LiNi0.5Mn1.5O4 Research Articles

Understanding and Mitigating the Dissolution and Delamination Issues Encountered with High-Voltage LiNi0.5Mn1.5O4

In our initial study on the high-voltage 5 V cobalt-free spinel LiNi0.5Mn1.5O4 (LNMO) cathode, we discovered a severe delamination issue in the laminates when cycled at a high upper cut-off voltage (UCV) of 4.95 V, especially when a large cell format was used. This delamination problem prompted us to investigate further by studying the transition metal (TM) dissolution mechanism of cobalt-free LNMO cathodes, and as a comparison, some cobalt-containing lithium nickel manganese cobalt oxides (NMC) cathodes, as the leachates from the soaking experiment might be the culprit for the delamination. Unlike other previous reports, we are interested in the intrinsic stability of the cathode in the presence of a baseline Gen2 electrolyte consisting of 1.2 M of LiPF6 in ethylene carbonate/ethyl methyl carbonate (EC/EMC), similar to a storage condition. The electrode laminates (transition metal oxides, transition metal oxides, TMOs, coated on an Al current collector with a loading level of around 2.5 mAh/cm2) or the TMO powders (pure commercial quality spinel LNMO, NMC, etc.) were stored in the baseline solution, and the transition metal dissolution was studied through nuclear magnetic resonance, such as 1H NMR, 19F NMR, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP-MS). Significant electrolyte decomposition was observed and could be the cause that leads to the TM dissolution of LNMO. To address this TM dissolution, additives were introduced into the baseline electrolyte, effectively alleviating the issue of TM dissolution. The results suggest that the observed delamination is caused by electrolyte decompositions that lead to etching, and additives such as lithium difluorooxalato borate and p-toluenesulfonyl isocyanate can alleviate this issue by forming a firm cathode electrolyte interface. This study provides a new perspective on cell degradation induced by electrode/electrolyte interactions under storage conditions.

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.

Hybrid High‐Voltage LiNi0.5Mn1.5O4/Graphite Cathodes Enabling Rechargeable Batteries with Simultaneous Anion‐ and Cation Storage

AbstractA hybrid cathode concept that targets combining the specific advantages of Li‐ion batteries and dual‐ion batteries is proposed. LiNi0.5Mn1.5O4 (LNMO), (de)inserting Li+, and graphite, capable to (de)intercalate PF6− present in the electrolyte, are combined in one cathode, aiming for synergy effects due to the presence of two electrochemically active species to overcome rate limitations caused by electrolyte depletion. Hybrid cathodes of different compositions and designs are prepared and investigated regarding their properties and the storage mechanism using electrochemical analyses combined with operando XRD and extensive materials characterization, including scanning electron microscopy and energy‐dispersive X‐ray spectroscopy. Finally, hybrid cathodes with higher areal capacity are prepared and investigated regarding rate performance. Model‐based analysis of the results reveals design criteria and material properties required to achieve synergistic effects between the components in hybrid cathodes. These insights lay the foundation for a new type of battery with advantageous properties in terms of cost, environmental friendliness, and electrochemical performance.

Ge-Regulated Ordered Phase in Pseudosphere-Structured LiNi0.5Mn1.5O4 Spinel Effectively Inhibits Mn Dissolution.

Due to the higher energy density, high thermal stability, and low cost, LiNi0.5Mn1.5O4 (LNMO) spinel, with a large voltage operating window, has been one of the most promising cathode materials for lithium-ion batteries (LIBs). However, the interfacial reaction between the cathode and electrolyte and the two-phase reaction within the bulk of LNMO would destroy the original structure and lead to capacity deterioration, posing a significant challenge. Therefore, the way to suppress the transition-metal (TM) dissolution in LNMO has attracted much attention. However, the ordered/disordered phase regulation by metal atom doping to prohibit TM dissolution has not been extensively explored. Herein, a Ge-doping strategy is proposed to adjust the ratio of disordered/ordered phases in LNMO, resulting in exceptional structural stability. For the modified spinel cathode, there is almost no voltage drop and the capacity retention is up to 92.2% over 1000 cycles at 1C. These results demonstrate that incorporating Ge into LNMO forms a robust structure that effectively increases the amount of Mn4+ while blocking the diffusion of TM ions. In addition, Ge-doping also protects the bulk from further reactions with electrolytes, significantly enhancing the interfacial stability and relieving voltage decay in cycling. This approach can also be applied to design other high-stability cathodes through ordered/disordered phase regulation.

Enhancing the operation stability of lithium-rich layered oxide Li1.2Ni0.2Mn0.6O2 by synergistic pinning effect and interface reconstruction for high-energy-density lithium-ion batteries

Lithium-rich manganese-based layered oxides are considered to be promising cathode materials for next-generation lithium-ion batteries (LIBs). However, their practical application is hindered due to both the rapid capacity attenuation and the unsatisfactory rate capability. In this work, to overcome these problems, layered oxide Li1.2Ni0.2Mn0.6O2 (LNMO) is modified via La3+ doping and perovskite type LaMnO3 coating layer, meanwhile, interface layer Li2MnO3 with monoclinic structure is formed between the doped-La3+ Li1.2Ni0.2Mn0.6O2 and LaMnO3 coating layer. The 0.02 wt% La modified Li1.2Ni0.2Mn0.6O2 can deliver much higher rate capability and cyclic stability than original LNMO, attributed that the LaMnO3 coating layer can not only isolate La-doped LNMO from the electrolyte to reduce the dissolution of manganese ions but also can reduces the polarization of electrode interface via inhibiting the continuous growth of SEI during the cycle. Besides, La3+ doping plays a pinning effect role in enhancing the structural stability of LNMO.

Fabrication and electrochemical properties of electrode composites for oxide-type all-solid-state batteries through electrostatic integrated assembly

All-solid-state batteries, which use flame-resistant solid electrolytes, are regarded as safer alternatives to conventional lithium-ion batteries for various applications including electric vehicles. Herein, we report the fabrication of cathode composites for oxide-type all-solid-state batteries through an electrostatic assembly method. A polyelectrolyte is used to adjust the surface charge of the matrix particles to positive/negative, and the aggregation resulting from electrostatic interactions is utilized. Composites consisting of cathode active material particles (LiNi1/3Mn1/3Co1/3O2 (NMC) or LiNi0.5Mn1.5O4 (LNMO)), solid electrolyte particles Li1.3Al0.3Ti1.7(PO4)3 (LATP), and electron conductive one-dimensional carbon nanotubes (CNT) are formed via an electrostatic integrated assembly of colloidal suspensions. Electrostatic integration increases the electronic conductivity by two orders of magnitude in the NMC–LATP–CNT composite (6.5 × 10−3 S cm−1/3.2 × 10−5 S cm−1) and by six orders of magnitude in the LNMO–LATP–CNT composite (6.4 × 10−3 S cm−1/2.3 × 10−9 S cm−1). The dispersion of CNTs in the cathode composite is enhanced, resulting in percolation of e− path even at 1 wt% (approximately 2.5 vol%) CNT. This study indicates that an integrated cathode composite can be fabricated with particles uniformly mixed by electrostatic interaction for oxide-type all-solid-state batteries.

Tris(trimethylsilyl) Phosphite and Lithium Difluoro(oxalato)borate as Electrolyte Additives for LiNi0.5Mn1.5O4‐Graphite Lithium‐Ion Batteries

AbstractRaising the energy density of lithium‐ion batteries (LIBs) through the operation of high‐voltage cathodes presents a challenge in terms of practical use due to electrolyte degradation. Consequently, it is imperative to explore new materials to circumvent this issue. In this study, a combination of tris(trimethylsilyl) phosphite (TMSPi) and lithium difluoro(oxalato)borate (LiDFOB) is presented as film‐forming additives in a conventional LiPF6‐containing carbonate‐based electrolyte solution in high‐voltage LiNi0.5Mn1.5O4‐graphite full cells. At high voltage, TMSPi oxidizes on the LiNi0.5Mn1.5O4 (LNMO) cathode surface prior to the decomposition of electrolyte solvents, promoting the formation of a stable cathode electrolyte interphase (CEI) layer. In tandem, given that LiDFOB has a lower reduction potential than ethylene carbonate (EC), it has the possibility of forming a solid electrolyte interphase (SEI) on the graphite anode surface. Combining the two additives was found to suppress the degradation of the electrolyte to a large extent. Among the investigated concentration of the additives, the combination of 1 wt. % TMSPi and 2 wt. % LiDFOB added to LP40 electrolyte exhibits improved capacity retention of 80 % after 400 cycles at 0.3 C, compared to the electrolyte with no additive with 67 % capacity retention over the same period. Thereby, the combination of TMSPi with LiDFOB provides an improvement for high voltage LIBs.

Cycling Stability of Lithium-Ion Batteries Based on Fe-Ti-Doped LiNi0.5 Mn1.5 O4 Cathodes, Graphite Anodes, and the Cathode-Additive Li3 PO4.

This study addresses the improved cycling stability of Li-ion batteries based on Fe-Ti-doped LiNi0.5 Mn1.5 O4 (LNMO) high-voltage cathode active material and graphite anodes. By using 1wt% Li3 PO4 as cathode additive, over 90% capacity retention for 1000 charge-discharge cycles and remaining capacities of 109 mAh g-1 are reached in a cell with an areal capacity of 2.3 mAh cm- 2 (potential range: 3.5-4.9V). Cells without the additive, in contrast, suffer from accelerated capacity loss and increase polarization, resulting in capacity retention of only 78% over 1000 cycles. An electrolyte consisting of ethylene carbonate, dimethyl carbonate, and LiPF6 is used without additional additives. The significantly improved cycling stability of the full cells is mainly due to two factors, namely, the low MnIII content of the Fe-Ti-doped LNMO active material and the use of the cathode-additive Li3 PO4 . Crystalline Li3 PO4 yields a drastic reduction of transition metal deposition on the graphite anode and prevents Li loss and the propagation of cell polarization. Li3 PO4 is added to the cathode slurry that makes it a very simple and scalable process, first reported herein. The positive effects of crystalline Li3 PO4 as electrode additive, however, should apply to other cell chemistries as well.

Inhibition of transition-metal dissolution with an inert soluble product interface constructed by high-concentration electrolyte

The formation of a compact and stable cathode electrolyte interphase (CEI) film is a promising way to improve the high voltage resistance of lithium-ion batteries (LIBs). However, challenges arise due to the corrosion of hydrogen fluoride (HF) and the dissolution of transition metal ions (TMs) in harsh conditions. To address this issue, researchers have constructed an anion-derived CEI film enriched with LiF and LiPO2F2 soluble product on the surface of LiNi0.5Mn1.5O4 (LNMO) cathode in highly concentrated electrolytes (HCEs). The strong binding of LiF and LiPO2F2 generated an inert LiPO2F2 soluble product interface, which inhibited HF corrosion and maintained the spinel structure of LNMO, contributing to a capacity retention of 92% after 200 cycles at 55°C in the resulting cell with a soluble LiPO2F2-containing CEI film. This new approach sheds light on improving the electrode/electrolyte interface for high-energy LIBs.

Quickly form stable cathode/electrolyte interface of LiNi0.5Mn1.5O4 (LNMO)/graphite high-voltage lithium ion cells by using tosylmethyl isocyanide (TosMIC) as electrolyte additive

Tosylmethyl isocyanide (TosMIC) is used as electrolyte additive to study the effect on the cycling performance of LiNi0.5Mn1.5O4 (LNMO)/graphite 5V lithium-ion cell. The constant current charge and discharge measurement results shows that the capacity retention rate of the cell containing 0.3 wt% TosMIC increases by 18% after 200 cycles, while 1.0 wt% TosMIC worsens the cycling performance of the cell. The decomposition product PF5 of electrolyte salt LiPF6 may interact with TosMIC to form TosMIC-PF5 complex. The results of surface and electrochemical analysis indicate that the complex can be oxidized at the cathode and reduced at the anode simultaneously prior to the solvent molecules of the electrolyte. Theoretical calculation further shows that TosMIC-PF5 can be oxidized to form a dimer (TosMIC-PF5)2 at 4.46V (vs. Li/Li+), which may be deposited on the LNMO cathode to help form a coating layer. This coating layer can be rapidly formed in the first cycle and can significantly alleviate the oxidation of the electrolyte, but it cannot inhibit the decomposition of excessive additive. Two proposed reduction reactions of TosMIC-PF5 occur at 1.66 V and 2.00 V (vs. Li/Li+). Unfortunately, the reduction of this additive has a negative impact on the cycling performance of the cell.

Cr-doped LiNi0.5Mn1.5O4 derived from bimetallic Ni/Mn metal-organic framework as high-performance cathode for lithium-ion batteries

Metal-organic frameworks (MOFs) have potential applications in the field of electrochemical energy storage due to their unique characteristics, such as structural diversity, tolerability, and chemical homogeneity. LiNi0.5Mn1.5O4 (LNMO) is a great cathode material due to its wide working voltage, high energy density, and excellent rate capability. In this study, bimetallic Ni/Mn-MOFs and Cr-doped Ni/Mn-MOFs have been prepared by solvothermal reaction, which can be used as the precursor for the synthesis of pristine and Cr-doped LNMOs. The results indicate that the MOF-derived LNMO has better electrochemical behavior than the sample obtained from the conventional co-precipitation route. The resulting MOF-derived LNMO exhibits a high specific capacity (SC, 132.4 mAh/g at 0.2C), good rate ability (116.5 mAh/g at 10C), and remarkable long-cycle performance (80.1 % capacity retention for 200 cycles at 4C). More significantly, the full lithium-ion batteries (LIBs) incorporated with the MOF-derived LNMO as a cathode and Li4Ti5O12 (LTO) as an anode exhibit superior energy storage properties. This finding provides an efficient strategy for preparing high-performance LNMO cathode materials.

Alginate-Xylan Biopolymer as a Multifunctional Binder for 5 V High-Voltage LNMO Electrodes.

LiNi0.5Mn1.5O4 (LNMO) with a spinel structure is one of the most promising cathode materials choices for Li-ion batteries (LIBs). However, at a high operating voltages, the decomposition of organic electrolytes and the dissolution of transition metals, especially Mn(II) ions, cause unsatisfactory cycle stability. The initial application of a sodium alginate (SA)-xylan biopolymer as an aqueous binder aims to address the aforementioned problems. The SX28-LNMO electrode has a sizable discharge capacity, exceptional rate capability, and long-term cyclability with a capacity retention of 99.8% after 450 cycles at 1C and a remarkable rate capability of 121 mAh g-1 even at 10C. A more thorough investigation illustrated that SX28 binder provides a substantial adhesion property and generates a uniform (CEI) layer on the LNMO surface, suppressing electrolytes' oxidative decomposition upon cycling and improving LIB performances. This work highlights the potential of hemicellulose as an aqueous binder for 5.0 V high-voltage cathodes.

Nonafluorobutane‐1‐Sulfonic Acid Induced Local High Concentration Additive Interface for Robust SEI Formation of High‐Voltage (5 V‐Class) Lithium Metal Batteries

AbstractTo optimize anode and cathode degradation issues in high‐voltage (5 V‐class) lithium metal batteries (LMBs), robust solid–electrolyte interfaces (SEI) on the surface of both anode and cathode are highly desired. Here, a nonafluorobutane‐1‐sulfonic acid (NFSA) additive is introduced to assist in the formation of the more stable and robust SEI to protect both anode and cathode. Typically, local high concentrations of lithium nonafluorobutane‐1‐sulfonate (NFSALi) and nonafluorobutane‐1‐sulfonate anion (NFSA−) could be achieved at the surface of anode and cathode respectively, through spontaneous chemical processes. The lowest unoccupied molecular orbital energy of NFSALi is lower and the highest occupied molecular orbital (energy of NFSA− is higher than electrolyte solvents. Thus, conformal and dense SEI passivation films are generated on the surface of both anode and cathode derived from electrochemical decomposition of NFSALi and NFSA−, respectively. Consequently, stable operation of Li metal anode and high‐voltage cathode are realized. The LiNi0.5Mn1.5O4(LNMO)//Li LMBs with NFSA‐containing electrolyte show great cycling stability with 93% capacity retention after 400 cycles and more stable Coulombic efficiency. This work specifies the double functions of NFSA as an interfacial layer forming additive to solve the degradation problems of high‐voltage (5 V‐class) LMBs, enabling high‐energy LMBs with significantly improved battery performance.

Bifunctional urea surface-modified high voltage LiNi0.5Mn1.5O4 cathode for enhanced electrochemical performance

Spinel LiNi0.5Mn1.5O4 (LNMO) cathode material has high specific energy density due to its high working voltage (4.7 V vs. Li/Li+). However, high voltage inevitably brings instability of the surface and interface layer properties and ultimately electrolyte decomposition and irreversible side reactions, which incurs structural degradation, capacity decline, and poor kinetics. Herein, a simple and novel surface modification strategy is proposed to obtain a bifunctional modification cathode material with carbon–nitrogen nanocoating and surface disorder phase transition, which is prepared through gas–solid heat treatment of pristine material and urea in a closed reactor. The surface disordered phase transition introduces favorable oxygen vacancies and synchronously constructs the fast diffusion channel of lithium ions, while the carbon–nitrogen nanocoating effectively alleviates the impedance growth of the electrode/electrolyte interface. Therefore, the surface modified U-LMNO exhibits an initial discharge capacity of 130.1 mAh g−1 at 0.2 C and a capacity retention rate of 95.1% after 200 cycles at 1 C, significantly superior to pristine P-LMNO. These results highlight the essentiality of high-voltage LNMO cathode material surface interface design and facilitate the development and commercialization of high-energy-density LNMO-based lithium-ion batteries.

Synthesis of high-voltage cathode material using the Taylor-Couette flow-based co-precipitation method.

LiNi0.5Mn1.5O4 (LNMO), a next-generation high-voltage battery material, is promising for high-energy-density and power-density lithium-ion secondary batteries. However, rapid capacity degradation occurs due to problems such as the elution of transition metals and the generation of structural distortion during cycling. Herein, a new LNMO material was synthesized using the Taylor-Couette flow-based co-precipitation method. The synthesized LNMO material consisted of secondary particles composed of primary particles with an octahedral structure and a high specific surface area. In addition, the LNMO cathode material showed less structural distortion and cation mixing as well as a high cyclability and rate performance compared with commercially available materials.

Low-Temperature Cation Ordering in High Voltage Spinel Cathode Material

The spinel cathode LiNi0.5Mn1.5O4 (LNMO) is a promising material for battery applications; however, issues regarding its cycling stability need to be addressed to fully utilize its potential. Specifically, LNMO suffers from rapid capacity loss following prolonged electrochemical cycling where the capacity drop occurs at an earlier stage for its transition metal ordered form. Further, the disordered form has been found to partially order during cycling, leading to the question if the failing of the disordered form is driven by Ni and Mn ordering in the structure. However, ordering is usually initiated at temperatures above 700 °C in the fully lithiated state, sparking the question if the energy barrier for the ordering process is lowered at the reduced Li content. In the work presented here, in situ neutron diffraction was used to further elucidate the ordering temperature and thermal stability of LixNi0.5Mn1.5O4 (0.000 (10) ≤ x ≤ 0.675 (10)). The temperature for Ni and Mn ordering was found to be dramatically lowered to 310–320 °C for LixNi0.5Mn1.5O4 compositions of 0.222 (8) ≤ x ≤ 0.675 (10), explained by a lower energy barrier for formation of intermediate Frenkel defect states. Li ordering and a lowering of symmetry to P213, together with formation of both a NiMn2O4-type spinel phase and a NiMnO3-type phase, could also be observed. The formation of NiMn2O4- and NiMnO3-type phases could be linked to reorganization of transition metals (TM) within the spinel structure and were found to be in competition with Ni and Mn ordering. At higher Li contents, transition metal diffusion tended to favor Ni and Mn ordering, while NiMn2O4- and NiMnO3-type phases were formed to a greater extent at lower Li contents. These results highlight the importance of suppressing transition metal reorganization in LiNi0.5Mn1.5O4, via increased TM diffusion energy barriers, as a key strategy for minimizing structural rearrangements and ultimately improving its electrochemical cyclability.

Improving the rate capability of LiNi0.5Mn1.3Ti0.2O4 by modifying the lithium insertion mechanism

Since lithium-ion batteries are becoming increasingly popular, we aimed to increase the power density of lithium-ion batteries by improving the rate capability of lithium insertion electrodes by controlling the reaction mechanism of lithium insertion materials. LiNi0.5Mn1.3Ti0.2O4 (Ti-LNMO), in which a part of Mn4+ in LiNi0.5Mn1.5O4 (LNMO) was replaced by Ti4+, was synthesized and proceeded in a single-phase reaction over the entire region. This resulted in two types of LNMOs with the same spinel structures and solid-state redox reactions of Ni2+/Ni4+, each with different reaction mechanisms. According to rate-capability tests of these two types of LNMOs, the Ti-LNMO exhibited superior rate capability than the LNMO without Ti-substitution, which demonstrated that high-power capabilities could be achieved by controlling the reaction mechanism. Furthermore, the solid-state Li-ion diffusion coefficient in the LNMOs was determined from the rate-capability using the diluted electrode method, and that of Ti-LNMO was more than three times greater than that of the LNMO. These results reveal that the lithium insertion mechanism is important for the kinetics of lithium insertion reaction.

Optimized Morphology and Tuning the Mn3+ Content of LiNi0.5Mn1.5O4 Cathode Material for Li-Ion Batteries.

The advantages of cobalt-free, high specific capacity, high operating voltage, low cost, and environmental friendliness of spinel LiNi0.5Mn1.5O4 (LNMO) material make it one of the most promising cathode materials for next-generation lithium-ion batteries. The disproportionation reaction of Mn3+ leads to Jahn-Teller distortion, which is the key issue in reducing the crystal structure stability and limiting the electrochemical stability of the material. In this work, single-crystal LNMO was synthesized successfully by the sol-gel method. The morphology and the Mn3+ content of the as-prepared LNMO were tuned by altering the synthesis temperature. The results demonstrated that the LNMO_110 material exhibited the most uniform particle distribution as well as the presence of the lowest concentration of Mn3+, which was beneficial to ion diffusion and electronic conductivity. As a result, this LNMO cathode material had an optimized electrochemical rate performance of 105.6 mAh g-1 at 1 C and cycling stability of 116.8 mAh g-1 at 0.1 C after 100 cycles.

Influence of electrode fabrication process on nanocrystalline tin oxide electrochemical behaviour for high voltage SnO2/LNMO full cell Li-ion battery

Tin oxide is one of the most promising anode materials to replace graphite in the next generation lithium-ion batteries thanks to its high theoretical specific capacity, low cost and large availability. Unfortunately, its large-scale application is still limited, due to marked capacity loss and poor cyclability. Recent findings demonstrated improved reversibility of the electrochemical reactions through the optimization of SnO2 particles size. In this frame, the sol-gel method has proved to be one of the most interesting synthesis processes to obtain mono and polycrystalline SnO2 particles, which guarantee higher reversibility of the conversion reaction. In this work, SnO2 nanoparticles was synthesized by sol-gel method, with an average size of 5–50 nm, depending on the post calcination temperature. Subsequently, the optimization of the electrode composition in terms of mass loading and binder allowed to achieve a specific capacity of 350 mAh g−1, with a Coulombic efficiency of 99.9 % after 100 cycles at high current rate of 0.75 A g−1. Finally, the optimized and pre-lithiated SnO2 anode was coupled with the high voltage LiNi0.5Mn1.5O4 (LNMO) cathode in full-cell configuration, and the contribution of the voltage window and formation step to the final cell capacity was studied to determine the optimum conditions at which high cycling stability can be obtained.

Zn-enriched cathode layer interface via atomic surface reduction of LiNi0.5Mn1.5O4: Computational and experimental insights

Despite having the ability to deliver 650 W h kg−1 in addition to the impressive rate capability, superior thermal stability, and facilitated electronic and ionic lithium conduction, LiNi0.5Mn1.5O4 (LNMO) is far from commercial applications. LNMO suffers from irreversible electrolytic degradation on its surface under high voltage operations leading to capacity fading and poor battery life. Therefore, this work aims to improve the stability and electrochemical behavior of LNMO by creating a Zn-enriched cathode layer interface via eccentric and facile diethyl zinc-assisted atomic surface reduction (Zn-ASR). In-depth surface characterization tools and computational calculations demonstrates a conformal 7-8 nm thin Zn-O and C-O enriched layer encapsulating the cathode particles resulting from Zn-ASR. The intensive comparative electrochemical and spectroscopic analysis, indicates superior electrochemical performance of the surface-reduced LNMO w.r.t rate capability (14% higher at 4C), cycling stability, and capacity retention (87% retention). A decrease in gaseous evolution on the surface-treated sample arising from the electrolyte degradation further explains the improvement in the stability and electrochemical behavior of Zn-ASR LNMO. This work proves that electrode material can be substantially improved and incentivized by the chemo-mechanical benefits of rationally designed surface layers.