Li-ion Transport Research Articles

Intergranular amorphous film in GeO2-enriched Li1.5Al0.5Ti1.5(PO4)3 composite electrolytes for high-performance solid-state lithium-ion batteries

Solid-state electrolytes have emerged as a key area of development in the field of Li-ion batteries owing to safety concerns surrounding liquid electrolytes. Among solid-state electrolytes, Li1.5Al0.5Ti1.5(PO4)3 (LATP), a NASICON-type material, is a leading candidate owing to its promising ionic conductivity, chemical and environmental stability, and cost-effectiveness. However, its ionic conductivity is limited by grain-boundary scattering, which hinders its broader adoption. Herein, we introduce a novel grain-boundary engineering strategy for the LATP electrolyte system using typical solid-state method, wherein a Ge-rich liquid phase spontaneously forms at the grain boundaries of GeO2-enriched LATP during synthesis, producing an intergranular amorphous film in the final material that significantly enhances Li-ion transport at the grain boundaries. With an optimal content of 4 wt% GeO2, the ionic conductivity reaches 8.92 × 10−4 S cm−1—an eightfold increase compared to that of pristine LATP. This high ionic conductivity also bestows 4 wt% GeO2-LATP with excellent cell performance, with a symmetric Li/4 wt% GeO2-LATP/Li cell exhibiting stable operation for over 500 h with low overpotentials. Our findings underscore the importance of grain-boundary engineering in advancing solid-state electrolytes and pave the way for the commercialization of next-generation all-solid-state Li-ion batteries.

Interface-Targeting Carrier-Catalytic Integrated Design Contributing to Lithium Dihalide-Rich SEI toward High Interface Stability for Long-Life Solid-State Lithium-Metal Batteries.

The generation of solid electrolyte interphase (SEI) largely determines the comprehensive performance of all-solid-state batteries. Herein, a novel "carrier-catalytic" integrated design is strategically exploited to in situ construct a stable LiF-LiBr rich SEI by improving the electron transfer kinetics to accelerate the bond-breaking dynamics. Specifically, the high electron transport capacity of Br-TPOM skeleton increases the polarity of C-Br, thus promoting the generation of LiBr. Then, the enhancement of electron transfer kinetics further promotes the fracture of C-F from TFSI- to form LiF. Finally, the stable and homogeneous artificial-SEI with enriched lithium dihalide is constructed through the in situ co-growth mechanism of LiF and LiBr, which facilitatse the Li-ion transport kinetics and regulates the lithium deposition behavior. Impressively, the PEO-Br-TPOM paired with LiFePO4 delivers ultra-long cycling stability over 1000 cycles with 81 % capacity retention at 1 C while the pouch cells possess 88 % superior capacity retention after 550 cycles with initial discharge capacity of 145 mAh g-1at 0.2 C in the absence of external pressure. Even under stringent conditions, the practical pouch cells possess the practical capacity with stable electric quantities plateau in 30 cycles demonstrates its application potential in energy storage field.

Dielectric LiNbO3 electrolyte regulating internal electric field in composite solid-state electrolyte to fundamentally boost Li-ion transport

Dielectric LiNbO3 electrolyte regulating internal electric field in composite solid-state electrolyte to fundamentally boost Li-ion transport

Facile Synthesis and Electrochemical Analysis of Zn-Doped V2O5 Anode Materials for High-Rate Li Storage

The surging demand for Li rechargeable batteries with high energy densities and rapid rate capability has propelled research on materials that can replace the conventional anode materials like graphite. Vanadium pentoxides (V2O5) have emerged as promising anode candidates owing to their excellent rate capability. Specifically, V2O5 allows the electrochemical prelithiation process, in which three Li-ions can be inserted to form Li3V2O5, followed by reversible insertion and extraction of two Li-ions. Nevertheless, the unsatisfactory Li-ion diffusion coefficients and electrical conductivities of these materials remain major drawbacks. Here, we propose a Zn-doped V2O5 anode, fabricated using a two-step sol–gel method, for high-rate Li-ion batteries. Zn was incorporated into V2O5 to enhance the Li-ion transport kinetics through the electrode. The crystal structure (orthorhombic) of Zn-doped V2O5 was identified by X-ray diffraction analysis, and the Zn doping was confirmed by X-ray photoelectron microscopy. The effect of Zn doping was thoroughly examined using various analytical methods, such as cyclic voltammetry and galvanostatic intermittent titration technique. The Zn-doped V2O5 electrode exhibited remarkable cycling durability, enduring for 1000 cycles, while retaining an enhanced capacity, even under a high rate of 2C.

Organic Solvent-Based Li–Air Batteries with Cotton and Charcoal Cathode

We report on the construction and investigation of Li–air batteries consisting of a charcoal cathode and cotton texture soaked with different organic solvents containing a lithium triflate (LiOTf) electrolyte. Charcoal was found to be an appropriate cathode for Li–air batteries. Furthermore, cycling tests showed stable operation at over 800 cycles when dimethyl sulfoxide (DMSO) and diethylene glycol dimethyl ether (DEGME) were used as solvents, whereas low electrochemical stability was observed when propylene carbonate was used. The charging, discharging, and long-term discharging steps were mathematically modeled. Electrochemical impedance spectroscopy showed Gerischer impedance, suggesting intensive oxygen transport at the surface of the charcoal cathode. Diffusion, charge transfer, and solid electrolyte interphase processes were identified using distribution of relaxation time analysis. In the polypropylene (PP) membrane soaked with LiOTf in DEGME, three different states of Li ions were identified by 7Li-triple-quantum time proportional phase increment nuclear magnetic resonance measurements. On the basis of the latter results, a mechanism was suggested for Li-ion transport inside the PP membrane. The activity of the charcoal cathode was confirmed by Raman and cyclic voltammetry measurements.

Additives strategies to improving cycling stability of Li metal batteries by modifying electrode electrolyte interphases

Li metal batteries (LMBs) have attracted much attention due to the ultra-high theoretical capacity of the Li metal anode (LMA). However, the uncontrollable dendrites growth and low coulombic efficiency hinder their practical application. Here, we explore 3,5-difluoropyridine (2F-BD) as a novel electrolyte additive to enable high-performance LMBs. The 2F-BD additive participates in and modifies the solvation structure of Li ions by reducing the coordinated number of PF6− at the electrode surface, leading to the formation of a LiF and Li3N-rich solid electrolyte interphase (SEI). The LiF component increases the robustness of SEI and suppresses the formation of Li dendrites, while the Li3N component facilitates the transportation and reaction kinetics of Li ions. As a result, the Li||Li symmetric cell presents a stable cycling performance of up to 500 ​h at a current density of 1 ​mA ​cm−2. After coupling with LiFePO4 cathode, the obtained full cell achieves high specific capacities of 106.06 ​mA ​h ​g−1 and 84.98 ​mA ​h ​g−1 at 2.55 ​mA ​cm−2 and 5.10 ​mA ​cm−2, respectively, and maintains a high capacity retention of 84.0% after 1000 cycles at 0.13 ​mA ​cm−2, with an average cycling CE of 99.58%.

Two in one: The use of hexagonal copper sulfide (CuS) nanoparticles as a bifunctional high-performance cathode and as a reinforced electrolyte additive for an all-solid-state lithium battery

All Solid-State Batteries (ASSBs) based on solid polymer electrolytes (SPEs) have improved safety, energy, and power densities than conventional liquid electrolyte-based Lithium-ion batteries (LIBs). However, two significant obstacles still need to be addressed, including the low ionic conductivities and the low interfacial contact between ASSB components. This study involves the fabrication of hexagonal CuS nanoparticles by a one-step hydrothermal method and uses them for both cathode and solid electrolyte formulation functions. The reasonable ionic conductivity of 4.68 × 10−4 S.cm−1 at 60℃ and the instant transport number of 0.86 of the designed CuS filler-incorporated solid electrolyte offered great promise for ASSBs applications. In particular, the CuS filler-incorporated solid electrolyte exhibited ceaseless and prompt Li-ion transportation kinetics and delivered a dendrite resistance capability over 200 cycles of stripping/plating of Li. In addition, the Li metal solid-state battery is also verified using CuS as the cathode and SPE electrolyte (PEO/LiTFSI/CuS SPE) system. It offers an initial discharge capacity of up to 695 mAh/g and keeps an average capacity of ∼ 365 mAh/g after 50 cycles at a current density of 0.5C. Thus, this study introduced a simple but effective solution to mitigate the dendrite problems associated with solid polymer electrolytes by using CuS as a durable inactive filler.

Role of Salt Concentration in Stabilizing Charged Ni-Rich Cathode Interfaces in Li-Ion Batteries.

The cathode-electrolyte interphase (CEI) in Li-ion batteries plays a key role in suppressing undesired side reactions while facilitating Li-ion transport. Ni-rich layered cathode materials offer improved energy densities, but their high interfacial reactivities can negatively impact the cycle life and rate performance. Here we investigate the role of electrolyte salt concentration, specifically LiPF6 (0.5-5 m), in altering the interfacial reactivity of charged LiN0.8Mn0.1Co0.1O2 (NMC811) cathodes in standard carbonate-based electrolytes (EC/EMC vol %/vol % 3:7). Extended potential holds of NMC811/Li4Ti5O12 (LTO) cells reveal that the parasitic electrolyte oxidation currents observed are strongly dependent on the electrolyte salt concentration. X-ray photoelectron and absorption spectroscopy (XPS/XAS) reveal that a thicker LixPOyFz-/LiF-rich CEI is formed in the higher concentration electrolytes. This suppresses reactions with solvent molecules resulting in a thinner, or less-dense, reduced surface layer (RSL) with lower charge transfer resistance and lower oxidation currents at high potentials. The thicker CEI also limits access of acidic species to the RSL suppressing transition-metal dissolution into the electrolyte, as confirmed by nuclear magnetic resonance (NMR) spectroscopy and inductively coupled plasma optical emission spectroscopy (ICP-OES). This provides insight into the main degradation processes occurring at Ni-rich cathode interfaces in contact with carbonate-based electrolytes and how electrolyte formulation can help to mitigate these.

Polyethylene oxide-Based solid electrolytes with fast Li-ion transport channels constructed from 2D montmorillonite for solid-state lithium-metal batteries

Polyethylene oxide (PEO)-based solid-state electrolytes (SSEs) typically struggle with poor ionic conductivity, low lithium (Li)-ion transference number, and narrow electrochemical window. For overcoming these drawbacks, we designed a promising composite SSE (CSSE), i.e., a Li-containing ionic liquid (LiIL) was inserted into the Li-montmorillonite (LiMNT) layered structure to form an active filler (LiIL@LiMNT), involving two-dimensional (2D) fast transport channels of Li-ion inside PEO electrolyte. Benefitting from an enhancement of the 2D Li-ion transport channels, the obtained CSSE exhibited an excellent ion conductivity of 1.38 × 10−4 S cm−1 at 30 °C as well as a satisfactory Li-ion transference number (0.38). A Li symmetric battery with the CSSE exhibited a steady cycle for 3000 h with 0.2 mA cm−2 at 60 °C. Under the rate of 0.5C at 60 °C, the solid-state Li-metal batteries (SSLMBs) assembled with LiFePO4 and LiNi0.33Co0.33Mn0.33O2 cathodes maintained a considerable reversible capacity after 400 and 100 cycles, respectively. The assembled SSLMB also achieved a satisfactory performance at 40 °C. The 2D active filler prepared in this work forms efficient 2D Li-ion transport channels inside the CSSE while maintaining a tight interfacial contact with electrodes, which is crucial to achieve a superior performance for CSSEs. This strategy of constructing 2D ion transport channels in polymer electrolytes also provides another way for the design of other CSSEs.

Control of Li-ion transport through a combination of conductive coating and charging protocol for a stable and extremely fast charging cathode

This study demonstrates the importance of controlling Li-ion transport through a combination of conductive coating and charging protocol to achieve a stable and extremely fast charging cathode. In this research, the LiFePO4 (LFP) material coated with carbon (C) and Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte exhibits superior performance to the conventional carbon-coated LFP (LFP@C), especially at high current rates, demonstrating the possibility of developing an extremely fast charging cathode for practical applications. Our systematic experimental results reveal that the LATP coating effectively regulates the surface reactions, prolongs the voltage plateaus, and contributes additional capacity to the olivine LFP cathode material. To take advantage of the coating, a charging protocol consisting of multi-step constant current (MCC) charging combined with constant voltage (CV) charging has been proposed. During MCC charging, the current gradually increases to initiate Li-ion transport on the particle surface before accelerating charging in a short time. Under the proposed charging protocol, the LFP@C_LATP can stably deliver an average charge capacity of 161.7 mAh g−1 within 10 min for 100 cycles. This research also demonstrates the advantage of incorporating a Li-ion conductor into the electrode for the development of an extremely fast charging electrode.

Regulating Metal Centers of MOF-74 Promotes PEO-Based Electrolytes for All-Solid-State Lithium-Metal Batteries.

Poly(ethylene oxide) (PEO)-based electrolytes have been extensively studied for all-solid-state lithium-metal batteries due to their excellent film-forming capabilities and low cost. However, the limited ionic conductivity and poor mechanical strength of the PEO-based electrolytes cannot prevent the growth of undesirable lithium dendrites, leading to the failure of batteries. Metal-organic frameworks (MOFs) are functional materials with a periodic porous structure that can improve the electrochemical performance of PEO-based electrolytes. However, the enhancement effect of MOFs with different metal centers and the interaction mechanism with PEO remain unclear. Herein, MOF-74s with Cu or Ni centers are prepared and used as fillers of PEO-based electrolytes. Adding 15 wt % of Cu-MOF-74 to the PEO-based electrolyte (15%Cu-MOF/P-Li) effectively improves the ionic conductivity, lithium transference number, and mechanical strength of the PEO-based electrolyte simultaneously. Furthermore, the ordered pore channels of Cu-MOF-74 provide uniform Li-ion transport pathways, facilitating homogeneous Li+ deposition. As a result, the lithium symmetric cell with 15%Cu-MOF/P-Li shows stable cycles for 1080 h at 0.1 mA cm-2 and 0.1 mAh cm-2, and the Li | 15% Cu-MOF/P-Li | LFP full cell exhibits a long cycle life up to 200 cycles at 60 °C and 0.5 C, with a capacity retention rate of 89.7%.

Two-dimensional Janus transition-metal carbide for flexible anode through surface engineering

Two-dimensional transition metal carbides (MXenes) have received tremendous attention because of their great promise in flexible energy storage. Although surface engineering plays an important role in regulating the properties of MXenes with the development of synthesis technology, an atomistic design of surface diversity for desired functionalities is generally limited by purely unified surface termination. Herein, the Janus MXenes consisting of different surface terminations are proposed for flexible anodes through first-principles calculations. Taking Ti2CTT' (T, T' = O, F, or OH) as an illustration of Janus MXenes, critical strains, ideal strengths, Li-ion diffusion barriers, equilibrium voltages, and theoretical capacities are determined and used as descriptors to evaluate the properties of flexible anodes. These Janus MXenes exhibit high critical strains and ideal strengths, indicating their mechanical flexibility. The strain-independent Li-ion diffusion barrier of Ti2COF suggests its fast Li-ion transport even suffering from mechanical deformation, endowing its application potential in flexible anodes. These results establish a theoretical framework for the comprehensive evaluation of flexible anode materials, providing a theoretical scheme for designing flexible anode materials.

A solid-state lithium-ion battery with micron-sized silicon anode operating free from external pressure

Applying high stack pressure (often up to tens of megapascals) to solid-state Li-ion batteries is primarily done to address the issues of internal voids formation and subsequent Li-ion transport blockage within the solid electrode due to volume changes. Whereas, redundant pressurizing devices lower the energy density of batteries and raise the cost. Herein, a mechanical optimization strategy involving elastic electrolyte is proposed for SSBs operating without external pressurizing, but relying solely on the built-in pressure of cells. We combine soft-rigid dual monomer copolymer with deep eutectic mixture to design an elastic solid electrolyte, which exhibits not only high stretchability and deformation recovery capability but also high room-temperature Li-ion conductivity of 2×10−3 S cm−1 and nonflammability. The micron-sized Si anode without additional stack pressure, paired with the elastic electrolyte, exhibits exceptional stability for 300 cycles with 90.8% capacity retention. Furthermore, the solid Li/elastic electrolyte/LiFePO4 battery delivers 143.3 mAh g−1 after 400 cycles. Finally, the micron-sized Si/elastic electrolyte/LiFePO4 full cell operates stably for 100 cycles in the absence of any additional pressure, maintaining a capacity retention rate of 98.3%. This significantly advances the practical applications of solid-state batteries.

Rapid ion conduction enabled by synergism of oriented liquid crystals and Electron-Deficient boron atoms in multiblock copolymer electrolyte for advanced Solid-State Lithium-Ion battery

Liquid crystals (LCs) with characteristics of self-orientation have exhibited superiorities in construction of ordered ion channels for rapid Li-ion transport. Herein, reversible addition-fragmentation chain transfer (RAFT) polymerization is employed to synthesize a unique type of boron-containing LCs based ABCBA type multiblock copolymers for the first time. The composite block copolymer electrolytes (BCPEs) are fabricated by introducing the copolymer electrolytes into glass fiber separator via solution-casting method. Noteworthily, LCs can not only provide ordered ion channels for efficient ion conduction, but also ameliorate the mechanical strength. Meanwhile, the nitrile groups with high polarity from LCs are able to further facilitate lithium salt dissociation and reinforce electrochemical stability of the system. Crucially, boron elements with electron deficiency can anchor anions and adsorb impurities to endow BCPEs with boosted ion transport capability and sufficient electrochemical stability. Consequently, the well-designed electrolyte shows high ionic conductivity of 1.13 × 10−4 S cm−1 (30 °C), and broadened electrochemical stability window of 4.85 V. Impressively, the assembled Li/LiFePO4 cells and even Li/LiMnxFe1-xPO4 high-voltage cells exhibit remarkable performances. This work provides a synthetic strategy of structure-controlled polymer electrolyte matrix and illustrates that the BCPEs are definitely a category of satisfactory electrolyte candidate for high-performance solid-state lithium-ion batteries.

Synergistic coupling among Mg2B2O5, polycarbonate and N,N-dimethylformamide enhances the electrochemical performance of PVDF-HFP-based solid electrolyte

Polymer solid electrolytes (SPEs) based on the [solvate-Li+] complex structure have promising prospects in lithium metal batteries (LMBs) due to their unique ion transport mechanism. However, the solvation structure may compromise the mechanical performance and safety, hindering practical application of SPEs. In this work, a composite solid electrolyte (CSE) is designed through the organic–inorganic synergistic interaction among N,N-dimethylformamide (DMF), polycarbonate (PC), and Mg2B2O5 in poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). Flame-retardant Mg2B2O5 nanowires provide non-flammability to the prepared CSEs, and the addition of PC improves the dispersion of Mg2B2O5 nanowires. Simultaneously, the organic–inorganic synergistic action of PC plasticizer and Mg2B2O5 nanowires promotes the dissociation degree of LiTFSI and reduces the crystallinity of PVDF-HFP, enabling rapid Li ion transport. Additionally, Raman spectroscopy and DFT calculations confirm the coordination between Mg atoms in Mg2B2O5 and N atoms in DMF, which exhibits Lewis base-like behavior attacking adjacent C–F and C–H bonds in PVDF-HFP while inducing dehydrofluorination of PVDF-HFP. Based on the synergistic coupling of Mg2B2O5, PC, and DMF in the PVDF-HFP matrix, the prepared CSE exhibits superior ion conductivity (9.78 × 10−4 S cm−1). The assembled Li symmetric cells cycle stably for 3900 h at a current density of 0.1 mA cm−2 without short circuit. The LFP||Li cells assembled with PDL-Mg2B2O5/PC CSEs show excellent rate capability and cycling performance, with a capacity retention of 83.3% after 1000 cycles at 0.5 C. This work provides a novel approach for the practical application of organic–inorganic synergistic CSEs in LMBs.

Numerical heat generation analysis of the tabbed and novel tabless designs of cylindrical-type lithium-ion batteries

The heat generation behaviours of a traditional tabbed cylindrical lithium-ion (Li-ion) battery are known to greatly affect its performance, cycle life, and safety. In this study, we explore the heat generation behaviours of the tabbed and novel tabless designs of a 21,700 cylindrical cell with graphite anode and NCA/LiNi0.8Co0.15Al0.05O2 cathode, by coupling the discreet layers of a three-dimensional (3D) disassembled electrochemical (EC) model with a two-dimensional (2D) axisymmetric heat transfer (HT) model. The respective heat generation mechanisms of each battery components of tabbed and tabless designs are first compared, and it is observed that the tabbed design generates significantly more heat than the tabless design, with the negative current collectors (NCC) in the tabbed design accounting for over 80 % of the total heats at 1C-rate. Also, the tabless design reduces the cell voltage drop due to its lower ohmic impedance and promotes a more homogenous cell temperature than the tabbed design. Next, the effects of particle size (ω) for the tabless design on the ohmic, reversible, and polarization heats of the battery’s electrodes are investigated at a high discharge rate of 10C, and the results show that polarisation heat decreases significantly in both electrodes as ω decreases. At the Negative Electrode (NE), the ohmic heating decreases initially as ω decreases because the battery is not drawing significant current. As the current drawn increases, Li-ion transport resistance also increases and at depth of discharge (DoD) = 36 %, a reverse in the trend is observed leading to an increase in Ohmic heating up to the end of life. In contrast, the ohmic heating at the Positive Electrode (PE) increases throughout the discharge process as ω decreases. For the reversible heat, the heat is negative in the NE side initially and fluctuates with ω towards the end of life (DOD = 88 %) when it changes from heat sink to heat source, whereas in the PE it remains unchanged for all ω throughout the discharge process. The resulting temperature drop is caused by the increase in the overall reversible heat sink effect in the NE side, as well as the weakened polarization heat in both electrodes. On the other hand, miniaturising the electrode thickness (η) causes a considerable decrease in ohmic heating in both electrodes resulting in larger temperature drops and elevated voltage curve. This study provides relevant insights in support of the development of battery thermal management systems (BTMS) for the tabbed and novel tabless batteries in a realistic environment.

Liquid Metal Loaded Molecular Sieve: Specialized Lithium Dendrite Blocking Filler for Polymeric Solid-State Electrolyte.

All-solid-state lithium metal batteries (LMBs) are currently one of the best candidates for realizing the yearning high-energy-density batteries with high safety. However, even polyethylene oxide (PEO), the most popular polymeric solid-state electrolyte (SSE) with the largest ionic conductivity in the category so far, has significant challenges due to the safety issues of lithium dendrites, and the insufficient ionic conductivity. Herein, molecular sieve (MS) is integrated into the PEO as an inert filler with the liquid metal (LM) as a functional module, forming an "LM-MS-PEO" composite as both SSE with enhanced ionic conductivity, and protection layer against lithium dendrites. As demonstrated by theoretical and experimental investigations, LM released from MS can be uniformly and efficiently distributed in PEO, which could avoid agglomeration, enable the effective blocking of lithium dendrites, and regulate the mass transport of Li ions, thus achieving even deposition of lithium during charge/discharge. Moreover, MS could reduce the crystallinity of PEO, improve lithium-ion conductivity, and reduce operating temperature. Benefiting from the introduction of the functional MS/LM, the LM-MS-PEO electrolyte exhibits fourfold higher lithium ionic conductivity than the pristine PEO at 40°C, while the as-assembled all-solid-state LMBs have four to five times longer stable cycle life.

Mechanically Interlocked Interphase with Energy Dissipation and Fast Li-Ion Transport for High-Capacity Lithium Metal Batteries.

Constructing an artificial solid electrolyte interphase (ASEI) on Li metal anodes (LMAs) is a potential strategy for addressing the dendrite issues. However, the mechanical fatigue of the ASEI caused by stress accumulation under the repeated deformation from the Li plating/stripping is not taken seriously. Herein, this work introduces a mechanically interlocked [an]daisy chain network (DC MIN) into the ASEI to stabilize the Li metal/ASEI interface by combining the functions of energy dissipation and fast Li-ion transport. The DC MIN featured by large-range molecular motions is cross-linked via efficient thiol-ene click chemistry; thus, the DC MIN has flexibility and excellent mechanical properties. As an ASEI, the crown ether units in DC MIN not only interact with the dialkylammonium of a flexible chain, forming the energy dissipation behavior but also coordinate with Li ion to support the fast Li-ion transport in DC MIN. Therefore, a stable 2800h-symmetrical cycling (1mA cm-2 ) and an excellent 5 C-rate (full cell with LiFePO4 ) performance are achieved by DC MIN-based ASEI. Furthermore, the 1-Ah pouch cell (LiNi0.88 Co0.09 Mn0.03 O2 cathode) with DC MIN-coated LMA exhibits improved capacity retention (88%) relative to the Control. The molecular design of DC MIN provides new insights into the optimization of an ASEI for high-energy LMAs.

Interface engineering with fluorine-doped amorphous carbon thin film coating on graphite anodes compatible with non-flammable sulfone-based electrolyte

To achieve full commercialization of Li-ion batteries, fire safety issues, which primarily start and accelerate from the electrode/electrolyte interface, should be resolved. Therefore, ionic liquids containing sulfone-based Li salts and solvents have been demonstrated to exhibit higher flame-retardancy than carbonate-based electrolytes. However, these sulfone-based electrolytes (sulfone EL) still face the challenges of sluggish Li-ion diffusivity of the electrolyte itself and poor compatibility especially with graphite anodes, lowering the specific capacity and high rate capability of the anodes. Herein, interface engineering was achieved by introducing a fluorine-doped amorphous carbon thin film coating (sub-20 nm) between graphite and sulfone EL, thereby simultaneously enhancing the ultrafast rate capability and flame-retardancy. The semi-ionic C–F abundant surface chemistry of graphite (F–C/Gra) not only induces robust solid electrolyte interface (SEI) formation with a LiF-rich composition and moderate thickness, but it also promotes fast-rated electron transfer into the graphite interior, which differs from bare graphite in sulfone EL. Surprisingly, this robust SEI formation on F–C/Gra was achieved at an elevated temperature (60 °C), enhancing Li-ion transport kinetics and allowing graphite-based anodes to achieve ultrafast longevity (discharge capacity of 152.6 mAh/g after 300 cycles at 1000 mA/g, 60 °C) even under harsh conditions.

Pomegranate-like α-MoO3-x/C nanospheres as a stable and high-performance Li-ion intercalation host

Orthorhombic MoO3 (α-MoO3) is extensively investigated as a cathode material in Li-ion batteries with high capacity. However, suffering from the irreversible structural transformation and rapid capacity decline during discharge-charge process are still annoyed issues for α-MoO3 based electrodes. Herein, novel pomegranate-like oxygen-deficient α-MoO3/C (α-MoO3-x/C) nanospheres are prepared. The α-MoO3-x/C nanosphere is comprised of ultrafine α-MoO3-x subunits and porous graphitic carbon framework. Interlayer expansions caused by different contents of oxygen vacancies are realized in α-MoO3-x via a controllable oxidation process. When evaluated as the Li-ion intercalation host, the α-MoO3-x/C containing appropriate oxygen vacancies is found to be optimal with remarkable rate capability (230.0 mAh g−1 at 1 C, 54.5 mAh g−1 at 50 C) and long lifetime (69.6% retention after 3000 cycles at 10 C). Electrochemical test shows that the behavior of Li-ion intercalation in the intralayers of α-MoO3-x/C is suppressed effectively and becomes reversible. The structure evolutions during Li-ion intercalation/deintercalation process are investigated by ex situ X-ray diffraction, which reveals that α-MoO3-x/C undergoes lattice breathing rather than structural collapse compared with pure α-MoO3. Moreover, α-MoO3-x/C exhibits enhanced pseudocapacitance and improved Li-ion transport kinetics than pure α-MoO3. These unique features render α-MoO3-x/C an advanced intercalation host for Li-ions.