Lithium Diffusion Research Articles

Influence of defects on enhancing lithium diffusivity in crystalline silicon anodes for fast charging lithium-ion batteries

The energy storage sector requires high capacity, long cycling life batteries. Silicon (Si) arises as a pivotal anode material for next-generation lithium-ion batteries owing to its exceptional capacity. However, challenges arise from lithium interactions, causing volumetric expansion and structural concerns like cracking. Si anodes also exhibit diverse phenomena during lithiation, influenced by crystal orientations. A thorough comprehension of the (de)lithiation process is essential to address challenges, despite existing gaps in knowledge, with strategic design and complementary materials, offering potential solutions by enhancing ion mobility and minimizing diffusion barriers. Here we have developed and applied first-principles simulations to offer fundamental insights into atomic interactions, providing a realistic atomistic representation of lithiation processes. Our simulations systematically incorporate Li+ into Si and Si- nitrogen vacancies (NV) orientations, and evaluation between Si and Si-NV (110) indicates a more favorable behavior in ionic diffusion for Si-NV(110), with a range of 2.55 × 10−3 to 1.64 × 10−2 (cm2/s) and a 15 % decrease in volume expansion. Our results explain the ternary Si–Li–N electrode materials and the identification of optimal site disorders to maximize the rate of Li+ diffusion in crystalline Si anodes.

The nonexistence of a paddlewheel effect in superionic conductors

Since the 1980s, the paddlewheel effect has been suggested as a mechanism to boost lithium-ion diffusion in inorganic materials via the rotation of rotor-like anion groups. However, it remains unclear whether the paddlewheel effect, defined as large-angle anion group rotations assisting Li hopping, indeed exists; furthermore, the physical mechanism by which the anion-group dynamics affect lithium-ion diffusion has not yet been established. In this work, we differentiate various types of rotational motions of anion groups and develop quaternion-based algorithms to detect, quantify, and relate them to lithium-ion motion in ab initio molecular dynamics simulations. Our analysis demonstrates that, in fact, the paddlewheel effect, where an anion group makes a large angle rotation to assist a lithium-ion hop, does not exist and thus is not responsible for the fast lithium-ion diffusion in superionic conductors, as historically claimed. Instead, we find that materials with topologically isolated anion groups can enhance lithium-ion diffusivity via a more classic nondynamic soft-cradle mechanism, where the anion groups tilt to provide optimal coordination to a lithium ion throughout the hopping process to lower the migration barrier. This anion-group disorder is static in nature, rather than dynamic and can explain most of the experimental observations. Our work substantiates the nonexistence of the long-debated paddlewheel effect and clarifies any correlation that may exist between anion-group rotations and fast ionic diffusion in inorganic materials.

PVP-assisted preparation of high-performance LiMn0.6Fe0.4PO4/C cathode materials

LiMnXFe1-XPO4 (X = 0.6) has excellent energy density and thermal stability, combining the excellent multiplicity performance of LiFePO4 and the high operating voltage of LiMnPO4. However, lower electronic conductivity and lithium ion diffusion rate are the main problems faced. We successfully synthesized LiMn0.6Fe0.4PO4 with uniform particles by a solvothermal method using surfactant PVP as an anti-agglomeration agent. At the same time, we found that the concentration of PVP in the reaction mixture plays a crucial role in the controllable structure and morphology of LiMn0.6Fe0.4PO4, thus accelerating the de-embedding of lithium ions reached 145.2 mAh g−1 under 1 C test. Therefore, the high-performance LiMn0.6Fe0.4PO4/C nanomaterials synthesized by the solvothermal method are significant for developing and applying lithium-ion batteries.

Boron-doped polyhedral graphite catalyzed by h-BN via structural induction for lithium storage

Artificial graphite is extensively used in power lithium-ion batteries for its exceptional stability and high-rate performance. However, the commercial high-temperature graphitization process is conducted at temperatures up to 3000 °C to enhance the degree of graphitization, resulting in significant electricity consumption and lengthy production cycles. This study aimed to lower graphitization temperatures and shorten times by using h-BN as a catalyst. Employing anthracite coal as the precursor and catalyzing with BN at 2800 °C for just 2 h, we achieved a remarkable graphitization degree of 93.3 %, compared to 83.5 % without BN. This indicates BN's effectiveness in accelerating graphite phase formation. Interestingly, the resultant graphite exhibited polyhedral morphology and incorporated boron doping. As edges increased, lithium-ion diffusion pathways and boron doping enhanced stability within the graphite layers, imparting high rate capability and robust cycle performance. The material delivered reversible specific capacities of 369.6 and 226 mA h g−1 at current densities of 0.1 and 3C, and maintained capacity retentions of 95 % and 92 % after 500 cycles at 0.5C and 1C. These results substantiate the potential for large-scale production of artificial graphite from anthracite coal using BN catalysis and underscore its promise as a superior anode material for lithium-ion batteries.

Thermal Studies of Lithium-Ion Cells: Ensuring Safe and Efficient Energy Storage

This work investigated the impact of temperature on the diffusion of lithium ions within cells. To achieve this, electrochemical impedance spectroscopy (EIS) analysis was conducted at various temperatures across three distinct cells. These cells utilized an electrode composed of corn starch meringue and were paired with three different electrolytes. Notably, one electrolyte included an additional 5% of starch. The objective of this study extends beyond merely determining resistance from graphical representations; it also entails performing a kinetic analysis of specific systems, with a particular emphasis on elucidating the significance of the lithium-ion diffusion coefficient as a critical parameter. The cell with 1 M LiPF6 in the EC/DMC/DEC electrolyte and corn starch-based electrode exhibited the most horizontally oriented Warburg curve, representing the smallest angle.

Constructing lithium-ion fast pathways via ZnO surface modification to enhance rate capability of graphite anode materials

Graphite materials have attracted widespread attention and application as anodes in lithium-ion batteries due to their abundant raw materials and environmental friendliness. However, poor rate performance is one of the most challenging issues for graphite anodes. In this work, a novel zinc oxide-graphite composite material has been fabricated, which effectively reduces the diffusion resistance of lithium ions during the charge-discharge process. Based on the analysis of the DFT calculations, the introduction of zinc oxide would be an effective way to improve the rate properties of graphite anode materials, owing to the higher lithium-ion diffusion kinetics. The concentration of zinc oxide has been optimized for the electrochemical performances of the composite electrode. Particularly, the 1%ZnO-graphite composite electrode demonstrates significant electrochemical performance with a discharge specific capacity of 337.6 mAh g−1 after 300 cycles at 1C (pure graphite is 300.6 mAh g−1) and excellent rate performance with 190 mAh g−1 at 5C (pure graphite is only 66 mAh g−1). These results pave a new direction for preparing the high rate and long cycle graphite anode materials.

High voltage electrochemical performance of single crystal LiNi0.8Co0.1Mn0.1O2 cathode materials with Al-Mg dual doping

Single-crystal materials have high structural stability and low parasitic side reactions for nickel-rich cathodes due to the absence of grain boundaries. However, they suffer challenges such as the complex synthesis route, sluggish lithium-ion diffusion kinetics, and microcracking evolution at high voltage. Bulk co-doping of Al and Mg into the precursors is first employed by a co-precipitation method, and then the Al-Mg dual-doped single-crystal NCM811 cathode is successfully prepared using a straightforward one-step method to reduce production cost. The cycle retention of the corresponding optimized single-crystal material is notably increased by 24.36% compared to the commercial counterpart at 1 C and a high voltage of 4.5 V. Additionally, the discharge capacity at 0.1 C is improved by 4.64% compared to the commercial one with an appropriate annealing temperature and lithium salt ratio. Some advances in the synthesis approach and modification strategy for developing commercial single-crystal material are provided.

Upgrading anode graphite from retired lithium ion batteries via solid-phase exfoliation by mechanochemical strategy

Vast quantities of anode graphite from waste lithium ion batteries (LIBs), as a type of underrated urban mine, has enormous potential to be exploited for resource recovery. Herein, we propose a benign process integrating low-temperature pyrolysis and mechanochemical techniques to upcycle spent graphite (SG) from end-of-life LIBs. Pyrolysis at 500 °C leads to about 82.2 % PVDF dissociation in thermal treated graphite (TG). Solid-phase exfoliation via ball milling assisted by urea successfully produces abundant graphite flakes and a small amount of monolayer graphene nanosheet at the edge of mechanochemically processed graphite (MG). Subsequent rinsing removes the residual LiF salts. High purity and unique edge structural features of the as-prepared MG offer more active sites and storage reservoir for intercalation and de-intercalation of lithium ions, resulting in enhanced lithium-ion diffusion kinetics, excellent reversible specific capacity and desirable rate capability. Inspiringly, MG exhibits a remarkably enhanced initial specific charge capacity of 521.3 mAh g−1 during the first charge–discharge, and only declines from 569.9 mAh g−1 to 538 mAh g−1 with slight attenuation after 50 consecutive cycles at 0.1 A/g, indicating satisfactory cycle stability. Additionally, the purification and reconstruction mechanism for MG have been illustrated in detail. This study offers a green strategy to reconstruct and upgrade anode graphite from LIBs, which can realize sustainable waste management.

Enable superior performance of ultra-high loading electrodes through the cost-efficient solvent-free electrode manufacturing technology

This research explores an innovative solvent-free method for fabricating ultra-high loading NMC811 and graphite electrodes (∼6mAh∙cm−2), showcasing remarkable electrochemical performance enhancements compared to the electrodes prepared by the conventional slurry-casting method. The optimized microstructure with dry-printed (DP) electrodes enhanced electrolyte penetration and minimized lithium-ion diffusion tortuosity resulting in improved rate performance at high current rates. Additionally, this innovative electrode manufacturing approach enables more uniform CEI and SEI formation and growth, which effectively doubles the cycle life of single-layer pouch cells with DP electrodes. Beyond the performance enhancements, this method also offers a notable 29.2 % overall cost advantages, potentially revolutionizing future battery manufacturing. The findings presented in this work underscore the potential of solvent-free manufacturing technology as a high-loading capable and cost-efficient path for advanced battery production.

Structures and properties of carbon-doped silicon as anode material for lithium ions battery: A first-principles study

Anode materials for lithium ions battery have been much less investigated than the cathode materials. Recently, silicon-based anode materials have attracted attentions for its high theoretical capacity. In the present work, the structures and properties of carbon doped silicon as the anode materials of lithium ions battery were investigated by first-principles method. In the doping concentration range from 1.56 % to 15.6 %, the results show that the stronger Si–C covalent bond leads to a higher bulk modulus of the carbon-doped silicon structures. The band gap of the doped structure decreases with increased doping concentration. The volume expansion can be suppressed by the doping of the carbon atom, and the structures with higher carbon concentrations had a better suppression effect. Meanwhile, the lithium diffusion energy barrier increases with the carbon doping concentration.

Engineering of Cerium Modified TiNb2O7 Nanoparticles For Low-Temperature Lithium-Ion Battery.

Although TiNb2O7 (TNO) with comparable operating potential and ideal theoretical capacity is considered to be the most ideal replacement for negative Li4Ti5O12 (LTO), the low ionic and electronic conductivity still limit its practical application as satisfactory anode for lithium-ion batteries (LIBs) with high-power density. Herein, TNO nanoparticles modified by Cerium (Ce) with outstanding electrochemical performance are synthesized. The successful introduction of Ce3+ in the lattice leads to increased interplanar spacing, refined grain size, more oxygen vacancy, and a smaller lithium diffusion barrier, which are conducive to improve conductivity of both Li+ and electrons. As a result, the modified TNO reaches high reversible capacity of 256.0mAhg-1 at 100mAg-1 after 100cycles, and 183.0mAhg-1 even under 3200mAg-1. In particular, when the temperature drops to -20°C, the cell undergoing 1500cycles at a high current density of 500mAg-1 can still reach 89.7mAhg-1, corresponding to a capacity decay rate per cycle of only 0.033%. This work provides a new way to improve the electrochemical properties of alternative anodes for LIBs at extreme temperature.

Thermodynamic stability and ionic conductivity in lithium–germanium binary system

Lithium–germanium binary compounds are promising anode materials for secondary lithium-ion batteries due to their high capacity, low operating voltage, and high electronic conductivity of lithiated Ge. For their successful application in batteries, it is essential to know the temperature stability of different Li–Ge phases and the variation of their ionic conductivity depending on the operating temperatures of the batteries. This work aims to comprehensively study the thermodynamic stability and ionic conductivity in Li–Ge binary compounds using a combination of first-principle computations and machine-learning interatomic potentials. We calculated convex hulls of the Li–Ge system at various temperatures and a temperature–composition phase diagram was obtained, delineating stability fields of each phase. Our calculations show that at temperatures higher than 590 K, LiGe undergoes a I41/a–P4/mmm transition, which leads to a change in the ionic conductivity. We show that all stable and metastable Li–Ge compounds have high ionic conductivity, but LiGe and Li7Ge12 have the lowest lithium diffusion. Trajectories of diffusion and Ge arrangements depend on lithium concentration. Based on advanced theoretical approaches, this study provides insights for the development of Li–Ge materials in lithium-ion and lithium-metal battery applications.

Non-destructive chemical prelithiation of VO2(B) anodes constructing a multifunctional interphase layer for advanced Li-Ion batteries

VO2(B) stands as a promising anode material, comparable to the disordered rock-salt phase Li3+xV2O5, owning to its ease of preparation, suitable redox potential, and remarkable rate capability. However, the practical application of VO2(B) anodes faces substantial limitations due to its low initial coulombic efficiency (ICE) and instability of solid electrolyte interface (SEI) layer during cycling. In this study, we introduce a highly efficient, controllable, and non-destructive chemical prelithiation method utilizing a reductive Li-arene reagent, formed by dissolving Li-metal to THF solutions containing biphenyl derivatives. This method enables the VO2(B) anode to achieve an ICE of nearly 100 %. The investigation on the chemical composition and mechanical properties of SEI layers reveals that the prelithiated VO2(B) electrode contains a more favorable LiF component, fewer adverse byproducts, and exhibits a thinner thickness with high structural strength. Kinetic analysis demonstrates that the prelithiation treatment accelerates the diffusion of lithium ions, reduces interfacial reaction resistances, and maintains interface stability during cycling. To demonstrate the practical application, we assemble a well-designed Prelithiation VO2(B)||NCM811 full cell, achieving an enhancement in the energy density of at least 20 %. This work underscores the potential of prelithiated VO2(B) electrodes for developing lithium-ion batteries (LIBs) with high-safety and high-energy/power density.

α-Graphyne nanotubes as a promising material for Li-ion battery anodes

Developing high storage capacity of lithium-ion batteries (LIBs) by applying novel anodes based on nanostructures has been allocated to extensive research. Although, SP2-hybrid carbon nanostructures exhibit a low storage capacity, a two-dimensional (2D) graphyne (Gy) monolayer is proved to be an efficient electrode material due to its large surface area and significant mechanical and chemical properties. Herein, a derivative of Gy called α-graphyne nanotube (αGyNT) is proposed as the anode material of LIBs, in which the adsorption of lithium (Li) on Gy nanobelt (GyNB) (one-segment) and short open-ended GyNTs with different lengths are modeled by implementing of ab initio first-principles calculations. Lithium diffusion behaviors inside and outside of GyNTs has been investigated by ab initio molecular dynamics (ABMD) to calculate open-circuit voltage. The results reveal that Li adsorption energies of short αGyNTs have no regular oscillatory dependence on the number of segments along the tube axis (length of the tubes). Furthermore, the largest storage capacity of C4Li4 (1273.75 mAh/g) was obtained for (4, 4) αGyNTs, which demonstrate better storage capacity compared to single/multiple graphyne nanostructures. The curvature of αGyNTs can enhance the diffusion of Li atoms and leads to promote storage capacities, which suggest these anode materials improve LIBs's performance.

On the analytical solution of single particle models and semi-analytical solution of P2D model for lithium-ion batteries

The Doyle–Fuller–Newman (DFN) model serves as a fundamental electrochemical modeling framework widely used in the field of lithium-ion batteries, especially in its pseudo-two-dimensional (P2D) formulation. Despite its widespread use, the DFN model imposes significant computational demands, especially for tasks such as cell characterization and state estimation in electric vehicles’ battery management systems (BMS). To mitigate these computational challenges, researchers have developed several reduced-order models. In this study, we tackle the associated computational efforts starting from the governing DFN equations. The analytical solutions for the transport equations in the electrode and the electrolyte are derived, considering generic time-varying boundary conditions under certain assumptions. The obtained exact solutions are then used to develop an analytical model for a single particle model with electrolyte dynamics (SPME) which provides higher predictive accuracy compared to a single particle model (SPM), especially in high C-rate scenarios, which are critical in many applications, including electric vehicles. Furthermore, the exact solution of lithium diffusion in active material particles is incorporated into the standard P2D model. This integration leads to a semi-analytical variant of the P2D model (SAP2D). A remarkable advantage of these analytical solutions is the significantly lower computational cost compared to corresponding numerical approaches. Spatial discretization becomes unnecessary, and the solutions can be obtained by a few explicit function evaluations. Moreover, when the time-varying boundary conditions are known, the need for time stepping is also eliminated.

Improving the electrochemical performances and structural stability of ultrahigh-Ni cathodes by using multi-element co-doping methods

Multi-element co-doping and its impact on the stability of the ultrahigh-Ni cathodes during extended cell cycling have not yet been fully established. Synergistic mechanisms still need to be thoroughly understood, and there is potential for further enhancing the structural stability and electrochemical performance of layered cathode materials. In this work, an Nb and Mg co-doped ultrahigh-Ni cathodes (LiNi0.92Co0.06Mn0.02O2) is prepared by solid-state synthesis methods. The effect of Nb and Mg dopants on the microstructure and electrochemical properties are systematically investigated. It is found that the Nb dopant can overcome the main shortcomings provided by Mg doping, including increasing the unit cell volume, suppress harmful phase transformation and enhancing lithium-ion diffusion kinetics. The cathode materials with optimized amounts of Nb and Mg dopants are demonstrated with excellent electrochemical performances. They reveal a specific capacity of 191 mAh g−1 at 1C with a good capacity retention of 92.8% after 500 cycles and a rated capacity of 141 mAh g−1 at 10C. It is also found that excessive Nb doping could lead to a decrease in rhombohedral ordering for crystal lattices, resulting in reduced structural stability and cyclability. This work investigates the strategy of Nb and Mg co-doping for enhancing electrochemical performances of ultrahigh-Ni cathodes, and the results obtained from this work can provide insights into improve the cyclability of these materials.

To achieve fast ion transport of engineered electrolyte and ultra-high rate of defected Nb16W5O55-based anode

The maximum output power and minimum charge time of a lithium-ion battery depend on ion transport and electron transport. The electron conduction/ion diffusion within the electrochemically active materials and the ion mobility of the electrolyte usually represent the fundamental limits of the battery charge and discharge rates. Nb16W5O55 is notable for its exceptional lithium-ion mobility and high electronic conductivity, making it a popular choice for fast-charging anode materials. However, the lithium-ion diffusion capability of the electrolyte is also crucial in determining the overall fast-charging performance of the battery. This can be a limiting factor for Nb16W5O55-based batteries. This work delves into the impact of electrolyte composition on fast-charging performance by examining the electrochemical properties of electrolytes with varying concentrations, in conjunction with molecular dynamics simulation. Specifically, increasing the concentration of LiTFSI salt alters the solvation structure of lithium ions due to the increasing coordination numbers of TFSI− and Li+, which hampers lithium-ion diffusion. Additionally, low-concentration electrolytes struggle with rapid mass transfer due to fewer lithium-ion carriers, limiting ultra-high-rate performance. To address these challenges, the solvation structure of the electrolyte was optimized, leading to enhanced fast-charging and discharging performance.

Electrochemical Lithium Deposition on LixTi5O12.

Lithium metal batteries (LMBs) have been regarded as one of the most promising next-generation high-energy-density storage devices. However, uncontrolled lithium dendrite growth leads to low Coulombic efficiencies and severe safety issues, hindering the commercialization of LMBs. Reducing the diffusion barrier of lithium is beneficial for uniform lithium deposition. Herein, a composite is constructed with Li4Ti5O12 as the skeleton of metallic lithium (Li@LixTi5O12) because Li4Ti5O12 is a "zero-strain" material and exhibits a low lithium diffusion barrier. It was found that the symmetric cells of Li@LixTi5O12 can stably cycle for over 400 h at 1 mA cm-2 in the carbonate electrolyte, significantly exceeding the usual lifespan (∼170 h) of the symmetric cell using a lithium metal electrode. In a full cell with Li@LixTi5O12 as the anode, the cathode LiFePO4 delivers a capacity retention of 78.2% after 550 cycles at 3.6C rate and an N/P ratio = 8.0. This study provides new insights for designing a practical lithium anode.

Innovative design of silicon-core mesoporous carbon composite for high performance anode material in advanced lithium-ion batteries

Silicon is widely recognized as an exceptionally auspicious anode material for lithium−ion batteries due to its remarkable specific capacity, suitable operational potential, and ecologically innocuous characteristics. This study presents a novel silicon@void@FC (fibrous carbon) composite anode material for lithium-ion batteries. Utilizing a one-step synthesis approach, the resulting hollow core–shell structure, combined with a mesoporous carbon shell, demonstrates exceptional electrochemical performance. The Si@Void@FC electrode exhibits remarkable cycle stability and rate performance, maintaining structural integrity over 500 cycles without observable degradation. The outer carbon shell acts as a protective layer and accommodates silicon volume expansion during cycling, preventing excessive contact with the electrolyte. The rich mesoporous structure facilitates efficient lithium-ion diffusion, enhancing lithiation and delithiation processes. The simplified one-step synthesis method further streamlines the preparation process, eliminating the need for complete silica template formation. This innovative Si@Void@FC composite material holds promise for advancing lithium-ion battery technology, addressing challenges associated with silicon-based anode materials, and offering insights into the design and synthesis of high-performance energy storage materials.

Optimizing the performance of a graphite anode for innovative metal-ion batteries and hybrid capacitors

Herein, we present an optimum method for maximizing the electrochemical performance of graphite anodes using two heat treatment methods involving graphite intercalated compound (GIC) group within graphite, namely, thermal shock (TS; directly input target temperature) and gradual heating (GH; including ramping time). Different heating methods for preparing expanded graphite (EG) involve different reactions, relaxation times, and diffusion pathways for the diffusion of metal ions into EG. We find that rapidly shocking the layered structure can facilitate faster lithium and potassium ion diffusion from EG (TS) (heated for 30 min) via different intercalation/deintercalation processes compared to that from EG (GH). Consequently, EG (TS) exhibits the most significantly improved electrochemical performance among the lithium and potassium ion half-cells. For full lithium-ion hybrid capacitors (LIHCs), EG (TS)||activated carbon (AC) shows reasonable values of maximum power density (2.8 kW kg−1 with 59.12 Wh kg−1) and energy density (196.41 Wh kg−1), demonstrating its ultrahigh durability (capacity retention: 70.01%) over 12000 cycles at 2.0 A g−1. In addition, for potassium-ion hybrid capacitors (PIHCs), reasonable performance is achieved (average capacity of 82.02 mAh g−1 at 1.0 A g−1 over 2000 cycles with 94.35% capacity retention), demonstrating the high efficiency of PIHCs for substituting LIHCs without any systematic alterations.