Electrolyte Therapy for Improving the Performance of LiNi0.5Mn1.5O4 Cathodes Assembled Lithium-Ion Batteries

Delineating the Impact of Diluent on High-Concentration Electrolytes for Developing High-Voltage LiNi0.5Mn1.5O4 Spinel Cathode

LiNi0.5Mn1.5O4 (LNMO) is a high-voltage spinel cathode with low nickel content, making it an attractive candidate for next-generation lithium-ion batteries (LIBs). However, its application is limited by interfacial instability with conventional carbonate-based electrolytes at high voltages. In this work, a localized saturated electrolyte (LSE) capable of stably operating up to 4.85 V is investigated. Molecular dynamics simulations and Fourier transform infrared spectroscopy reveal that adding "non-solvating" 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether diluent in the saturated electrolyte, more PF6 - anions are present in the first solvation shell of Li+, at the expense of solvent molecules. This tailored solvation environment promotes the formation of a robust, LiF-rich cathode-electrolyte interphase that mitigates transition metal dissolution and parasitic side reactions. The optimized LSE enables excellent cycling performance, with 95% capacity retention in Li|LNMO half-cells after 100 cycles and 94% retention in Li4Ti5O12|LNMO full cells after 250 cycles, even at a practically relevant LNMO cathode loading of ≈15 mg cm-2. These results highlight the benefits of electrolyte engineering and solvation structure control in advancing high-voltage LIB technologies.

Enhancing the electrochemical performance of high-voltage LiNi0.5Mn1.5O4 batteries with a multifunctional inorganic MgHPO4 electrolyte additive

The instability of the electrode/electrolyte interface and the metal-ions dissolution of high-voltage LiNi0.5Mn1.5O4 (LNMO) material lead to significant degradation of cycling performance, thereby limiting the large-scale application of LNMO-based batteries. Here, inorganic Mg/Ca/Sr-contained phosphates (MgHPO4, CaHPO4, and SrHPO4) are used individually as functional additives of standard electrolytes to enhance the cycling performance of LNMO. Combined with theoretical calculations, a series of electrochemical measurements and characteristics corroborate that the MgHPO4 is the optimal additive and can preferentially undergo oxidation and reduction decomposition over carbonate solvents. Electrochemical results reveal that the LNMO/Li half-cell containing the MgHPO4 additive shows a capacity retention of 91.9% after 500 cycles at 5 C, higher than that obtained with STD (76.5%). In addition, the LNMO/graphite (Gr) full-cell with MgHPO4 additive increases the capacity retention from 70.8 to 78.0% after 100 cycles at 0.5 C. The addition of MgHPO4 allows a thin, uniform, and conductive cathode-electrolyte interphase (CEI) and solid-electrolyte interphase (SEI) film to be formed on the LNMO cathode and graphite anodes. Furthermore, the preferential reduction of MgHPO4 inhibits the lithium dendritic growth and enables the formation of a more stable SEI on the Li anode. Besides, the MgHPO4 additive serves as a scavenger of detrimental HF, thus suppressing the Ni/Mn ions dissolution and improving the structural stability of LNMO. This study provides a cost-effective strategy involving the use of an inorganic additive for improving the electrochemical performance of high-voltage lithium-ion batteries.

The Cathode-Electrolyte Interface Constructed with Antioxidant Ascorbic Acid Guides LNMO to Achieve Stable Cycling Under High Voltage Conditions

LiNi0.5Mn1.5O4 (LNMO) is considered one of the most promising cathode materials for high-energy-density lithium-ion batteries (LIBs). However, free-radical-induced carbonate electrolyte decomposition is a key factor hindering the improvement of battery stability. Inspired by the antioxidative properties of ascorbic acid (AA) in scavenging free radicals, the addition of AA during the electrode fabrication process can effectively terminate free radical chain reactions within the cycling of LNMO. This action prevents severe electrolyte decomposition, thus stabilizing the cathode-electrolyte interface (CEI) and ultimately enhancing battery stability. The results demonstrate that LNMO||Li half-cell with the addition of AA show significantly improved cycling performance after 1000 cycles at 1 C, with a high capacity retention rate of 87.4%, surpassing the 43.6% retention rate achieved by batteries using PVDF alone as a binder. This work introduces an efficient and straightforward strategy for designing functional additives to stabilize phase interfaces, offering an economically efficient choice to enhance the electrochemical performance of the LNMO.

Kinetically controlled synthesis of low-strain disordered micro-nano high voltage spinel cathodes with exposed {111} facets

High-voltage LiNi0.5Mn1.5O4 (LNMO) is one of the most promising cathode candidates for rechargeable lithium-ion batteries (LIBs) but suffers from deteriorated cycling stability due to severe interfacial side reactions and manganese dissolution. Herein, a micro-nano porous spherical LNMO cathode was designed for high-performance LIBs. The disordered structure and the preferred exposure of the {111} facets can be controlled by the release of lattice oxygen in the high-temperature calcination process. The unique configuration of this material could enhance the structural stability and play a crucial role in inhibiting manganese dissolution, promoting the rapid transport of Li+, and reducing the volume strain during the charge/discharge process. The designed cathode exhibits a remarkable discharge capacity of 136.7 mA h g-1 at 0.5C, corresponding to an energy density of up to 636.4 W h kg-1, unprecedented cycling stability (capacity retention of 90.6% after 500 cycles) and superior rate capability (78.9% of initial capacity at 10C). The structurally controllable preparation strategy demonstrated in this work provides new insights into the structural design of cathode materials for LIBs.

The Role of the Molecular Encapsulation Effect in Stabilizing Hydrogen-Bond-Rich Gel-State Lithium Metal Batteries

Gel-state polymer electrolytes with superior mechanical properties, self-healing abilities and high Li+ transference numbers can be obtained by in situ polymerization of monomers with hydrogen-bonding moieties. However, it is overlooked that the active hydrogen atoms in hydrogen-bond donors experience displacement reactions with lithium metal in lithium metal batteries (LMBs), leading to corrosion of the lithium metal. Herein, it is discovered that the addition of hydrogen-bond acceptors to hydrogen-bond-rich gel-state electrolytes modulates the chemical activity of the active hydrogen atoms via the formation of hydrogen-bonded intermolecular interactions. The characterizations reveal that the added hydrogen-bond acceptors encapsulate the active hydrogen atoms to suppress the interfacial chemical corrosions of lithium metals, thereby enhancing the chemical stability of the polymer structure and interphase. With the employment of this strategy, a 1.1 Ah LiNi0.8Co0.1Mn0.1O2/Li metal pouch cell achieves stable cycling with 96.3 % capacity retention at 100 cycles. This new approach indicates a feasible path for achieving in situ polymerization of highly stable gel-state-based LMBs.

Engineering Cathode-Electrolyte Interface of High-Voltage Spinel LiNi0.5Mn1.5O4 via Halide Solid-State Electrolyte Coating

The high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) cathode material with high energy density, low cost, and excellent rate capability has grabbed the attention of the field. However, a high-voltage platform at 4.7 V causes severe oxidative side reactions when in contact with the organic electrolyte, leading to poor electrochemical performance. Furthermore, the contact between the liquid electrolyte and LNMO leads to Mn dissolution during cycles. In this work, we applied the sol-gel method to prepare Li3InCl6-coated LNMO (LIC@LNMO) to address the mentioned problems of LNMO. By introducing a protective layer of halide-type solid-state electrolyte on LNMO, we can prevent direct contact between LNMO and electrolyte while maintaining good ionic conductivity. Thus, we could demonstrate that 5 wt % LIC@LNMO exhibited a good cycle performance with a Coulombic efficiency of 99% and a capacity retention of 80% after the 230th cycle at the 230th cycle at 1C at room temperature.

An electrolyte additive for the improved high voltage performance of LiNi0.5Mn1.5O4 (LNMO) cathodes in Li-ion batteries

High-voltage cathode materials are important for the implementation of high-energy-density Li-ion batteries. However, with increasing cut-off voltages, interfacial instabilities between electrodes and the electrolyte limit their commercial development. This study addresses this issue by proposing a new electrolyte additive, (3-aminopropyl)triethoxysilane (APTS). APTS stabilises the interface between the LiNi_0.5Mn_1.5O₄ (LNMO) cathode and the electrolyte in LNMO‖Li half-cells due to its multifunctional character. The amino groups in APTS facilitate the formation of a robust protective cathode layer. Its silane groups improve layer stability by neutralising the electrolyte's detrimental hydrogen fluoride and water. Electrochemical measurements reveal that the addition of 0.5 wt% APTS significantly improves the long-term cycling stability of LNMO‖Li half-cells at room temperature and 55 °C. APTS-addition to the electrolyte delivers excellent capacity retention of 92% after 350 cycles at room temperature and 71% after 300 cycles at 55 °C (1C) contrasting with the much lower performances of the additive-free electrolyte. The addition of a 0.5 wt% (3-glycidyloxypropyl)trimethoxysilane (GLYMO) additive, which contains only the siloxane group, but lacks the amine group, displayed a capacity retention of 73% after 350 cycles at room temperature but degraded significantly upon cycling at 55 °C.

LiNi0.5Mn1.5O4 Cathode Microstructure for All-Solid-State Batteries

Solid-state batteries (SSBs) have received attention as a next-generation energy storage technology due to their potential to superior deliver energy density and safety compared to commercial Li-ion batteries. One of the main challenges limiting their practical implementation is the rapid capacity decay caused by the loss of contact between the cathode active material and the solid electrolyte upon cycling. Here, we use the promising high-voltage, low-cost LiNi_0.5Mn_1.5O₄ (LNMO) as a model system to demonstrate the importance of the cathode microstructure in SSBs. We design Al₂O₃-coated LNMO particles with a hollow microstructure aimed at suppressing electrolyte decomposition, minimizing volume change during cycling, and shortening the Li diffusion pathway to achieve maximum cathode utilization. When cycled with a Li₆PS₅Cl solid electrolyte, we demonstrate a capacity retention above 70% after 100 cycles, with an active material loading of 27 mg cm^-2 (2.2 mAh cm^-2) at a current density of 0.8 mA cm^-2.

Effects of the Separator MOF-Al2O3 Coating on Battery Rate Performance and Solid-Electrolyte Interphase Formation

Metal organic frameworks (MOFs) have unique advantages in optimizing the ionic conductivity of battery separators because of their rich cavity structure and highly ordered and connected pores. In this study, we used a hydrothermal method to synthesize a functional material, Ag-MOF crystal, as a separator coating content, and then studied the properties and application effect of the MOF-Al₂O₃-blended coating applying to a polyethylene (PE) separator (MOF_xAl_1-x/PE). Results show that MOF_0.08Al_0.92/PE (MOF/Al₂O₃ = 0.08:0.92) used in NCM811||Li cells significantly not only improves the fast charge-discharge performance of the cells but also inhibits the growth of lithium dendrites during long-term charge-discharge cycling; the Li⁺ transference number (t_Li⁺) of the MOF_0.08Al_0.92/PE composite separator is 0.61; the Li||separator||Li half-cell circulates stably for 1000 h at varying current density from 0.5 to 10 mA cm^-2 and only produces low overpotentials, indicating that MOF_0.08Al_0.92 stabilizes lithium. The initial capacity of the NCM811||Li cell using the MOF_0.08Al_0.92/PE separator is 165.0 mA h g^-1, its capacity retention is 70.67% after 300 cycles at 5 C, and the interface resistance of the cells only increases from 13.8 to 31.5 Ω, whereas the capacity retention of Al₂O₃/PE separator batteries is only 40.41% (62.2 mA h g^-1) under the same conditions. During the charge-discharge cycling, the MOF-Al₂O₃ coating induces the lithium anode to quickly form a stable and dense solid-electrolyte interphase layer, promotes the uniform deposition of Li⁺, and inhibits the growth of lithium dendrites as well.

Stabilized Cathode Interphase for Enhancing Electrochemical Performance of LiNi0.5Mn1.5O4-Based Lithium-Ion Battery via cis-1,2,3,6-Tetrahydrophthalic Anhydride

The continuous degradation of carbonate electrolytes and the dissolution of transition metal cations due to parasitic reactions on the cathode-electrolyte interphase (CEI) block the practical application of LiNi_0.5Mn_1.5O₄-based lithium-ion batteries (LNMO-based LIBs) at a high voltage. cis-1,2,3,6-Tetrahydrophthalic anhydride (CTA) has been used as a functional additive in a carbonate baseline electrolyte (BE) for constructing the CEI film to enhance the cyclic stability of LNMO-based LIBs. The LNMO/Li cell with CTA exhibits a preponderant capacity retention of 83.3% compared with those of propionic anhydride (PA) (46.5%) and BE (13.6%) after 500 cycles at the current density of 1 C from 3.5 to 4.9 V. Additionally, the LNMO/graphite full cell with CTA still has a higher capacity retention of 95.46% even after 300 cycles at 1 C. By characterizations, it is reasonably demonstrated that CTA was oxidated to participate in the construction of a CEI film. An unsaturated aromatic group was introduced into the composition of the CEI film along with CTA in the formation process of the CEI film, which further improved the antioxidative activity of the CEI film under the influence of field-effect. Specifically, the CEI film obtains appreciable stability because of its higher antioxidative activity under the influence of field-effect. The stabilized CEI can significantly suppress the parasitic reactions of electrolytes, decrease the consumption of active-Li⁺, and protect the LNMO cathode structure, thereby enhancing the cyclic compatibility of LNMO-based LIBs with the carbonate electrolytes from 3.5 to 4.9 V.

Ultrahigh-Areal-Capacity Battery Anodes Enabled by Free-Standing Vanadium Nitride@N-Doped Carbon/Graphene Architecture

Nanostructured anode materials have attracted significant attention for lithium-ion batteries (LIBs) due to their high specific capacity. However, their practical application is hindered by the rather low areal capacity in the ultrathin electrode (∼1 mg cm^-2). Herein, we propose a new strategy of an all-conductive electrode to fabricate a flexible and free-standing vanadium nitride@N-doped carbon/graphene (VN@C/G) thick electrode. Due to the free-standing structure and absence of any nonconductive components in the electrode, the obtained thick electrode displays excellent cycling performances. With the high mass loading of 5 mg cm^-2, VN based electrodes achieve a reversible capacity of 2.6 mAh cm^-2 after 200 cycles. Moreover, the all-conductive electrode allows an ultrahigh areal capacity of 7 mAh cm^-2 with a high mass loading of 18.3 mg cm^-2, which is comparable to state-of-the-art graphite anodes (4 mAh cm^-2). Theoretical calculations prove the metallic conductivity of VN, which allows fast charge transport in the thick electrode. This strategy of fabricating all-conductive electrodes shows great potentials to achieve high areal capacity in practical lithium-ion batteries.