Discharge Capacity Loss Research Articles

On ways of conversion of silicon dioxide SiO2 in lithium battery systems: a review

Silicon and silicon oxide compounds SiO, SiO2, SiOx and SiOC are considered as a promising family of materials for high-energy lithium batteries due to their high theoretical capacity, widespread in nature, low cost, environmental safety and ease of synthesis. Silicon oxide compounds have replaced silicon in the hope of improving the discharge characteristics of lithium batteries. Oxides of silicon show excellent stability during cycling after structure optimization. However, they suffer from the problem of low Coulomb efficiency and high voltage hysteresis (difference in charge and discharge voltage), which prevents their practical application. Significant bulk expansion of silicon oxides during cycling and irreversible loss of capacity in the initial cycles are an obstacle to their large-scale practical use. This review pays attention to the peculiarities of the conversion of SiO2 and its hybrid compounds into the redox reaction with lithium and ways to overcome existing problems. Silicon dioxide is more resistant to bulk expansion than silicon. Various structural formats of nanometer SiO2 have been developed and tested for lithium batteries, such as nanotubes, nanorods, nanowires, nanoparticles, thin films. To solve problems in the SiO2/Li system, a number of SiO2 composites with carbon, graphene, active and inactive metals, etc. have also been proposed and studied. Analyzing the results of the studies, we found a significant role of the solid electrolyte interphase film in the efficient conversion of SiO2. In turn, the formation of a film on silicon dioxide depends on the method of synthesis of dioxide, which introduces impurities into the final synthesis product. Impurities contribute to the distortion of the solid electrolyte interphase film during the cycling of the SiO2/Li system, and the loss of discharge capacity. SiO2 dioxide obtained in a dry environment of a ball mill differs favorably from that obtained from solutions. Many efforts have been made to overcome the problems in Si-containing electrode materials, however, they have to go a certain way for large-scale practical application.

Identification of mechanism consistency for LFP/C batteries during accelerated aging tests based on statistical distributions

This study establishes a novel approach to investigate if accelerated aging tests can accurately model realistic cell aging in a short time while also maintaining the consistency of the involved aging mechanisms. As a trade-off between efficiency and consistent mechanism, the application of accelerated aging necessitates carefully selecting stress factors to identify the operational range and the significance of aging-related stress factors. Based on three levels of major stress factors designed for 43-month calendar aging tests and 10-month cyclic aging tests, this work aims at the stress ranking and indicating suitable operational intervals for commercial LFP/C batteries, taking two of the most popular lifetime distributions for batteries, namely log-normal and Weibull. Statistical distributions of lithium-ion batteries are attained from discharge capacity loss with nonlinear mixed-effects (NLME) models. Results prove that log-normal is the preferred model, and the right-skewed Weibull becomes more pronounced with deeper aging, especially in calendar aging. The evolution law of distribution parameters guided by the consistent acceleration factor was derived. The likelihood ratio parametric bootstrap approach based on the NLME model for life samples consistently yields that test conditions with the temperature above 47.5 °C and average state-of-charge (SOC) for cycling aging above 72.5% can result in different life behaviors. In contrast, the combination of SOC levels and higher temperatures does not lead to a change in the calendar aging mechanisms. The temperature is the most significant stress, followed by temperature-coupled cycle depth and SOC levels. This method can offer a reference to make reasonable test plans for detecting battery's performance to predict their life more accurately.

Organized macro-scale membrane size reduction in vanadium redox flow batteries: Part 1. General concept

The high costs of the currently used membranes in vanadium redox flow batteries (VRFBs) contribute to the price of the vanadium redox flow battery systems and therefore limit the market share of the VRFBs. Here we report a detailed simulation and experimental studies on the effect of membrane reduction of single-cell VRFB. Different simulated designs demonstrate that a proposed centred and double-strip membrane coverage showed a promising performance. Experimental charge-discharge profile of different membrane size reduction, which showed good agreement with simulated data, suggests that the membrane size can comfortably be reduced by up to 20% without severe efficiency or discharge capacity loss. Long-term cycling of 80% centred membrane coverage showed improved capacity retention during the latter cycles with almost 1% difference in capacity and only 2% in energy efficiency when compared to the fully covered-membrane cell. The results hold great promise for the development of cheap RFB stacks and facilitate the way to develop new cell designs with non-overlapping electrodes geometry. Therefore, giving more flexibility to improve the overall performance of the system.

Mechanisms of Si Nanoparticle Formation by Molten Salt Magnesiothermic Reduction of Silica for Lithium‐ion Battery Anodes

AbstractMolten salt methods enable the synthesis of Si nanostructures by moderating the thermal energy evolved in highly exothermic magnesiothermic reduction reactions (MRR) of silica. Due to their cost‐effectiveness and scalability, these techniques are well suited for producing nanoscale Si for a number of applications, including energy storage. To control the microstructure morphology and particle size, it is necessary to understand the formation mechanism of the Si produced. By evaluating the time‐resolved phase evolution, when NaCl moderates the thermal energy generated by MRR of SiO2, we elucidate 3 parallel interfacial reaction mechanisms yielding Si nanoparticles – via Mg vapor, Mg‐rich eutectic liquid, and Mg ions dissolved in molten NaCl. These individual Si nanoparticles offer a striking contrast to the typical by‐product of MRR of SiO2 with and without NaCl, which yields a 3‐dimensional (3‐D) porous network of sintered Si nanoparticles. Lithium‐ion battery half‐cells with electrodes composed of individual Si nanoparticles showed a greater first‐cycle irreversible discharge capacity and faster capacity loss over the first 5 cycles at a current density of 200 mA g−1 compared to half‐cells with electrodes of a porous 3‐D Si network–indicative due to thicker solid electrolyte interphase (SEI) formation on individual particles. At a higher current rate of 400 mA g−1, once SEI formation and activation of Si are established, both cells exhibit a similar capacity retention rate over 100 cycles.

A Metal-free ionic liquid Dual-ion battery based on the reversible interaction of 1-Butyl-1-Methylpyrrolidinium cations with 1,4,5,8-Naphthalenetetracarboxylic dianhydride

The strong self-discharge reaction is one of the key factors limiting the practical use of dual-ion batteries, which leads to low coulombic efficiency and discharge capacity loss. It is of great significance to effectively reduce the self-discharge effect through redox reactions between organic electrodes and electrolytes. Herein, a dual-ion battery study that uses 1,4,5,8-naphthalenetetracarboxylic dianhydride as the anode and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide as the electrolyte is conducted. Due to the introduction of organic materials, the storage mechanism of cations on the anode is changed, which weakens the self-discharge effect. The battery shows a low self-discharge rate of 6.12% h−1 and a high discharge capacity of 114 mAh g−1. The voltage declines by only 0.14 V after resting for 15 h due to the strong redox reaction between Pyr14+ cations and the CO groups of NTCDA. Meanwhile, a double-layer filter paper system with small porosity is used to improve the cycle performance of the battery.

The functional separator for lithium-ion batteries based on phosphonate modified nano-scale silica ceramic particles

In lithium-ion batteries (LIBs), benefiting from various functional components, functional separators can possess different capabilities to cope with the risks in complex application scenarios. In this work, a functional separator based on the phosphonate-modified nano-scale silica ceramic particles is fabricated to reduce the safety risks in LIBs. Through an anhydrous polymerization process, dimethyl vinylphosphonate (DMVP), a kind of widely used flame retardants, is grafted on silica (SiO2). Then the modified SiO2 (mSiO2) is coated on the pristine polyethylene separator by a typical coating process. Combining the function of the ceramic and phosphonate, the modified ceramic separator displays substantially enhanced thermal stability, without visual thermal shrink up to 200 °C. The flame resistances of separator itself and pouch cells are also significantly improved, even though flammable electrolyte is added. Different from the case when the phosphonate is used as an additive in electrolyte, the phosphonate is fixed firmly on the separator and not easy to be embedded in carbon anode after battery cycles. The coin cells assembled with the modified separators are away from the irreversible loss of discharge capacity and low Coulombic efficiency for the first cycle, which can be attributed to the firm immobilization of organic phosphonate.

Al substituted Mn position on Li[Ni0.5Co0.2Mn0.3]O2 for high rates performance of cathode material

Li[Ni0.5Co0.2Mn0.3-xAlx]O2 cathode materials were successfully synthesized via a facile ball milling method. XRD refinement analysis proves that Al element is favourably substituted the position of Mn in the transition metal layer and solidly restrains the cationic mixing. After 150 cycles at 10 C, compared with NCM whose discharge capacity loss is 56.3 mAhg−1, Li[Ni0.5Co0.2Mn0.275Al0.025]O2 (NCM-25) loses only 32.9 mAhg−1. Even at higher 15 C, NCM-25 still delivers the highest initial discharge capacity of 97.8 mAhg−1, and exhibits prominent capacity retention than NCM after 300 cycles. EIS measurement suggests NCM-25 has 3.24 × 10−8 cm2 s−1 of the coefficient lithium ion and 0.32395 mA cm−2 of the exchange current density after cycling, which indicates that Rct is validly restrained and alleviates the degree of polarization. After cycling, XRD and XPS results indicate Al-doped furnishes surface protection avoiding the electrolyte corrosion and restrains the formation of oxygen species in the process of lithiation/delithiation. Electrochemical tests suggest Al-doped samples have appealing improvements in cycling at high rates.

A combination state of charge estimation method for ternary polymer lithium battery considering temperature influence

Under the actual operating conditions of electric vehicle, the temperature of the battery system changes with the ambient temperature, its influence is rarely considered on state of charge (SOC) estimation. Aiming at this problem, this work explores the relationship between temperature and battery discharge capacity, capacity loss, coulomb efficiency and open circuit voltage, and establishes a temperature correction model. Then, a temperature-based coulomb counting (TBCC) method is proposed. To eliminate the cumulative errors of SOC estimation, a TBCC combined adaptive particle filter (APF) combination estimation method is proposed, which can update the temperature-related variables, and estimates the system state with the identified model parameters. The estimation method adapts to the temperature change of the power lithium battery while taking into account the superiority of the APF in non-linear and non-Gaussian systems, so as to improve the accuracy of the SOC estimation in the changing temperature range. Simulations under urban dynamometer driving schedule (UDDS) are conducted, and the results show that compared with the method without temperature correction, the proposed combination method can improve the accuracy and convergence ability of SOC estimation under the influence of temperature.

Influence of electrode design parameters on the performance of vanadium redox flow battery cells at low temperatures

Performance of electrochemical batteries suffers at cold temperatures. In this paper, we report on an experimental investigation of sensitivity of the vanadium redox flow battery (VRFB) to the cell operating temperature. Experiments have been carried out on a VRFB cell with an active area of 426 cm2 at cell temperatures of 25, +10 and −10 °C. Measured parameters include cycle efficiency and discharge capacity at three current densities and two flow rates, peak power and cell impedance obtained through electrochemical impedance spectroscopy (EIS) studies. The influence of electrode compression and electrode thickness has also been studied through comparative experimental protocols. Results indicate significant loss of discharge capacity and cell efficiency at low temperatures; this can be attributed to substantial increase in ohmic resistance and even higher increase in charge transfer resistance of the cell. Two methods known to reduce cell resistance, namely, increasing compression ratio of the electrode and using thinner electrode, have led to restoring much of the lost discharge capacity and energy efficiency. Optimizing the electrode parameters such as its compression, permeability and thickness for industrial scale cells, together with possible use of electrocatalysts, seems to be a promising way of improving low temperature performance of VRFB cells.

One-time sintering process to modify xLi2MnO3 (-x)LiMO2 hollow architecture and studying their enhanced electrochemical performances

Abstract To solve the critical problems of lithium rich cathode materials, e.g., structure instability and short cycle life, we have successfully prepared a ZrO2-coated and Zr-doping xLi2MnO3∙(1–x)LiMO2 hollow architecture via one-time sintering process. The modified structural materials as lithium-ion cathodes present good structural stability and superior cycle performance in LIBs. The discharge capacity of the ZrO2-coated and Zr-doped hollow pristine is 220 mAh g−1 at the 20th cycle at 0.2 C (discharge capacity loss, 2.7%) and 150 mAh g−1 at the 100th cycle at 1 C (discharge capacity loss, 17.7%), respectively. However, hollow pristine electrode only delivers 203 mAh g−1 at the 20th cycle at 0.2 C and 124 mAh g−1 at the 100th cycle at 1 C, respectively, and the corresponding to capacity retention is 92.2% and 72.8%, respectively. Diffusion coefficients of modified hollow pristine electrode are much higher than that of hollow pristine electrode after 100 cycles (approach to 1.4 times). In addition, we simulate the adsorption reaction of HF on the surface of ZrO2-coated layer by the first-principles theory. The calculations prove that the adsorption energy of HF on the surface of ZrO2-coated layer is about -1.699 eV, and the ZrO2-coated layer could protect the hollow spherical xLi2MnO3∙(1–x)LiMO2 from erosion by HF. Our results would be applicable for systematic amelioration of high-performance lithium rich material for anode with the respect of practical application.

Extended Interfacial Stability through Simple Acid Rinsing in a Li-Rich Oxide Cathode Material.

Layered Li-rich Ni, Mn, Co (NMC) oxide cathodes in Li-ion batteries provide high specific capacities (>250 mAh/g) via O-redox at high voltages. However, associated high-voltage interfacial degradation processes require strategies for effective electrode surface passivation. Here, we show that an acidic surface treatment of a Li-rich NMC layered oxide cathode material leads to a substantial suppression of CO2 and O2 evolution, ∼90% and ∼100% respectively, during the first charge up to 4.8 V vs Li+/0. CO2 suppression is related to Li2CO3 removal as well as effective surface passivation against electrolyte degradation. This treatment does not result in any loss of discharge capacity and provides superior long-term cycling and rate performance in comparison to as-received, untreated materials. We also quantify the extent of lattice oxygen participation in charge compensation ("O-redox") during Li+ removal by a novel ex situ acid titration. Our results indicate that the peroxo-like species resulting from O-redox originate on the surface at least 300 mV earlier than the activation plateau region at around 4.5 V. X-ray photoelectron spectra and Mn L-edge X-ray absorption spectra of the cathode powders reveal a Li+ deficiency and a partial reduction of Mn ions on the surface of the acid-treated material. More interestingly, although the irreversible oxygen evolution is greatly suppressed through the surface treatment, O K-edge resonant inelastic X-ray scattering shows that the lattice O-redox behavior is largely sustained. The acidic treatment, therefore, only optimizes the surface of the Li-rich material and almost eliminates the irreversible gas evolution, leading to improved cycling and rate performance. This work therefore presents a simple yet effective approach to passivate cathode surfaces against interfacial instabilities during high-voltage battery operation.

Improve electrochemical performance of spinel LiNi0.5Mn1.5O4 via surface modified by Li1.2Ni0.2Mn0.6O2 layered materials

Spinel LiNi0.5Mn1.5O4(LNMO) is one of the most promising cathode materials for lithium-ion batteries due to its high operating voltage (4.7 V, vs. Li / Li+). However, the high operating voltage will cause the LNMO capacity to decay due to the dissolution of its Mn and the decomposition of the electrolyte. Although surface modification can improve the cycle stability of LNMO, most of the current surface modification will cause different degrees of loss in discharge capacity. Herein, for the first time, Li1.2Ni0.2Mn0.6O2(LIR) is coated on the host material LNMO as the surface material by co-precipitation method. As the coating materials, LIR does not destroy the crystal structure and micromorphology of LNMO. The surface-modified material (LNMO@LIR) has higher reversible capacity with better cycle stability than LNMO. The LNMO@LIR delivers a discharge capacity of 128.32 mAh g−1 at 0.5 °C, and the capacity retention rate is up to 97.2% after 300 cycles. This work indicates that LIR coating can efficiently enhance the electrochemical performance of LNMO.

Synthesis of Argentum Vanadate’s Obtained by Ion-Exchanging Way on the Base of Synthesized Electrochemically V2O5-X·yH2O, and Their Behavior in the Electrodes for Lithium Accumulator

V2O5 is known as inexpensive, high energy, environmental secure the electrode material in lithium accumulators. The loss of discharge capacity at cycling due to structure degradation of crystal lattice V2O5 is one from the deterrent for expanded production of Li/V2O5 accumulators. For improvement of stability of V2O5∙cycling, obtained electrochemically V2O5-X·yH2O oxides were doped by argentum using ion-exchanging method with following their annealing. Synthesized argentum vanadate’s in the electrodes for lithium accumulator show raised discharge capacity and stability in comparison with those of V2O5.

Graphene Wrapped FeSe2 Nano‐Microspheres with High Pseudocapacitive Contribution for Enhanced Na‐Ion Storage

AbstractPseudocapacitance is a Faradaic process that involves surface or near surface redox reactions. Increasing the pseudocapacitive contribution is one of the most effective means to improve the rate performance of electrode materials. In this study, graphene oxide is used as a template to in situ synthesize burr globule‐like FeSe2/graphene hybrid (B‐FeSe2/G) using a facile one‐step hydrothermal method. Structural characterization demonstrates that graphene layers not only wrap the surfaces of FeSe2 particles, but also stretch into the interior of these particles, as a result of which the unique nano‐microsphere structure is successfully established. When serving as anode material for Na‐ion batteries, B‐FeSe2/G hybrid displays high electrochemical performance in the voltage range of 0.5–2.9 V. The B‐FeSe2/G hybrid has high reversible capacity of 521.6 mAh·g−1 at 1.0 A g−1. Meanwhile, after 400 cycles, high discharge capacity of 496.3 mAh g−1 is obtained at a rate of 2.5 A g−1, with a high columbic efficiency of 96.6% and less than 1.0% loss of discharge capacity. Even at the ultrahigh rate of 10 A g−1, a specific capacity of 316.8 mAh g−1 can be achieved. Kinetic analyses reveal that the excellent performance of the B‐FeSe2/G hybrid is largely attributed to the high pseudocapacitive contribution induced by the special nano‐micro structure.

Formation and Effect of Residual Lithium Compounds on Li-Rich Cathode Material Li1.35[Ni0.35Mn0.65]O2.

Li-rich cathode materials are regarded as ideal cathode materials, owing to their excellent electrochemical capacity. However, residual lithium compounds, which are formed on the surface of the materials by reacting with moisture and carbon dioxide in ambient atmosphere, can impair the surface structure, injure the capacity, and impede the electrode fabrication using Li-rich materials. Exposure to air atmosphere causes the formation of residual lithium compounds; the formation of such compounds is believed to be related to humidity, temperature, and time during handling and storage. In this study, we demonstrated for the first time an artificial strategy for controlling time, temperature, and humidity to accelerate exposure. The formation and effect of residual lithium compounds on Li-rich cathode material Li1.35[Ni0.35Mn0.65]O2 were systematically investigated. The residual lithium compounds formed possessed primarily an amorphous structure and were partially coated on the surface. These compounds include LiOH, Li2O, and Li2CO3. Li2CO3 is the major component in residual lithium compounds. The presence of residual lithium compounds on the material surface led to a high discharge capacity loss and large discharge voltage fading. Understanding the formation and suppressing the effect of residual lithium compounds will help prevent their unfavorable effects and improve the electrochemical performance.

SnO-GeO2-Sb2O3 glass anode network mixed with different Ba2+ fractions: Investigations on Na-ion storage capacity and stability

Microstructure and electrochemical characteristics of glass anode composition (100-x) (0.7[0.625SnO-0.375GeO2]-0.3Sb2O3)-xBaO (x = 0, 2, 4, 6 and 8 mol%, labeled as Bx) for the sodium battery is analyzed. The absence of peaks in the XRD traces related to glass former (Sb2O3) after discharging is directly confirmed that the antimony content retains its amorphous phase even after the samples are being discharged. Several nanosized amorphous intermediate domains are precipitated in the bright region of Sn-Ge-Sb glass network as appeared in TEM results. Except for the sample B6, all the other samples exhibited two sloping sodiation and de-sodiation plateaus which are almost constant at around 0.62 V and 0.14 V due to the formation of amorphous intermediates domains such as Na9Sn4 and NaSn3 in the glass network. The initial discharge capacity achieved to be highest for B6 sample (838 mA h g−1) and loss of discharge capacity is up to ~31.18% even at high rate 5C. A systematic study can monitor the stable cycle performance and shed light on the design of target glass anode with high capacity and stability.

Mn substitution controlled Li-diffusion in single crystalline nanotubular LiFePO4 high rate-capability cathodes: Experimental and theoretical studies

Carbon-coated single crystalline nanotubular (NT) and nanoparticular (NP) LiFe1-xMnxPO4 (x = 0, 0.2, and 0.5) cathodes are fabricated to study the effect of compositional and microstructural changes on Li+ diffusion and electrochemical properties. Insight in to the compositional effect on Li+ diffusion is obtained from DFT facilitated climbing image nudged elastic band (CI-NEB) simulations. NT cathodes exhibit exceptionally good discharge capacities ∼60 (∼165) mAhg−1, ∼32 (∼110) mAhg−1 and ∼22 (∼82) mAhg−1 at 25C (1C) rate for x = 0, 0.2, 0.5, respectively. NP cathodes show capacity <5 mAhg−1 at 5C/2C-rate. The high-rate capability with two orders larger diffusion coefficient in nanotubes is due to improved access to Li+ intercalation channels. Whereas, nanoparticles are agglomerated, making b-axis inaccessible. While, Mn substitution affects the discharge capacity, it significantly improves capacity retention from ∼60% (x = 0) to ∼88% (x = 0.2) measured over 1000 cycles at ≥5C. From CI-NEB calculations we infer that Mn increases the activation barrier in its neighbourhood, thereby creating a steep potential hump (∼0.15 eV) for the Li+ diffusion. This largely impedes the ion transport and accounts for the steep loss of discharge capacity. We observe, while single crystalline nanotubular LiFePO4 are useful for high power density applications, Mn substitution in small quantities (x∼0.2) is ideal for cathodes with increased cyclic stability at high C-rates.

Bulk and surface reconstructed Li-rich Mn-based cathode material for lithium ion batteries with eliminating irreversible capacity loss

Bulk and surface reconstructed Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode materials induced by spinel embedment and γ-MnO2 modification were synthesized by a one-step hydrothermal method. The results of XRD, XPS and SEM confirmed the introduction of γ-MnO2. The analysis of XPS, TEM images, dQ/dV curves and CV curves demonstrated that a spinel phase is embedded synchronously in the bulk of layered structure during the process of γ-MnO2 modification. The results of charge-discharge profiles and dQ/dV curves demonstrated the irreversible discharge capacity loss in the initial cycle is reduced with the introduction and collaboration of spinel and γ-MnO2. Namely, the initial coulombic efficiency is improved up to approximately 100%. Furthermore, the specific discharge capacity and rate performances are enhanced by a structure breakthrough for Li+ transport through blending with electrochemical active spinel-phase and γ-MnO2. In addition, the capacity retention of the material is enhanced from 64% up to 85% after 200 cycles. The main reasons are that the surface of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 is stabilized and the phase transformation from surface to bulk is mitigated under the protection of γ-MnO2 coating layer.

Electrochemical performance of SnO\u2013V2O5\u2013SiO2 glass anode for Na-ion batteries

SnO–V2O5–SiO2 glass anode sample prepared by simple a mechanical milling technique. The amorphous nature of sample identified using with XRD technique. This glass anode has an initial charge capacity of 560 mAhg−1 and discharge capacity of 483 mAhg−1. After 20 charge–discharge cycles, charge and discharge capacities achieved to be 389 and 379 mAhg−1 at 0.1C, respectively. The loss in discharge capacity is up to ~ 45.22% even at high rate 5C.

Ultrahigh rate and long-life nano-LiFePO4 cathode for Li-ion batteries

LiFePO4 is one of the most promising cathode materials for Li-ion batteries. However, its low electronic conductivity and slow Li-ion diffusion rate lead to poor electrochemical performance, especially poor rate performance. The hybrid of LiFePO4/Nitrogen and Sulfur co-doped graphene is successfully synthesized via a self-assembly method. Given its Nitrogen and Sulfur co-doped graphene matrix, the hybrid exerts a significantly impact on the electron conductivity of LiFePO4, resulting in excellent electrochemical properties and power density. The LiFePO4 composite has reversible capacity of 106.1 mAhg −1 at 10 C and 94.6 mAhg−1at 15 C. Moreover, with less than 5% loss of discharge capacity after 500 cycles at 10 C, the Nitrogen and Sulfur co-doped graphene can effectively improve the electrochemical performance of LiFePO4.