Cathode Electrolyte Interphase Research Articles

Comparative Study of High Voltage Spinel∥Lithium Titanate Lithium‐ion Batteries in Ethylene Carbonate Free Electrolytes

AbstractA persistent obstacle towards the realization of high voltage cathodes is electrolyte instability where oxidation and transition metal dissolution manifest in rapid capacity failure with both issues connected to the presence of ethylene carbonate in the electrolyte. Here, alternative electrolyte co‐solvents are investigated and compared, where the cyclic carbonate is replaced with sulfones ethyl methyl sulfone (EMS) and tetra methylene sulfone (TMS) and fluoroethylene carbonate (FEC). The best full cell performance was observed for cells cycled in a FEC/EMC (3/7) and FEC/EMC (1/1) electrolytes which exhibited 84–85 % capacity retention after 500 cycles. TMS/EMC (3/7), was determined to be the best performing sulfone electrolyte and maintained 71 % capacity after 500 cycles. Post‐mortem XPS analysis indicated different film forming mechanisms for the respective co‐solvent. A thicker cathode electrolyte interphase (CEI) on the LNMO was observed for the FEC containing electrolytes (relative to when TMS was used as the co‐solvent) indicating more effective passivation of the reactive cathode surface which correlated well with the enhanced cycling stability observed. For LTO, more evidence of transition metal migration and a thicker solid electrolyte interphase (SEI) layer was observed for the sulfone electrolyte suggesting more parasitic anode‐electrolyte interactions and an inability to mitigate Mn2+/Ni2+ crosstalk.

Dual Function of Hydrogen Bond and CEI to Enhanced Lithium-Ion Battery Performance.

The stability of the commercial electrolyte is linked to the internal solvent molecule, particularly in enhancing the stability of these molecules. Hereby, we introduce a dual function strategy involving hydrogen bond induced solvent molecules and the in situ fabrication cathode-electrolyte interphase (CEI) to address this issue. The additive N-(4-(2,5-dioxo-4-oxazolidinyl)butyl)-2,2,2-trifluoroacetamide (DOTFA), with its oxazolidinyl and trifluoroacetamide functional units, establishes hydrogen bonds with the solvent, forming CEI films on the cathode surface that enhance the antioxidation ability of the electrolyte. These hydrogen bonds contribute to enhancing the high-pressure structural stability of the solvent molecule. Additionally, the uniform and robust in situ constructed CEI films act as a shield, protecting the cathode from various side reactions and enhancing interface compatibility. By incorporation of the DOTFA additive in the electrolyte, lithium-ion batteries with NCM811 cathodes exhibit excellent cycling performance. The work highlights the significance of dual function in solvent molecules and provides an effective method for enhancing the antioxidation ability of the electrolyte.

Transforming Zinc-Ion Batteries with DTPA-Na: A Synergistic SEI and CEI Engineering Approach for Exceptional Cycling Stability and Self-Discharge Inhibition.

Aqueous zinc-ion batteries (ZIBs) hold immense potential for large-scale energy storage, but their practical implementation faces significant challenges related to the zinc anode, including dendrite formation, corrosion, and hydrogen evolution. This study addresses these challenges by introducing diethylenetriamine pentaacetate sodium salt (DTPA-Na) as a novel electrolyte additive. DTPA-Na exhibits a unique dual functionality, enabling the formation of a robust, multi-layered solid electrolyte interphase (SEI) on the zinc anode and a stable cathode electrolyte interphase (CEI) on the MnOOH cathode. The engineered SEI effectively suppresses interfacial side reactions, facilitates uniform zinc deposition, and mitigates dendrite growth, while the CEI inhibits MnOOH dissolution and detrimental cathode side reactions. This synergistic SEI/CEI engineering approach significantly enhances ZIB performance, achieving remarkable cycling stability and self-discharge inhibition, as evidenced by the extended lifespan of Zn||Zn symmetrical cells (4400 hours at 0.5 mA/cm2) and the exceptional capacity retention of Zn||MnOOH full cells after prolonged rest (98.61 % after 720 hours).

Solvation Regulation via Hydrogen Bonding to Mitigate Al Current Collector Corrosion for High‐Voltage Li‐Ion Batteries

AbstractThe exceptional thermal stability and conductivity of lithium bis(fluorosulfonyl)imide (LiFSI) have made it a preferred salt for lithium‐ion batteries (LIBs). However, the corrosion of aluminum (Al) current collectors by LiFSI at low potentials (3.8 V vs Li/Li+) poses a persistent challenge, hindering the application of LiFSI in 4 V‐class LIBs. Herein, 2,2,2‐trifluoroethyl methanesulfonate (TFMS) is proposed as a versatile co‐solvent to address the issue of Al current collector corrosion. It is demonstrated that incorporating TFMS into a conventional LiFSI‐based carbonate electrolyte can precisely tailor the Li+ solvation structure by hydrogen bonding interactions with dimethyl carbonate (DMC) solvent. This weakens the coordination between DMC and Li+ while increasing the participation of FSI− anions in the primary solvation shell, effectively suppressing the Al current collector caused by free FSI− anions attacking. Furthermore, TFMS and FSI− synergically induce the formation of an inorganic‐rich and compact cathode electrolyte interphase, significantly avoiding undesired side reactions. As a result, the TFMS‐electrolyte enables 1.2 Ah‐graphite||NCM811 (LiNi0.8Co0.1Mn0.1O2) pouch‐cells to achieve 89.9% capacity retention with high average Coulombic efficiency of >99.9% for 200 cycles at a cut‐off voltage of 4.4 V, opening up opportunities for the development of advanced high‐voltage LIBs.

Conformational isomerism breaks the electrolyte solubility limit and stabilizes 4.9 V Ni-rich layered cathodes

By simply increasing the concentration of electrolytes, both aqueous and non-aqueous batteries deliver technical superiority in various properties such as high-voltage operation, electrode stability and safety performance. However, the development of this strategy has encountered a bottleneck due to the limitation of the intrinsic solubility, and its comprehensive performance has reached its limit. Here we demonstrate that the conformational isomerism of the solvent would significantly affect the solubility of electrolytes. By transforming the configuration of solvent from cis-cis to cis-trans upon thermal triggering, we successfully break the solubility limit, and a beyond concentrated electrolyte with the lowest solvent-to-salt molar ratio of 0.70 is constructed. Transitions between cis-cis and cis-trans conformers are observed through Nuclear Magnetic Resonance (NMR) testing. The electrolyte consists entirely of anion-mediated solvation structures and promotes the formation of robust inorganic-dominated cathode electrolyte interphase. As a result, it enables stable cycling of 4.9 V-class LiNi0.8Co0.1Mn0.1O2 positive electrodes. Moreover, a high capacity of 151.2 mAh g−1 can be maintained after 1000 cycles at cut-off voltage of 4.8 V. This work provides a chemical pathway to build new concept electrolytes working under harsh conditions.

Catalytic Strategies Enabled Rapid Formation of Homogeneous and Mechanically Robust Inorganic‐Rich Cathode Electrolyte Interface for High‐Rate and High‐Stability Lithium‐Ion Batteries

AbstractLithium iron phosphate (LFP) cathode is renowned for high thermal stability and safety, making them a popular choice for lithium‐ion batteries. Nevertheless, on one hand, the fast charge/discharge capability is fundamentally constrained by low electrical conductivity and anisotropic nature of sluggish lithium ion (Li+) diffusion. On the other hand, the interface and internal structural degradation occurs when subjected to high‐rate condition. Herein, a multifunctional boron‐doping graphene/lithium carbonate (BG/LCO) nanointerfacial layer on surface of commercial LiFePO4 particles is designed, in which the BG layer catalyzes the rapid reaction of Li2CO3‐LiPF6 for homogeneous and mechanically robust inorganic LiF‐rich structure across the cathode‐electrolyte interphase (CEI), forms a conductive network to significantly enhance both electron and Li+ transport, and strengthens the FeO bonding to minimize both Fe loss and the formation of Fe‐Li antisite defects. Correspondingly, the modified LFP cathode achieves a high capability of 113.2 mAh g−1 at 10 C and extraordinary cyclic stability with 88.0% capacity retention over 1000 cycles as compared to the pristine LFP cathode with a capacity of only 94.0 mAh g−1 and 64.6% capacity retention. It also exhibits great enhancements of 20.1% and 3.7% at higher‐rate condition (room temperature/15 C) and the low temperature condition (−10 °C/1 C), respectively.

Sulfolane-Based Flame-Retardant Electrolyte for High-Voltage Sodium-Ion Batteries

HighlightsNaTFSI/SUL:OTE:FEC facilitates the formation of S, N-rich, dense and robust cathode–electrolyte interphase on NaNMF cathode, which improves the cycling stability under high voltage.By utilizing NaTFSI/SUL:OTE:FEC, the Na||NaNMF batteries achieved an impressive retention of 81.15% after 400 cycles at 2 C with the cutoff voltage of 4.2 V.The study offers a reference for the utilization of sulfolane-based electrolytes in sodium-ion batteries (SIBs), while the nonflammability of the NaTFSI/SUL:OTE:FEC enhances the safety of SIBs.

Revealing the Dynamic Evolution of Electrolyte Configuration on the Cathode‐Electrolyte Interface by Visualizing (De) Solvation Processes

AbstractElectrolyte engineering is crucial for improving cathode electrolyte interphase (CEI) to enhance the performance of lithium‐ion batteries, especially at high charging cut‐off voltages. However, typical electrolyte modification strategies always focus on the solvation structure in the bulk region, but consistently neglect the dynamic evolution of electrolyte solvation configuration at the cathode‐electrolyte interface, which directly influences the CEI construction. Herein, we reveal an anti‐synergy effect between Li+‐solvation and interfacial electric field by visualizing the dynamic evolution of electrolyte solvation configuration at the cathode‐electrolyte interface, which determines the concentration of interfacial solvated‐Li+. The Li+ solvation in the charging process facilitates the construction of a concentrated (Li+‐solvent/anion‐rich) interface and anion‐derived CEI, while the repulsive force derived from interfacial electric field induces the formation of a diluted (solvent‐rich) interface and solvent‐derived CEI. Modifying the electrochemical protocols and electrolyte formulation, we regulate the “inflection voltage” arising from the anti‐synergy effect and prolong the lifetime of the concentrated interface, which further improves the functionality of CEI architecture.

Promoting Interfacial Reaction via Quantifying NMC811 CEI Evolution and Li+ Desolvation Using Single‐Particle Electrochemical Methods

AbstractPromoting interfacial kinetics of high‐nickel LiNi0.8Mn0.1Co0.1O2 (NMC811) is a critical strategy for enhancing rate capability of lithium‐ion batteries (LIBs). At the solid‐liquid interface of positive electrode, charge transfer across the cathode‐electrolyte interphase (CEI) is responsible for the interfacial redox reaction, which is dominated by desolvation process of Li+ and NMC811 CEI evolution. Since these two processes are significantly impacted by the solvation effect of electrolytes, herein single‐particle Raman spectroscopy and single‐particle probes are established to quantitatively study the influences of solvation effect on CEI evolution and desolvation process of Li+, respectively. Owing to oxidation of the unstable free cyclic carbonate ester from dissociation of solvation structure, the CEI is found to grow thicker during discharge process. Due to the decreased concentration of cyclic carbonate in the solvation structure, the desolvation process of Li+ in the ethyl methyl carbonate‐ethylene carbonate electrolyte can be reduced by 11.8% compared to that in the dimethyl carbonate‐ethylene carbonate electrolyte. With the presence of ethyl methyl carbonate‐ethylene carbonate electrolyte, thinner CEI and easier desolvation process of Li+ can be simultaneously achieved on the NMC811 surface. Accordingly, its corresponding LIBs deliver the highest specific capacity ≈138.8 mAh g−1 at 5C among the LIBs with the other commonly used electrolytes.

Dual-Anionic Coordination Manipulation Induces Phosphorus and Boron-Rich Gradient Interphase Towards Stable and Safe Sodium Metal Batteries.

High-voltage sodium metal batteries (SMBs) present a viable pathway towards high-energy-density sodium-based batteries due to the competitive cost advantage and abundant supply of sodium resources. However, they still suffer from severe capacity decay induced by the notorious decomposition of the electrolyte under high voltage and unstable cathode/electrolyte interphase (CEI). In addition, the high reactivity of Na metal and flammable electrolytes push SMBs to their safety limits. Herein, a special dual-anion aggregated Na+ solvation structure is designed in a nonflammable trimethyl phosphate-based localized high-concentration electrolyte, and a gradient CEI enriched with phosphorus and boron compounds is formed on the cathode. This thin and stable interphase effectively suppresses the parasitic reaction, improves the interfacial stability of the cathode, and facilitates Na+ transport through the interface by the synergistic effect of multi-components, thus optimizing the cycling stability and safety of SMBs. The Na0.95Ni0.4Fe0.15Mn0.3Ti0.15O2//Na batteries employing such electrolyte provide a discharge capacity of 167.5 mA h g-1 and high retention in the capacity of 85.2% after 800 cycles at 1 C. This approach offers a general strategy for the design of flame-retardant high-voltage electrolytes and the practical application of SMBs.

Understanding the improved performances of Lithium–Sulfur batteries containing oxidized microporous carbon with an affinity-controlled interphase as a sulfur host

Li–S batteries (LSBs) based on the solid-phase conversion reaction that contain microporous carbon (MC) materials as their S hosts exhibit high cycling stabilities. Oxidized MC with O-containing functional groups increases the capacity of LSBs and lowers their internal resistance. Although these polar functional groups should improve the electrolyte affinities of electrode materials, their effects on the MC–S cathode/electrolyte interface have not yet been clarified. Herein, we report the affinity between the MC–S cathode and electrolyte. Contrary to conventional wisdom, the O-containing functional groups form affinity-controlled interphases on the MC–S cathodes, alleviating electrolyte decomposition and the formation of a cathode–electrolyte interphase during LSB cycling. This lowers the internal resistance of the LSB by facilitating unhindered Li-ion conduction, which stabilizes cycling at a low electrolyte [μL]/S [mg] ratio of 2.0, with an improved capacity (from 6.58 to 309.4 mAh g−1) in the second cycle. Thus, the use of an affinity-controlled interphase should improve the energy densities of LSBs and other energy storage devices.

Densification of Cathode/Electrolyte Interphase to Enhance Reversibility of LiCoO2 at 4.65V.

For LiCoO2 (LCO) operated beyond 4.55V (vs Li/Li+), it usually suffers from severe surface degradation. Constructing a robust cathode/electrolyte interphase (CEI) is effective to alleviate the above issues, however, the correlated mechanisms still remain vague. Herein, a progressively reinforced CEI is realized via constructing Zr─O deposits (ZrO2 and Li2ZrO3) on LCO surface (i.e., Z-LCO). Upon cycle, these Zr─O deposits can promote the decomposition of LiPF6, and progressively convert to the highly dispersed Zr─O─F species. In particular, the chemical reaction between LiF and Zr─O─F species further leads to the densification of CEI, which greatly reinforces its toughness and conductivity. Combining the robust CEI and thin surface rock-salt layer of Z-LCO, several benefits are achieved, including stabilizing the surface lattice oxygen, facilitating the interface Li+ transport kinetics, and enhancing the reversibility of O3/H1-3 phase transition, etc. As a result, the Z-LCO||Li cells exhibit a high capacity retention of 84.2% after 1000 cycles in 3-4.65V, 80.9% after 1500 cycles in 3-4.6V, and a high rate capacity of 160mAhg-1 at 16 C (1 C=200mAg-1). This work provides a new insight for developing advanced LCO cathodes.

Dual-Salts Localized High-Concentration Electrolyte for Li- and Mn-Rich High-Voltage Cathodes in Lithium Metal Batteries.

Limited electrochemical stability windows of conventional carbonate-based electrolytes pose a challenge to support the Lithium (Li)- and manganese (Mn)-rich (LMR) high-voltage cathodes in rechargeable Li-metal batteries (LMBs). To address this issue, a novel localized high-concentration electrolyte (LHCE) composition incorporating LiPF6 and LiTFSI as dual-salts (D-LHCE), tailored for high-voltage (>4.6Vvs.Li) operation of LMR cathodes in LMBs is introduced. 7Li nuclear magnetic resonance and Raman spectroscopy revealed the characteristics of the solvation structure of D-LHCE. The addition of LiPF6 provides stable Al-current-collector passivation while the addition of LiTFSI improves the stability of D-LHCE by producing a more robust cathode-electrolyte interphase (CEI) on LMR cathode and solid-electrolyte interphase (SEI) on Li-metal anode. As a result, LMR/Li cell, using the D-LHCE, achieved 72.5% capacity retention after 300 cycles, a significant improvement compared to the conventional electrolyte (21.9% after 100 cycles). The stabilities of LMR CEI and Li-metal SEI are systematically analyzed through combined applications of electrochemical impedance spectroscopy and distribution of relaxation times techniques. The results present that D-LHCE concept represents an effective strategy for designing next-generation electrolytes for high-energy and high-voltage LMB cells.

Simultaneous structure and surface engineering of metal-organic framework derived LiNi0.5-xFe2xMn1.5-xO4 cathode material for improving high voltage performance of lithium-ion batteries

This study presents a novel material synthesis approach utilizing a terephthalic acid-based metal-organic framework as a precursor and employing an ethanol-assisted hydrothermal treatment to produce high-performance Fe-doped LiNi0.5Mn1.5O4 (LNMO) cathode material. This strategy yields a well-crystallized spinel structure with uniformly distributed transition metal ions. Additionally, the appropriate quantity of Fe dopant can achieve the desired Mn3+/Mn4+ ratio, level of structural disordering, and crystal phase purity for Fe-doped LNMO. The synthesis process also aids in forming an amorphous Li2CO3 surface layer, approximately 1 nm thick, which protects the active material from excessive reaction with electrolyte. The typical Fe-doped LNMO cathode (S-05) exhibits superior performance compared to a commercialized LNMO counterpart. It delivers an initial discharge capacity of 135 mAh g-1 at 1 C with exceptional cycling stability over 500 cycles (capacity retention of 90%) under high voltage (5.0 V vs. Li+/Li). Furthermore, its rate capability significantly improves, with a capacity retention of 85% (5 C/0.2 C). This enhanced performance aligns with evidence of activated Ni2+/Ni3+/Ni4+ redox reactions and suppressed cathode electrolyte interphase resistance, leading to promoted Li+ diffusion. Moreover, it is found the cathode helps alleviate electrolyte degradation at high voltages by inhibiting the formation of singlet oxygen in the electrolyte.

Ultrafast Tailoring Amorphous Zn0.25V2O5 with Precision‐Engineered Artificial Atomic‐Layer 1T′‐MoS2 Cathode Electrolyte Interphase for Advanced Aqueous Zinc‐Ion Batteries

Vanadium (V)‐based oxides as cathode materials for aqueous zinc‐ion batteries (AZIBs) still encounter challenges such as sluggish Zn2+ diffusion kinetics and V‐dissolution, thus leading to severe capacity fading and limited life span. Here, we designed an ultrafast and facile colloidal chemical synthesis strategy based on crystalline Zn0.25V2O5 (c‐ZVO) to successfully prepare a‐ZVO@MoS2 core@shell heterostructures, where atomic‐layer MoS2 uniformly coats on the surface of amorphous a‐ZVO. The tailored amorphous structure of a‐ZVO provides more isotropic pathways and active sites for Zn2+, thus significantly enhancing the Zn2+ diffusion kinetics during charge‐discharge processes. Meanwhile, as an efficient artificial cathode electrolyte interphase, the precision‐engineered atomic‐layer MoS2 with semi‐metallic 1T′ phase not only contributes to improved electron transport but also effectively inhibits the V‐dissolution of a‐ZVO. Therefore, the prepared a‐ZVO@MoS2 and conceptually validated a‐V2O5@MoS2 derived from commercial c‐V2O5 exhibit excellent cycling stability at an ultralow current density (0.05 A g−1) while maintaining good rate capability and capacity retention. This research achievement provides a new effective strategy for various amorphous cathode designs for AZIBs with superior performance.

Ultrafast Tailoring Amorphous Zn0.25V2O5 with Precision-Engineered Artificial Atomic-Layer 1T'-MoS2 Cathode Electrolyte Interphase for Advanced Aqueous Zinc-Ion Batteries.

Vanadium (V)-based oxides as cathode materials for aqueous zinc-ion batteries (AZIBs) still encounter challenges such as sluggish Zn2+ diffusion kinetics and V-dissolution, thus leading to severe capacity fading and limited life span. Here, we designed an ultrafast and facile colloidal chemical synthesis strategy based on crystalline Zn0.25V2O5 (c-ZVO) to successfully prepare a-ZVO@MoS2 core@shell heterostructures, where atomic-layer MoS2 uniformly coats on the surface of amorphous a-ZVO. The tailored amorphous structure of a-ZVO provides more isotropic pathways and active sites for Zn2+, thus significantly enhancing the Zn2+ diffusion kinetics during charge-discharge processes. Meanwhile, as an efficient artificial cathode electrolyte interphase, the precision-engineered atomic-layer MoS2 with semi-metallic 1T' phase not only contributes to improved electron transport but also effectively inhibits the V-dissolution of a-ZVO. Therefore, the prepared a-ZVO@MoS2 and conceptually validated a-V2O5@MoS2 derived from commercial c-V2O5 exhibit excellent cycling stability at an ultralow current density (0.05 A g-1) while maintaining good rate capability and capacity retention. This research achievement provides a new effective strategy for various amorphous cathode designs for AZIBs with superior performance.

Revisiting ether electrolytes for high-voltage sodium-ion batteries

While ether electrolytes show great potential for anode materials of sodium-ion batteries (SIBs), they are perceived to be intolerant to high voltage (4.0 V and above) and are rarely employed in cathode materials. Herein, four typical ether electrolytes are examined and the oxidative stability is demonstrated to be closely related to their solvation structures. The anion-involved solvation structure lowers the tolerance of weakly solvated electrolyte to high voltage, and the resulting inorganics-rich cathode electrolyte interphase is equipped with high resistance and friability, leading to undesired rate and cycle performance. In contras, strongly solvated electrolytes can cycle stably at a high voltage of 4.3 V with high rate performance. As a proof-of-concept, the Graphite//Na3(VOPO4)2F full cell based on G2 electrolyte (1 M NaPF6 in glyme) can deliver a high energy density of 126.3 Wh kg−1 at 61.2 W kg−1 and a desirable power density of 5424.3 W kg−1 at 65.1 Wh kg−1, providing a demonstration for the potential application of ether electrolytes in high-voltage SIBs.

Realizing the single-crystalline LiNi0.90Mn0.05Co0.05O2 cathode with long-life and high-safety property driven by polysiloxane covering and PO43− doping

As a promising cathode for lithium-ion batteries, the ultra-high nickel content layered oxide LiNi0.90Co0.05Mn0.05O2 demonstrates the great attention for the high discharging capacity. However, the serious capacity attenuation resulted from the instable interface, crystal structure degeneration and strong side-reactions on cathode-electrolyte interphase with charging-discharging drastically restricts its extensive application. To alleviate the intrinsic drawbacks, the combination improvement strategy for polysiloxane covering and PO43− doping is adopted to lower the surface residual alkali amounts, defend the HF/F− attacking and enhance the cation location order of LiNi0.90Co0.05Mn0.05O2. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) are used to evaluate the synthesized samples. The cathodes after the polysiloxane covering and PO43− doping deliver the improved crystal structure, larger lattice parameters and superior electrochemical properties. The polysiloxane coated and PO43− doped sample exhibits a high discharging capacity of 147.5 mAh g−1 at 10.0C rate and 155.4 mAh g−1 at −30 °C, remains a capacity of 193.2 mAh g−1 at 1.0C after 300 cycles with a retention of 91.2 %. Besides, when applied in pouch full batteries, it could pass the rigorous safety tests of Bar impact, Overcharging test and Nail penetration successfully, and still maintain the superior cycling stability in practice application.

Challenges and Modification Strategies on High-voltage Layered Oxide Cathode for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have attracted great attention due to their advantages on resource abundance, cost and safety. Layered oxide cathodes (LOCs) of SIBs possess high theoretical capacity, facile synthesis and low cost, and are promising candidates for large scale energy storage application. Increasing operating voltage is an effective strategy to achieve higher specific capacity and also high energy density of SIBs. However, at high operating voltages, LOCs will undergo a series of phase transitions in bulk phase, leading to huge change of volume and layer spacings accompanied by severe lattice stress and cracking formation. Degeneration of surface also occurs between LOCs and electrolytes, resulting in sustained growth of cathode electrolyte interphase (CEI) and release of O2 and CO2. These induce structural destruction and electrochemical performance degradation in high voltage regions. Recently, many strategies have been proposed to improve electrochemical performance of LOCs under high voltages, including bulk element doping, structural design, surface coating and gradient doping. This review describes pivotal challenges and occurrence mechanisms at high voltages, and summarizes strategies to improve stability of bulk and surface. Viewpoints will be provided to promote development of high energy density SIBs.

Enhancing the performance of LiNi0.8Mn0.1Co0.1O2-based pouch cells through advanced electrolyte additive systems for high-temperature lithium-ion batteries

Next-generation lithium-ion batteries, which achieve high energy densities and prolonged cycle performance, require cathode materials with high operating voltages and specific capacities. Because of their high capacity and operating voltage, nickel-rich layered oxides like LiNi0.8Mn0.1Co0.1O2 (NMC811) are attractive cathodes; nevertheless, they have drawbacks such capacity loss, poor cycle performance, structural instability, and thermal instability. Enhancing the stability of the NMC811 cathode-electrolyte interphase demands improvements in both cathode materials and electrolytes. This study explores the enhancement of NMC811-based battery systems through electrolyte modification, focusing on mixed additive combinations to evaluate their synergistic effects at elevated temperatures, relevant for tropical climates. A ternary additive system comprising vinylene carbonate (VC), lithium difluorophosphate (LiPO2F2), and p-toluenesulfonyl isocyanate (PTSI) in a LiPF6-based electrolyte showed significant improvements. This system mitigated capacity fading for cells cycled over 3 V–4.2 V at both 25 °C and 45 °C, outperforming the baseline electrolyte. The designed electrolyte stabilized the electrode-electrolyte interface, enhancing cell performance and the cathode's structural integrity. Notably, the graphite/NMC811 pouch cell's cycling performance showed an increase in capacity retention from 82.4% to 90.2% after 150 cycles at C/2 at 45 °C. Moreover, the deactivation of PF5 by PTSI can help to suppress the side reaction from the instability of LiPF6-based electrolytes, especially at elevated temperatures. These findings carried out from this strategic electrolyte additive system can substantially improve nickel-rich LIBs, especially in challenging thermal environments.