Realization of a High-Voltage and High-Rate Nickel-Rich NCM Cathode Material for LIBs by Co and Ti Dual Modification

Constructing novel hydrated metal molten salt with high self-healing as the anode material for lithium-ion batteries

Lithium-ion batteries (LIBs) are greatly limited in their practical application because of their poor cycle performance, low conductivity and volume expansion. Herein, molten salts (MSs) FeCl3·6H2O-NMP with low temperature via simple preparation are used as the anode material of LIBs for the first time to break through the bottleneck of LIBs. The good fluidity and high self-healing of FeCl3·6H2O-NMP effectively avoid the collapse and breakage of the structure. Based on this feature, the initial discharge specific capacity reached 770.28 mA h g-1, which was more than twice that of the commercial graphite anode. After 200 cycles at a current density of 100 mA g-1, the specific capacity did not decrease rather it was found to be higher than the initial discharge specific capacity, reaching 867.24 mA h g-1. Besides, the good conductivity of MSs provides convenience for the removal and intercalation of Li+. The active H sites that can combine with lithium ions form LiH and provide capacity for LIBs. Density functional theory (DFT) calculation also provided theoretical proof for the mechanism of LIBs.

Doping Effects on Ternary Cathode Materials for Lithium-Ion Batteries: A Review

The ongoing advancements in lithium-ion battery technology are pivotal in propelling the performance of modern electronic devices and electric vehicles. Amongst various components, the cathode material significantly influences the battery performance, such as the specific capacity, capacity retention and the rate performance. Ternary cathode materials, composed of nickel, manganese, and cobalt (NCM), offer a balanced combination of these traits. Recent developments focus on elemental doping, which involves substituting a fraction of NCM constituent ions with alternative cations such as aluminum, titanium, or magnesium. This strategic substitution aims to enhance structural stability, increase capacity retention, and improve resistance to thermal runaway. Doped ternary materials have shown promising results, with improvements in cycle life and operational safety. However, the quest for optimal doping elements and concentrations persists to maximize performance while minimizing cost and environmental impact, ensuring the progression towards high-energy-density, durable, and safe battery technologies.

Stabilizing High-Voltage Performance of Nickel-Rich Cathodes via Facile Solvothermally Synthesized Niobium-Doped Strontium Titanate

Ni-rich layered ternary cathodes are promising candidates thanks to their low toxic Co-content and high energy density (∼800 Wh/kg). However, a critical challenge in developing Ni-rich cathodes is to improve cyclic stability, especially under high voltage (>4.3 V), which directly affects the performance and lifespan of the battery. In this study, niobium-doped strontium titanate (Nb-STO) is successfully synthesized via a facile solvothermal method and used as a surface modification layer onto the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode. The results exhibited that the Nb-STO modification significantly improved the cycling stability of the cathode material even under high-voltage (4.5 V) operational conditions. In particular, the best sample in our work could provide a high discharge capacity of ∼190 mAh/g after 100 cycles under 1 C with capacity retention over 84% in the voltage range of 3.0-4.5 V, superior to the pristine NCM811 (∼61%) and pure STO modified STO-811-600 (∼76%) samples under the same conditions. The improved electrochemical performance and stability of NCM811 under high voltage should be attributed to not only preventing the dissolution of the transition metals, further reducing the electrolyte's degradation by the end of charge, but also alleviating the internal resistance growth from uncontrollable cathode-electrolyte interface (CEI) evolution. These findings suggest that the as-synthesized STO with an optimized Nb-doping ratio could be a promising candidate for stabilizing Ni-rich cathode materials to facilitate the widespread commercialization of Ni-rich cathodes in modern LIBs.

Improving the Rechargeable Li-CO2 Battery Performances by Tailoring Oxygen Defects on Li-Ni-Co-Mn Multi-Metal Oxide Catalysts Recycled from Spent Ternary Lithium-Ion Batteries

Rechargeable Li-CO2 batteries are considered as a promising carbon-neutral energy storage technology owing to their ultra-high energy density and efficient CO2 capture capability. However, the sluggish CO2 reduction/evolution kinetics impedes their practical application, which leads to huge overpotentials and poor cyclability. Multi-element transit metal oxides (TMOs) are demonstrated as effective cathodic catalysts for Li-CO2 batteries. But there are no reports on the integration of defect engineering on multi-element TMOs. Herein, the oxygen vacancy-bearing Li-Ni-Co-Mn multi-oxide (Re-NCM-H3) catalyst with the α-NaFeO2-type structure is first fabricated by annealing the NiCoMn precursor that derived from spent ternary LiNi0.8Co0.1Mn0.1O2 cathode, in H2 at 300 °C. As demonstrated by experimental results and theory calculations, the introduction of moderate oxygen vacancy has optimized electronic state near the Fermi level (Ef), eventually improving CO2 adsorption and charge transfer. Therefore, the Li-CO2 batteries with Re-NCM-H3 catalyst deliver a high capacity (11808.9 mAh g-1), a lower overpotential (1.54 V), as well as excellent stability over 216 cycles at 100 mA g-1 and 165 cycles at 400 mA g-1. This study not only opens up a sustainable application of spent ternary cathode, but also validates the potential of multi-element TMO catalysts with oxygen defects for high-efficiency Li-CO2 batteries.

A Fresh One-Step Spray Pyrolysis Approach to Prepare Nickel-Rich Cathode Material for Lithium-Ion Batteries

The Ni-rich layered cathode material LiNi0.8Co0.1Mn0.1O2 (NCM811) with high specific capacity and acceptable rate performance is one of the key cathode materials for high-energy-density lithium-ion batteries. Coprecipitation, the widely utilized method in the precursor synthesis of NCM811 materials, however, suffers long synthetic processes and challenges in uniform element distribution. The spray pyrolysis method is able to prepare oxide precursors in seconds where all transition-metal elements are well distributed, but the difficulty of lithium distribution will also arise when the lithium salts are added in the subsequent sintering process. Herein, a fresh one-step spray pyrolysis approach is proposed for preparing high-performance NCM811 cathode materials by synthesizing lithium-contained precursors in which all elements are well distributed at a molecular level. The precursors with folded morphology and exceptional uniformity are successfully obtained at a low pyrolysis temperature of 300 °C by an acetate system. Furthermore, the final products commendably inherit the folded morphology of the precursors and exhibit excellent cyclic retentions of 94.6% and 88.8% after 100 and 200 cycles at 1 C (1 C = 200 mA g-1), respectively.

Atomic Horizons Interpretation on Enhancing Electrochemical Performance of Ni-Rich NCM Cathode via W Doping: Dual Improvements in Electronic and Ionic Conductivities from DFT Calculations and Experimental Confirmation

The rapid capacity degradation and poor rate capability hinder the application of Rich-Ni layered LiNi_x Co_y Mn_z O₂ (NCM) as cathode materials for high-energy lithium-ion batteries. In this study, density functional theory (DFT) calculations, combined with conventional electrochemical measurements, reveal from the atomic view that the dual improvements in electronic and ionic conductivities are the main facts for the property enhancement. The bandgap of the cathode material is reduced to 1.1623 eV due to the increased number of electrons near the Fermi level after W intercalation. Such improved electronic conductivity subsequently leads to a suppressed polarization and reduced resistance, enabling an improved cycle life of up to 93.97% after 100 cycles at 0.5 C. Furthermore, the doping with W⁶⁺ also introduced a strong WO bond into the layered structure so that the thickness of the Li slab is expanded to 2.6476 Å, which reduces the energy barrier from 0.355 to 0.308 eV for the migration of Li⁺ within the Li slab, as confirmed by the DFT calculation. Consequently, the rate performance is greatly improved due to the reduced diffusion energy, with a specific capacity of 159.11 mAg^-1 even at 5 C rate, indicating high potential for future applications.

Conformal PEDOT Coating Enables Ultra-High-Voltage and High-Temperature Operation for Single-Crystal Ni-Rich Cathodes

Single-crystal Ni-rich Li[Ni_xMn_yCo_1-x-y]O₂ (SC-NMC) cathodes represent a promising approach to mitigate the cracking issue of conventional polycrystalline cathodes. However, many reported SC-NMC cathodes still suffer from unsatisfactory cycling stability, particularly under high charge cutoff voltage and/or elevated temperature. Herein, we report an ultraconformal and durable poly(3,4-ethylenedioxythiophene) (PEDOT) coating for SC-NMC cathodes using an oxidative chemical vapor deposition (oCVD) technique, which significantly improves their high-voltage (4.6 V) and high-temperature operation resiliency. The PEDOT coated SC LiNi_0.83Mn_0.1Co_0.07O₂ (SC-NMC83) delivers an impressive capacity retention rate of 96.7% and 89.5% after 100 and 200 cycles, respectively. Significantly, even after calendar aging at 45 °C and 4.6 V, the coated cathode can still retain 85.3% (in comparison with 59.6% for the bare one) of the initial capacity after 100 cycles at a 0.5 C rate. Synchrotron X-ray experiments and interface characterization collectively reveal that the conformal PEDOT coating not only effectively stabilizes the crystallographic structure and maintains the integrity of the particles but also significantly suppresses the electrolyte's corrosion, resulting in improved electrochemical/thermal stability. Our findings highlight the promise of an oCVD PEDOT coating for single-crystal Ni-rich cathodes to meet the grand challenge of high-energy batteries under extreme conditions.

Combining Surface Holistic Ge Coating and Subsurface Mg Doping to Enhance the Electrochemical Performance of LiNi0.8Co0.1Mn0.1O2 Cathodes

Nickel-rich layered cathode LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) is the most promising cathode material due to its high specific capacity and lower cost than lithium cobalt oxides. However, NCM811 suffers from structural instability and capacity degradation during charge-discharge cycles. Herein, we report a strategy to construct a conductive network by employing a holistic Ge coating, which interconnects Mg-doped NCM811 particles. Dopant Mg ions, serving as a "pillar" in the Li slab of NCM811, substantially enhance the structural reversibility. The Ge particles are not only coated on the electrode surface but also enter into the electrode pores to form a multidimensional conductive structure, which improves the conductivity of the electrode and slows down the interface side reaction, thus minimizing the irreversible loss of NCM811 upon long cycling. The modified NCM811 electrode delivers a high discharge capacity (∼204 mAh g^-1 at 0.1C), excellent rate performance (∼155 mAh g^-1 at 10C), and high capacity retention (83% after 200 cycles) even at 4.4 V. Additionally, a cylindrical full battery with graphite/modified NCM811 undergoes 1000 cycles with 86% capacity retention at 2C.

Engineering a High-Voltage Durable Cathode/Electrolyte Interface for All-Solid-State Lithium Metal Batteries via In Situ Electropolymerization

Poly(ethylene oxide) (PEO)-based polymer electrolytes have been widely studied as a result of their flexibility, excellent interface contact, and high compatibility with a lithium metal anode. Owing to the poor oxidation resistance of ethers, however, the PEO-based electrolytes are only compatible with low-voltage cathodes, which limits their energy density. Here, a high-voltage stable solid-state interface layer based on polyfluoroalkyl acrylate was constructed via in situ solvent-free bulk electropolymerization between the LiNi_0.8Mn_0.1Co_0.1O₂ (NCM811) cathode and the PEO-based solid polymer electrolyte. The electrochemical oxidation window of the as-synthesized electrolyte was therefore expanded from 4.3 V for the PEO-based matrix electrolyte to 5.1 V, and the ionic conductivity was improved to 1.02 × 10^-4 S cm^-1 at ambient temperature and 4.72 × 10^-4 S cm^-1 at 60 °C as a result of the improved Li⁺ migration. This fabrication process for the interface buffer layer by an in situ electrochemical process provides an innovative and universal interface engineering strategy for high-performance and high-energy-density solid-state batteries, which has not been explicitly discussed before, paving the way toward the large-scale production of the next generation of solid-state lithium batteries.

Improved cycling stability of high nickel cathode material for lithium ion battery through Al- and Ti-based dual modification

The high nickel layered oxide cathode is considered to be one of the most promising cathode materials for lithium-ion batteries because of its higher specific capacity and lower cost. However, due to the increased Ni content, residual lithium compounds inevitably exist on the surface of the cathode material, such as LiOH, Li₂CO₃, etc. At the same time, the intrinsic instability of the high nickel cathode material leads to the structural destruction and serious capacity degradation, which hinder practical applications. Here, we report a simple and scalable strategy using hydrolysis and lithiation process of aluminum isopropoxide (C₉H₂₁AlO₃) and isopropyl titanate (C₁₂H₂₈O₄Ti) to prepare a novel α-LiAlO₂ and Li₂TiO₃ double-coated and Al³⁺ and Ti⁴⁺ co-doped cathode material (NCAT15). The Al and Ti doping stabilizes the layered structure due to the strong Al-O and Ti-O covalent bonds and relieves the Li⁺/Ni²⁺ cation disorder. Besides, the capacity of the cathode material for 100 cycles reaches 163.5 mA h g^-1 and the capacity retention rate increases from 51.2% to 90.6% (at 1C). The microscopic characterization results show that the unique structure can significantly suppress side reactions at the cathode/electrolyte interface as well as the deterioration of structure and microcracks. This innovative design strategy combining elemental doping and construction of dual coating layers can be extended to other high nickel layered cathode materials and help improve their electrochemical performance.

Interface-Stabilized Layered Lithium Ni-Rich Oxide Cathode via Surface Functionalization with Titanium Silicate

Nickel-rich lithium metal oxide cathode materials have recently be en highlighted as next-generation cathodes for lithium-ion batteries. Nevertheless, their relatively high surface reactivity must be controlled, as fading of the cycling retention occurs rapidly in the cells. This paper proposes functionalized nickel-rich lithium metal oxide cathode materials by a multipurpose nanosized inorganic material-titanium silicon oxide-via a simple thermal treatment process. We examined the topologies of the nano-titanium silicate-functionalized nickel-rich lithium metal oxide cathodes with scanning electron microscopy and quantitatively analyzed their improved mechanical properties using microindentation. The cell containing nickel-rich lithium metal oxide cathodes suffered from poor cycling behavior as the electrolytes persistently decomposed; however, this behavior was effectively inhibited in the cell by nano-titanium silicate-functionalized nickel-rich lithium metal oxide cathodes. Further ex situ analyses indicated that the particle hardness of the nano-titanium silicate-functionalized nickel-rich lithium metal oxide cathode materials was maintained, and decomposition of the electrolyte by the dissolution of transition metals was thoroughly inhibited even after 100 cycles. Based on these results, we concluded that the use of nano-titanium silicate as a coating material for nickel-rich lithium metal oxide cathode materials is an effective way to enhance the cycling performance of lithium-ion batteries.

Dual-Element-Modified Single-Crystal LiNi0.6Co0.2Mn0.2O2 as a Highly Stable Cathode for Lithium-Ion Batteries

Single-crystalline LiNi_0.6Co_0.2Mn_0.2O₂ cathodes have received great attention due to their high discharge capacity and better electrochemical performance. However, the single-crystal materials are suffering from severe lattice distortion and electrode/electrolyte interface side reactions when cycling at high voltage. Herein, a unique single-crystal LiNi_0.6Co_0.2Mn_0.2O₂ with Al and Zr doping in the bulk and a self-formed coating layer of Li₂ZrO₃ in the surface has been constructed by a facile strategy. The optimized cathode material exhibits excellent structural stability and cycling performance at room/elevated temperatures after long-term cycling. Specifically, even after 100 cycles (1C, 3.0-4.4 V) at 50 °C, the capacity retention for the Al and Zr co-doped sample reaches 92.1%, which is much higher than those of the single Al-doped (85.4%), single Zr-doped (87.1%), and bare samples (76.3%). The characterization results and first-principles calculations reveal that the excellent electrochemical properties are attributed to the stable structure and interface, in which the Al and Zr co-doping hinders cation mixing and suppresses detrimental phase transformations to reduce internal stress and mitigate microcracks, and the coating layer of Li₂ZrO₃ can protect the surface and suppress interfacial parasitic reactions. Overall, this work provides important insights into how to simultaneously build a stable bulk structure and interface for the single-crystal NCM cathode via a facile preparation process.