Lithium Migration Research Articles

Atomic insights of structural, electronic properties of B, N, P, S, Si-doped fullerenes and lithium ion migration with DFT-D method.

Battery interface research can effectively guide battery design and material selection to improve battery performance. However, current electrode material interface studies still have significant limitations. In this paper, by employing DFT-D method, the influences of doping elements (boron, nitrogen, phosphorus, sulfur, and silicon) on the properties of C60 fullerene, such as structural stability, electronic properties, and the adsorption and migration of lithium ion, are comprehensively investigated. It is demonstrated that doping can bolster the fullerene molecule's structural integrity and enhance charge transfer comparing with C60, thereby augmenting the material's electrical conductivity. Among the five doping elements, B-doping exhibits the most favorable adsorption energies, indicating a strong lithium binding affinity. This observation is supported with energy barrier of lithium ion migration. B-doping leads to an elevated barrier (0.37eV) comparing with pristine C60 (0.19eV), whereas Si-doping significantly reduced barrier (0.038eV) indicates enhanced lithium-ion mobility. These findings solid the efficacy of doping as a strategy to enhance the performance of fullerene electrodes. All DFT calculations were performed using the VASP software package. The chosen computational technique was a combination of the generalized approximate gradient function PBE with the dispersion correction (DFT-D3) developed by Grimme. The results of the calculations were analyzed with the help of VASPKIT.

Superionic conducting vacancy-rich β-Li3N electrolyte for stable cycling of all-solid-state lithium metal batteries.

The advancement of all-solid-state lithium metal batteries requires breakthroughs in solid-state electrolytes (SSEs) for the suppression of lithium dendrite growth at high current densities and high capacities (>3 mAh cm-2) and innovation of SSEs in terms of crystal structure, ionic conductivity and rigidness. Here we report a superionic conducting, highly lithium-compatible and air-stable vacancy-rich β-Li3N SSE. This vacancy-rich β-Li3N SSE shows a high ionic conductivity of 2.14 × 10-3 S cm-1 at 25 °C and surpasses almost all the reported nitride-based SSEs. A Li- and N-vacancy-mediated fast lithium-ion migration mechanism is unravelled regarding vacancy-triggered reduced activation energy and increased mobile lithium-ion population. All-solid-state lithium symmetric cells using vacancy-rich β-Li3N achieve breakthroughs in high critical current densities up to 45 mA cm-2 and high capacities up to 7.5 mAh cm-2, and ultra-stable lithium stripping and plating processes over 2,000 cycles. The high lithium compatibility mechanism of vacancy-rich β-Li3N is unveiled as intrinsic stability to lithium metal. In addition, β-Li3N possesses excellent air stability through the formation of protection surfaces. All-solid-state lithium metal batteries using the vacancy-rich β-Li3N as SSE interlayers and lithium cobalt oxide (LCO) and Ni-rich LiNi0.83Co0.11Mn0.06O2 (NCM83) cathodes exhibit excellent battery performance. Extremely stable cycling performance is demonstrated with high capacity retentions of 82.05% with 95.2 mAh g-1 over 5,000 cycles at 1.0 C for LCO and 92.5% with 153.6 mAh g-1 over 3,500 cycles at 1.0 C for NCM83. Utilizing the vacancy-rich β-Li3N SSE and NCM83 cathodes, the all-solid-state lithium metal batteries successfully accomplished mild rapid charge and discharge rates up to 5.0 C, retaining 60.47% of the capacity. Notably, these batteries exhibited a high areal capacity, registering approximately 5.0 mAh cm-2 for the compact pellet-type cells and around 2.2 mAh cm-2 for the all-solid-state lithium metal pouch cells.

Facilitating Cathode Regeneration via Defect‐Driven Prelithiation

AbstractDirect regeneration of electrode materials has been in the spotlight due to its potential resource recovery and environmental benefits, especially for LiNixCoyMnzO2 (NCM) cathode materials. Yet, prior studies have predominantly emphasized innovating regeneration methods, overlooking the intrinsic defects of spent NCM and their effects in the regeneration process. This study proposes a mechanism aimed at facilitating lithiation regeneration by modulating the surface defects of spent NCM. The generation of oxygen defects in degraded NCM intensifies the adsorption of lithium source, effectively reducing the energy barrier for Li+ migration from surface to bulk. Simultaneously, mechanical energy is employed to alter the local thermodynamic state to provide a driving force for lithium migration, allowing it to undergo a prelithiation reaction before roasting. The temperature range in which the phase transition occurs during the roasting process becomes more concentrated. This contributes to increasing opportunities for lithium insertion and accelerates the repair of crystal structure, resulting in favorable properties of regenerated materials. This strategy innovatively exploits the inherent defects of spent NCM, proposes the critical role of synergistically regulating defect kinetic and thermodynamic features in facilitating regeneration, providing a unique perspective for the design of direct NCM regeneration technology.

Aligned Hollow Silicon Nanorods Containing Ionic Liquid Enhanced Solid Polymer Electrolytes with Superior Cycling and Rate Performance.

The low lithium-ion conductivity of polyethylene oxide (PEO)-based polymer electrolytes limits their application in solid-state lithium batteries and related fields. Here, ionic liquids (ILs) are injected into hollow silicon nanorods (HSNRs) to prepare a composite solid polymer electrolyte (CSPE) with aligned HSNRs containing ILs (F-ILs@HSNRs). Applying a magnetic field promoted uniform dispersion and orientation of F-ILs@HSNRs in CSPE. The addition of F-ILs@HSNRs reduced PEO crystallinity and formed Li+ transport pathways at the F-ILs@HSNRs/PEO interface. Calculations and multi-physics simulations reveal that ILs within F-ILs@HSNRs contribute most to lithium-ion conduction, followed by the F-ILs@HSNRs/PEO interface. When F-ILs@HSNRs are arranged perpendicular to the electrodes, the CSPE exhibits the shortest Li+ migration pathways, resulting in stable and efficient lithium-ion conduction. The conductivity (2.14 × 10-4 S cm-1) and lithium-ion migration number tLi+ (0.307) are the highest, being 125 times and 184% higher, respectively, than those of PEO-LiTFSI, when compared to CSPEs with randomly arranged or parallel-aligned F-ILs@HSNRs. Furthermore, Li|CSPE|Li batteries and LiFePO4|CSPE|Li batteries display stable cycling for over 2000h, with coulombic efficiency approaching 100%. Excellent electrochemical reversibility is also confirmed in the rate performance test.

Optimising lithium lanthanum cerate garnet ceramic electrolytes for fast lithium-ion conduction

The garnet-type electrolytes are promising for solid-state lithium-metal batteries, while it is still challenging to realize fast lithium-ion conduction with moderate sintering process. To solve the problem, we proposed a novel cerium (Ce)-based cubic garnet electrolyte – Li6.25La3Ce1.25Ta0.75O12 (LLCTO-0.75). The Ta5+ doping of the tetragonal Li7La3Ce2O12 (LLCO) results in a stable cubic phase at room temperature, whilst the presence of Ce4+ is associated with enlarging lattice parameters to facilitate lithium-ion migration and promoting sintering. As a result, the LLCTO-0.75 achieves a dense ceramic microstructure with only 30 min sintering at 1150 °C, and an outstanding lithium-ion conductivity of 1.09 mS cm−1 at 30 °C. Benefiting from a small Li/LLCTO-0.75 interfacial resistance of 52.8 Ω cm2 at 30 °C, the Li-Li symmetric cell cycles for over 700 h without short circuit, and the quasi-solid state LiFePO4/LLCTO 0.75/Li battery delivers a satisfying specific capacity of 127.0 mAh g−1 after 300 cycles. This work provides new insights into the development of practical solid-state oxide electrolytes for safe high-energy batteries.

An In Situ Polymerization Gel Polymer Electrolyte Based on Pentaerythritol Tetracrylate for High-Performance Lithium-Ion Batteries.

Problems occur frequently during the application of traditional liquid electrolyte batteries, such as fluid leakage and low energy density. As a product of liquid electrolyte transition to solid electrolyte, gel polymer electrolyte has its own advantages for achieving high conductivity and good thermal stability. In this study, pentaerythritol tetracrylate (PETEA) was used as the precursor to prepare polymer-based materials with the assistance of azobis(isobutyronitrile) (AIBN) as the initiator. Because fluorine is beneficial to improving the migration efficiency of Li+ and the electrochemical performance of the gel polymer electrolyte, dodecafluoroheptyl methacrylate (DFHMA) is introduced to the PETEA-based gel polymer electrolyte (GPE) system. The DFHMA-introduced GPE shows better electrochemical performance, battery cycle performance, conductivity, and lithium-ion migration number compared with the pristine PETEA-based GPE. In particular, the DFHMA-introduced GPE exhibits the best performance because the molar ratio of PETEA to DFHMA is 5:1. Herein, the electrochemical window is 4.6 V, the ionic conductivity reaches 1.207 mS cm-1, and the number of lithium-ion migrations reaches the value of 0.663. Because the electric current density is 2 C, the specific capacity of LiNi0.5Co0.2Mn0.3O2 (NCM523)/GPE/Li reaches 143.1 mAh g-1 after 100 cycles.

A star polymer POSS-PMMA based gel electrolyte with balanced electrochemical and mechanical properties for lithium metal battery

Gel polymer electrolyte (GPE) is one of the promising candidates to overcome the defects of liquid and solid electrolyte for lithium metal batteries (LMBs). The obstacle for the practical application of GPEs lies in achieving a balance between ion transport, mechanical properties and interface stability. In this work, a star shaped polymer matrix polyhedral oligomeric silsesquioxane-polymethyl methacrylate (POSS-PMMA) is successfully synthesized with POSS as the core via atom transfer radical polymerization (ATRP) method. 1-ethyl-3-methylimidazole bis(trifluoromethanesulfon)imide ([EMIM][TFSI]) and bistrifluoromethanesulfonimide lithium salt (LiTFSI) are blended with the matrix to increase ionic conductivity. Attributed to the star structure and the lithium ion migration channel provided by POSS, the synthesized GPE possesses excellent balanced mechanical and electrochemical properties. To further stabilize the Li/GPE interface, a polymer and plastic crystalline electrolyte (PPCE) is coated as interface modification layer on both sides of GPE. Benefitting from the design, the synthesized GPE reaches a highly stable Li striping/plating cycling for 1000 h at 0.1 mA cm−2 with ionic conductivity of 3.5 × 10−4 S cm−1, Li+ transference number of 0.35, and electrochemical stability window of 4.9 V. Furthermore, the Li||POSS-PMMA-PPCE||LiFePO4 (LFP) full cell shows a high capacity retention of 99.5 % after 100 cycles at 0.2 C under room temperature (RT), and the high voltage Li||POSS-PMMA-PPCE||LiNi1-x-yMnxCoyO2 (NCM811) cell shows a high capacity retention of 88.3 % after 50 cycles at 0.1 C under RT. This work opens up a new frontier to stabilize the Li/GPE interface and enables safe operation of room temperature lithium metal batteries.

Morphological evolution and surface orientation effects of nickel manganese oxide in the preparation of LNMO cathode material

The study investigated the evolution of LNMO (LiNi0.5Mn1.5O4) morphology and surface orientation as a function of increasing temperature. The results show that at an initial calcination temperature of 750 °C, LNMO exhibits spherical polyhedral with (111), (110), and (100) facets and relatively small particle sizes. In response to increasing temperatures, the particle size increases, the number of crystal facets decreases, and the material ultimately transitions to a typical spinel structure. Notably, the LNMO material calcined at 750 °C demonstrates a high lithium-ion migration rate, retaining 81.24% of its capacity after 500 cycles at a 2 C rate. This exceptional performance is attributed to the exposure of multiple crystal facets, suitable particle size, and the presence of Mn³⁺, which collectively stabilize the crystal structure and provide suitable pathways for Li⁺ transport.

A Li-Rich Fluorinated Lithium Zirconium Chloride Solid Electrolyte for 4.8 V-Class All-Solid-State Batteries.

Chloride solid-state electrolytes (SEs) represent an important advance for applications in all-solid-state batteries (ASSBs). Among various chloride SEs, lithium zirconium chloride (Li2ZrCl6) is an attractive candidate considering the high natural abundance of Zr. However, Li2ZrCl6 meets the challenge in practical ASSBs because of its limited ionic conductivity and instability when paired with high-voltage cathodes. This is a major drawback, which can result in a high internal resistance, a low capacity utilization of cathode, and poor cycle stability, especially at high voltage. Existing methods cannot achieve simultaneous enhancement on both ionic conductivity and high-voltage stability due to a trade-off between lithium-ion migration and structural stability. Here a two-pronged strategy based on partial fluorination and incorporation of lithium ions in excess of stoichiometric ratios is introduced that enables high-voltage stability while increasing ionic conductivity concurrently. The Li-rich fluorinated halide SE (Li2.3ZrCl6.1F0.2) exhibits a significant advancement in performance, with an ionic conductivity that is double that of the pristine Li2ZrCl6 and much better high-voltage stability. By leveraging Li2.3ZrCl6.1F0.2 with the LiCoO2 cathode and the Li-In anode, the all-solid-state cell exhibits a remarkable initial specific capacity (198.0 mAh g-1 at 0.1 C) and a high capacity retention (78.5% after 150 cycles) within 3.0-4.8V.

Realizing interfacial coupled electron/ion transport through reducing the interfacial oxygen density of carbon skeletons for high-performance lithium metal anodes

Lithium plating/stripping occurs at the anode/electrolyte interface which involves the flow of electrons from the current collector and the migration of lithium ions from the solid-electrolyte interphase (SEI). The dual continuous rapid transport of interfacial electron/ion is required for homogeneous Li deposition. Herein, we propose a strategy to improve the Li metal anode performance by rationally regulating the interfacial electron density and Li ion transport through the SEI film. This key technique involves decreasing the interfacial oxygen density of biomass-derived carbon host by regulating the arrangement of the celluloses precursor fibrils. The higher specific surface area and lower interfacial oxygen density decrease the local current density and ensure the formation of thin and even SEI film, which stabilized Li+ transfer through the Li/electrolyte interface. Moreover, the improved graphitization and the interconnected conducting network enhance the surface electronegativity of carbon and enable uninterruptible electron conduction. The result is continuous and rapid coupled interfacial electron/ion transport at the anode/electrolyte reaction interface, which facilitates uniform Li deposition and improves Li anode performance. The Li/C anode shows a high initial Coulombic efficiency of 98% and a long-term lifespan of over 150 cycles at a practical low N/P (negative-to-positive) ratio of 1.44 in full cells.

VS2/ Blue Phosphorus composites for high speed lithium ions storage

Based on first-principles calculations, the potential of the H-VS2/Blue P heterojunction composite as a lithium-ion battery anode is systematically investigated. This heterojunction composite enhances the stability of the VS2 structure and increases its overall mechanical strength.The Young's modulus of the composite is 144.69 N/m, markedly exceeding that of the single layer. Furthermore, it modifies the electronic properties of the Blue P monolayer, converting it from an insulating to a metallic state.The H-VS2/Blue P heterojunction composite exhibits a high lithium adsorption energy of 4.34 eV and a low diffusion barrier of 0.15–0.19 eV, facilitating rapid lithium-ion migration during charge/discharge cycles. And the theoretical capacity of the heterojunction composite is up to 1211 mAh/g. The combination of elevated adsorption energy, low diffusion barrier, and high theoretical capacity indicates that the H-VS2/Blue P heterojunction composite is a highly promising anode material for lithium-ion batteries.

Inhibiting the current spikes within the channel layer of LiCoO2-based three-terminal synaptic transistors

Synaptic transistors, which emulate the behavior of biological synapses, play a vital role in information processing and storage in neuromorphic systems. However, the occurrence of excessive current spikes during the updating of synaptic weight poses challenges to the stability, accuracy, and power consumption of synaptic transistors. In this work, we experimentally investigate the main factors for the generation of current spikes in the three-terminal synaptic transistors that use LiCoO2 (LCO), a mixed ionic-electronic conductor, as the channel layer. Kelvin probe force microscopy and impedance testing results reveal that ion migration and adsorption at the drain–source-channel interface cause the current spikes that compromise the device's performance. By controlling the crystal orientation of the LCO channel layer to impede the in-plane migration of lithium ions, we show that the LCO channel layer with the (104) preferred orientation can effectively suppress both the peak current and power consumption in the synaptic transistors. Our study provides a unique insight into controlling the crystallographic orientation for the design of high-speed, high-robustness, and low-power consumption nano-memristor devices.

Machine learning-based design of electrocatalytic materials towards high-energy lithium||sulfur batteries development

The practical development of Li | |S batteries is hindered by the slow kinetics of polysulfides conversion reactions during cycling. To circumvent this limitation, researchers suggested the use of transition metal-based electrocatalytic materials in the sulfur-based positive electrode. However, the atomic-level interactions among multiple electrocatalytic sites are not fully understood. Here, to improve the understanding of electrocatalytic sites, we propose a multi-view machine-learned framework to evaluate electrocatalyst features using limited datasets and intrinsic factors, such as corrected d orbital properties. Via physicochemical characterizations and theoretical calculations, we demonstrate that orbital coupling among sites induces shifts in band centers and alterations in the spin state, thus influencing interactions with polysulfides and resulting in diverse Li-S bond breaking and lithium migration barriers. Using a carbon-coated Fe/Co electrocatalyst (synthesized using recycled Li-ion battery electrodes as raw materials) at the positive electrode of a Li | |S pouch cell with high sulfur loading and lean electrolyte conditions, we report an initial specific energy of 436 Wh kg−1 (whole mass of the cell) at 67 mA and 25 °C.

Bimetal Fluorides with Adjustable Vacancy Concentration Reinforcing Ion Transport in Poly(ethylene oxide) Electrolyte.

The poor ambient ionic transport properties of poly(ethylene oxide) (PEO)-based SPEs can be greatly improved through filler introduction. Metal fluorides are effective in promoting the dissociation of lithium salts via the establishment of the Li-F bond. However, too strong Li-F interaction would impair the fast migration of lithium ions. Herein, magnesium aluminum fluoride (MAF) fillers are developed. Experimental and simulation results reveal that the Li-F bond strength could be readily altered by changing fluorine vacancy (VF) concentration in the MAF, and lithium salt anions can also be well immobilized, which realizes a balance between the dissociation degree of lithium salts and fast transport of lithium ions. Consequently, the Li symmetric cells cycle stably for more than 1400 h at 0.1 mA cm-2 with a LiF/Li3N-rich solid electrolyte interphase (SEI). The SPE exhibits a high ionic conductivity (0.5 mS cm-1) and large lithium-ion transference number (0.4), as well as high mechanical strength owing to the hydrogen bonding between MAF and PEO. The corresponding Li//LiFePO4 cells deliver a high discharge capacity of 160.1 mAh g-1 at 1 C and excellent cycling stability with 100.2 mAh g-1 retaining after 1000 cycles. The as-assembled pouch cells show excellent electrochemical stability even at rigorous conditions, demonstrating high safety and practicability.

Lithium-rich manganese-based layered oxide cathode materials for lithium-ion batteries modified by MoS2 coatings with two-dimensional graphene-like structures

Lithium-rich manganese-based layered oxide cathode materials (LRMCs) have some unique advantages such as high theoretical capacity (≥ 250 mAh g−1) and high energy density. Therefore, they are deemed as a kind of cathode material for lithium-ion batteries with an excellent prospect of application. However, the redox of oxygen anion is able to generate irreversible lattice oxygen loss, leading to irreversible loss of capacity, bringing about a sharp drop of working voltage, and seriously restricting the commercialization of LRMCs. In this paper, MoS2 coating with two-dimensional graphene-like structure was coated on the surface of LRMCs materials for improving the cycling stability and rate performance. The MoS2 coating can provide a two-dimensional diffusion channel for the migration of lithium-ions, which facilitates the fast release of lithium-ions during cycling process. The results show that the first discharge capacity, initial Coulomb efficiency and rate performance of LRMCs are improved. When the current density is 1 C, the first discharge specific capacity of LRMCs@MoS2 reaches 227.69 mAh g−1, and the capacity retention ratio is 84.98 % after 100 cycles. When the current density is 5 C, it can still provide a discharge specific capacity of 137.87 mAh g−1, demonstrating excellent electrochemical performance. This study comes up a simple and practical idea to realize the modification of cathode materials for high performance lithium-ion batteries.

Enhancing ion conductivity in polyethylene oxide-based polymers through semi-interpenetrating networks with liquid crystalline polymer for lithium metal batteries

Solid electrolytes play a pivotal role in these batteries but are hindered by challenges such as low ion conductivity and inadequate mechanical properties. In this study, a synergistic multi-component system was fabricated using a microphase separation technique to integrate liquid crystal polymers with self-assembly characteristics and polyethylene oxide (PEO) known for its excellent ion transport performance. Molecular-level control was achieved by adjusting the ratio of liquid crystal monomers, facilitating the construction of ordered ion transport pathways that significantly enhance room temperature ion transport efficiency. The resulting solid polymer electrolyte adopts a semi-interpenetrating network structure, where the rigid framework of liquid crystalline polymers is interpenetrated with flexible PEO chains. It exhibits a high room-temperature ion conductivity of 4.7 × 10−4 S/cm and a lithium-ion migration number of 0.71. Benefitting from its tailored microstructure and mechanical properties, the assembled lithium symmetric battery demonstrated stable operation over 2800 h at a room temperature current density of 0.1 mA/cm−2. This research presents a promising pathway for the advancement of advanced electrolyte materials, providing valuable insights into improving the efficiency and safety of lithium metal batteries in practical applications.

Synergistic Enhancement of Biaxial Stretching and Multilayer Composites in All-Solid-State Polymer Electrolytes.

As an important component of lithium-ion batteries, all-solid-state electrolytes should possess high ionic conductivity, excellent flexibility, and relatively high mechanical strength. All-solid-state polymer electrolytes (ASSPEs) based on polymers seem to be able to meet these requirements. However, pure ASSPEs have relatively low ionic conductivity, and the addition of inorganic fillers such as lithium salts will reduce their flexibility and mechanical strength. To address the above issues, in this paper, the solvent-free method was used to prepare a poly(vinylidenefluoride-co-hexafluoropropylene)/lithium bis(trifluoromethanesulfonyl) imide/poly(ethylene oxide) all-solid-state polymer electrolyte, which was then subjected to 4 × 4 magnification synchronous bidirectional stretching. Subsequently, it was multilayered with PEO-based composite polymer electrolytes to obtain multilayered composite polymer electrolytes (MCPEs). Bidirectional stretching provides superior in-plane and out-of-plane mechanical properties to MCPEs by inducing molecular chain orientation, which suppresses the growth of lithium dendrites. Concurrently, it facilitates the formation of the β-crystal form of PVDF-HFP, thereby weakening the ion solvation effect and reducing the lithium-ion migration energy barrier. Multilayered compounding improves the interfacial contact between MCPEs and electrodes, thereby reducing the interfacial impedance. Experiments have demonstrated that the MCPEs prepared in this paper exhibit high ionic conductivity at room temperature (1.83 × 10-4 S cm-1), low interfacial resistance (547 Ω cm-2), excellent mechanical properties (26 MPa), and excellent cycling rate performance (a capacity retention rate of 90% after 110 cycles at 0.1 C), which can meet the performance requirements of lithium-ion batteries for ASSPEs.

First principles study of the electronic structure and Li-ion diffusion properties of co-doped LIFex-1MxPyNy-1O4 (M=Co/Mn, N[dbnd]S/Si) Li-ion battery cathode materials

In this work, a first-principles method based on density functional theory was systematically employed to investigate the stability, electronic properties, lithium-ion migration rates, and capacity-voltage curves of the LiFex-1MxPyNy-1O4 (M = Co/Mn, NS/Si) system. The results indicate that the lattice constants of the LiFex-1MxPyNy-1O4 (M = Co/Mn, NS/Si) system show little variation, and the system exhibits low formation and binding energies. Among the investigated systems, LFP-Mn/S demonstrates the best structural and thermodynamic stability. The bandgap of the doped systems decreases, leading to enhanced electronic conductivity. The LiFe0.875Co0.125P0.875Si0.125O4 and LiFe0.875Mn0.125P0.875Si0.125O4 systems remain semiconductors, while the LiFe0.875Co0.125P0.875S0.125O4 and LiFe0.875Mn0.125P0.875S0.125O4 systems exhibit semi-metallic properties due to the introduction of sulfur. Differential charge density calculations reveal changes in the covalent bond strength of the doped systems, with the introduction of Si and S respectively increasing and decreasing the covalency of their bonds with surrounding oxygen atoms. Additionally, doping reduces the Li-ion diffusion energy barriers, with the LiFe0.875Co0.125P0.875Si0.125O4 system exhibiting the lowest migration energy barrier. The Li-ion diffusion rate is four orders of magnitude faster than that of the intrinsic system. This is attributed to changes in the average lengths of Li–O, Co–O, and Fe–O bonds. Finally, doping also alters the de-lithiation voltage, with values ranging from 2.69 V to 3.65 V for the doped systems, and the LiFe0.875Co0.125P0.875Si0.125O4 system shows the highest complete de-lithiation voltage of 3.65 V. The overall performance improvements of the doped system have significant implications for enhancing the performance of Li-ion batteries.

Constructing nano spinel phase and Li+ conductive network to enhance the electrochemical stability of ultrahigh-Ni cathode

The tungsten with high oxidation states (W6+) had been proved to effectively improve the electrochemical performance of ultrahigh-nickel (Ni ≥ 90 %) cathode materials due to the unique microstructures. However, the exat location and underlying action mechanism of tungsten are still not well-understood, and there have been no reports on in-situ modification from bulk to surface simultaneously for these novel cathode materials. Here, a novel integrated strategy is proposed for in-situ modification of LiNi0.9Co0.09W0.01O2 (NCW). Innovatively, the introduction of nano spinel phase and titanium pinned into the lattice further suppresses the anisotropic variation of unit cell and promotes the lithium-ion migration kinetics within the bulk. Additionally, the Li2TiO3 conductive network enhances migration kinetics across interface and protects the active material against electrolyte erosion. Furthermore, the combination of in-situ analysis and DFT calculation reveals the ordered distribution of tungsten and the suppression effects of titanium on phase transition and cobalt redox. Consequently, the titanium-modified NCW exhibits significantly improved electrochemical performance, such as capacity retention of 93.0 % at 1C after 500 cycles in pouch-type full-cell, along with stable lattice oxygen during operation.

Mildly expanded graphite with exceptional performance from waste lithium ion batteries by space-confined intercalation of deep eutectic solvent

Reclaiming the spent graphite (SG) in the anodes of end-of-life lithium-ion batteries (LIBs) is of tremendous significance for addressing resource shortage and eco-friendliness. The impurities embedded into the graphite interlayer after multiple charge–discharge cycles hinder the free migration of lithium ions, resulting in inferior lithium storage capacity. Herein, a space-confined intercalation of deep eutectic solvent (DES) strategy is proposed, to dissolve the impurities by utilizing its great ability to form hydrogen bonds (O–H…Cl-, O–H…O and O–H…F) with PVDF binder, SEI film and the residual electrolytes within the SG, simultaneously enlarging the interlayer distance to upgrade the anode graphite. After the further pyrolysis, the as-obtained mildly expanded graphite (MEG-800) exhibited well-defined graphite microcrystalline layer structure and high graphitization degree. The moderately enlarged graphite layers provided more space for the insertion and extraction of lithium ions, endowing MEG-800 with exceptional performance in LIBs, such as extremely high charge capacity of 477.4 mAh/g at a current density of 0.1 A/g and superior reversibility and desirable cycle stability. After 100 cycles at 0.1 A/g, its capacity still retained 470.9 mAh/g with a Coulombic efficiency as high as 99.76 %. The structure-dependent lithium-ion diffusion features of MEG-800 were also examined by electrochemical kinetics analysis. This study opened up a prospective avenue for the green and efficient recycling of spent anode graphite in retired LIBs, offering a solution to the problem of shortage of battery materials and promoting sustainable development.