymer Electrolytes Enable Stable Solid Electrolyte Interface for High-Performance Lithium Metal Batteries.

Carbonate-based electrolytes show distinct advantages in high-voltage cathodes but generate nonuniform and mechanically fragile solid-electrolyte interphase (SEI) in lithium (Li) metal batteries. Herein, we propose a LiF-rich SEI incorporating an in situ polymerized poly(hexamethylene diisocyanate)-based gel polymer electrolyte (GPE) to improve the homogeneity and mechanical stability of SEI. Fluoroethylene carbonate (FEC) as a fluorine-based additive for building LiF-rich SEI on Li metal electrodes. With this strategy, the assembled Li symmetric batteries cycled stably for 700 h, and the formation of byproducts on the Li electrode surface was significantly inhibited. The Li/LiFePO4 battery delivered significant capacity retention (91% retention after 800 cycles) at 1 C. With high-voltage LiNi0.8Co0.1Mn0.1O2 (NCM811) as cathode, the Li/GPE-FEC/NCM811 cell delivered a discharge capacity of 168.9 mAh g-1 with a capacity retention of 82% after 300 cycles at 0.5 C. From the above, the work could assist the rapid development of high-energy-density rechargeable Li metal batteries toward remarkable performance.

(Invited) Electrolyte Design for Wide-Temperature Lithium Batteries

Improving the wide temperature performance of rechargeable batteries is vital to the operation of electronics and vehicles in extreme environments, where systems capable of higher energy, high-rate discharge and long cycling are in short supply. In this talk, we will show electrolyte designs to achieve high-energy density and stable cycling performance in wide temperature range, especially in extremely low-temperature environment. We will use a few examples, including ester- and ether-based electrolyte with different concentrations to showcase the critical role of solvation and desolvation in determining the charge-transfer kinetics at low-temperature. We will also discuss the role of solvation structure in shaping interfacial stability in different cathode and anode systems. These fundamental understanding may provide viable design strategies for high energy density and long-life batteries for both high and extremely low temperatures such as rechargeable Li metal batteries using both high-Ni oxide and sulfur cathodes.

CF3-Substituted Ethylene Carbonates for High-Voltage/High-Energy Rechargeable Lithium Metal-LiNi0.8Co0.1Mn0.1O2 Batteries.

The development of advanced liquid electrolytes for high-voltage/high-energy rechargeable Li metal batteries is an important strategy to attain an effective protective surface film on both the Li metal anode and the high-voltage composite cathode. Herein, we report a study of two CF3-substituted ethylene carbonates as components of the electrolyte solutions for Li metal|NCM811 cells. We evaluated trifluoromethyl ethylene carbonate (CF3-EC) and trans-ditrifluoromethylethylene carbonate Di-(CF3)-EC as cosolvents and additives to the electrolyte solutions. Using CF3-substituted ethylene carbonates as additives to a fluoroethylene carbonate (FEC)-based electrolyte solution enables improved capacity retention of high-power Li metal|NCM811 cells. The composition of the products from the transformations of CF3-EC and Di-(CF3)-EC in Li|NCM811 cells was studied by FTIR, XPS, and 19F NMR spectroscopy. We concluded that fluorinated Li alkyl carbonates are the main reaction products formed from these cyclic carbonates during the cycling of Li|NCM 811 cells, and fragmentation of the ring with the formation of CO2, CO, or olefins is not characteristic of CF3-substituted ethylene carbonates. The NCM 811 cathodes and Li metal anodes were characterized by X-ray diffraction, SEM, XPS, and FTIR spectroscopy. The role of CF3-substituted ethylene carbonate additives in stabilizing high energy density secondary batteries based on Li metal anodes was discussed. A bright horizon for developing sustainable rechargeable batteries with the highest possible energy density is demonstrated.

Accelerated Selective Li+ Transports Assisted by Microcrack-Free Anionic Network Polymer Membranes for Long Cyclable Lithium Metal Batteries.

Rechargeable Li metal batteries have the potential to meet the demands of high-energy density batteries for electric vehicles and grid-energy storage system applications. Achieving this goal, however, requires resolving not only safety concerns and a shortened battery cycle life arising from a combination of undesirable lithium dendrite and solid-electrolyte interphase formations. Here, a series of microcrack-free anionic network polymer membranes formed by a facile one-step click reaction are reported, displaying a high cation conductivity of 3.1 × 10-5 S cm-1 at high temperature, a wide electrochemical stability window up to 5V, a remarkable resistance to dendrite growth, and outstanding non-flammability. These enhanced properties are attributed to the presence of tethered borate anions in microcrack-free membranes, which benefits the acceleration of selective Li+ cations transport as well as suppression of dendrite growth. Ultimately, the microcrack-free anionic network polymer membranes render Li metal batteries a safe and long-cyclable energy storage device at high temperatures with a capacity retention of 92.7% and an average coulombic efficiency of 99.867% at 450 cycles.

Polymer electrolytes with high cation transport number for rechargeable Li–metal batteries: current status and future direction

The high-cation transport number polymer electrolytes (HTPEs) with simultaneously high cation transport number and high ionic conductivity could provide a solution to enable high-performance solid-state batteries.

Recent Progress on Nanomodification Applied in Anodes of Rechargeable Li Metal Batteries

Recent Progress on Nanomodification Applied in Anodes of Rechargeable Li Metal Batteries

A highly stable Li metal anode enabled by -SO3− group modification for high energy rechargeable Li metal batteries

A highly stable Li metal anode enabled by -SO3− group modification for high energy rechargeable Li metal batteries

Quantifying Capacity Loss Mechanisms of Li Metal Anodes Beyond Inactive Li0

Lithium metal anodes are promising alternatives to graphite for use in next-generation lithium-ion batteries due to their higher capacity (3,860 mAh/g vs. 372 mAh/g). However, Li anodes still display excessive capacity loss over cycling, leading to underwhelming Coulombic efficiency (CE, <99.9%) compared to graphite (>99.95%).1 These losses can derive from: (1) the formation of electronically isolated Li0 (often referred to as ‘dead’ or inactive’); and (2) the parasitic reactions between Li and the electrolyte that form the solid electrolyte interphase (SEI). Characterization of the Li anode has historically relied on surface characterization techniques such as XPS and FTIR, which cannot quantitatively reveal the total amounts of specific SEI phases. More precise quantification has recently become possible due to advances in chemical titration, which notably revealed that inactive Li0 is the dominant loss mechanism at low-to-moderate CE (<90%).2 At high CE (>90%), SEI losses are increasingly dominant and become the loss mode to minimize. Despite its importance, titration of SEI losses have thus far largely focused on LiH,3-5 with precise quantification of other accompanying phases still lacking.To bridge this gap, here we apply quantitative titration based on GC, ICP-AES and NMR to track an extended array of key SEI phases: semicarbonates (ROCO2Li), lithium carbide (Li2C2), olefins (RLi), LiF, P-containing phases, and total Li loss with, which teach new insights beyond inactive Li0. In 1 M LiPF6 EC/DEC, we demonstrate chemical resolution up to 71% of Li loss and 33% of SEI loss inventory. The analysis was also expanded to additional carbonate electrolytes of varying CEs (from <10% to >96%). Soluble SEI phases were particularly important at ultra-low CE (<10%), and their formation was suppressed higher CEs. Among the quantifiable SEI phases, ROCO2Li was consistently the major phase, but its proportions were invariant with CE. Instead, Li2C2, a minor phase, exhibited clear inverse correlation with CE. These results add further nuance beyond inactive Li0 to the current understanding of capacity loss, and demonstrate that, while minor phases often receive less focus and are harder to characterize, they can play governing roles in SEI function, particularly at high CE when formation of inactive Li0 is minimized. Hobold, G. M.; Lopez, J.; Guo, R.; Minafra, N.; Banerjee, A.; Shirley Meng, Y.; Shao-Horn, Y.; Gallant, B. M., Moving Beyond 99.9% Coulombic Efficiency for Lithium Anodes in Liquid Electrolytes. Nat. Energy 2021, 6 (10), 951-960. Fang, C.; Li, J.; Zhang, M.; Zhang, Y.; Yang, F.; Lee, J. Z.; Lee, M. H.; Alvarado, J.; Schroeder, M. A.; Yang, Y.; Lu, B.; Williams, N.; Ceja, M.; Yang, L.; Cai, M.; Gu, J.; Xu, K.; Wang, X.; Meng, Y. S., Quantifying Inactive Lithium in Lithium Metal Batteries. Nature 2019, 572 (7770), 511-515. Tao, M.; Xiang, Y.; Zhao, D.; Shan, P.; Sun, Y.; Yang, Y., Quantifying the Evolution of Inactive Li/Lithium Hydride and Their Correlations in Rechargeable Anode-Free Li Batteries. Nano Lett. 2022. Xu, G.; Li, J.; Wang, C.; Du, X.; Lu, D.; Xie, B.; Wang, X.; Lu, C.; Liu, H.; Dong, S.; Cui, G.; Chen, L., The Formation/Decomposition Equilibrium of LiH and Its Contribution on Anode Failure in Practical Lithium Metal Batteries. Angew. Chem. Int. Ed. Engl. 2021, 60 (14), 7770-7776. Xiang, Y.; Tao, M.; Zhong, G.; Liang, Z.; Zheng, G.; Huang, X.; Liu, X.; Jin, Y.; Xu, N.; Armand, M.; Zhang, J. G.; Xu, K.; Fu, R.; Yang, Y., Quantitatively Analyzing the Failure Processes of Rechargeable Li Metal Batteries. Sci. Adv. 2021, 7 (46), eabj3423.

Highly lithiophilic and structurally stable Cu–Zn alloy skeleton for high-performance Li-rich ternary anodes

Lithium (Li)-rich ternary alloy, comprising a multi-alloy phase as the built-in three-dimensional (3D) framework and a Li metal phase as a reversible Li reservoir, is a promising high-energy–density anode for rechargeable Li metal batteries. The introduction of metal/metalloid components to the alloy can effectively regulate Li deposition and maintain the dimensional integrity of the Li anode. Herein, the lithium–copper–zinc (Li–Cu–Zn) ternary alloy, as a new type of alloy anode, is synthesized via a facile thermal melting method. The fully delithiated 3D scaffold comprised two Cu–Zn alloy phases named CuZn and CuZn5. These alloy phases exhibit higher lithiophilicity and structural stability than Li–Zn and Li–Cu alloys. Moreover, the CuZn phase is electrochemically inert, ensuring the geometric stability of the anode, while the CuZn5 phase can readily undergo alloying reaction with Li to form the LiZn phase, thereby facilitating uniform Li nucleation and deposition. The hybridized multiphase alloy structure and specific energy storage mechanism of the Cu–Zn based alloy scaffold in the ternary alloy anode facilitate dendrite-free Li deposition and prolonged cycle lifetime. The Li metal full battery based on lithium iron phosphate (LiFePO4) cathode exhibits high cycling stability with high-capacity retention of 95.4% after 1000 cycles at 1C.

Morphology evolution of electrodeposited lithium on metal substrates

Lithium (Li) metal is deemed to be the high-energy-density anode material for next generation batteries, but its practical application is impeded by the uneven electrodeposition during charge of battery, which leads to the low Coulombic efficiency and potential safety issue. Here, multiscale modeling is fabricated to understand the morphology evolution of Li during electrodeposition process, from the self-diffusion of Li adatoms on electrode surface, to the nucleation process, and to the formation of Li microstructures, revealing the correlation between final morphology and deposition substrates. Energy batteries and self-diffusion of Li adatom on various substrates (lithium, copper, nickel, magnesium, and silver) result in the different nucleation size, which is calculated by kinetic Monte Carlo simulation based on classical nucleation theory. Formation of Li substructures that are grown from Li nuclei, is revealed by phase field modeling coupled with cellular automaton method. Our results show that larger Li nuclei is obtained under faster self-diffusion of Li adatom, leading to the low aspect ratio of Li substructures and the subsequent morphology evolution of electrodeposited Li. Furthermore, the electrodeposition of Li is strongly regulated by the selection of substrates, giving the practical guideline of anode design in rechargeable Li metal batteries. It is worthy to mention that this method to investigate the electro-crystallization process involving nucleation and growth can be transplanted to the other metallic anode, such as sodium, potassium, zinc, magnesium, calcium and the like.

Enabling Long Cycling with Excellent Structure Stability for High-Nickel Layered Cathodes in Lithium Metal Batteries

Rechargeable Li metal batteries (LMBs) constructed from Li metal and high-Ni NMCs have attracted much attention because of their high energy density in electrical vehicles. The choice of electrolyte plays a crucial role in determining the performance of Li||high-Ni NMC LMBs. In this work, we investigated the electrochemical performance and microstructure change of Li||0.7Nb-NMC 9055 LMBs using ether-based electrolyte (LiFSI–1.2DME–3TTE) and carbonate electrolyte (1 M LiPF6 in EC/DMC). The results show that ether-based electrolyte can significantly enhance the cycling life of Li||0.7Nb-NMC 9055 battery, providing a capacity of 203 mAh/g vs 179 mAh/g (carbonate electrolyte) for 150 cycles without voltage decay at C/5 charge and C/2 discharge rates. The excellent electrochemical performance (capacity and voltage) originates from the perfect structural stability confirmed by the dQ/dV versus V curves, which was further supported by electrochemical impedance spectroscopy test, showing nearly no surface charge transfer resistance increase in ether-based electrolyte, versus continuous growth in carbonate electrolyte.

3D Free‐Standing Carbon Nanofibers Modified by Lithiophilic Metals Enabling Dendrite‐Free Anodes for Li Metal Batteries

Li metal with high‐energy density is considered as the most promising anode for the next‐generation rechargeable Li metal batteries; however, the growth of Li dendrites seriously hinders its practical application. Herein, 3D free‐standing carbon nanofibers modified by lithiophilic metal particles (CNF/Me, Me=Sn, Fe, Co) are obtained in situ by the electrospinning method. Benefiting from the lithophilicity, the CNF/Me composite may effectively prevent the formation of Li dendrites in the Li metal batteries. The optimized CNF/Sn–Li composite electrode exhibits a stable cycle life of over 2350 h during Li plating/stripping. When matched with typical commercial LiFePO4 (LFP) cathode, the LFP//CNF/Sn–Li full cell presents a high initial discharge specific capacity of 139 mAh g−1 at 1 C, which remains at 146 mAh g−1 after 400 cycles. When another state‐of‐the‐art commercial LiNi0.8Co0.1Mn0.1O2 (NCM(811)) cathode is used, the assembled NCM//CNF/Sn–Li full cell shows a large initial specific discharge capacity of 206 mAh g−1 at substantially enhanced 10 C, which keeps at the good capacity of 99 mAh g−1 after 300 cycles. These results are greatly superior to the counterparts with Li as the anodes, indicating the great potential for practical utilization of the advanced CNF/Sn–Li electrode.

Cu-CNTs current collector fabricated by deformation-driven metallurgy for anode-free Li metal batteries

Rechargeable anode-free Li metal batteries (AFLMBs) with improved energy density and reduced cost are beneficial for emission peak and carbon neutralization. Herein, multi-walled carbon nanotubes reinforced Cu matrix composite (Cu-CNTs) enabled by deformation-driven metallurgy (DDM) technology is proposed to retrieve the lithiophilicity of current collectors (CCs) in AFLMBs. Fine-grained Cu-CNTs with a large number of grain boundaries and homogenous distribution of broken CNTs are achieved based on the severe plastic deformation principle since the CNTs inhibit slide of dislocations and migration of grain boundaries. Grain boundaries in fine-grained Cu-CNTs with low-size distribution gradients provide desirable nucleation sites due to their higher disorder and active state. Excellent lithiophilicity of the broken CNTs is exhibited where its layered structure for Li ion insertion contributes to uniform Li deposition. Half cells assembled by Cu-CNTs CC with 2 vol% CNTs display advanced cycling stability with an average coulombic efficiency of 97.8% after 500 cycles at 1.0 mA‧cm−2. Full cells with LiFePO4 cathode possess excellent capacity retention of 69.4% after 100 cycles at 0.5 C. This work provides a novel strategy for fabricating CCs to achieve superior electrochemical performances for future applications of AFLMBs.

Introducing KI as a functional electrolyte additive to stabilize Li metal anode

A lithium metal battery (LMBs) is an excellent battery system for advanced electrochemical energy storage. However, the growth of lithium dendrites, the accumulation of inactive lithium, and the side reactions between lithium metal and electrolytes limit the cycling stability of LMBs. Herein, we introduce KI additive into lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/ether-based electrolyte and lithium hexafluorophosphate (LiPF6)/ester-based electrolyte for cycling stability improvement of LMBs. Cu-mesh@Ag||Li half-cell with 0.01 M KI additive exhibits a Coulombic efficiency as high as 98.8 % over 200 cycles. The improved performance due to the electrostatic shielding effect formed by K+ at low concentration and the rapid recovery of inactive lithium by iodine redox. The corresponding Li||Li symmetrical cell shows an outstanding lifespan of 1400 h at 1.0 mA cm−2 with 1.0 mAh cm−2. Meanwhile, in the 1 M LiTFSI + 0.01 M KI electrolyte, the Cu-mesh@Ag-Li||LiFePO4 (LFP) full cell holds capacity retention of 91.7 % over 800cycles at 2.0 C, the Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) full cell possesses much better capacity retention of 54 % after 500 cycles at 1.0 C. This work offers a cost-effective proposal to improve application potential with the electrolyte engineering of rechargeable Li metal batteries.

Resolving Current-Dependent Regimes of Electroplating Mechanisms for Fast Charging Lithium Metal Anodes.

Poor fast-charge capabilities limit the usage of rechargeable Li metal anodes. Understanding the connection between charging rate, electroplating mechanism, and Li morphology could enable fast-charging solutions. Here, we develop a combined electroanalytical and nanoscale characterization approach to resolve the current-dependent regimes of Li plating mechanisms and morphology. Measurement of Li+ transport through the solid electrolyte interphase (SEI) shows that low currents induce plating at buried Li||SEI interfaces, but high currents initiate SEI-breakdown and plating at fresh Li||electrolyte interfaces. The latter pathway can induce uniform growth of {110}-faceted Li at extremely high currents, suggesting ion-transport limitations alone are insufficient to predict Li morphology. At battery relevant fast-charging rates, SEI-breakdown above a critical current density produces detrimental morphology and poor cyclability. Thus, prevention of both SEI-breakdown and slow ion-transport in the electrolyte is essential. This mechanistic insight can inform further electrolyte engineering and customization of fast-charging protocols for Li metal batteries.

(Invited) Electrolyte Design for Wide-Temperature Li-Ion and Li-Metal Batteries

Improving the wide temperature operation of rechargeable batteries is vital to the operation of electronics in extreme environments, where systems capable of higher energy, high-rate discharge and long cycling are in short supply. In this talk, we will show electrolyte designs to achieve high-energy density and stable cycling performance in wide temperature range for both lithium-ion and lithium metal batteries. We will show how to circumvent the sluggish ion desolvation process found in typical lithium-ion batteries during discharge. These batteries are enabled by a novel ester electrolyte, which simultaneously provided high electrochemical stability and ionic conductivity at low temperature. Then we will extend the fundamental understanding developed from these system to other high-capacity, high-rate electrodes, leading to further improved energy density and stability for both high and extremely low temperatures, demonstrated by rechargeable Li metal batteries using both high-Ni oxide and sulfur cathodes.

Single Iron Atom Anchored on ZIF‐8 Derived Carbon Framework to Directionally Regulate Lithium Deposition with Minimum Nucleation Overpotential

AbstractLithium (Li) metal has earned valuable status among the most auspicious anodes for the assembly of next‐generation rechargeable batteries. However, the dendritic growth and infinite change in volume of metallic Li anode strongly hinder its use for practical applications. Here, the preparation of atomically dispersed iron doped ZIF‐8 through pyrolysis (Fe@NC) to lower the Li nucleation overpotential and control the Li deposition on specific positions is reported. Thermodynamic and kinetic simulations show that the doped single Fe atoms can improve the atomic structure, increase the adsorption energy and enhance the diffusion capacity of Li. Moreover, the specific framework structure of Fe@NC can induce Li metal to nucleate in interior space of the material which can hinder the Li growth along one direction and restrain its volume expansion. As‐fabricated electrode displays nearly no nucleation overpotential at current density of 2 mA cm–2 and offers higher average Coulombic efficiency up to 99.0% for 100 cycles at current density 2 mA cm–2, and higher areal capacity up to 5 mAh cm–2. Also, the fabricated Fe@NC/LiFePO4 based full cells exhibit a longer lifespan of 100 cycles at 0.5 C. The results provide new insights for future rechargeable Li metal batteries.

(Invited) Pressure-Tailored Lithium Deposition and Dissolution in Lithium Metal Batteries

Unregulated lithium (Li) growth is the major cause of low Coulombic efficiency, short cycle life and safety hazards for rechargeable Li metal batteries. Strategies that aim to achieve large granular Li deposits have been extensively explored, and yet it remains a challenge to achieve the ideal Li deposits, which consist of large Li particles that are seamlessly packed on the electrode and can be reversibly deposited and stripped. Here we report a dense Li deposition (99.49% electrode density) with an ideal columnar structure that is achieved by controlling the uniaxial stack pressure during battery operation. Using multiscale characterization and simulation, we elucidate the critical role of stack pressure on Li nucleation, growth and dissolution processes and propose a Li-reservoir-testing protocol to maintain the ideal Li morphology during extended cycling. The precise manipulation of Li deposition and dissolution is a critical step to enable fast charging and a low-temperature operation for Li metal batteries.

Diluted High‐Concentration Electrolyte Based on Phosphate for High‐Performance Lithium‐Metal Batteries

AbstractLithium (Li) metal is an ultra‐high specific capacity and low potential ‘‘holy grail’’ anode for developing high energy density rechargeable Li metal batteries (LMBs), but its practical application suffers from the low Coulombic efficiency (CE) and dendritic lithium growth due to its thermodynamic instability to organic solvents. Here, we report a new diluted high concentration electrolyte (DHCE) containing lithium bis(fluorosulfonyl)imide, triethyl phosphate and fluorobenzene cosolvent, which not only guarantees lithium metal anode (LMA) with an 98.4 % high average CE over 250 cycles but greatly improves Li||NMC622 cells property (70 % capacity retention after 200 cycles at C/3 current density). Therefore, this new electrolyte can provide more possibilities for developing high‐energy‐density LMBs.

Electro‐Chemo‐Mechanical Modeling of Artificial Solid Electrolyte Interphase to Enable Uniform Electrodeposition of Lithium Metal Anodes

AbstractNonuniform electrodeposition of lithium during charging processes is the key issue hindering development of rechargeable Li metal batteries. This deposition process is largely controlled by the solid electrolyte interphase (SEI) on the metal surface and the design of artificial SEIs is an essential pathway to regulate electrodeposition of Li. In this work, an electro‐chemo‐mechanical model is built and implemented in a phase‐field modelling to understand the correlation between the physical properties of artificial SEIs and deposition of Li. The results show that improving ionic conductivity of the SEI above a critical level can mitigate stress concentration and preferred deposition of Li. In addition, the mechanical strength of the SEI is found to also mitigate non‐uniform deposition and influence electrochemical kinetics, with a Young's modulus around 4.0 GPa being a threshold value for even deposition of Li. By comparison of the results to experimental results for artificial SEIs it is clear that the most important direction for future work is to improve the ionic conductivity without compromising mechanical strength. In addition, the findings and methodology presented here not only provide detailed guidelines for design of artificial SEI on Li‐metal anodes but also pave the way to explore strategies for regulating deposition of other metal anodes.