Li-ion Transport Research Articles

Nb-doping of cation-disordered rocksalt oxides with B2O3 surface modification for superior performance cathode

As the growing price and inadequate reserves of cobalt, the demand for cobalt-free materials with superior energy density to apply in Li-ion batteries has increased distinctly. Li-rich cation disordered rocksalt (DRX) material has aroused research hotspot because of high specific capacity and wide compositional space. However, irreversible oxygen loss as well as sluggish kinetic raise the problem in large polarization and inevitable capacity decay in cycling process, which have impeded the commercialization of these electrode materials. In this work, we have synthesized cobalt-free boron trioxide (B2O3)-modified Li1.2Ni0.3Ti0.3Nb0.2O2 compounds with cation disordered rocksalt structure through mechanochemical method. It is a fact that B2O3-modified cathodes possess outstanding cyclic stability as well as rate properties. Particularly, the Li1.2Ni0.3Ti0.3Nb0.2O2 electrode with 2.0 wt% B2O3 displayed a competitive capacity of 192.4 mAh/g at 10 mA g−1 and retained 134.7 mAh/g after 100 charge/discharge times. The redox mechanism is explored through ex-situ XPS measurement, verifying the reversible cationic redox of Ni2+/Ni4+ accompanying small Ti4+/Ti3+ reduction and anionic O2−/O− evolution, which results in unusual high capacity. Such an optimized surface modification combines with the Nb doping, can promote Li ion transport, reduce polarization, protect cathode from reacting with electrolyte. These findings provide important implications to improve performance of DRX cathodes.

Co-Intercalation-Free Graphite Anode Enabled by an Additive Regulated Interphase in an Ether-Based Electrolyte for Low-Temperature Lithium-Ion Batteries.

Graphite (Gr) anode, which is endowed with high electronic conductivity and low volume expansion after Li-ion intercalation, establishes the basis for the success of rocking-chair Li-ion batteries (LIBs). However, due to the high barrier of the Li-ion desolvation process, sluggish transport of Li ions through the solid electrolyte interphase (SEI) and the high freezing points of electrolytes, the Gr anode still suffers from great loss of capacity and severe polarization at low temperature. Here, 1,2-diethoxyethane (DEE) with an intrinsically wide liquid region and weak solvation ability is applied as an electrolyte solvent for LIBs. By rationally designing the additives of electrolytes, an intact SEI with fast Li-ion conductivity is constructed, enabling the co-intercalation-free Gr anode with long-term stability (91.8% after 500 cycles) and impressive low-temperature characteristics (82.6% capacity retention at -20 °C). Coupled with LiFePO4 and LiNi0.8Mn0.1Co0.1O2 cathodes, the optimized electrolyte also demonstrates low polarization under -20 °C. Our work offers a feasible approach to enable ether-based electrolytes for low-temperature LIBs.

Unveiling the Role of Fluorination in Hexacyclic Coordinated Ether Electrolytes for High-Voltage Lithium Metal Batteries.

Fluorinated ethers have become promising electrolyte solvent candidates for lithium metal batteries (LMBs) because they are endowed with high oxidative stability and high Coulombic efficiencies of lithium metal stripping/plating. Up to now, most reported fluorinated ether electrolytes are -CF3-based, and the influence of ion solvation in modifying degree of fluorination has not been well-elucidated. In this work, we synthesize a hexacyclic coordinated ether (1-methoxy-3-ethoxypropane, EMP) and its fluorinated ether counterparts with -CH2F (F1EMP), -CHF2 (F2EMP), or -CF3 (F3EMP) as terminal group. With lithium bis(fluorosulfonyl)imide as single salt, the solvation structure, Li-ion transport behavior, lithium deposition kinetics, and high-voltage stability of the electrolytes were systematically studied. Theoretical calculations and spectra reveal the gradually reduced solvating power from nonfluorinated EMP to fully fluorinated F3EMP, which leads to decreased ionic conductivity. In contrast, the weakly solvating fluorinated ethers possess higher Li+ transference number and exchange current density. Overall, partially fluorinated -CHF2 is demonstrated as the desired group. Further full cell testing using high-voltage (4.4 V) and high-loading (3.885 mAh cm-2) LiNi0.8Co0.1Mn0.1O2 cathode demonstrates that F2EMP electrolyte enables 80% capacity retention after 168 cycles under limited Li (50 μm) and lean electrolyte (5 mL Ah-1) conditions and 129 cycles under extremely lean electrolyte (1.8 mL Ah-1) and the anode-free conditions. This work deepens the fundamental understanding on the ion transport and interphase dynamics under various degrees of fluorination and provides a feasible approach toward the design of fluorinated ether electrolytes for practical high-voltage LMBs.

Impact of Polymer Interlayers on All-Solid-State Battery Performance Using a Physicochemical Modeling Approach

Recent studies presented the advantages of incorporating solid-polymer-electrolyte (SPE) interlayers in all-solid-state batteries (ASSB). Still, drawbacks regarding the cell performance are expected due to additional polymer-related overpotentials. The pseudo-two-dimensional (p2D) physicochemical model is extended to account for Li-ion transport in the SPE interlayer and in the ceramic LLZO solid electrolyte (SE), as well as for the charge transfer at the SPE∣LLZO interface using Butler-Volmer-like kinetics. The overpotential analysis for a reference parameterization disclosed a dominant overpotential contribution from the SPE∣LLZO charge transfer and a facilitation with increasing discharge C-rate. Variance-based global sensitivity analyses demonstrate that as the exchange current density between SPE and LLZO increases, polarization losses exhibit an exponential-like reduction. Additionally, the radius of the active material (AM) particles within the composite cathode exerts a significant and dominant influence on cell performance. With an optimization of the SPE∣LLZO exchange current density, the accessible capacity could be increased compared to the reference parameterization from 41% to 61% for a 2C discharge.

Amorphous Oxyhalide Matters for Achieving Lithium Superionic Conduction.

The recently surged halide-based solid electrolytes (SEs) are great candidates for high-performance all-solid-state batteries (ASSBs), due to their decent ionic conductivity, wide electrochemical stability window, and good compatibility with high-voltage oxide cathodes. In contrast to the crystalline phases in halide SEs, amorphous components are rarely understood but play an important role in Li-ion conduction. Here, we reveal that the presence of amorphous component is common in halide-based SEs that are prepared via mechanochemical method. The fast Li-ion migration is found to be associated with the local chemistry of the amorphous proportion. Taking Zr-based halide SEs as an example, the amorphization process can be regulated by incorporating O, resulting in the formation of corner-sharing Zr-O/Cl polyhedrons. This structural configuration has been confirmed through X-ray absorption spectroscopy, pair distribution function analyses, and Reverse Monte Carlo modeling. The unique structure significantly reduces the energy barriers for Li-ion transport. As a result, an enhanced ionic conductivity of (1.35 ± 0.07) × 10-3 S cm-1 at 25 °C can be achieved for amorphous Li3ZrCl4O1.5. In addition to the improved ionic conductivity, amorphization of Zr-based halide SEs via incorporation of O leads to good mechanical deformability and promising electrochemical performance. These findings provide deep insights into the rational design of desirable halide SEs for high-performance ASSBs.

Interface Engineering Enables Wide-Temperature Li-Ion Storage in Commercial Silicon-Based Anodes.

Silicon-based materials have been considered potential anode materials for next-generation lithium-ion batteries based on their high theoretical capacity and low working voltage. However, side reactions at the Si/electrolyte interface bring annoying issues like low Coulombic efficiency, sluggish ionic transport, and inferior temperature compatibility. In this work, the surface Al2 O3 coating layer is proposed as an artificial solid electrolyte interphase (SEI), which can serve as a physical barrier against the invasion of byproducts like HF(Hydrogen Fluoride) from the decomposition of electrolyte, and acts as a fast Li-ion transport pathway. Besides, the intrinsically high mechanical strength can effectively inhibit the volume expansion of the silicon particles, thus promoting the cyclability. The as-assembled battery cell with the Al2 O3 -coated Si-C anode exhibits a high initial Coulombic efficiency of 80% at RT and a capacity retention ratio up to ≈81.9% after 100 cycles, which is much higher than that of the pristine Si-C anode (≈74.8%). Besides, the expansion rate can also be decreased from 103% to 50%. Moreover, the Al2 O3 -coated Si-C anode also extends the working temperature from room temperature to 0 °C-60 °C. Overall, this work provides an efficient strategy for regulating the interface reactions of Si-based anode and pushes forward the practical applications at real conditions.

Ultra‐Low 4.3 wt% Silicon Thermal Reducing Doped Porous Si@MoC as Highly Capable and Stable Li‐Ion Battery Anode

AbstractSilicon is a promising anode material in lithium‐ion batteries (LIBs) for its ultra‐high theoretical capacity; however, its large volume expansion and low electrical conductivity trigger capacity degradation and poor stability. Herein, an ultra‐low 4.3 wt% Si‐doped porous MoC (p‐Si@MoC) is constructed by a facile thermal reduction on a core‐shelled precursor of ZnMo‐hybrid zeolitic imidazole framework (HZIF‐ZnMo) coated by tetraethyl orthosilicate (TEOS), delivering a high capacity and superior cycling stability (976.6 mAh g−1 after 250 cycles at 0.2 A g−1) in LIBs. The homogeneous distribution in the porous MoC matrix contributes to its maximum capacity utilization. Meanwhile, the porous substrate enhances Li ion transport kinetics and reduced the volume expansion of Si. The excellent electronic conductivity of p‐Si@MoC is revealed by the density functional theory (DFT) calculations. The Mo─Si bonds formed by Si‐doped in the MoC matrix are verified by X‐ray absorption near‐edge structure (XANES) and extended X‐ray absorption fine structure (EXAFS). Moreover, the in situ X‐ray diffraction (in situ XRD) reveals the lithium storage mechanism. This work presents an excellent structural design and synthesis strategy for high‐performance silicon‐based anode materials.

Interfacial Modification of Lithium Metal Anode by Boron Nitride Nanosheets.

Metallic lithium (Li) is the most attractive anode for Li batteries because it holds the highest theoretical specific capacity (3860 mA h g-1) and the lowest redox potential (-3.040 V vs SHE). However, the poor interface stability of the Li anode, which is caused by the high reactivity and dendrite formation of metallic Li upon cycling, leads to undesired electrochemical performance and safety issues. While two-dimensional boron nitride (BN) nanosheets have been utilized as an interfacial layer, the mechanism on how they stabilize the Li-electrolyte interface remains elusive. Here, we show how BN nanosheet interlayers suppress Li dendrite formation, enhance Li ion transport kinetics, facilitate Li deposition, and reduce electrolyte decomposition. We show through both simulation and experimental data that the desolvation process of a solvated Li ion within the interlayer nanochannels kinetically favors Li deposition. This process enables long cycling stability, reduced voltage polarization, improved interface stability, and negligible volume expansion. Their application as an interfacial layer in symmetric cells and full cells that display significantly improved electrochemical properties is also demonstrated. The knowledge gained in this study provides both critical insights and practical guidelines for designing a Li metal anode with significantly improved performance.

Li-rich Mn-based Li1.2Mn0.54 Ni0.13Co0.13O2 with carbothermal reduction coated spinel heterogeneous layer to enhance the electrochemical performance

High-capacity Li-rich Manganese-based cathode materials (LMCs) have been considered ideal cathodes for Li-ion batteries (LIBs) because of the Li2MnO3 phase with anion activity and the LiTMO2 phase (TM: transition metal) with cation activity. However, the LMCs suffer from oxygen and Li irreversible loss in the cycles, which results in voltage decline, capacity attenuation, and a low initial Coulomb efficiency (ICE). Herein, we report co-precipitation synthesis of Li1.2Mn0.54Ni0.13 Co0.13O2 (LMNCO) cathodes by citric acid pretreatment, followed by carbothermal reduction to obtain a heterogeneous spinel layer of LMNCO surface. Organic acid undergoes carbonation and thermal reduction during annealing in an Ar atmosphere, contributing to the heterogeneous spinel layer reconstruction and the Mn reduction. The heterogeneous spinel layer facilitates Li-ion transportation by providing 3D Li diffusion channels and avoids bulk-phase corrosion by the electrolyte, as a buffer layer. At 0.1C, the surface-modified LMNCO cathodes render discharge capacity reaches up to 303.7 mAh g−1, and the ICE is 85.6%. Furthermore, at a 1C current, the discharge capacity is found to be 248.4 mAh g−1, and after 100 cycles, the capacity retention is 84.6%. These consequences demonstrate that the heterogeneous spinel layer significantly improves the capacity, ICE, and cyclic stability of the surface-modified LMNCO cathodes. The current study presents a successful modification to enhance the LMCs electrochemical performance, which is of utmost significance for practical applications.

Modification of solid electrolyte interface layer between PVDF-based electrolyte and lithium anode

Poly(vinylidene fluoride) (PVDF)-based polymer electrolytes (PEs) with good electrochemical performance and processability as well as low-cost advantage, have great potential applications in solid-state lithium (Li) metal batteries (SSLMBs). PVDF-based PEs are generally produced by employing a solution-casting approach with N,N-dimethylformamide (DMF) as the solvent, accompanied by the formation of [DMF-Li+] complex, which facilitates the Li-ion transport. However, the residual DMF can react continuously with lithium (Li) metal, thereby deteriorating the interface layer in the middle of the PVDF-based PEs and Li anodes. Herein, we introduce propylene carbonate (PC) into the PVDF-based PEs to regulate the solvation structure and stabilize the interface layer between the PEs and Li anodes. PC accelerates the dissociation of lithium oxalyldifluoroborate (LiODFB). Consequently, “lithium propylene dicarbonate (LPDC)‒B-O″ oligomer forms as the interfacial layer with high tenacity, homogeneity, and densification, which improves the interfacial contact and suppresses the continuous reaction between the residual DMF and Li anode. We further demonstrate that the PVDF-based PE prepared with DMF-PC mix-solvents shows improved room-temperature ionic conductivity (1.18 × 10−3 S/cm), enhanced stability against electrodes, and superior cycling performance in LiCoO2-based SSLMBs (maintaining 84 % of the initial discharge capacity after 300 cycles).

Novel design of high elastic solid polymer electrolyte for stable lithium metal batteries

Li metal anodes have high specific capacity and low electrode potential, and have always been considered as one of the most promising anode materials. However, the growth of Li dendrites, unstable solid electrolyte interface layer (SEI), severe side reactions at the Li/electrolyte interface, and infinite volume expansion of the Li anode seriously hinder the practical application of solid-state Li metal batteries (LMBs). Herein, we report a polyurethane elastomer (TPU) material with high elasticity and interfacial stability as a solid polymer electrolyte (SPE) for LMBs. The synergistic effects of its designed soft chain forging (PEO) and hard chain segments (IPDI) can enhance Li ion conductivity, elastic modulus and flexibility of the SPE to settle the challenges of the Li metal anodes. Moreover, Li2S, as a solid-state electrolyte additive, is able to effectively inhibit the occurrence of side reactions at the interface between Li metal and SPE, promote the decomposition of N(CF3SO2)2− and in-situ generation of LiF with low Li+ diffusion barrier and excellent electronic insulation, achieving rapid Li ion transport and uniform Li deposition. As a result, stable cycle of up to 1400 h has been achieved for a Li||TPU-Li2S||Li battery at 0.1 mA/cm2 at 50 ℃, accompanied with a stable cycling performance of 350 h at a higher current density of 0.5 mA/cm2. Finally, the LiFePO4||TPU-Li2S||Li full battery exhibits an excellent cycling performance with a capacity retention rate of 80 % after 500 cycles at 1C. This simple and low-cost strategy provides novel design thoughts for practical application of high-performance SPEs in stable and long-life LMBs.

Promoting stability and fast-charging capability of LiCoO2 thin-film battery achieving 500 Wh/kg energy density through MgO co-sputtering

As the earliest commercial cathode material, LiCoO2 (LCO) offers advantages in high capacity and fast charging. However, only half the energy density is implemented in the current batteries limited by materials instability at high voltages. The mechanisms of the instability of LCO cathodes include irreversible phase transition (>4.3 V), cathode–electrolyte interface formation, oxygen evolution, and cobalt dissolution. To overcome the challenges of existing practical implications, implement applications for LCO cathode of voltage and energy density limitations. The co-sputtering technique incorporating Mg dopants are proposed in this research to provide not only excellent pillar effect to stabilize structure but also faster Li-ion transportation. The best LCO cathode (45 Mg-LCO) with the optimum Mg concentration demonstrates outstanding rate capability (61.7% when comparing 5 C–0.1 C) and cycling stability (47.1% capacity retention over 100 cycles at 1 C as charging to the ultrahigh voltage of 4.7 V), surpassing pristine LCO. Consequently, the energy density leaps forward from 352.8 Wh/kg (LCO cut-off at 4.2 V) to 494.1 Wh/kg (45 Mg-LCO cut-off at 4.7 V). This work provides comprehensive understanding of the working mechanisms behind the doping strategy for LCO electrode materials.

One-dimensional van der Waals transition metal chalcogenide as an anode material for advanced lithium-ion batteries

1D vdW Nb2Se9 is a promising advanced anode material for LIBs due to superior electrochemical performance originating from its unique structural properties, which allow swift transport of Li ions and buffer the volume changes during Li-ion storage.

An integrated dual-gradient host facilitates oriented bottom-up lithium growth in lithium metal anodes.

Integrated gradient hosts, composed of poorly conductive frameworks on copper current collectors, have been extensively explored for the development of Li metal anodes (LMAs). Despite their potential, high Li nucleation overpotentials and slow interface kinetics often lead to inferior performance. Herein, we combine electrospinning and electrodeposition to create an integrated gradient host, namely OPAN/rGO-Cu2O/Cu. This involves electrodeposition of graphene oxide onto copper foil, reacting in situ to form a lithiophilic rGO-Cu2O layer, which is then covered with an oxidized polyacrylonitrile (OPAN) nanofiber layer, establishing conductivity and lithiophilicity dual gradients. The insulating OPAN top layer blocks electron transmission to the surface and prevents Li deposition, while the lithiophilic rGO-Cu2O layer facilitates Li ion transport to the bottom and reduces the nucleation barrier, both of which promote uniform Li deposition from bottom to top. As a result, the battery achieves an average coulombic efficiency of 98.4% over 500 cycles at 1 mA cm-2, and the symmetric cell sustains an ultra-long cycle life of 1600 h with a minimal polarization voltage of 12 mV. When paired with a LiFePO4 cathode, the full cell demonstrates a capacity retention of 92.6% after 300 cycles at 1 C, with an average capacity decay rate of just 0.025% per cycle. This innovative approach offers a promising pathway for developing high-performance LMAs.

A new paradigm for battery structural design towards interface-free, all-in-one cell configuration

The novel all-in-one cell configuration contributes to developing batteries of extremely high rate performance and long durability by eliminating the internal interfaces and adopting a nonporous cell separator.

Linear ether-based highly concentrated electrolytes for Li-sulfur batteries.

Li-S batteries have attracted attention as next-generation rechargeable batteries owing to their high theoretical capacity and cost-effectiveness. Sparingly solvating electrolytes hold promise because they suppress the dissolution and shuttling of polysulfide intermediates to increase the coulombic efficiency and extend the cycle life. This study investigated the solubility of polysulfide (Li2S8) in a range of liquid electrolytes, including organic electrolytes, highly concentrated electrolytes, and ionic liquids. The Li2S8 solubility was well correlated with the donor number (DNNMR), estimated via23Na-NMR, and was lower than 100 mM_(elemental sulfur) in electrolytes with DNNMR < 14, regardless of the type of electrolyte. Highly concentrated electrolytes comprising lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and linear chain dialkyl ethers such as methyl propyl ether (MPE), n-butyl methyl ether (BME), and ethyl propyl ether (EPE) were studied as sparingly solvating electrolytes for Li-S batteries. Monomethyl ethers, such as BME, showed more pronounced Li-ion coordination and higher ionic conductivity, whereas the steric hindrance of the longer alkyl chains in EPE lowered the solvation number, enhanced ion association, and lowered the ionic conductivity despite the solvents having similar dielectric constants. The charge-discharge rate capabilities of Li-S cells with dialkyl ether-based electrolytes were more impressive than those of cells with a localized high-concentration electrolyte using sulfolane (SL) and hydrofluoroether (HFE), [Li(SL)2][TFSA]-2HFE. The higher rate performance was attributed to the superior Li-ion transport properties of the dialkyl ether-based electrolytes. A pouch-type cell using lightweight [Li(BME)3][TFSA] demonstrated an energy density exceeding 300 W h kg-1 under lean electrolyte conditions.

Tough and single lithium-ion conductive nanocomposite electrolytes based on PAES-g-PEG and POSS–PEG for lithium–sulfur batteries

Tough nanocomposite solid electrolytes exhibit facile single Li-ion transport using POSS–PEG and simultaneously achieve both superior conductivity and excellent thermal/mechanical stability via self-assembled PAES-g-PEG for long-term safe LSBs.

An ultrathin phase-inversion induced co-assembly separator for high-performance lithium-metal batteries

An ultra-thin composite separator, consisting of ANF, MPS–HGO and MA–POSS, not only acts as a physical obstacle but also efficiently regulates Li-ion transport to hinder irregular dendritic growth.

A novel LaCl3-based oxychloride solid-state electrolyte enables fast Li-ion transport and compatible with lithium metal

Solid electrolytes are pivotal in ushering in the new era of energy technology, offering fresh prospects for its advancement. Recently, halide solid electrolytes have garnered significant attention due to their...

Building continuous Li-ion transport channels from cathode to anode in solid-state lithium-metal batteries

Homogeneous Li+ transport channels through the electric core were built by surface modifications of both the solid-state electrolyte membrane and the binder phase in the cathode, thus improving the performance of solid-state lithium batteries.