Localized High-concentration Electrolyte Research Articles

Upgrading Electrolyte Antioxidant Chemistry by Constructing Potential Scaling Relationship.

Rational design of advanced electrolytes to improve the high-voltage capability has been attracting wide attention as one critical solution to enable next-generation high-energy-density batteries. However, the limited understanding of electrolyte antioxidant chemistry as well as the lack of valid quantization approaches have resulted in knowledge gap, which hinders the formulation of new electrolytes. Herein, we construct a standard curve based on representative solvation structures to quantify the oxidation stability of ether-based electrolytes, which reveals the linear correlation between the oxidation potential and the atomic charge of the least oxidation-resistant solvent. Dictating by the regularity between solvation composition and oxidation potential, a (Trifluoromethyl)cyclohexane-based localized high-concentration electrolyte dominated by anion-less solvation structures was designed to optimize the cycling performance of 4.5 V 30-μm-Li||3.8-mAh cm-2-LiCoO2 batteries, which maintained 80% capacity retention even after 440 cycles. The consistency of experimental and computational results validates the proposed principles, offering a fundamental guideline to evaluate and design aggressive electrochemical systems.

Regulate the Solvation Structure and Interface by Nitrate in Phosphate-Based Electrolytes for 4.5V-Class Ni-Rich Batteries.

Phosphate-based electrolyte propels the advanced battery system with high safety. Unfortunately, restricted by poor electrochemical stability, it is difficult to be compatible with advanced lithium metal anodes and Ni-rich cathodes. To alleviate these issues, the study has developed a phosphate-based localized high-concentration electrolyte with a nitrate-driven solvation structure, and the nitrate-derived N-rich inorganic interface shows excellent performance in stabilizing the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode interface and modulating the lithium deposition morphology on the anode. The results show that the Li|| NCM811 cell has exceptional long-cycle stability of >80% capacity retention after 800 cycles at 4.3V, 1 C. A more prominent capacity retention rate of 93.3% after 200 cycles can be reached with the high voltage of 4.5V. While being compatible with the phosphate-based electrolyte with good flame retardancy and the good electrochemical stability of Ni-rich lithium metal battery (LMBs) systems, the present work expands the construction of anion-rich solvation structures, which is expected to promote the development of the high-performance LMBs with safety.

Localized High-Concentration Sulfone Electrolytes with High-Voltage Stability and Flame Retardancy for Ni-Rich Lithium Metal Batteries.

The localized high-concentration electrolyte (LHCE) propels the advanced high-voltage battery system. Sulfone-based LHCE is a transformative direction compatible with high energy density and high safety. In this work, the application of lithium bis(trifluoromethanesulphonyl)imide and lithium bis(fluorosulfonyl)imide (LiFSI) in the LHCE system constructed from sulfolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) is investigated. The addition of diluent causes an increase of contact ion pairs and ionic aggregates in the solvation cluster and an acceptable quantity of free solvent molecules. A small amount of LiFSI as an additive can synergistically decompose with TTE on the cathode and participate in the construction of both electrode interfaces. The designed electrolyte helps the Ni-rich system to cycle firmly at a high voltage of 4.5V. Even with high mass load and lean electrolyte, it can keep a reversible specific capacity of 91.5% after 50 cycles. The constructed sulfone-based electrolyte system exhibits excellent thermal stability far beyond the commercial electrolytes. Further exploration of in-situ gelation has led to a quick conversion of the designed liquid electrolyte to the gel state, accompanied by preserved stability, which provides a direction for the synergistic development of LHCE with gel electrolytes.

The high-fluorinated bi-molecular combination enables high-energy lithium batteries under challenging environment

The drawbacks of temperature sensitivity, high voltage intolerance, and flammability of lithium batteries are gradually brought to light in conventional carbonate electrolytes. To solve these problems, a localized high concentration electrolyte (LHCE) employing highly fluorinated ethyl trifluoroacetate (TFAE) and 2,2,3,3-tetrafluoro-1-(1,1,2,2-tetrafluoroethoxy) propane (TFEP) is designed. When applied in high-energy lithium batteries, the discharge specific capacity of Li||NMC811 battery can maintain 143.6 mAh/g after 500 cycles at 4.6 V and 1C, and the capacity retention of Li||LNMO battery retains as high as 89.99 % after 500 cycles at 5 V. In addition, this LHCE also possesses the ability to operate the battery under challenging conditions including low temperature, fast charge, safety risks, etc. The LHCE based on TFAE and TFEP has unique solvated structures to generate a moderate LiF-rich interfacial layer, ensuring the fast Li+ migration. This work will provide strong guidance for future electrolyte industrial design of high-energy lithium battery.

Stable room-temperature sodium-sulfur battery enabled by pre-sodium activated carbon cloth anode and nonflammable localized high-concentration electrolyte

Room-temperature (RT) sodium-sulfur (Na–S) battery is a promising energy storage technology with low-cost, high-energy-density and environmental-friendliness. However, the current RT Na–S battery suffers from various problems, such as poor cycling stability and poor electrolyte-electrode compatibility caused by polysulfide shuttling and active Na-metal anode. Here, a nonflammable localized high-concentration electrolyte (LHCE) (sodium bis(trifluoromethanesulfonyl)imide salt, sulfolane solvent and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether diluent in a molar ratio of 1:2:2), and a pre-sodium activated carbon cloth (NaACC) anode, are combined to enable stable and high-safety RT Na–S battery. In LHCE, the shuttle effect of polysulfide is greatly alleviated, a stable anions-derived NaF-rich cathode electrolyte interphase is formed, and a solid-solid conversion mechanism of a solid S8-solid Na2Sn (1 ≤ n ≤ 3) is achieved. Meanwhile, the Na dendrites and side reactions between electrolyte and anode are effectively inhibited by using NaACC anode. Therefore, under the synergistic effect of electrolyte regulation and negative electrode structure optimization, although using a low N/P ratio of 1.7, the RT Na–S battery also delivers a high initial capacity of 1220.8 mAh g−1, good rate capability and stable cycling performance with a high average Coulombic efficiency of 99.1 %. The capacity still remains at 704.5 mAh g−1 after 100 cycles. This innovative combination of LHCE and NaACC anode in Na–S batteries provides a new idea for further achieving stable RT Na–S batteries with long-cycle-life and high-safety.

Enhanced Electrochemical Performance of Disordered Rocksalt Cathodes in a Localized High‐Concentration Electrolyte

Enhanced Electrochemical Performance of Disordered Rocksalt Cathodes in a Localized High‐Concentration Electrolyte

Achieving Uniform Li Deposition and Suppressed Electrolyte Flammability in Li‐Metal Batteries via Designing Localized High‐Concentration Electrolytes

AbstractThe increasing need for energy storage devices with high energy density has led to significant interest in Li‐metal batteries (LMBs). However, the use of commercial electrolytes in LMBs is problematic due to their flammability, inadequate performance at low temperatures, and tendency to promote the growth of lithium dendrites and other flaws. This study introduces a localized high‐concentration electrolyte (LHCE) that addresses these issues by employing non‐flammable electrolyte components and incorporating carefully designed additives to enhance flame retardancy and low‐temperature performance. By incorporating additives to optimize the electrolyte, it is possible to attain inorganic‐dominated solid electrolyte interphases on both the cathode and anode. This achievement results in a uniform deposition of lithium, as well as the suppression of electrolyte decomposition and cathode deterioration. Consequently, this LHCE achieve over 300 stable cycles for both LiNi0.9Mn0.05Co0.05O2||Li cells and LiCoO2||Li cells, as well as 50 cycles for LiNi0.8Mn0.1Co0.1O2 (NCM811||Li) pouch cells. Furthermore, NCM811||Li cells maintain 84% discharge capacity at −20 °C, in comparison to the capacity at room temperature. The utilization of this electrolyte presents novel perspectives for the safe implementation of LMBs.

Empowering the Potassium-Sulfur Battery with Commendable Reaction Kinetics and Capacity Output by Localized High-Concentration Electrolytes.

Potassium-sulfur (K-S) batteries are one of the promising high-energy-density candidates beyond current lithium-ion batteries. Nevertheless, in practice, the utilization of K-S batteries is largely hindered due to the dissolution and shuttle effect of the cathode redox intermediates and the scarcity of an effective anode protection layer in conventional electrolytes. Herein, electrolyte engineering is applied to formulate an ether-based localized high-concentration electrolyte (LHCE) for the first time in a K-S cell with the mitigated parasitic effect of polysulfide dissolution and shuttle and the tuned anode-electrolyte interface property. A nonsolvating and polysulfide-stable fluoroether is sieved as a cosolvent in such an LHCE, which possesses the ultralow polysulfides solubility due to less roaming solvents and thus alleviates the polysulfides shuttle effect. The anion-derived solid electrolyte interphase enriched in inorganic components is constructed due to the strengthened cation-anion interplay in the primary solvation sheath and highlighted with accelerated interfacial kinetics in a K-S cell. It is validated that the proposed LHCE unlocks the theoretical capacity of the K-S cell based on the conversion between S and K2S3. It is further revealed that the lifespan is limited to the anode corrosion with severe cosolvent degradation caused by limited solvating solvent compatibility with metallic K, and the inevitable byproduct accumulation at the S cathode. The K-S cell based on the designed LHCE could achieve a prolonged lifespan with a reversible capacity of 448 mA h/gs after 80 cycles with an elaborate cathode design. This work shines a light on the electrolyte design perspective for full utilization and an in-depth mechanistic understanding of high-energy-density K-S batteries.

Additive-Driven Nanoscale Architecture of Solid Electrolyte Interphase Revealed by Cryogenic Transmission Electron Microscopy.

In Li metal batteries (LMBs), which boast the highest theoretical capacity, the chemical structure of the solid electrolyte interphase (SEI) serves as the key component that governs the growth of reactive Li. Various types of additives have been developed for electrolyte optimization, representing one of the most effective strategies to enhance the SEI properties for stable Li plating. However, as advanced electrolyte systems become more chemically complicated, the use of additives is empirically optimized. Indeed, their role in SEI formation and the resulting cycle life of LMBs are not well-understood. In this study, we employed cryogenic transmission electron microscopy combined with Raman spectroscopy, theoretical studies including molecular dynamics (MD) simulations and density functional theory (DFT) calculations, and electrochemical measurements to explore the nanoscale architecture of SEI modified by the most representative additives, lithium nitrate (LiNO3) and vinylene carbonate (VC), applied in a localized high-concentration electrolyte. We found that LiNO3 and VC play distinct roles in forming the SEI, governing the solvation structure, and influencing the kinetics of electrochemical reduction. Their collaboration leads to the desired SEI, ensuring prolonged cycle performance for LMBs. Moreover, we propose mechanisms for different Li growth and cycling behaviors that are determined by the physicochemical properties of SEI, such as uniformity, elasticity, and ionic conductivity. Our findings provide critical insights into the appropriate use of additives, particularly regarding their chemical compatibility.

Strongly solvating triglyme-based electrolyte realizes stable lithium metal batteries at high-voltage and high-temperature

The electrolyte in lithium-metal batteries (LMBs) plays a pivotal role in stabilizing the surface of the lithium metal anode (LMA) and high-voltage cathode. However, currently widely studied ether-based electrolytes, although it has good compatibility with LMA due to their lower reactivity, are facing significant challenges related to poor oxidation resistance and cathode/electrolyte interface (CEI) instability when combined with the high-voltage cathode, particularly at elevated temperatures. Therefore, there is an urgent need to design advanced electrolytes capable of maintaining high stability under high-voltage and high-temperature conditions. Here, we have developed an ultra-stable localized high-concentration electrolyte (LHCE) by introducing triethylene glycol dimethyl ether (TG), which exhibits strong solvation ability. Computational and experimental results demonstrate that the designed TG-based dilute high-concentration electrolyte (TG-DHCE) possesses a stable solvation structure, high oxidation resistance, and thermal stability, making it ideal for LMBs. Furthermore, the unique solvation structure of TG-DHCE promotes the preferential decomposition of anions while facilitating the formation of stable, inorganic-rich electrode/electrolyte interfaces on the anode and cathode. Consequently, equipped with TG-DHCE, Li||Li cells (more than 1600 h) and Li||NCM523 cells (80.6%, 250 cycles) show superior stability and also demonstrate remarkable performance even at elevated temperatures (60 °C). Additionally, under the harsh conditions of ultrahigh loading NCM523 cathode (19.7 mg/cm2) and limited Li reservoir (twice excess Li was deposited on Cu, Li@Cu) (N/P = 2), Li@Cu||NCM523 cells still maintain stable operation. This work pioneers a new path by choosing strongly solvating solvents, effectively enhancing the cycle life of LMBs under high-voltage and high-temperature conditions.

Revealing the key role of non-solvating diluents for fast-charging and low temperature Li-ion batteries

Fast-charging and low temperature operation are of vital importance for the further development of lithium-ion batteries (LIBs), which is hindered by the utilization of conventional carbonate-based electrolytes due to their slow kinetics, narrow operating temperature and voltage range. Herein, an acetonitrile (AN)-based localized high-concentration electrolyte (LHCE) is proposed to retain liquid state and high ionic conductivity at ultra-low temperatures while possessing high oxidation stability. We originally reveal the excellent thermal shielding effect of non-solvating diluent to prevent the aggregation of Li+ solvates as temperature drops, maintaining the merits of fast Li+ transport and facile desolvation as at room temperature, which bestows the graphite electrode with remarkable low temperature performance (264 mA h g−1 at −20 °C). Remarkably, an extremely high capacity retention of 97% is achieved for high-voltage high-energy graphite||NCM batteries after 250 cycles at −20 °C, and a high capacity of 110 mA h g−1 (71% of its room-temperature capacity) is retained at −30 °C. The study unveils the key role of the non-solvating diluents and provides instructive guidance in designing electrolytes towards fast-charging and low temperature LIBs.

Cycling performance of Li metal anode in localized high concentration electrolyte and dynamic mechanism analysis

In this work, we investigated the apparent cycling performance of lithium metal at different chemical compositions and series current densities; examined the microscopic morphology and thickness variation of the deposition layer on the surface of lithium metal anode and the concentration-depth distribution of trace elements in the solid electrolyte interphase (SEI) film; and characterized the kinetic behavior and features of the elementary steps (mass transfer, charge transfer, electro-crystallization) at Li-electrolyte interface using microelectrode technology and various electrochemical test methods. The results show that the lithium metal anode has better cycling performance in high concentration and localized high concentration electrolyte. At the same time, the experimental results confirm that the formation of spherical crystal nucleus is favored only under certain chemical conditions and certain reaction rate; under these conditions, the induction period and the self-smoothing process of critical crystal nucleus can be found. It suggests that there are determined causal among the apparent performance of lithium metal anode, the kinetic parameters of the interfacial charge transfer step and the electro-crystallization step, and these correlations can be used as a reference for screening and evaluating electrolyte systems and battery operating conditions, providing a reliable kinetic basis for future work.

Efficient Lithium Transport and Reversible Lithium Plating in Silicon Anodes: Synergistic Design of Porous Structure and LiF‐Rich SEI for Fast Charging

AbstractSilicon (Si) anodes hold great promise for enhancing the energy density of lithium‐ion batteries (LIBs). However, issues such as slow intrinsic kinetics and unstable interfaces caused by significant volume changes hinder the practical deployment of Si anodes. Fast charging is desired by Si‐related issues that worsen Li plating and dead Li, making it essential to overcome these for safe, reversible charging. Herein, a novel approach is proposed by combining structural design and solid electrolyte interface (SEI) modulation to enable efficient and safe fast charging of LIBs. 3D porous micro‐particles consisting of Si nanosheets coated with a pitch‐based carbon layer are successfully prepared. This design provides enhanced ion transport pathways while maintaining the material's intrinsic rate performance and tap density. Furthermore, the designed localized high‐concentration electrolyte (LHCE) exhibits a lower Li+ desolvation energy barrier and leads to the formation of a LiF‐rich SEI, mitigating the Li plating “tip effect” during fast charging, maintaining interface stability, and demonstrating high Coulombic efficiency. Overall, this study highlights the synergistic importance of structure design and SEI regulation in enhancing LIB anodes for fast charging, aiding in developing superior, safe energy storage.

Dual-salt strategy tuning the solvation structure to achieve high cycling stability for FeS2 cathodes

Pyrite FeS2, as a promising conversion-type cathode material, faces rapid capacity degradation due to challenges such as polysulfide shuttle and massive volume changes. Herein, a localized high-concentration electrolyte (LHCE) based on dual-salt lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) is designed to address the challenges. By the dual-salt strategy, we tailor a more desirable solvation structure than that in the single-salt system. Specifically, the solvation structure involving FSI− and TFSI− enables milder electrolyte decomposition, which reduces initial capacity loss. Meanwhile, it facilitates the formation of a stable and flexible cathode/electrolyte interphase (CEI), effectively mitigating side effects and accommodating volume changes. Consequently, the micro-sized FeS2 realizes a capacity of 641 mAh g−1 after 600 cycles with a retention rate of 90%, significantly improving the cycling stability of the FeS2 cathode. This work underscores the pivotal role of solvation structure in modulating electrochemical performances and provides a simple and effective electrolyte design concept for conversion-type cathodes.

Stabilizing cathode-electrolyte interphase by localized high-concentration electrolytes for high-voltage sodium-ion batteries

Sodium-ion batteries (SIBs) operating under high-voltages suffer from unstable cathode-electrolyte interphase (CEI) formed on the cathode surface, resulting in continuous electrolyte decomposition, surface reconstruction, transition metal dissolution, and eventually capacity decay. Therefore, designing high-voltage electrolyte and constructing the robust CEI are critical for high-energy SIBs. Herein, a localized high-concentration electrolyte (LHCE) is fabricated by dissolving sodium hexafluorophosphate in methyl ethyl carbonate, fluorinated ethylene carbonate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, which demonstrates oxidative stability exceeding 6 V relative to Na+/Na. The dense and homogeneous inorganics-rich CEIs are generated by the preferential decomposition of PF6− anions during the electrochemical charge to 4.4 V, which lower interface impedance, facilitate Na+ transportation and suppress subsequent side reactions. Consequently, the cell integrating high-voltage P2-Na0.7Li0.03Mg0.03Ni0.27Mn0.6Ti0.07O2 cathode and Na anode exhibits a capacity retention of 87.3% after 200 cycles and a high-rate discharge capacity of 84 mA h g−1 at 20 C under a high cut-off voltage of 4.4 V. This work offers a feasible pathway to tailor electrolyte chemistry and interphase properties for practical next generation high-voltage SIBs.

Localized Medium Concentration Electrolyte with Fast Kinetics for Lithium Metal Batteries.

Localized high-concentration electrolyte is widely acknowledged as a cutting-edge electrolyte for the lithium metal anode. However, the high fluorine content, either from high-concentration salts or from highly fluorinated diluents, results in significantly higher production costs and an increased environmental burden. Here, we have developed a novel electrolyte termed "Localized Medium-Concentration Electrolyte" (LMCE) to effectively address these issues. This LMCE is designed and produced by diluting a medium concentration (0.5 M-1.5 M) electrolyte which is incompatible with lithium metal anode before diluting. It has ultralow concentration (0.1 M) and demonstrates remarkable compatibility with lithium metal anode. Surprisingly, our LMCE, despite having an ultralow concentration (0.1 M), exhibits excellent kinetics in Li/Cu, Li/Li, LiFePO4 /Li, and NCM811/Li batteries. Additionally, LMCE effectively inhibits the corrosion of the Al current collector caused by LiTFSI salt under high voltage (>4 V) conditions. This groundbreaking LMCE design transforms the seemingly "incompatible" into the "compatible", opening up new avenues for exploring various electrolyte formulations, including all liquid electrolyte-based batteries.

Balancing salt concentration and fluorinated cosolvent for graphite cathode-based dual-ion batteries

High-concentration electrolytes (HCEs) are favored in graphite cathode-based dual-ion batteries (DIBs) due to their high oxidative stability and good interphase compatibility with both anode and cathode. Although a localized high-concentration electrolyte (LHCE) with the similar solvation structure as HCE is proposed for graphite cathode by adding weakly solvated fluorinated cosolvents, the balance between salt concentration and fluorinated cosolvent has not been investigated. Herein, various electrolytes were prepared by introducing tris(2,2,2-trifluoroethyl) phosphate (FTEP) into the HCE composed of potassium bis(fluorosulfonyl)imide (KFSI) and triethyl phosphate (TEP), and the moderate concentrated electrolyte at the TEP/FTEP volume ratio of 5:1 can stabilize K/graphite DIBs with the capacity of 45 mAh g−1 after 300 cycles at 0.5 A g−1. The abundant ion–solvent complexes as HCE and the entrance of FTEP contribute to building stable FSI−-derived cathode/electrolyte interphase with the KF-rich inner layer. Importantly, FTEP replaces partial TEP solvents to coordinate with FSI−, enhancing the electrolyte oxidative stability, whereas their weak interaction further suppresses the solvent co-intercalation. As a proof, this electrolyte enables high output voltage (3.75 V) and good cyclability of dual-ion full cells coupled with tellurium anode. This work will promote the development of fluorinated cosolvent-modified LHCEs for high-performance DIBs.

Novel propylene carbonate based localized high concentration electrolyte with high voltage, flame retardant and wide temperature characteristics enables excellent electrochemical performances of lithium metal batteries

A novel propylene carbonate based localized high concentration electrolyte using for lithium metal batteries achieves flame retardancy, a broad electrochemical stability window, dendrite-free Li deposition, and a wide operating temperature range.

Regulating the solvation structure of an acetonitrile-based electrolyte for Li/NMC811 batteries cycled at low temperature

An acetonitrile-based localized high concentration electrolyte has been developed for low temperature lithium metal batteries. The corresponding Li/NMC811 cell delivers a high capacity of 113 mA h g−1 at −40 °C with 85.5% capacity retention.

(Invited) Extending Cycle and Calendar Life of Si Based Li-Ion Batteries By Localized High Concentration Electrolytes

Si is one of the most promising anode materials for the next generation of lithium (Li) ion batteries (LIBs). Recently, we have developed a porous Si with a unique carbon coating structure (“carbon on Si” instead of “Si on carbon”). The nano-porosity of the materials absorbed most of volume expansion so the particles (between 3-5 mm) can retain their integrity during cycling instead of breakdown observed in bulk Si particles. Although single layer pouch cells (Si/NMC622, 62 mAh) with this porous Si anode and baseline electrolyte (1.2 M LiPF6 in EC-EMC (3:7 by wt.) +10 wt.% FEC) can retain 91% capacity after 800 cycles, their calendar life is still far shorter from 10-year target required by electrical vehicles.In this work, we present a systematic investigation of the application of localized high concentration electrolyte (LHCE) to extend the cycle life and calendar life of Si-LIBs. A typical LHCE contains a Li salt (typically LiFSI) with high solubility in a common solvent (such as DMC), and a diluent (such as TTE) with minimal solubility of the Li salt. Compared with other electrolyte design, one distinct advantage of LHCE is that solvent and diluent in LHCE can be largely decoupled from each other: change in once components will have not significantly affect the functionality of other components. This characteristic of LHCE enables much more freedom in the electrolyte designs to satisfy different practical application needs (such as long cycle life, long calendar life, high rate, high temperature, and high voltage). For example, Si/NMC622 cells with a composition of LiFSI-2.15DMC-0.17VC-0.69FEC-4.31TTE (in molar ratio) have increased cycle life of Si/NMC622 pouch cells to 2000 cycles with 80% capacity retention at 25°C as compared with 1000 cycles when baseline electrolyte was used. However, this electrolyte is less stable when LiCoO2 is used as the cathode, leading to rapid capacity loss at elevated temperatures (45°C). One possible reason for this is that cobalt in the cathode leads to more rapid decomposition of FEC than in the case of NMC622 at 45°C. On the other hand, the stability of LHCE is significantly affected by the amount of free (unbound) solvent (including DMC, VC, and FEC in the above example) in the electrolyte. By minimizing the amount of total free solvents, an electrolyte with a composition of LiFSI-2DMC-0.1EC-0.1FEC-3TTE has led to a long cycle life of Si/NMC622 cells at 25°C. Increasing the amount of main solvent in the electrolyte can further increase the conductivity of the electrolyte and significantly increase the charge/discharge rate of the cells.The long calendar life of Si-LIBs can be measured by accelerated tests at elevated temperatures (up to 55°C). Although FEC-containing electrolytes can increase the cycle life of Si-LIBs at room temperature, most Si-LIBs with FEC-containing electrolytes exhibit a rapid increase in impedance at elevated temperature, leading to a short projected-calendar-life. We designed a series of experiments to investigate the effect of FEC on the calendar life of Si-LIBs. The results clearly indicate that the formation of a high impedance interphase layer on the anode and cathode surfaces due to the decomposition of FEC at high temperatures is one of the fundamental reasons for the short calendar life of Si-LIBs. By replacing FEC with an alternative additive, a new LHCE electrolyte has been designed that led to much better cycling stability of Si-LIBs at 45°C (less than 5% capacity loss in 500 cycles) and much longer calendar life. More details of these investigations will be reported in this presentation.