Juggling Formation of HF and LiF to Reduce Crossover Effects in Carbonate Electrolyte with Fluorinated Cosolvents for High-Voltage Lithium Metal Batteries

Fluorinated solvents emerge as a promising strategy to improve performance of lithium metal batteries (LMBs). However, most of them are prone to produce corrosive HF and deteriorate electrode interface, inducing cathode-to-anode detrimental crossover of transition metal-ions. Here, fluorinated aromatic hydrocarbons in dimethyl carbonate (DMC)-based diluted highly concentrated electrolyte (DHCE) are employed to juggle formation of HF and LiF, enabling stable cycling of high-voltage LiNi_0.7Co_0.1Mn_0.2O₂ (NCM712) and LiCoO₂ (LCO). The nature of aromatics in this carbonate-based DHCE makes them difficult to undergo β-hydrogen assisted defluorination, evidencing by the high energy barrier and high bond energy of β-sites hydrogen. The advanced DHCE restrains HF formation but strengthens LiF formation, which not only suppresses impedance growth, transition-metal dissolution, and stress crack on the cathode, but achieves highly reversible Li stripping/plating with an outstanding average Coulombic efficiency up to 99.3%. The Li||NCM712 cell and Li||LCO cell both exhibits superior cycling stability at high operation voltage. Even under stringent conditions, the 4.4 V Li||NCM712 full battery retains >95% of the initial capacity over 100 cycles, advancing practical high-voltage LMBs. This study designs an efficient electrolyte that generates robust electrode/electrolyte interphases and restrains by-products formation spontaneously, thus shedding new light on electrolyte toward applicable LMBs.     

Hydrofluoric Acid-Removable Additive Optimizing Electrode Electrolyte Interphases with Li+ Conductive Moieties for 4.5 V Lithium Metal Batteries

High-voltage lithium metal batteries (LMBs) are capable to achieve the increasing energy density. However, their cycling life is seriously affected by unstable electrolyte/electrode interfaces and capacity instability at high voltage. Herein, a hydrofluoric acid (HF)-removable additive is proposed to optimize electrode electrolyte interphases for addressing the above issues. N, N-dimethyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) aniline (DMPATMB) is used as the electrolyte additive to induce PF₆⁻ decomposition to form a dense and robust LiF-rich solid electrolyte interphase (SEI) for suppressing Li dendrite growth. Moreover, DMPATMB can help to form highly Li⁺ conductive Li₃N and LiBO₂, which can boost the Li⁺ transport across SEI and cathode electrolyte interphase (CEI). In addition, DMPATMB can scavenge traced HF in the electrolyte to protect both SEI and CEI from the corrosion. As expected, 4.5 V Li|| LiNi_0.6Co_0.2Mn_0.2O₂ batteries with such electrolyte deliver 145 mAh g⁻¹ after 140 cycles at 200 mA g⁻¹. This work provides a novel insight into high-voltage electrolyte additives for LMBs.     

Catalytically Induced Robust Inorganic-Rich Cathode Electrolyte Interphase for 4.5 V Li||NCM622 Batteries

Tailoring inorganic components of cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) is critical to improving the cycling performance of lithium metal batteries. However, it is challenging due to complicated electrolyte reactions on cathode/anode surfaces. Herein, the species and inorganic component content of the CEI/SEI is enriched with an objectively gradient distribution through employing pentafluorophenyl 4-nitrobenzenesulfonate (PFBNBS) as electrolyte additive guided by engineering bond order with functional groups. In addition, a catalytic effect of LiNi_0.6Mn_0.2Co_0.2O₂ (NCM622) cathode is proposed on the decomposition of PFBNBS. PFBNBS with lower highest occupied molecular orbital can be preferentially oxidized on the NCM622 surface with the help of the catalytic effect to induce an inorganic-rich CEI for superior electrochemical performance at high voltage. Moreover, PFBNBS can be reduced on the Li surface due to its lower lowest unoccupied molecular orbital , increasing inorganic moieties in SEI for inhibiting Li dendrite generation. Thus, 4.5 V Li||NCM622 batteries with such electrolyte can retain 70.4% of initial capacity after 500 cycles at 0.2 C, which is attributed to the protective effect of the excellent CEI on NCM622 and the inhibitory effect of its derived CEI/SEI on continuous electrolyte decomposition.     

Tandem Design of Functional Separators for Li Metal Batteries with Long-Term Stability and High-Rate Capability

The lithium (Li) dendrite growth seriously hinders the applications of lithium metal batteries (LMBs). Numerous methods have been proposed to restrict the formation of Li dendrites by improving the Li-ion transference number (t_Li⁺) through separator modification according to Sand's time equation. However, ignoring the positive contribution of anion motion to solid electrolyte interphase (SEI) formation will result in insufficient inorganic components, which impedes practical implementation of LMBs. Herein, a “tandem” separator is constructed (ZSM-5-Poly dimethyl diallyl ammonium chloride (PDDA)/Polyethylene (PE)/SbF₃), which anchored anions and built an inorganic-rich SEI at the same time. The resulting SEI from SbF₃ (SBF) coating on side facing Li is rich in Li-Sb alloy (Li₃Sb) and LiF. Li₃Sb can significantly reduce the migration energy barrier of Li ion (Li⁺) and facilitate Li⁺ transport. Simultaneously, ZSM-5-PDDA (Z5P) coating at the other side can effectively immobilize anions and increase the t_Li⁺. Moreover, the regular pore structure is conducive to homogenizing Li⁺ flux and also capable to uniform temperature distribution, significantly improving safety. Hence, the lifespan of Li|Li and Li|Cu cells assemble with Z5P/PE/SBF separator is significantly extended. In addition, full cells with LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) and LiFePO₄ (LFP) cathodes show excellent cycle stability and superior rate performance.     

Stable Non-flammable Phosphate Electrolyte for Lithium Metal Batteries via Solvation Regulation by the Additive

The application of lithium metal batteries (LMBs) is impeded by safety concerns. Employing non-flammable electrolytes can improve battery reliability while the cost and performance deterioration limit their popularization. Herein, a high-performance non-flammable electrolyte is designed, 1.5 m LiTFSI in propylene carbonate (PC)/triethyl phosphate (TEP) (4:1 by vol.) with 4-nitrophenyl trifluoroacetate (TFANP) as the additive, which can facilitate the construction of LiF-rich solid electrolyte interphase (SEI) on Li anode surface and cathode electrolyte interphase (CEI) on cathode surface through its prioritized decomposition. In TFANP-containing electrolyte, the decreased TEP coordination number in the solvation sheath relieves the adverse effect of active TEP on both the SEI and CEI for suppressing the growth of Li dendrites and reducing the continuous electrolyte consumption. Thus, the Li||LiNi_0.6Co_0.2Mn_0.2O₂ battery with such an electrolyte can deliver 132 mAh g⁻¹ after 150 cycles with high coulombic efficiency (99.5%) and superior rate performance (110 mAh g⁻¹ at 5 C, 1 C = 200 mA g⁻¹). This work provides a new additive insight on non-flammable electrolyte for reliable 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.     

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.     

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.     

Multiscale Structural Gel Polymer Electrolytes with Fast Li+ Transport for Long-Life Li Metal Batteries

Li metal batteries (LMBs) are considered as promising candidates for future rechargeable batteries with high energy density. However, Li metal anode (LMA) is extensively sensitive to general liquid electrolytes, leading to unstable interphase and dendrites growth. Herein, a novel gel polymer electrolyte consisting of a micro-nanostructured poly(vinylidene fluoride-co-hexafluoropropylene) matrix and inorganic fillers of Zeolite Socony Mobil-5 (ZSM-5) and SiO₂ nanoparticles, is fabricated to expedite Li⁺ ions transport and suppress Li dendrite growth. Due to the Lewis acid interaction, SiO₂ can absorb amounts of PF₆⁻ and promote the dissociation of LiPF₆. The specific sub-nanometer pore structure of ZSM-5 greatly enhances the Li⁺ ion transference number. These structures can restrain the decomposition of electrolytes and build stable interphase on LMA. Therefore, the Li||Ni_0.8Co_0.1Mn_0.1O₂ full cell maintains 92% capacity retention after 300 cycles at 1 C (1 C ≈190 mAh g⁻¹) in carbonate electrolyte. This multiscale design provides an effective strategy for electrolyte exploration in high-performance LMBs.     

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.     

Low Resistance and High Stable Solid–Liquid Electrolyte Interphases Enable High-Voltage Solid-State Lithium Metal Batteries

Solid-state batteries (SSBs) with addition of liquid electrolytes are considered to possibly replace the current lithium-ion batteries (LIBs) because they combine the advantages of benign interfacial contact and strong barriers for unwanted redox shuttles. However, solid electrolyte and liquid electrolyte are generally (electro)-chemically incompatible and the resistance of the newly formed solid–liquid electrolyte interphase (SLEI) appears as an additional contribution to the overall battery resistance. Herein, a boron, fluorine-donating liquid electrolyte (B, F-LE) is introduced into the interface between the high-voltage cathode and ultrathin composite solid electrolyte (CSE), which is fabricated by adhering a high content of nanosized Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), to generate a low resistance and high stable SLEI in situ, giving a stable high-voltage output with a reinforced cathode|CSE interface. B, F-LE, consisting of a highly fluorinated electrolyte with a lithium bis(oxalato)borate additive, exhibits good chemical compatibility with CSE and enables rapid and uniform transportation of Li⁺, with its electrochemically and chemically stable interface for high-voltage cathode. Eventually, the B, F-LE assisted LiNi_0.6Co_0.2Mn_0.2O₂|Li battery displays the enhanced rate capability and high voltage cycling stability. The findings provide an interfacial engineering strategy to turn SLEI from a “real culprit” into the “savior” that may pave a brand-new way to manipulate SLEI chemistry in hybrid solid–liquid devices.     

Solvent-Free Electrolyte for High-Temperature Rechargeable Lithium Metal Batteries

The formation of lithiophobic inorganic solid electrolyte interphase (SEI) on Li anode and cathode electrolyte interphase (CEI) on the cathode is beneficial for high-voltage Li metal batteries. However, in most liquid electrolytes, the decomposition of organic solvents inevitably forms organic components in the SEI and CEI. In addition, organic solvents often pose substantial safety risks due to their high volatility and flammability. Herein, an organic-solvent-free eutectic electrolyte based on low-melting alkali perfluorinated-sulfonimide salts is reported. The exclusive anion reduction on Li anode surface results in an inorganic, LiF-rich SEI with high capability to suppress Li dendrite, as evidenced by the high Li plating/stripping CE of 99.4% at 0.5  mA cm⁻² and 1.0 mAh cm⁻², and 200-cycle lifespan of full LiNi_0.8Co_0.15Al_0.05O₂ (2.0 mAh cm⁻²) || Li (20 µm) cells at 80 °C. The proposed eutectic electrolyte is promising for ultrasafe and high-energy Li metal batteries.     

Durable Li2CN2 Solid Electrolyte Interphase Wired by Carbon Nanodomains via In Situ Interface Lithiation to Enable Long-Cycling Li Metal Batteries

Lithium metal batteries (LMBs) are becoming the promising candidate of high-energy storage systems. However, the fragile natural solid electrolyte interphase (SEI) cannot retard the Li dendrite growth at anode, which will cause the low coulombic efficiency (CE) of Li plating/stripping and safety hazards in LMBs. Here, an in situ construction strategy of novel artificial SEI consisting of Li₂CN₂ ionic conductor wired by carbon nanodomains via dicyandiamide solution reaction method on Li metal surface is proposed. This lithiophilic Li₂CN₂ has the higher anti-reduction stability and longer critical length for Li dendrite, showing the excellent dendrite suppressing ability. The wired carbon domains promote the electron connection and charge homogenization in SEI, leading to the uniform Li nucleation around Li₂CN₂/C grains with enhanced interface kinetics and reduced polarization. This dual conductive Li₂CN₂/C network enables the durable preservation of high CE and low voltage hysteresis during Li plating/stripping, endowing LiNi_0.8Mn_0.1Co_0.1O₂/Li cells with ultralong cycling life exceeding 1000 cycles at high rate. The cycling stabilization effect is also remarkable even under thin Li anode and high-loading cathode conditions. This study provides a solution to robust SEI configuration of high conductivity via in situ interface lithiation reaction for high-performance LMBs.     

In-Built Quasi-Solid-State Poly-Ether Electrolytes Enabling Stable Cycling of High-Voltage and Wide-Temperature Li Metal Batteries

Developing solid-state electrolytes with good compatibility for high-voltage cathodes and reliable operation of batteries over a wide-temperature-range are two bottleneck requirements for practical applications of solid-state metal batteries (SSMBs). Here, an in situ quasi solid-state poly-ether electrolyte (SPEE) with a nano-hierarchical design is reported. A solid-eutectic electrolyte is employed on the cathode surface to achieve highly-stable performance in thermodynamic and electrochemical aspects. This performance is mainly due to an improved compatibility in the electrode/electrolyte interface by nano-hierarchical SPEE and a reinforced interface stability, resulting in superb-cyclic stability in Li || Li symmetric batteries ( > 4000 h at 1 mA cm⁻²/1 mAh cm⁻²; > 2000 h at 1 mA cm⁻²/4 mAh cm⁻²), which are the same for Na, K, and Zn batteries. The SPEE enables outstanding cycle-stability for wide-temperature operation (15–100 ° C) and 4 V-above batteries (Li || LiCoO₂ and Li || LiNi_0.8Co_0.1Mn_0.1O₂). The work paves the way for development of practical SSMBs that meet the demands for wide-temperature applicability, high-energy density, long lifespan, and mass production.     

Manipulating Ion Transfer and Interface Stability by A Bulk Interphase Framework for Stable Lithium Metal Batteries

Lithium metal batteries (LMBs) have attracted widespread concern as the next-generation energy storage devices with high energy density. At the surface of lithium metal anodes (LMAs) toward electrolytes, lithium plating always competes with interfacial reactions. This makes interfacial reactions light shadow right behind lithium plating, leading to performance degradation. Herein, lithium plating is spatially decoupled from interfacial reactions by constructing a 3D solid electrolyte interphase framework (3D-SEIF) inside LMAs. Spontaneous while mild chemical reactions between lithium metal and lithium bisfluorosulfonimide/lithium nitrate form the robust 3D-SEIF, mainly consisting of LiF, Li₃N, and LiN_xO_y. The built-in 3D-SEIF avoids electrolyte contact but enables the diffusion and reduction of Li⁺ ions in the bulk phase, thus isolating the plating sites and electrolyte contact interface. The 3D-SEIF facilitates large granular plating and the generation of thin, inorganic-rich SEI. When assembled with high-loading LiNi_0.6Co_0.2Mn_0.2O₂ cathode (3 mAh cm⁻²), the cells present capacity retention of 92.0% after 130 cycles with barren electrolyte (≈30 µL) at 0.5 C. The conception of 3D inner interphase allows breaking the coupling of interfacial reactions with electrochemical reactions, which is taken for granted in electrochemical consortium. It also desires to inspire new thoughts to develop scalable solutions for the early industrialization of LMBs.     

Regulating Cathode-Electrolyte Interphase by Confining Functional Aluminum Compound within Ni-Rich Cathodes

The oxidative capability of Ni⁴⁺ and high operation voltage of nickel-rich LiNi_1−x−yCo_xMn_yO₂ (Ni-rich NCM) cause its continuous and deleterious side reactions with electrolyte and irreversible phase transition, which hinder its industrial application. To mitigate these issues, Al (CF₃SO₃)₃ is proposed as a solid electrolyte additive that can be readily oxidized to regulate the cathode-electrolyte interphase (CEI) due to the highest occupied molecular orbital-level of CF₃SO₃⁻, meanwhile being confined within the single-crystalline NCM811. CF₃SO₃⁻ prior to the electrolyte is oxidized upon increasing voltage to produce sulfur components and involve CEI formation. Concurrently, the released Al³⁺ ions are combined with reactive oxygen from NCM811 particles and HF from the electrolyte to form Al₂O₃ and AlF₃, respectively. A robust sandwich CEI film containing sulfur and aluminum species is formed, which cannot only prevent decomposition of the electrolyte, but also alleviate the formation of inactive rock-salt phase on NCM811 surface. Consequently, such CEI leads to high-performance batteries with a high-capacity retention of 91.5% after 200 cycles under 0.5 C compared to 72.4% of pristine NCM811. This facile and environmentally benign method provides a new avenue to develop high-capacity and durable cathodes for lithium-ion batteries.     

Armoring LiNi1/3Co1/3Mn1/3O2 Cathode with Reliable Fluorinated Organic–Inorganic Hybrid Interphase Layer toward Durable High Rate Battery

Ternary layered oxide materials have attracted extensive attention as a promising cathode candidate for high‐energy‐density lithium‐ion batteries. However, the undesirable electrochemical degradation at the electrode–electrolyte interface definitively shortens the battery service life. An effective and viable approach is proposed for improving the cycling stability of the LiNi_1/3Co_1/3Mn_1/3O₂ cathode using lithium difluorophosphate (LiPO₂F₂) paired with fuoroethylene carbonate (FEC) as co‐additives into conventional electrolytes. It is found that the co‐additives can greatly reduce the interface charge transfer impedance and significantly extend the life span of LiNi_1/3Co_1/3Mn_1/3O₂//Li (NMC//Li) batteries. The developed cathode demonstrates exceptional capacity retention of 88.7% and remains structural integrity at a high current of 5C after 500 cycles. Fundamental mechanism study indicates a dense, stable fluorinated organic–inorganic hybrid cathode‐electrolyte interphase (CEI) film derived from LiPO₂F₂ in conjunction with FEC additives on the surface of NMC cathode material, which significantly suppresses the decomposition of electrolyte and mitigates the dissolution of transition metal ions. The interfacial engineering of the electrode materials stabilized by the additives manipulation provides valuable guidance for the development of advanced cathode materials.     

Composite Lithium Metal Anodes with Lithiophilic and Low-Tortuosity Scaffold Enabling Ultrahigh Currents and Capacities in Carbonate Electrolytes

The practical application of lithium metal anode has been hindered by safety and cyclability issues due to the uncontrollable dendrite growth, especially during fast cycling and deep plating/stripping process. Here, a composite Li metal anode supported by periodic, perpendicular, and lithiophilic TiO₂/poly(vinyl pyrrolidone) (PVP) nanofibers via a facial rolling process is reported. TiO₂/PVP nanofibers with good Li affinity provide low-tortuosity and directly inward Li⁺ transport paths to facilitate Li nucleation and deposition under high areal capacities and current densities. The micrometer-scale interspaces between TiO₂/PVP walls offer enough space to circumvent the huge volume variation and avoid structure collapsing during the repeated deep Li plating/stripping. The unique structure enables stable cycling under ultrahigh currents (12 mA cm⁻²), and ultra-deep plating/stripping up to 60 mAh cm⁻² with a long cycle life in commercial carbonate electrolytes. The gassing behavior in operating pouch cells is observed using ultrasonic transmission mapping. When paired with LiFePO₄ (5 mAh cm⁻²), sulfur (3 mAh cm⁻²), and high-voltage LiNi_0.8Co_0.1Mn_0.1O₂ cathodes, the composite Li anodes deliver remarkably improved rate performance and cycling stability, demonstrating that it could be a promising strategy for balancing high-energy density and high-power density in Li metal batteries.     

Enabling Superior Cycling Stability of LiNi0.9Co0.05Mn0.05O2 with Controllable Internal Strain

Intergranular cracking of Ni-rich layered LiNi_1-x-yCo_xMn_yO₂ (1-x-y ≥  0.8) cathode particles deteriorate the chemo–electro–mechanical stability of high-energy lithium-ion batteries (LIBs), thus presenting a challenge to typical modification methods to establish robust structures with highly efficient lithium-ion storage. Herein, the ZrTiO₄ (ZTO) as an epitaxial layer to enhance mechanical stability of ultrahigh-Ni LiNi_0.9Co_0.05Mn_0.05O₂ (NCM90) is reported for the first time. Intensive exploration from structure characterizations (X-ray absorption spectroscopy and in situ X-ray diffraction techniques), multi-physics field analysis, and first-principles calculations disclose that the conformal ZTO layers and Zr doping effectively suppresses the internal strain and the release of lattice oxygen, which prodigiously restrains the local stress accumulation during whole (de)lithiation processes, thereby maintaining good mechanical stability of the materials. Meanwhile, the protective ZTO layer also prevents electrolyte erosion, thus keeping an intact surface structure of NCM90. Notably, ZTO-modified NCM90 achieves significantly improved cyclability under high-voltage (4.5 V) operation, expressing a 17% increase in capacity retention (71% vs 88%) after 100 cycles. Overall, this work reveals the role of internal strain in the original degradation behavior and effectiveness of surface engineering strategy to solve the challenge, emphasizing that the conformal surface protection mitigates the internal stress of Ni-rich NCM by anchoring the lattice oxygen.     

Hexafluoroisopropyl Trifluoromethanesulfonate-Driven Easily Li+ Desolvated Electrolyte to Afford Li||NCM811 Cells with Efficient Anode/Cathode Electrolyte Interphases

Solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) with optimized components and structures are considered to be crucial for lithium-ion batteries. Here, gradient lithium oxysulfide (Li₂SO_x, x = 0, 3, 4)/uniform lithium fluoride (LiF)-type SEI is designed in situ by using hexafluoroisopropyl trifluoromethanesulfonate (HFPTf) as electrolyte additive. HFPTf is more likely to be reduced on the surface of Li anode in electrolytes due to its high reduction potential. Moreover, HFPTf can make Li⁺ desolvated easily, leading to the increase in the flux of Li⁺ on the surface of Li anode to avoid the growth of Li dendrites. Thus, the cycling stability of Li||Li symmetric cells is improved to be 1000 h at 0.5 mA cm⁻². In addition, HFPTf-contained electrolyte could make Li||NCM811 batteries with a capacity retention of 70% after 150 cycles at 100 mA g⁻¹, which is attributed to the formation of uniform and stable CEI on the cathode surface for hindering the dissolvation of metal ions from the cathode. This study provides effective insights on the strong ability of additives to adjust electrolytes in “one phase and two interphases” (electrolyte and SEI/CEI).