High-performance Lithium Metal Batteries Research Articles

In situ synthesis of cross-linking gel polymer electrolyte for lithium metal batteries

AbstractThe room temperature ionic conductivity of polyethylene oxide (PEO)-based polymer electrolytes is low, the electrochemical window is narrow, and the mechanical strength is relatively poor. In this work, a cross-linking gel-based solid composite polymer electrolyte (CG-SCPE) was synthesized by introducing electrochemically stable carbonate-based functional groups. The synthesized CG-SCPE presents excellent tensile strength (26 MPa) and a wide electrochemical stability window (> 4.5 V vs. Li/Li+). Meanwhile, the in situ polymerization method induced by thermal heating resulted in good compatibility between electrodes/electrolytes. In addition, the assembled LiNi0.5Co0.2Mn0.3O2/CG-SCPE/Li battery exhibited satisfactory electrochemical performance. Therefore, the gel polymer electrolyte CG-SCPE with cross-linking network provides the possibility for future application of safe and high-performance solid-state lithium metal batteries. The results indicate that the introduction of cross-linking framework can simultaneously improve the mechanical strength, thermal stability, and electrochemical performance of solid polymer electrolyte.

First-Principles Study on Polymer Electrolyte Interface Engineering for Lithium Metal Anodes.

Modifying the interface between the lithium metal anode (LMA) and the electrolyte is crucial for achieving high-performance lithium metal batteries (LMBs). Recent research indicates that altering Li-metal interfaces with polymer coatings is an effective approach to extend LMBs' cycling lifespan. However, the physical properties of these polymer-Li interfaces have not yet been fully investigated. Therefore, the structural stability, electronic conductivity, and ionic conductivity of polymer-Li interfaces were examined based on first-principles calculations in this study. Several representative polymer compounds utilized in LMBs were assessed, including polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyethylene oxide (PEO). Our research revealed that lithium fluoride is formed upon fluoropolymer degradation, explaining previously observed experimental results. Polymers containing nitrile groups exhibit strong adhesion to lithium metal, facilitating the formation of the stable interface layer. Regarding electronic conductivity, the fluoropolymers preserve a good insulating property, which diminished marginally in the presence of lithium, but that of PAN and PEO significantly reduces. Additionally, lithium diffusion on PTFE and PEO demonstrates low diffusion barriers and high coefficients, enabling easy transportation. Overall, our investigation reveals that the interfaces formed between various polymers and LMA have distinct characteristics, providing new fundamental insights for designing composites with tailored interface properties.

Non-flammable long chain phosphate ester based electrolyte via competitive solventized structures for high-performance lithium metal batteries

Safety remains a persistent challenge for high-energy–density lithium metal batteries (LMBs). The development of safe and non-flammable electrolytes is especially important in harsh conditions such as high temperatures. Herein, a flame-retardant, low-cost and thermally stable long chain phosphate ester based (tributyl phosphate, TBP) electrolyte is reported, which can effectively enhance the cycling stability of highly loaded high-nickel LMBs with high safety through co-solvation strategy. The interfacial compatibility between TBP and electrode is effectively improved using a short-chain ether (glycol dimethyl ether, DME), and a specially competitive solvation structure is further constructed using lithium borate difluorooxalate (LiDFOB) to form the stable and inorganic-rich electrode interphases. Benefiting from the presence of the cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) enriched with LiF and LixPOyFz, the electrolyte demonstrates excellent cycling stability assembled using a 50 μm lithium foil anode in combination with a high loading NMC811 (15.4 mg cm−2) cathode, with 88% capacity retention after 120 cycles. Furthermore, the electrolyte exhibits excellent high-temperature characteristics when used in a 1-Ah pouch cell (N/P = 0.26), and higher thermal runaway temperature (238 °C) in the ARC (accelerating rate calorimeter) demonstrating high safety. This novel electrolyte adopts long-chain phosphate as the main solvent for the first time, and would provide a new idea for the development of extremely high safety and high-temperature electrolytes.

Design a polymer-based composite electrolyte with high ionic conductivity for high-performance lithium-metal batteries

Constructing a stable and robust solid polymer electrolyte (SPE) is crucial for achieving dendrite-free lithium-metal anodes and high-performance lithium batteries. However, realizing the integrity of solid electrolytes with high ion conductivity during long-life cycling under high current density remains a significant challenge. In this study, we propose a multifunctional SPE with a polyvinylidene fluoride (PVDF)/co-polyphenol coordination polymer (EACo2) hybrid composite to improve the durability of Li metal anode during repeat plating/stripping cycles by using a facile solution-casting method. The PVDF as a substrate with high mechanical strength and improved lithiophilicity exhibits high ionic conduction and excellent dendrite inhibition ability; meanwhile, the EACo2 fillers with a high density of Lewis-acidic sites contribute to the dissociation of lithium salts and decrystallization of the PVDF, resulting in a high Li-ion transference number and ion conductivity (2.66 × 10−3 S cm−1 at 30 ℃). The symmetrical cells with PVDF/EACo2 SPE can stabilize cycling over 1200 hours at a deposition capacity of 0.1 mAh cm−2. Moreover, the assembled full cells Li|LiFePO4 demonstrate long-term stability (1000 cycles at 1 C) with impressive capacity retention of 75 %, offering a promising approach towards high-performance lithium metal batteries.

Functionalized polypropylene separator coated with polyether/polyester blend for high-performance lithium metal batteries

Commercial polyolefin separators used in lithium metal batteries (LMBs) have the disadvantages of insufficient thermal stability and poor wettability with electrolytes, which causes bad safety and battery performance. Poly(ε-caprolactone) (PCL)-based electrolytes have drawn widespread attention in the field of polymer electrolytes owing to their electrochemical stability and high lithium-ion transference number. This work proposes a strategy of functionalizing commercial polypropylene (PP) separator coated by blending PCL (M w ~ 50,000) and poly(ethylene oxide) (PEO, M V ~ 600,000). Compared to commercial PP separators, PP-blended PEO60w/PCL5w separators possess better wettability with electrolytes and electrochemical performances. The initial discharge specific capacity of LiFePO4-based LMBs assembled with PP-blended PEO60w/PCL5w separators reaches 144 mAh g-1 (1C) and 103 mAh g-1 (5C) at room temperature, respectively. Notably, Li/PP-blended PEO60w/PCL5w/LiFePO4 shows an improved capacity retention rate of 77% after 800 cycles, confirming that the functionalized separator with coated PEO/PCL blend has great potential for application in the field of LMBs.

Ultrafast-Loaded Nickel Sulfide on Vertical Graphene Enabled by Joule Heating for Enhanced Lithium Metal Batteries.

The design and fabrication of a lithiophilic skeleton arehighly important for constructing advanced Li metal anodes. In this work, a new lithiophilic skeleton is reported by planting metal sulfides (e.g., Ni3S2) on vertical graphene (VG) via a facile ultrafast Joule heating (UJH) method, which facilitates the homogeneous distribution of lithiophilic sites on carbon cloth (CC) supported VG substrate with firm bonding. Ni3S2 nanoparticles are homogeneously anchored on the optimized skeleton as CC/VG@Ni3S2, which ensures high conductivity and uniform deposition of Li metal with non-dendrites. By means of systematic electrochemical characterizations, the symmetric cells coupled with CC/VG@Ni3S2 deliver a steady long-term cycle within 14mV overpotential for 1800h (900 cycles) at 1mA cm-2 and 1 mAh cm-2. Meanwhile, the designed CC/VG@Ni3S2-Li||LFP full cell shows notable electrochemical performance with a capacity retention of 92.44% at 0.5 C after 500 cycles and exceptional rate performance. This novel synthesis strategy for metal sulfides on hierarchical carbon-based materials sheds new light on the development of high-performance lithium metal batteries (LMBs).

Identifying ultrathin dielectric nanosheets induced interface polarization for high-performance solid-state lithium metal batteries

Solid-state lithium metal batteries (SSLMBs) with polymer electrolytes are promising due to enhanced safety and high energy density, but the low ionic conductivity of polymer electrolytes and the unstable interface of lithium metal anode hinder the development of SSLMBs. Herein, we propose a unique strategy to address these challenges by coupling ultrathin high-dielectricity Ca2Nb3O10 (CNO) nanosheets with PEO-based electrolyte. The interfacial polarization originating from the distortion of NbO6 octahedra along the vertical direction of CNO nanosheets is maximized and so the interaction between CNO and LiTFSI, which greatly supports the dissociation of LiTFSI and improves the ionic conductivity (2.0 × 10−4 S cm−1) of the composite polymer electrolyte, compared to that without CNO. The optimized interfacial polarization effect is thoroughly demonstrated by theoretical calculation and experimental results. Moreover, due to a homogeneous, robust and LiF-rich solid electrolyte interphase film with promoted Li ion transport being formed at the lithium metal interface, the superior cycling stability (90 % capacity retention after 440 cycles at 0.5 C) and rate capability for LFP||Li full batteries are achieved. This design of composite polymer electrolyte with ultrathin dielectric nanosheet fillers demonstrates a new approach to the development of high-performance polymer electrolytes for SSLMBs.

Three-dimensional cross-linked network deep eutectic gel polymer electrolyte with the self-healing ability enable by hydrogen bonds and dynamic disulfide bonds

Solid polymer electrolytes (SPEs) are effective solutions for the development of high-performance and flexible lithium metal batteries (LMBs). However, the key problems of SPEs including low ionic conductivity and inability to repair damage have hindered their industrialization process. In this work, a three-dimensional (3D) cross-linked network gel polymer electrolyte (CNGPE) is designed. The addition of deep eutectic solvent (DES) improves the ionic conductivity of CNGPE. The hydrogen bonds and dynamic disulfide bonds in the 3D cross-linked network endow CNGPE rapid self-healing ability at ambient temperature. In addition, the addition of lithium difluoro(oxalato)borate (LiDFOB) and lithium nitrate (LiNO3) helps to form a stable solid electrolyte interface (SEI). Due to the ingenious design, the Li/CNGPE/Li symmetrical cell exhibits excellent interface stability and no short circuit occurs for more than 800 h. The assembled LiFePO4/CNGPE/Li cell exhibits a discharge specific capacity of 126 mAh g−1 after 960 cycles at 0.5C. This work has shown that the self-healing gel polymer electrolyte containing DES provides an effective and feasible method for the development of high-performance LMBs.

Garnet-based solid state batteries benefitting from an ionic/electronic mixed conductive interface constructed by lithiation of porous FeS2

Garnet-based solid-state lithium metal batteries are considered as the potential candidates for the next-generation energy storage systems due to their high energy density, wide operating temperature, and high safety. However, the poor wettability of the lithium metal anode/garnet interface, the large interface resistance, and the risk of lithium dendrites growing and even penetrating electrolytes during cycling limit the practical application of garnet-based solid-state lithium metal batteries. In this work, a porous network FeS2 with an amorphized structure is prepared by using the solvothermal method and used as the Li/garnet interface modification layer. The porous FeS2 can be in situ converted into a Li2S/Fe mixed conductive layer by the thermal lithiation of molten metallic lithium. This mixed conductive layer can significantly reduce the interface resistance, ensure the close contact between Li and garnet, and inhibit the growth of lithium dendrites. The interface resistance of the modified Li/FeS2-LLZTO (LLZTO is Li6.5La3Zr1.5Ta0.5O12) interface at 60 °C is as small as 15.20 Ω cm2. The ionic conductivity of fully lithiated FeS2 is estimated to be 1.58 × 10−6 S cm−1 at room temperature. The Li/FeS2-LLZTO/Li symmetrical cell can cycle stably for more than 400 h at a high current density of 400 μA cm−2, with the voltage polarization of only about 25 mV, and can withstand a larger current density of 600 μA cm−2 without the polarization exceeding 50 mV. These results demonstrate the feasibility of in situ lithiation of porous iron sulfide into a mixed ion/electron conductive layer as a solid-state garnet interface modification strategy and provide the new interface method for the development of high-performance solid-state lithium metal batteries.

Functional metal-organic framework membranes with uniform unsaturated pyridine-nitrogen sites as separators for high-performance lithium metal batteries

Lithium metal batteries are a promising successor to lithium-ion batteries due to high specific capacity, low density, and low electrochemical reduction potential. However, inhomogeneous lithium deposition on the Li surface will result in the formation of lithium dendrites and eventually puncture the separator and cause a short circuit. Herein, a functional metal-organic framework membrane with uniform unsaturated pyridine-nitrogen sites is synthesized via coating UiO-67-BPY (2,2 -bipyridine- 5,5 -dicarboxylic acid, named as BPY) on a commercial polypropylene (PP) separator. By replacing the benzene ring with a pyridine ring, the functionalization and porosity of MOF is fully utilized while maintaining the excellent porosity and pore size of MOF. The Li-ion transference number (tLi+) with the functional separator is 0.69 and the ionic conductivity is improved by order of magnitude compared to a plain PP separator. The N atom of the pyridine ring on the UiO-67-BPY has a strong electrostatic interaction force, and a weak coordination bond (N–Li bonding lattice) is formed between N and Li, which leads to an increase in the concentration of free lithium ions and makes their distribution more uniform. This allows lithium ions to migrate more smoothly, which is conducive to ionic conductivity and hinders dendrite formation.

Multifunctional Additive Enables a "5H" PEO Solid Electrolyte for High-Performance Lithium Metal Batteries.

The solid-state battery with a lithium metal anode is a promising candidate for next-generation batteries with improved energy density and safety. However, the current polymer electrolytes still cannot fulfill the demands of solid-state batteries. In this work, we propose a "5H" poly(ethylene oxide) (PEO) electrolyte via introducing a multifunctional additive of tris(pentafluorophenyl)borane (TPFPB) for high-performance lithium metal batteries. The addition of TPFPB improves the ionic conductivity from 6.08 × 10-5 to 1.54 × 10-4 S cm-1 via reducing the crystallinity of the PEO electrolyte and enhances the lithium-ion transference number from 0.19 to 0.53 via anion trapping due to its Lewis acid nature. Furthermore, the fluorine and boron segments from TPFPB can optimize the composition of the solid-electrolyte interphase and cathode-electrolyte interphase, providing a high electrochemical stability window over 4.6 V of the PEO electrolyte along with significantly improved interface stability. At last, TPFPB can ensure improved safety through a self-extinguishing effect. As a result, the "5H" electrolyte enables the Li/Li symmetric cells to achieve a stable cycle over 2200 h at the current density of 0.2 mA cm-2 with a capacity of 0.2 mA h cm-2; the LiFePO4/Li full cells with a high LFP loading of 8 mg cm-2 exhibits decay-free capacity of 140 mA h g-1 (99% capacity retention) after 100 cycles; and the NCM811/Li cells exhibit a high capacity of 160 mA h g-1 after 50 cycles at 0.5 C. This work presents an innovative approach to utilizing a "5H" electrolyte for high-performance solid-state lithium batteries.

Manipulating the diffusion energy barrier at the lithium metal electrolyte interface for dendrite-free long-life batteries.

Constructing an artificial solid electrolyte interphase (SEI) on lithium metal electrodes is a promising approach to address the rampant growth of dangerous lithium morphologies (dendritic and dead Li0) and low Coulombic efficiency that plague development of lithium metal batteries, but how Li+ transport behavior in the SEI is coupled with mechanical properties remains unknown. We demonstrate here a facile and scalable solution-processed approach to form a Li3N-rich SEI with a phase-pure crystalline structure that minimizes the diffusion energy barrier of Li+ across the SEI. Compared with a polycrystalline Li3N SEI obtained from conventional practice, the phase-pure/single crystalline Li3N-rich SEI constitutes an interphase of high mechanical strength and low Li+ diffusion barrier. We elucidate the correlation among Li+ transference number, diffusion behavior, concentration gradient, and the stability of the lithium metal electrode by integrating phase field simulations with experiments. We demonstrate improved reversibility and charge/discharge cycling behaviors for both symmetric cells and full lithium-metal batteries constructed with this Li3N-rich SEI. These studies may cast new insight into the design and engineering of an ideal artificial SEI for stable and high-performance lithium metal batteries.

High-Performance PVDF-HFP-PVAc-LLZTO Composite Solid-State Electrolyte for Lithium Metal Battery

Composite solid-state electrolytes are highly promising contenders for next-generation lithium-metal batteries due to their high safety, good flexibility, and compatibility with lithium metal. In this work, Poly(vinyl acetate) (PVAc) was incorporated into PVDF-HFP in order to reduce the crystallinity of the PVDF-HFP matrix, improve the ionic conductivity of the electrolyte, and greatly reduce the interfacial impedance of the electrolyte by utilizing the low-temperature flexibility, excellent amorphous nature, and strong bonding properties of PVAc. On this basis, the active filler LLZTO was introduced to further reduce the crystallinity of the PVDF-HFP matrix and provide more Li+ transport channels. The PP60-10LLZTO composite solid electrolyte has exceptional mechanical and electrochemical characteristics with a high ionic conductivity of 7.2*10−4 S cm−1 and the Li+ transference number of 0.57 at 30 °C. The assembled LFP/Li battery can be stably cycled for 450 cycles at 30 °C and 0.5C, and its capacity retention rate is as high as 89%. The strategy of constructing composite solid-state electrolytes in this paper presents new insights for designing and developing high-performance solid-state lithium metal batteries.

Ionic liquid-based self-healing gel electrolyte for high-performance lithium metal batteries

The gel electrolytes with self-healing function are being considered as promising replacement for traditional liquid electrolytes in lithium metal batteries due to their excellent battery safety, high energy density and minimum electrolyte damage. However, balancing self-healing, conductivity and mechanical properties remains a challenge for their practical application. Herein, a new ion liquid-based self-healing gel polymer electrolyte (IL-SHGPE) is introduced. The electrolyte was synthesized via UV-induced cross-linking of a polymer containing quadruple hydrogen bond units and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM-TFSI) ion liquid. The resultant IL-SHGPE demonstrates exceptional self-healing ability (with 95% healing efficiency within 30 min), excellent thermal stability over a wide temperature range up to 410 °C. It also exhibits impressive mechanical strength with 41.3% elongation and 1.9 MPa tensile stress, room temperature ionic conductivity of 1.29 × 10−3 S/cm, and a wide electrochemical stability window of 5.18V (vs Li/Li+). Lithium metal batteries with this electrolyte showed an initial discharge capacity of 139 mAh g−1 at 1C rate, and a capacity retention of 88.3% after 200 cycles. Therefore, this work provides a significant exploration for balancing self-healing ability, mechanical attributes, and electrochemical performance of lithium batteries, and thus contributing valuable insights towards the development of high-performance self-healing gel electrolytes for lithium metal batteries.

Transesterification Induced Multifunctional Additives Enable High-Performance Lithium Metal Batteries.

The electrolyte chemistry is crucially important for promoting the practical application of lithium metal batteries (LMBs). Here, we demonstrate for the first time that 1,3-dimethylimidazolium dimethyl phosphate (DIDP) and trimethylsilyl trifluoroacetate (TMSF) can undergo in situ transesterification in carbonate electrolyte to generate dimethyl trimethylsilyl phosphate (DTMSP) and 1,3-dimethylimidazolium trifluoroacetate (DITFA) as multifunctional additives for LMBs. H2O and HF can be removed by the Si-O group in DTMSP to improve the moisture resistance of electrolyte and the stability of cathode. Furthermore, the dissolution of lithium nitrate (LiNO3) in carbonate electrolyte can be promoted by the trifluoroacetate anion (TFA-) in DITFA, thereby optimizing the solvation structure and transport kinetics of Li+. More importantly, both DTMSP and DITFA tend to preferential redox decomposition due to the low lowest unoccupied molecular orbital (LUMO) and high highest occupied molecular orbital (HOMO). Consequently, a thin and robust layer rich in P/N/Si on the cathode and an inorganic-rich layer (e.g. Li3N/Li3P) on the anode can be constructed and superior electrochemical performances are achieved. This artificial transesterification strategy to introduce favorable additives paves an efficient and ingenious route to high-performance electrolyte for LMBs.

Ionic potency regulation of coagulation bath induced by saline solution to control over the pore structure of PBI membrane for high-performance lithium metal batteries

In this study, we have explored the use of water as a non-solvent for tuning the microstructure of polybenzimidazole (PBI) membranes, which are potential separators for lithium metal batteries (LMBs). The traditional method for membrane synthesis called nonsolvent-induced phase separation (NIPS), usually relies on hazardous and costly organic non-solvents. By dissolving sodium chloride (NaCl) in water, we could adjust the water ionic potency and the exchange speed of the non-solvent with the DMAC solution to change the micropore structure of the PBI membrane. With increasing NaCl concentration, the micropores in the PBI membrane transitioned from finger-like to sponge-like morphology. Compared to commercial separators like the Celgard separator, the PBI membrane with sponge-like micropores exhibited better regulation of lithium deposition and improved Li+ transportation capability due to its good wettability with the electrolyte. Consequently, the PBI membrane-based Li/Li symmetric cell and Li/LiFePO4 full cell demonstrated superior performance compared to the Celgard-based ones. This research proposes an eco-friendly and scalable synthetic approach for fabricating commercial separators for LMBs, addressing the issue of lithium dendrite growth and improving overall battery safety and performance.

Enabling an Inorganic-Rich Interface via Cationic Surfactant for High-Performance Lithium Metal Batteries

HighlightsCetyltrimethylammonium cations can shield the repelling force on anions to attract more anions into electric double layer region during lithium plating process, facilitating the formation of inorganic-rich solid-state electrolyte interphase (SEI).An inorganic-rich (N/F-containing species) structure of SEI can be evidenced by the in-depth analysis.The cycling lifetime of Li||Li symmetric cell in the designed electrolyte can be extended from 500 to 1300 h. Moreover, full cells with a high cathode mass loading of >10 mg cm-2 can be stably cycled over 180 cycles.

Lithiophilic Hydrogen-Substituted Graphdiyne Aerogels with Ionically Conductive Channels for High-Performance Lithium Metal Batteries.

Lithium (Li) metal stands as a promising anode in advancing high-energy-density batteries. However, intrinsic issues associated with metallic Li, especially the dendritic growth, have hindered its practical application. Herein, we focus on molecular combined structural design to develop dendrite-free anodes. Specifically, using hydrogen-substituted graphdiyne (HGDY) aerogel hosts, we successfully fabricated a promising Li composite anode (Li@HGDY). The HGDY aerogel's lithiophilic nature and hierarchical pores drive molten Li infusion and reduce local current density within the three-dimensional HGDY host. The unique molecular structure of HGDY provides favorable bulk pathways for lithium-ion transport. By simultaneous regulation of electron and ion transport within the HGDY host, uniform lithium stripping/platting is fulfilled. Li@HGDY symmetric cells exhibit a low overpotential and stable cycling. The Li@HGDY||lithium iron phosphate full cell retained 98.1% capacity after 170 cycles at 0.4 C. This study sheds new light on designing high-capacity and long-lasting lithium metal anodes.

Poly (Vinylidene Fluoride-Hexafluoropropylene)-Lithium Titanium Aluminum Phosphate-Based Gel Polymer Electrolytes Synthesized by Immersion Precipitation for High-Performance Lithium Metal Batteries.

Gel polymer electrolytes (GPEs) have high safety and excellent electrochemical performance, so applying GPEs in lithium batteries has received much attention. However, their poor lithium ion transfer number, cycling stability, and low room temperature ionic conductivity seriously affect the utilization of gel polymer electrolytes. This paper successfully synthesized flexible poly (vinylidene fluoride-hexafluoropropylene)-lithium titanium aluminum phosphate (PVDF-HFP-LATP) gel polymer electrolytes using the immersion precipitation method. The resulting GPE has a porous honeycomb structure, which ensures that the GPE has sufficient space to store the liquid electrolyte. The GPE has a high ionic conductivity of 1.03 ×10-3 S cm-1 at room temperature (25 °C). The GPE was applied to LiFePO4/GPE/Li batteries with good rate performance at room temperature. The discharge specific capacity of 1C was as high as 121.5 mAh/g, and the capacity retention rate was 94.0% after 300 cycles. These results indicate that PVDF-HFP-LATP-based GPEs have the advantage of simplifying the production process and can improve the utility of gel polymer lithium metal batteries.

Integrating N, P, Ni into 3D carbon felt anode for high-performance lithium metal batteries

Integrating N, P, Ni into 3D carbon felt anode for high-performance lithium metal batteries