Fast Li+ Transport via Silica Network-Driven Nanochannels in Ionomer-in-Framework for Lithium Metal Batteries

For the development of all-solid-state lithium metal batteries (LMBs), a high-porous silica aerogel (SA)-reinforced single-Li⁺ conducting nanocomposite polymer electrolyte (NPE) is prepared via two-step selective functionalization. The mesoporous SA is introduced as a mechanical framework for NPE as well as a channel for fast lithium cation migration. Two types of monomers containing weak-binding imide anions and Li⁺ cations are synthesized and used to prepare NPEs, where these monomers are grafted in SA to produce SA-based NPEs (SANPEs) as ionomer-in-framework. This hybrid SANPE exhibits high ionic conductivities (≈10⁻³ S cm⁻¹), high modulus (≈10⁵ Pa), high lithium transference number (0.84), and wide electrochemical window (>4.8 V). The resultant SANPE in the lithium symmetric cell possesses long-term cyclic stability without short-circuiting over 800 h under 0.2 mA cm⁻². Furthermore, the LiFePO₄|SANPE|Li solid-state batteries present a high discharge capacity of 167 mAh g⁻¹ at 0.1 C, good rate capability up to 1 C, wide operating temperatures (from −10 to 40 °C), and a stable cycling performance with 97% capacity retention and 100% coulombic efficiency after 75 cycles at 1 C and 25 °C. The SANPE demonstrates a new design principle for solid-state electrolytes, allowing for a perfect complex between inorganic silica and organic polymer, for high-energy-density LMBs.     

Spherical Lithium Deposition Enables High Li-Utilization Rate,Low Negative/Positive Ratio,and High Energy Density in Lithium Metal Batteries

Lithium metal battery promises an attractively high energy density. A high Li-utilization rate of Li metal anode is the prerequisite for the high energy density and avoiding a huge waste of the Li resource. However, the dendritic Li deposition gives rise to “dead Li” and parasitic interfacial reactions, resulting in a low Li utilization rate. Herein, Li deposition is regulated to spherical Li by designing an MXene host with an egg-box structure, suitable curvature, and continuous gradient lithiophilic structure. Because the spherical Li greatly reduces the interfacial side reactions and avoids the formation of dead Li, the Li anode affords a high plating/stripping efficiency. Furthermore, the gradient lithiophilic design results in a bottom-up growth of the spherical Li within the host, safely away from the separator. Thus, the spherical Li anode realizes a long life of >3000 h with a high Li-utilization rate of >90%, stable cycling in full cells at an areal capacity up to 5 mAh cm⁻² with a low negative/positive ratio of 0.8, which is critical for high energy density. Such spherical deposition highlights the critical role of the morphological control of alkali metals and provides a viable method to build practical high-energy metal batteries.     

Lithiophilic and Antioxidative Copper Current Collectors for Highly Stable Lithium Metal Batteries

Designing copper (Cu) current collectors is a convenient way to stabilize lithium (Li) metal anodes. However, Cu current collectors and their derived Li/Cu anodes still face several obstacles, including lithiophobic and oxidizable Cu surface, cumbersome anode fabrication process, and low Li utilization. Here, a formate-treatment strategy is presented to reconstruct Cu current collectors with a passivation layer covered Cu(110) surface. This method can easily be generalized to increase the lithiophilicity and oxidation resistibility of Cu current collectors. Using the formate-treated Cu nanowire network as an anode current collector, the full cell consisting of a LiFePO₄ cathode and Li/Cu anode with a low negative/positive capacity ratio delivers an excellent cycling performance with 74.8% capacity retention after 1000 cycles at 1 C. In addition, a concept of an upper current collector is introduced to simplify the manufacturing procedure of Li/Cu anodes. This work provides new insights into the design and construction of high-performance Li/Cu anodes.     

Lithiophilic MXene-Guided Lithium Metal Nucleation and Growth Behavior

The positive effects of a lithiophilic substrate on the electrochemical performance of lithium metal anodes are confirmed in several reports, while the understanding of lithiophilic substrate-guided lithium metal nucleation and growth behavior is still insufficient. In this study, the effect of a lithiophilic surface on lithium metal nucleation and growth behaviors is investigated using a large-area Ti₃C₂T_x MXene substrate with a large number of oxygen and fluorine dual heteroatoms. The use of the MXene substrate results in a high lithium-ion concentration as well as the formation of uniform solid–electrolyte-interface (SEI) layers on the lithiophilic surface. The solid–solid interface (MXene-SEI layer) significantly affects the surface tension of the deposited lithium metal nuclei as well as the nucleation overpotential, resulting in the formation of uniformly dispersed lithium nanoparticles ( ≈ 10–20 nm in diameter) over the entire MXene surface. The primary lithium nanoparticles preferentially coalesce and agglomerate into larger secondary particles while retaining their primary particle shapes. Subsequently, they form close-packed structures, resulting in a dense metal layer composed of particle-by-particle microstructures. This distinctive lithium metal deposition behavior leads to highly reversible cycling performance with high Columbic efficiencies >  99.0% and long cycle lives of over 1000 cycles.     

Nanoflake Arrays of Lithiophilic Metal Oxides for the Ultra‐Stable Anodes of Lithium‐Metal Batteries

A molten lithium infusion strategy has been proposed to prepare stable Li‐metal anodes to overcome the serious issues associated with dendrite formation and infinite volume change during cycling of lithium‐metal batteries. Stable host materials with superior wettability of molten Li are the prerequisite. Here, it is demonstrated that a series of strong oxidizing metal oxides, including MnO₂, Co₃O₄, and SnO₂, show superior lithiophilicity due to their high chemical reactivity with Li. Composite lithium‐metal anodes fabricated via melt infusion of lithium into graphene foams decorated by these metal oxide nanoflake arrays successfully control the formation and growth of Li dendrites and alleviate volume change during cycling. A resulting Li‐Mn/graphene composite anode demonstrates a super‐long and stable lifetime for repeated Li plating/stripping of 800 cycles at 1 mA cm^?2 without voltage fluctuation, which is eight times longer than the normal lifespan of a bare Li foil under the same conditions. Furthermore, excellent rate capability and cyclability are realized in full‐cell batteries with Li‐Mn/graphene composite anodes and LiCoO₂ cathodes. These results show a major advancement in developing a stable Li anode for lithium‐metal batteries.     

Non-Flammable Electrolyte with Lithium Nitrate as the Only Lithium Salt for Boosting Ultra-Stable Cycling and Fire-Safety Lithium Metal Batteries

Lithium metal batteries (LMBs) attract considerable attention for their incomparable energy density. However, safety issues caused by uncontrollable lithium dendrites and highly flammable electrolyte limit large-scale LMBs applications. Herein, a low-cost, thermally stable, and low environmentally-sensitive lithium nitrate (LiNO₃) is proposed as the only lithium salt to incorporate with nonflammable triethyl phosphate and fluoroethylene carbonate (FEC) co-solvent as the electrolyte anticipated to enhance the performance of LMBs. Benefiting from the presence of NO₃⁻ and FEC with strong solvation effect and easily reduced ability, a Li₃N–LiF-rich stable solid electrolyte interphase is constructed. Compared to commercial electrolytes, the proposed electrolyte has a high Coulombic efficiency of 98.31% in Li-Cu test at 1 mA cm⁻² of 1.0 mAh cm⁻² with dendrite-free morphology. Additionally, the electrolyte system shows high voltage stability and cathode electrolyte interphase film-forming properties with stable cycling performances, which exhibit outstanding capacity retention rates of 96.39% and 83.74% after 1000 cycles for LFP//Li and NCM811//Li, respectively. Importantly, the non-flammable electrolyte delays the onset of combustion in lithium metal soft pack batteries by 255 s and reduces the peak heat release by 21.02% under the continuous external high-temperature heating condition. The novel electrolyte can contribute immensely to developing high-electrochemical-performance and high-safety LMBs.     

An Intrinsically Nonflammable Electrolyte for Prominent-Safety Lithium Metal Batteries with High Energy Density and Cycling Stability

Nex-generation high-energy-density storage battery, assembled with lithium (Li)-metal anode and nickel-rich cathode, puts forward urgent demand for advanced electrolytes that simultaneously possess high security, wide electrochemical window, and good compatibility with electrode materials. Herein an intrinsically nonflammable electrolyte is designed by using 1 M lithium difluoro(oxalato)borate (LiDFOB) in triethyl phosphate (TEP) and N-methyl-N-propyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide [Pyr₁₃][TFSI] ionic liquid (IL) solvents. The introduction of IL can bring plentiful organic cations and anions, which provides a cation shielding effect and regulates the Li⁺ solvation structure with plentiful Li⁺-DFOB⁻ and Li⁺-TFSI⁻ complexes. The unique Li⁺ solvation structure can induce stable anion-derived electrolyte/electrode interphases, which effectively inhibit Li dendrite growth and suppress side reactions between TEP and electrodes. Therefore, the LiNi_0.9Co_0.05Mn_0.05O₂ (NCM90)/Li coin cell with this electrolyte can deliver stable cycling even under 4.5 V and 60 °C. Moreover, a Li-metal battery with thick NCM90 cathode (≈ 15 mg cm⁻²) and thin Li-metal anode (≈ 50 µm) (N/P ≈ 3), also reveals stable cycling performance under 4.4 V. And a 2.2 Ah NCM90/Li pouch cell can simultaneously possess prominent safety with stably passing the nail penetration test, and high gravimetric energy density of 470 Wh kg⁻¹ at 4.4 V.     

Tuning a Solvation Structure of Lithium Ions Coordinated with Nitrate Anions through Ionic Liquid-Based Solvent for Highly Stable Lithium Metal Batteries

Rational design of promising electrolyte is considered as an effective strategy to improve the cycling stability of lithium metal batteries (LMBs). Here, an elaborately designed ionic liquid-based electrolyte is proposed that is composed of lithium bis(trifluoromethanesulfonyl)imide as the lithium salt, 1-ethyl-3-methylimidazolium nitrate ionic liquid ([EMIm][NO₃] IL) and fluoroethylene carbonate (FEC) as the functional solvents, and 1,2-dimethoxyethane (DME) as the diluent solvent. Using [EMIm][NO₃] IL as the solvent component facilitates a special Li⁺-coordinated NO₃⁻ solvation structure, which enables the continues electrochemical reduction of solvated NO₃⁻ and the formation of remarkably stable and conductive solid electrolyte interface. With FEC as another functional solvent and DME as the diluent solvent, the formulated electrolyte delivers high oxidative stability and ionic conductivity, and endows improved electrochemical reaction kinetics. Therefore, the formulated electrolyte demonstrates exceedingly reversible and stable Li stripping/plating behavior with high average Coulombic efficiency (98.8%) and ultralong cycling stability (3500 h). Notably, the high-voltage Li|LiNi_0.8Co_0.1Mn_0.1O₂ full cell with IL-based electrolyte exhibits enhanced cyclability with a capacity retention of 65% after 200 cycles under harsh conditions of low negative/positive ratio (3.1) and lean electrolyte (2.5 µL mg⁻¹). This study creates the first NO₃⁻-based ionic liquid electrolyte and evokes the avenue for practical high-voltage LMBs.     

Advances and Prospects in Improving the Utilization Efficiency of Lithium for High Energy Density Lithium Batteries

Lithium-ion batteries have attracted much attention in the field like portable devices and electronic vehicles. Due to growing demands of energy storage systems, lithium metal batteries with higher energy density are promising candidates to replace lithium-ion batteries. However, using excess amounts of lithium can lower the energy density and cause safety risks. To solve these problems, it is crucial to use limited amount of lithium in lithium metal batteries to achieve higher utilization efficiency of lithium, higher energy density, and higher safety. The main reasons for the loss of active lithium are the side reactions between electrolyte and electrode, growth of lithium dendrites, and the volume change of electrode materials during the charge and discharge process. Based on these issues, much effort have been put to improve the utilization efficiency of lithium such as mitigating the side reactions, guiding the uniform lithium deposition, and increasing the adhesion between electrolyte and electrode. In this review, strategies for high utilization efficiency of lithium are presented. Moreover, the remaining challenges and the future perspectives on improving the utilization of lithium are also outlined.     

Long Cycle Life Lithium Metal Batteries Enabled with Upright Lithium Anode

The lithium metal anode is the holy grail of the battery field due to its lowest reduction potential and high specific capacity; however, its application is hindered by severe safety hazards and inferior cyclic stability due to dendrites and unstable solid electrolyte interphase (SEI). Aiming at these problems, a coiled Li anode with a unique upright structure is proposed. The upright structure endows coiled Li anode with abundant inner reaction interface/space/mass for lithium deposit/storage/transport, which can induce the inner growth of Li dendrites and SEI. The Li⁺ transport/deposit behavior and mechanism of coiled Li anode are clarified via in situ observation and numerical simulation. Benefiting from the small volume expansion and sufficient Li⁺ transport, the coiled Li anodes combined with Li₄Ti₅O₁₂ cathodes achieve a long life of over 2000 cycles at 5C with a reversible capacity of 129 mAh g^?1 and 100% Coulombic efficiency.     

Dendrite-Free and Long-Cycling Sodium Metal Batteries Enabled by Sodium-Ether Cointercalated Graphite Anode

Stable and dendrite-free Na metal plating–stripping is achieved on the graphite electrode. The sodium-ether cointercalated graphite exhibits ultrahigh Na deposition efficiency of 99.86% over 900 cycles at a current density of 2 mA cm⁻². The discharge process involves the [Na-ether]⁺ cointercalation and Na deposition. Density functional theory calculations demonstrate that the cointercalated graphite is critical for uniform Na deposition and stable Coulombic efficiency, which is ascribed to both the robust binding sites to Na by the diglyme molecules and a low lattice mismatch for Na growth on the cointercalated graphite. Also, a full cell consisting of Na₄Fe₃(PO₄)₂(P₂O₇) cathode and 0.5 mAh cm⁻² Na predeposited graphite anode shows excellent cycling stability. The full cell delivers a capacity of 95 mAh g⁻¹ based on the weight of cathode materials, with a high capacity retention of 91% over 300 cycles.     

Lithium Induced Nano-Sized Copper with Exposed Lithiophilic Surfaces to Achieve Dense Lithium Deposition for Lithium Metal Anode

Li metal batteries have attracted extensive research attention because of their extremely high theoretical capacity. However, the commercialization of the Li metal batteries is hindered, as uncontrolled Li dendrites growth leads to safety concerns and a low coulombic efficiency. To suppress Li dendrites growth and achieve dense Li deposition, a lithiophilic 3D Cu host is designed for Li metal anode, in which the nano-sized Cu is in situ formed with the aid of infused Li metal. The fabricated Li metal anode exhibit a superior electrochemical stability than raw Li metal anode, and compact Li is maintained during cycling. The experimental results and density functional theory calculations demonstrate that the nano-sized Cu formed on the surface of the skeleton host shows highly exposed Cu (100) and Cu (110) surfaces, which exhibits a strong affinity toward Li, and effectively eliminates the formation of Li dendrites, leading to a dense Li deposition. With the strategy of adjusting exposed surfaces of Cu host, the optimized Li metal anode enhances the electrochemical performance of full cells, and concomitantly demonstrates their potential for future designs of next-generation Li metal anodes or Li-free anodes for Li metal batteries.     

A Supertough,Nonflammable, Biomimetic Gel with Neuron-Like Nanoskeleton for Puncture-Tolerant Safe Lithium Metal Batteries

To overcome the critical safety and performance issues of lithium metal batteries, it is urgent to develop advanced electrolytes with multi-defensive properties against fire, mechanical puncture, and dendrite growth simultaneously, in addition to high ion-conductivity. However, realizing these essential properties by one electrolyte has proved to be extremely challenging due to the inherent conflicts among them. Herein, to circumvent this challenge, a neuron-like gel polymer electrolyte (simply referred as Neu-PE) to simultaneously achieve supertoughness, nonflammability, dendrite-suppression capability and self-driven property is reported. This Neu-PE takes advantage of nano-phase separation regulated by highly ion-conductive deep-eutectic solvent. As a result, the Neu-PE holds high ambient ionic conductivity (1.27±0.09 mS cm⁻¹), super-toughness and strength (22.52 MJ m⁻³ and 13.5±0.6 MPa), fire resistance and importantly, lithium-metal anode protection capability. Lithium metal batteries assembled with this multi-defensive Neu-PE can work normally even under metal-probe puncture or serious damage by cutting.     

Synchronous Promotion in Sodiophilicity and Conductivity of Flexible Host via Vertical Graphene Cultivator for Longevous Sodium Metal Batteries

Sodium (Na) metal batteries are nowadays appealing due to high specific capacity and low cost. However, major caveats including severe Na dendrite growth, unstable solid electrolyte interphase formation, and poor mechanical robustness have hampered its practicability. In this report, a highly sodiophilic and conductive host harnessing hierarchical vertical graphene (VG) cultivator and Co nanoparticle/N-doped carbon decorator (Co-VG/CC) is designed to accommodate Na metal throughout a facile infusion route. The strong interaction between Co-VG/CC and Na is realized by sodiophilic Co nanoparticle/N-doped carbon hybrid, resulting in excellent structural stability of the electrode. The well-regulated Na adsorption behavior and uniform stripping/plating mechanism is systematically investigated via theoretical simulation in harmonization with in situ/ex situ electroanalytical analysis. In consequence, as-derived Na@Co-VG/CC electrode effectively inhibits the dendrite formation, resulting in promising electrochemical performances in symmetric cell configuration (functioning at an elevated rate of 5.0 mA cm⁻² under 5.0 mAh cm⁻² for 280 h, delivering a high capacity of 6.0 mAh cm⁻² at 3.0 mA cm⁻² for 1000 h and maintaining an ultralong lifespan up to 2000 h). Meanwhile, assembled flexible Na metal battery full cell can sustain to work for 120 h, representing a great advance in practical energy storage applications.     

General Synthesis of Transition Metal Oxide Ultrafine Nanoparticles Embedded in Hierarchically Porous Carbon Nanofibers as Advanced Electrodes for Lithium Storage

A unique general, large‐scale, simple, and cost‐effective strategy, i.e., foaming‐assisted electrospinning, for fabricating various transition metal oxides into ultrafine nanoparticles (TMOs UNPs) that are uniformly embedded in hierarchically porous carbon nanofibers (HPCNFs) has been developed. Taking advantage of the strong repulsive forces of metal azides as the pore generator during carbonization, the formation of uniform TMOs UNPs with homogeneous distribution and HPCNFs is simultaneously implemented. The combination of uniform ultrasmall TMOs UNPs with homogeneous distribution and hierarchically porous carbon nanofibers with interconnected nanostructure can effectively avoid the aggregation, dissolution, and pulverization of TMOs, promote the rapid 3D transport of both Li ions and electrons throughout the whole electrode, and enhance the electrical conductivity and structural integrity of the electrode. As a result, when evaluated as binder‐free anode materials in Li‐ion batteries, they displayed extraordinary electrochemical properties with outstanding reversible capacity, excellent capacity retention, high Coulombic efficiency, good rate capability, and superior cycling performance at high rates. More importantly, the present work opens up a wide horizon for the fabrication of a wide range of ultrasmall metal/metal oxides distributed in 1D porous carbon structures, leading to advanced performance and enabling their great potential for promising large‐scale applications.     

Dendrite-Free Reverse Lithium Deposition Induced by Ion Rectification Layer toward Superior Lithium Metal Batteries

Considerable endeavors are developed to suppress lithium (Li) dendrites and improve the cycling stability of Li metal batteries in order to promote their commercial application. Herein, continuous zinc (Zn) nanoparticles-assembled film with homogenous nanopores is proposed as a modified layer for separator via a scalable method. The in situ formed LiZn alloy film during initial Li plating can serve as a Li⁺ ion rectification and lithiophilic layer to regulate the nucleation and reverse deposition of Li. When applied in Li|LiFePO₄ full cells with traditional carbonate-based electrolyte, the modified separator enables outstanding cycling stability of up to 350 cycles without capacity loss at a large rate of 5 C (3.4 mA cm⁻²) and a remarkable reversible capacity of 144 mAh g⁻¹ after 120 cycles at a commercial mass loading as high as 19.72 mg cm⁻². The excellent electrochemical performances are ascribed to the dendrite-free reverse Li deposition induced by modified layer by means of its lithiophilic property for regulating homogeneous Li nucleation on the separator as well as its well-distributed nanopores for homogenizing Li⁺ ion flux and enhancing electrolyte wetting.     

Fluorobenzene,A Low-Density,Economical, and Bifunctional Hydrocarbon Cosolvent for Practical Lithium Metal Batteries

Highly concentrated electrolytes (HCEs) significantly improve the stability of lithium metal anodes, but applications are often impeded by their limitation of density, viscosity, and cost. Here, fluorobenzene (FB), an economical hydrocarbon with low density and low viscosity, is demonstrated as a bifunctional cosolvent to obtain a novel FB diluted highly concentrated electrolyte (FB-DHCE). First, the addition of FB suppresses the decomposition of dimethoxyethane (DME) on the Li metal by strengthening the interactions of DME and FSI⁻ around Li⁺. Second, FB efficiently elevates the content of LiF in the solid electrolyte interphase (SEI) based on its electrochemical reduction reaction. The unique solvation and interfacial chemistry of FB-DHCE enable dendrite-free deposition of lithium with high Coulombic efficiency (up to 99.3%) and prolong cycling life (over 500 cycles at 1 mA cm⁻²). The performance of FB-DHCE is further demonstrated in full cells under practical conditions, including ambient to low temperature (–20 °C), high areal capacity (7.6 mAh cm⁻²), high current density (3 mA cm⁻²), limited excess Li (20 µm Li), and lean electrolyte (3 g Ah⁻¹). Employing FB as a cosolvent not only opens a novel pathway to stabilize Li metal anodes, but also could greatly advance the development of Li metal batteries.     

Critical Review of Fluorinated Electrolytes for High-Performance Lithium Metal Batteries

Lithium metal batteries (LMBs), due to their ultra-high energy density, are attracting tremendous attentions. However, their commercial application is severely impeded by poor safety and unsatisfactory cycling stability, which are induced by lithium dendrites, side reactions, and inferior anodic stability. Electrolytes, as the indispensable and necessary components in lithium metal batteries, play a crucial role in regulating the electrochemical performance of LMBs. Recently, the fluorinated electrolytes are widely investigated in high-performance LMBs. Thus, the design strategies of fluorinated electrolytes are thoroughly summarized, including fluorinated salts, fluorinated solvents, and fluorinated additives in LMBs, and insights of the fluorinated components in suppressing lithium dendrites, improving anodic stability and cycling stability. Finally, an outlook with several design strategies and challenges will be proposed for novel fluorinated electrolytes.     

Electrolytes Enriched by Crown Ethers for Lithium Metal Batteries

Lithium (Li) metal battery is considered the most promising next-generation battery due to its low potential and high theoretical capacity. However, Li dendrite growth causes serious safety problems. Herein, the 15-Crown-5 (15-C-5) is reported as an electrolyte additive based on solvation shell regulation. The strong complex effect between Li⁺ ion and 15-C-5 can reduce the concentration of Li ions on the electrode surface, thus changing the nucleation, and repressing the growth of Li dendrites in the plating process. Significantly, the strong coordination of Li⁺/15-C-5 would be able to make them aggregate around the Li crystal surface, which could form a protective layer and favor the formation of a smooth and dense solid electrolyte interphase with high toughness and Li⁺ ion conductivity. Therefore, the electrolyte system with 2.0 wt% 15-C-5 achieves excellent electrochemical performance with 170 cycles at 1.0 mA cm⁻² with capacity of 0.5 mA h cm⁻² in symmetric Li|Li cells. The obviously enhanced cycle and rate performance are also achieved in Li|LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) full cells. The 15-C-5 demonstrates to be a promising additive for the electrolytes toward safe and efficient Li metal batteries.     

Impact of Fluorine-Based Lithium Salts on SEI for All-Solid-State PEO-Based Lithium Metal Batteries

LiF-rich solid-electrolyte-interphase (SEI) can suppress the formation of lithium dendrites and promote the reversible operation of lithium metal batteries. Regulating the composition of naturally formed SEI is an effective strategy, while understanding the impact and role of fluorine (F)-based Li-salts on the SEI characteristics is unavailable. Herein, LiFSI, LiTFSI, and LiPFSI are selected to prepare solid polymer electrolytes (SPEs) with poly(ethylene oxide) and polyimide, investigating the effects of molecular size, F contents and chemical structures (F-connecting bonds) of Li-salts and revealing the formation of LiF in the SEI. It is shown that the F-connecting bond is more significant than the molecular size and F element contents, and thus the performances of cells using LiPFSI are slightly better than LiTFSI and much better than LiFSI. The SPE containing LiPFSI can generate a high amount of LiF, and SPEs containing LiPFSI and LiTFSI can generate Li₃N, while there is no Li₃N production in the SEI for the SPE containing LiFSI. The preferential breakage bonds in LiPFSI are related to its position to Li anode, where Li-metal as the anode is important in forming LiF, and consequently the LiPFSI reduction mechanism is proposed. This study will boost other energy storage systems beyond Li-ion chemistries.