Rate Performance For Lithium Ion Batteries Research Articles

Molecular design of highly Li-ion conductive cathode-electrolyte interface enabling excellent rate performance for lithium-ion batteries

The structural stability and ionic conductivity of the cathode electrolyte interface (CEI) film at high voltages are crucial to the nickel-rich layered cathode in Li-ion batteries (LIBs). These characteristics are largely determined by electrolyte components. Herein, an air-stable organic cyclophosphate salt named lithium 1, 3, 2-dioxaphosphinan-2-olate-2-oxide (LiDOP) is designed and synthesized as a CEI forming additive. It preferentially oxidizes and undergoes opening-ring polymerization under charging to form an organic–inorganic hybrid polymers with –LiPO4 segments and –(CH2)3– alternately connected on the cathode surface. Such a structure endows CEI film with high ionic conductivity, flexibility and mechanical strength, which can ameliorate the structure phase transformation, suppress the transition metal ion dissolution and enhance the interfacial stability at high cut-off voltage. The electrolyte with 0.2 wt% LiDOP endows 4.3 V-charged Li||LiNi0.8Co0.1Mn0.1O2 battery with 83.2 % capacity retention after 200 cycles at 5C rate. The graphite||NCM811 pouch cell shows a capacity retention of 85.6 % after 150 cycles under a 4.5 V voltage, while the cell without LiDOP shows only 23.5 %. Our work demonstrates the effectiveness of covalently coupled P-O-Li compounds as CEI film in stabilizing the interface, which provides a guidance for the electrolyte design in high-voltage LIBs.

In-situ formed porous heteroatomic ladder polymer-based fibrous composite anode for high-rate and ultrastable lithium-ion batteries

Heteroatomic ladder polymers (HLPs) with high theoretical capacity are considered as the most promising electrode materials for next-generation green sustainable lithium-ion batteries (LIBs) due to their abundant resources, low cost, diverse structures and good safety features. However, the issues of low specific capacity and unsatisfactory reversibility, caused by underutilization and sluggish reaction kinetics, have thus far hindered the practical application of these materials. Herein, a porous heteroatomic ladder polymer-based fibrous composite anode (HLP/RGO/C) with interconnected conductive networks is designed and obtained by a simple electrospinning technique and in-situ heat treatment for LIB applications. Benefit from in-situ transformation and interconnected conductive porous networks, the obtained HLP/RGO/C anode achieves uniform distribution of HLP and rapid ionic/electronic transport, thereby realizing efficient utilization and rapid reaction kinetics of HLP in LIBs. Consequently, the HLP/RGO/C anode achieves a highly reversible specific capacity of 748 mA h g−1, ultra-long cyclic stability and exceptional rate performance for LIBs. Furthermore, the HLP/RGO/C anode also delivers superior electrochemical performance for LIBs over a broad temperature range, especially achieving ultrahigh reversible capacities of 186 mA h g−1 even at −30 °C. This research provides a straightforward method to construct green and sustainable polymer-based anode for LIBs.

Facile electrodeposition of copper layers on graphene film as high performance current collector for lithium-ion batteries

The increasing demand on high energy density and rate performance of lithium-ion batteries (LIBs) drives all battery components forward, including electrochemically inactive components. Herein, Cu coated graphene film (GF@Cu) is fabricated via electroplating method as a composite current collector with low areal density (3.44 mg cm−2), high electrical conductivity (3.25*107 S m−1), excellent thermal conductivity (836.20 W m−1K−1), and good weldability. By substituting Cu current collector with this lightweight GF@Cu in lithium-ion batteries, the graphite anode realizes an 246.01 % increasement of gravimetric capacity at 1C. The lithium-ion batteries equipped with GF@Cu current collector can also obviously improve the rate and cycling performance during charging/discharging at high current density by reducing the interfacial contact resistance and increasing the electrical and thermal conductivities.

Oxygen Defect and Cl--Doped Modulated TiNb2O7 Compound with High Rate Performance in Lithium-Ion Batteries.

TiNb2O7 has attracted extensive attention from lithium-ion battery researchers due to its superior specific capacity and safety. However, its poor ion conductivity and electron conductivity hinder its further development. To improve the ion/electron transport of TiNb2O7, we report that chlorine doping and oxygen vacancy engineering regulate the energy band and crystal structure simultaneously through a simple solid-phase method. NH4Cl was used to realize Cl- doping and oxygen vacancy production. A Rietveld refinement demonstrates an effective substitution of Cl in the O sites of Nb-O octahedra, with an enlarged crystal plane spacing. The oxygen vacancies provide more active sites for lithium intercalation. The diffusion coefficient of Li+ is inceased from 2.39 × 10-14 to 1.50 × 10-13 cm2 s-1, which reveals the positive influence of Cl- doping and oxygen vacancies on the promoted Li+ transport behavior. Charge compensation is introduced by the doping of Cl- and the generation of oxygen vacancies, leading to the formation of Ti3+ and Nb4+ and the adjustment of the electronic structure. DFT calculations reveal that TiNb2O7 with Cl- doping and an O vacancy shows a metallic property with a finite value at the Fermi level, which is conducive to electron transfer in the electrode material. Benefiting from these advantages, the modified TiNb2O7 presents superior rate performance with a commendable capacity of 172.82 mAh g-1 at 50 C. This work provides guidance to design high-performance anode materials for high-rate lithium-ion batteries.

Roll-to-roll solvent-free manufactured electrodes for fast-charging batteries

Roll-to-roll solvent-free manufactured electrodes for fast-charging batteries

Microwave-Assisted Metal-Organic Frameworks Derived Synthesis of Zn2GeO4 Nanowire Bundles for Lithium-Ion Batteries.

Germanium-based multi-metallic-oxide materials have advantages of low activation energy, tunable output voltage, and high theoretical capacity. However, they also exhibit unsatisfactory electronic conductivity, sluggish cation kinetics, and severe volume change, resulting in inferior long-cycle stability and rate performance in lithium-ion batteries (LIBs). To solve these problems, we synthesize metal-organic frameworks derived from rice-like Zn2GeO4 nanowire bundles as the anode of LIBs via a microwave-assisted hydrothermal method, minimizing the particle size and enlarging the cation's transmission channels, as well as, enhancing the electronic conductivity of the materials. The obtained Zn2GeO4 anode exhibits superior electrochemical performance. A high initial charge capacity of 730 mAhg-1 is obtained and maintained at 661 mAhg-1 after 500 cycles at 100 mA g-1 with a small capacity degradation ratio of ~0.02% for each cycle. Moreover, Zn2GeO4 exhibits a good rate performance, delivering a high capacity of 503 mA h g-1 at 5000 mA g-1. The good electrochemical performance of the rice-like Zn2GeO4 electrode can be attributed to its unique wire-bundle structure, the buffering effect of the bimetallic reaction at different potentials, good electrical conductivity, and fast kinetic rate.

Descriptor-Based Graded Electrode Microstructures Design Strategies of Lithium-Ion Batteries for Enhanced Rate Performance

Microstructure engineering of electrodes is one of the efficient routes to improve rate performance of lithium-ion batteries (LIBs). Currently, there is a lack of descriptors to rationally guide the regional electrode design. Here, we propose two descriptors, the time differential of the average state of lithium (SoL) and the span of SoL in individual particles, to identify the rate performance constraints across the electrode depth. 3D microstructure-based electrochemical simulations are performed on a homogeneous electrode, and the predictability of the microstructure-based model is verified with the experimental measurement on a LiNi1/3Mn1/3Co1/3O2 electrode. At electrode level, the descriptors divide the electrode into four regions, namely, a solid-state transport (SST)-controlled region, two mixed SST and liquid-state transport (LST)-controlled regions (SST-dominant and LST-dominant, respectively), and an LST-controlled region. Based on these insights, dual-gradient electrodes are designed with smaller particles in the SST-controlled region and graded porosity increasing from current collector to the separator. Results show that the optimized dual-gradient electrode has significantly more excellent LST capability compared to the homogeneous electrode, thus improving the utilization of particles near the collector. As a result, the capacity performance of the optimized dual-gradient electrode increases by 39% at 5C without sacrificing the gravimetric energy density.

Molten salt synthesis of submicron NiNb2O6 anode material with ultra-high rate performance for lithium-ion batteries

Niobium-based oxides as lithium-ion battery anode materials have attracted much attention due to their excellent fast-charging capability. However, the solid-phase synthesis of niobates often involves harsh reaction conditions, especially high temperature over 1100 °C. Herein, a molten salt method is proposed to synthesize NiNb2O6 submicron particles, with synthetic temperature of 900 °C, gram-scale production and high reaction yield of 96.6%. Remarkably, NiNb2O6 at the sub-micron scale shows superior electrochemical performance compared to the micron and nano scale sizes, i.e., reversible capacity of 320.9 mAh g−1 after 500 cycles at 2.0 A g−1 (≈8.5C) and high capacity retention of 85.8% over 5000 cycles at 20 A g−1 (≈85C), mainly arising from the pseudo-capacitance electrochemical behavior and stable structure of material during repeated cycles. Moreover, the assembled NiNb2O6||LiFePO4 full cell can retain 89.3% capacity after 800 cycles at 1.0 A g−1. This work offers a simple and efficient method for preparing NiNb2O6 submicron particles as anode material for fast -charging lithium-ion batteries.

Diffusion-limited C-rate: A criterion of rate performance for lithium-ion batteries

Rate performance is one of the important indexes of lithium-ion batteries. However, the discharge capacity would sometimes collapse after a critical C-rate, which is related to a classic concept termed the diffusion-limited C-rate (DLC). In this work, DLC is revisited using the Pseudo-Two-Dimensional model. The DLC analytical model is improved by incorporating the concentration-dependent liquid diffusion coefficient and shows good effectiveness compared with the simulation results. Subsequently, the impact of rate-limiting factors on the rate performance is examined to determine the effective scope of the proposed DLC model. Based on the adjustment of resistance ratios and time constant ratios of different kinetic processes, we find that the rate performance below DLC is hardly limited by electronic transports and charge transfer processes while the discharge capacity below DLC may be severely decayed if the solid-state diffusion in the electroactive particles is too slow. DLC helps identify the ‘knee’ on discharge capacity curves with discharge C-rate, which is a criterion of rate performance in some scenarios.

Correlation between Lithium Titanium Oxide Powder Morphology and High Rate Performance in Lithium-Ion Batteries

This study determined the measurable factor responsible for the high rate performance of lithium titanium oxide (Li4Ti5O12, LTO) powders in lithium-ion batteries. The structural and morphological properties of various Li4Ti5O12 materials and their correlation with electrochemical performance were analysed. The results showed that there was a strong correlation between high capacity retention at 10 C and the specific surface area. Other electrochemical and structural factors, such as the crystal size and pore structure, were not correlated with 10 C performance. We found that an increase in the specific surface area of Li4Ti5O12 above c.a. 15 m2 g−1 neither improved the high rate capacity retention nor its specific discharge capacity at high current rates. We also showed that the sol–gel synthesized lithium titanium oxide powders could retain similar or higher discharge specific capacities than materials synthesized via more complex routes.

Alloy-Type Lithium Anode Prepared by Laser Microcladding and Dealloying for Improved Cycling/Rate Performance.

Nanosized alloy-type materials (Si, Ge, Sn, etc.) present superior electrochemical performance in rechargeable batteries. However, they fail to guarantee cycling capacity and stability under high mass loading required by industrial applications due to low electric contact and adhesive strength, which has long been a challenge. This work proposes a rational design for an alloy-type anode via facile and versatile laser microcladding and dealloying. The proposed anode features a large-area porous network composed of continuous nano-ligaments, which consist of evenly distributed nanosized alloy-type material metallurgically bonded with conductive material. The fabrication of the structure is validated using Ge-Cu and Sn-Cu anodes, both exhibiting enhanced cycling stability at high areal capacity and rate performance in lithium-ion batteries. The enhancement is attributed to the structural features, which contribute to lithiation-delithiation stability and intact electron/Li ion transference path, as verified by in situ and ex situ transmission electron microscopy observations. More importantly, the critical solidification conditions of laser microcladding are provided by a multiphysics simulation, allowing for a thorough understanding of the structural formation mechanism. The study provides a possible approach to improve mass loading and performance of an alloy-type anode for practical application.

F-Doped Ni-Rich Layered Cathode Material with Improved Rate Performance for Lithium-Ion Batteries

Ni-rich layered cathode materials for lithium-ion batteries have received widespread attention due to their large capacity and low cost; however, the structural stability of the material needs to be improved. Herein, F-doped and undoped cathode materials prepared with an advanced co-precipitation method were used to measure the effect of F doping on the material. Compared to the undoped sample, the F-doped cathode materials exhibited an improved rate performance, because the porous structure of F-doped cathode materials is favorable for the infiltration of the electrolyte and the material, and the F-doped cathode material has a larger (003) crystal plane and a smaller Li+ migration barrier energy. This simple F-doping treatment strategy provides a promising way to improve the performance of Ni-rich layered cathode materials for lithium-ion batteries.

Introducing nanodiamonds in electrolyte and SEI for highly improving performances of lithium-ion batteries

Designing and synthesizing novel electrolyte and solid electrolyte interfaces (SEIs) are greatly desirable for improving the performance of lithium-ion batteries (LIBs). Taking into account the large surface area, chemical inertness, high lithium adsorption and surface modifiability, in this work, detonation nanodiamonds (NDs) with an average size of 5 nm were introduced to commercial LiPF6 electrolyte and a NDs-rich SEI was formed on graphitic anodes surface during charge–discharge processes. The NDs-rich SEIs have low interfacial resistance, fast ion transport and additional Li+ storage sites, which are favorable to improve the capacity and rate performance of LIBs. The half cells with ND-electrolyte exhibit capacities of ∼ 400 mA h g−1 at 5C (1C ∼ 372 mA h g−1) after 1000 cycles and ∼ 700 mA h g−1 at 0.2C after 100 cycles, which are nearly 2 times that for original electrolyte without NDs performed under the same processes. Further considering the compatibility with industrial processes, the strategy of forming SEIs consisting of NDs from electrolytes is helpful for fabricating high-performance LIBs with high capacity and stability for practical industrial applications.

Quantifying the Effect of Separator Thickness on Rate Performance in Lithium-Ion Batteries

In addition to improving parameters such as energy density and stability, it is important to maximise rate performance in lithium-ion batteries. While much work has focused on rate-limiting factors associated with the electrodes, much less attention has been paid to the effect of the separator on rate-performance. Here we perform a quantitative study on the effect of separator thickness on the rate-performance of a model system of NMC-based half cells. By fitting experimental capacity vs rate curves, we measured the characteristic time associated with charge/discharge as a function of separator thickness, finding a roughly linear increase for separator thicknesses below ∼65 μm. This behaviour is consistent with a simple physical model which shows the separator thickness dependence to be dominated by electrolyte resistance effects. The predictions of the model match the data extremely well with no adjustable parameters.

Fast and extensive intercalation chemistry in Wadsley-Roth phase based high-capacity electrodes

Wadsley-Roth (W-R) structured oxides featured with wide channels represent one of the most promising material families showing compelling rate performance for lithium-ion batteries. Herein, we report an in-depth study on the fast and extensive intercalation chemistry of phosphorus stabilized W-R phase PNb9O25 and its application in high energy and fast-charging devices. We explore the intercalation geometry of PNb9O25 and identify two geometrical types of stable insertion sites with the total amount much higher than conventional intercalation-type electrodes. We reveal the ion transportation kinetics that the Li ions initially diffuse along the open type III channels and then penetrate to edge sites with low kinetic barriers. During the lithiation, no remarkable phase transition is detected with nearly intact host phosphorous niobium oxide backbone. Therefore, the oxide framework of PNb9O25 keeps almost unchanged with all the fast diffusion channels and insertion cavities well-maintained upon cycling, which accomplishes the unconventional electrochemical performance of W-R structured electrodes.

High rate performance of Lithium-ion batteries with Co-free LiNiO2 cathode

Co-free LiNiO2 (H-LNO) nanoparticles were synthesized by the urea-based hydrothermal synthesis in the presence of sodium dodecyl sulfate as an anionic surfactant, followed by a high-temperature calcination process with a lithium source. Compared to the LiNiO2 samples prepared via the co-precipitation method (C-LNO), the H-LNO samples exhibited superior electrochemical properties, such as charge/discharge capacity, rate capability, and cycle performance. Electrochemical tests showed that the H-LNO cathode reached an ultra-high initial discharge capacity of 211.9 mAh/g at 0.1C and maintained a capacity of 131.9 mAh/g at 5C, approximately twice greater than that of the C-LNO cathode. The H-LNO sample retained 77.33 % of its capacity, which is higher than that for the C-LNO sample (65.84 %) after 50 cycles at 0.5C. These results were attributed to the combined effect of the high Li+ diffusion coefficient and low charge transfer resistance, suggesting that the H-LNO powder is beneficial for practical applications in Li-ion batteries.

A Descriptor-Based Design of Graded Electrode Microstructures for Improved Rate Performance of Lithium-Ion Batteries

A Descriptor-Based Design of Graded Electrode Microstructures for Improved Rate Performance of Lithium-Ion Batteries

Large-Scale Synthesis of Ninb2o6 Submicron Particles with Ultra-High Rate Performance for Lithium-Ion Batteries

Large-Scale Synthesis of Ninb2o6 Submicron Particles with Ultra-High Rate Performance for Lithium-Ion Batteries

Self-supporting ZnP2@N, P co-doped carbon nanofibers as high-performance anode material for lithium-ion batteries

Searching for high specific capacity anode materials with an optimized structure to achieve high energy density, long cycling life-span, and high rate performance for lithium-ion batteries (LIBs) is a pressing assignment. Metal phosphides have aroused much attention, however, enormous volume variations, poor electrical conductivity, and aggregation of nanoparticles hamper their practical applications. Herein, ZnP2 nanoparticles grown on N, P co-doped carbon nanofibers (ZnP2 @NPCNFs) composite synthesized by electrospinning and heat treatment is reported to directly act as binder-free anode in LIBs. The 3D self-standing ZnP2 @NPCNFs featuring good flexibility can not only boost conductivity and alleviate the volumetric fluctuations in the cycling course, but also buffer the agglomeration and pulverization of nanoparticles. Lithium storage of ZnP2 @NPCNFs electrode obey the conversion reaction mechanism. Besides, the additional lithium intercalation active sites created by the doped-nitrogen and the existence of PC bond along with the space-confined effect of NPCNFs are conjointly beneficial to endow the ZnP2 @NPCNFs electrode with distinctive electrochemical properties. When assembled as the anode, the ZnP2 @NPCNFs electrode reached a high reversible capacity of 746 mA h g−1 after 100 cycles at 0.2 A g−1 and 406.49 mA h g−1 after 1000 cycles at 2 A g−1. Electrochemical tests manifest that most of the capacity contribution comes from capacitive process. Moreover, the similar superior electrochemical performances are obtained in the LiFePO4//ZnP2 @NPCNFs full cell. Generally, this study widens researchers’ horizons to conceive rational structure of metal phosphides anodes in LIBs with high capacity conservation.

Accelerated lithium ions diffusion at the interface between LiFePO4 electrode and electrolyte by surface-nitride treatment

Improving the rate performance of lithium-ion batteries is important for the widespread utilization of electric vehicles and energy grids. Because the rate-determining step for cathode materials with a two-phase reaction is nucleation reaction at the material surface, surface modification is a promising approach for achieving this goal. However, the cause of this improvement in the reaction rate at the interface between the surface-modified cathode and the electrolyte is not clearly understood. In this study, we prepared a surface-nitrided LiFePO4 thin film and investigated its electrochemical properties. In addition, we examined its surface structure using surface-sensitive X-ray absorption spectroscopy measurements and first-principles calculations, and discussed the correlation between the rate performance and the interfacial reaction. The experiments revealed the formation of a new energy level and the increase of the FeO bond distance at the surface of LiFePO4 due to nitrogen doping. The electronic and local structural changes accelerated lithium ion diffusion at the interface between surface-nitrided LiFePO4 and the electrolyte, improving the rate performance.