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With lithium-ion batteries being utilized in all aspects of life, accurately estimating the state of charge (SOC) of a battery has become a key issue in battery management systems. In this paper, an improved hybrid model based on adaptive extended Kalman filter (AEKF) and improved long short-term memory (ILSTM) neural network is proposed. The proposed model is based on a second-order RC equivalent circuit model, and the dynamic forgetting factor recursive least squares (DFFRLS) and AEKF algorithms are utilized to obtain the initial SOC estimates. And the estimation error in the AEKF algorithm due to neglecting the higher order terms of the Taylor expansion equations is compensated by the improvement of the LSTM network. The results under different working conditions indicate that the SOC estimation of the hybrid model has good convergence and high system robustness. The maximum error (MAX) of this algorithm is less than 2.3 %, especially the root mean square error (RMSE) and mean absolute error (MAE) are less than 0.84 % and 0.65 %, respectively. • A model and data-driven fusion method for battery SOC estimation is proposed. • It is based on the battery model and supplemented by the data-driven model. • Introduced the dynamic forgetting factor recursive least squares method. • The ILSTM algorithm is proposed to compensate for the high-order error of AEKF. • The proposed method can accurate SOC estimation at various operating conditions. [ABSTRACT FROM AUTHOR]

Abstract: Equilibrium potential hysteresis of electrode materials refers to the phenomenon that discharge equilibrium potential is lower than charge equilibrium potential. It is induced by the strain accommodation energy of phase transformation. Taking LiFePO4 as an example, the equilibrium potential hysteresis and accommodation energy of two LiFePO4 with different particle sizes were characterized using galvanostatic intermittent titration technique (GITT), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) methods. The LiFePO4 sample with 40nm particle size has lower accommodation energy than that of 100nm LiFePO4, which is due to a narrower miscibility gap and smaller potential hysteresis of 40nm LiFePO4 comparing to 100nm LiFePO4. The phase transformation of LiFePO4 occurs only at potential levels above delithiation (charge) equilibrium potential and below lithiation (discharge) equilibrium potential. No phase transformation occurs when charge/discharge is limited in the potential hysteresis range, i.e. LiFePO4 behaves like a solid solution in the potential hysteresis range. A reliable EIS can only be obtained when it is performed at the center of potential hysteresis and the potential amplitude does not exceed the range of equilibrium potential hysteresis. The analysis on strain accommodation and potential hysteresis of LiFePO4 cathodes during Li ion insertion/extraction is also suitable for other phase transformation electrodes. [ABSTRACT FROM AUTHOR]

Abstract: The rate performances of four mixed conductive electrodes (Li4/3Ti5/3O4, LiFePO4, LiCoO2 and LiCo1/3Ni1/3Mn1/3O2) were investigated using galvanostatic charge/discharge, electrochemical impedance Spectroscopy (EIS) and galvanostatic intermittent titration (GITT). These four electrode materials can be roughly divided into two groups according to the structure change during Li intercalation/extraction, i.e. the phase transition materials (Li4/3Ti5/3O4 and LiFePO4) and mixed phase transformation and solid solution materials (LiNi1/3Mn1/3Co1/3O2 and LiCoO2). Both the ionic conductivity and phase transition kinetics have a strong impact on the rate capability of the electrode material in addition to the generally accepted factors such as particle size and electronic conductivity. The rate capabilities of Li4/3Ti5/3O4 and LiFePO4, which have an extended flat region in the charge/discharge curves, mainly depended on their phase transition kinetics. The rate performance of the solid solution materials were controlled by the ionic conductivity, with some influence from the electronic conductivity. [Copyright &y& Elsevier]

Abstract: The increase in energy density and power density requirements for lithium-ion secondary cells for commercial applications has led to a search for higher capacity electrode materials than those available today. Silicon would seem to be a possible alternative for the graphite or carbon anode because its intercalation capacity is the highest known. However, the large capacity fade observed during initial cycling has prevented the silicon anode from being commercialized. Here we present a review of methodologies adopted for reducing the capacity fade observed in silicon-based anodes, discuss the challenges that remain in using silicon and silicon-based anodes, and propose possible approaches for overcoming them. [Copyright &y& Elsevier]

Abstract: LiFe0.9Mg0.1PO4 material was prepared by mechanical milling method, followed by heat treatment. The equilibrium potential-composition isotherm of LiFe0.9Mg0.1PO4 and charge–discharge kinetics of LiFe0.9Mg0.1PO4 were measured using galvanostatic intermittent titration technique (GITT), potential-step chronoamperometry (PSCA), and electrochemical impedance spectroscopy (EIS). The rate performance of the cathode is controlled by the charge-transfer kinetics, electronic conductivity, Li-ion diffusion capability, and phase transformation rate. Since LiFe0.9Mg0.1PO4 has a fast charge-transfer reaction and high electronic and ionic diffusivity, the phase transformation between LiFe0.9Mg0.1PO4 and Li0.1Fe0.9Mg0.1PO4 begins to play a more important role in the charge–discharge process, as is evident by an inductive loop induced by the phase transformation in the low frequency region of EIS. The phase purity and morphology of LiFe0.9Mg0.1PO4 were also observed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). [Copyright &y& Elsevier]

Lithium-ion capacitors, as a hybrid electrochemical energy storage device, realize high specific energy and power density within one device, thus attracting extensive attention. Here, hierarchically porous Li 3 VO 4 /C nanocomposite is prepared by a solvo-thermal reaction, followed with a post-annealing process. This composite has macropores at the center and mesopores in the wall, thus effectively promoting electrolyte penetration and structure stability upon cycling simultaneously. Compared to mesoporous Li 3 VO 4 , the enhanced rate capability and specific capacity of hierarchically porous Li 3 VO 4 /C indicate the synergistic effect of mesopores and macropores. Inspired by these results, this composite is coupled with mesoporous carbon (CMK-3) for lithium-ion capacitors, generating a specific energy density of 105 Wh kg −1 at a power density of 188 W kg −1 . Even if the power density increases to 9.3 kW kg −1 , the energy density still remains 62 Wh kg −1 . All these results demonstrate the promising potential of hierarchically porous Li 3 VO 4 in lithium ion capacitors. [ABSTRACT FROM AUTHOR]

Transition metal fluorides (such as FeF 3 and FeF 2 ) based on conversion chemistry have been considered as a promising alternative to the intercalation cathode materials due to the high capacity and high energy density. However, the critical challenges for these materials come from the absence of Li source in them, and low power density and poor cycling stability. Herein, pre-lithiated FeF 3 with extremely small size of Fe and LiF nanoparticles (both ∼6 nm) homogeneously embedded in the carbon matrix were synthesized using a facile and scalable in situ strategy. Benefited from the ultra-small Fe and LiF nanoparticles, uniform distribution, and intimate contact between the active species and the carbon matrix, the particle-to-particle interfacial resistance and diffusion length for Li and F are dramatically reduced. As a result, a high specific capacity of over 400 mA h g −1 with a discharge energy density of ∼700 W h kg −1 and favorable cycling performance are achieved, making such composite a promising high-capacity cathode for LIBs. Furthermore, the built-in Li source in this composite renders it a drop-in replacement for cathode materials used in the current LIB configurations, thus paving the way for the practical applications in the next generation of high energy density LIBs. [ABSTRACT FROM AUTHOR]

A system of electrolytes using water as a solvent was successfully used to support a typical lithium-ion battery chemistry that operates at 3.7V–4.2 V using standard ultraviolet-cured acrylic-based polymers as hydrophobic barriers. The aqueous electrolyte is contained in a system of poly(ethylene glycol) acrylate polymers crosslinked to produce an electrolyte gel that has electrochemical properties similar to that of the liquid phase component. The electrolyte gels have elastic moduli in the kPa range, making them soft enough to tolerant flexing, cutting, and blunt force impacts while keeping the electrodes covered and safe from shorting. While batteries based on water-in-salt electrolyte provides intrinsic safety that is otherwise unavailable from typical non-aqueous electrolytes, acrylate-based aqueous gel electrolytes offer the potential of large-scale manufacturing owing to the relatively low volatility of the electrolyte components and the low complexity of the proposed manufacturing process. • UV-cured gel electrolytes were used to construct a 4 V lithium ion battery. • The main gel electrolyte was water-based, making the battery safe. • Gel electrolytes had conductivity ≥0.3 mS/cm. • Gel electrolytes exhibited favorable impedance characteristics. • Battery cells used graphite anodes and LiCoO 2 cathodes. [ABSTRACT FROM AUTHOR]