The hydrogen evolution and oxidation kinetics during overdischarging of sealed nickel-metal hydride batteries

The hydrogen evolution and oxidation kinetics in NiMH batteries have been investigated under temperature-controlled, steady-state, overdischarging conditions within a temperature range of 10 and 50°C and at discharging currents of 1–330 mA (0.0009 to 0.3 C rate). In situ Raman spectroscopic analyses of the gas phase showed that hydrogen is the only gas evolving inside the battery during overdischarge at the above-mentioned conditions. The pressure increase could be very critical at low temperatures, leading to opening of the safety vent at relatively low discharging currents, for example, only 220 mA at 10°C. The polarization parameters for the hydrogen evolution reaction, such as Tafel slopes and exchange currents were determined at the different temperatures as well as the activation energy for the evolution and oxidation processes. The reaction mechanisms and the rate-determining steps are discussed. These are highly valuable information in NiMH modeling as they are obtained directly from the system of interest. Furthermore, the obtained results make battery simulations more realistic by minimizing the number of parameters involved and making the correct assumptions

A facile physics-based model for non-destructive diagnosis of battery degradation

The identification of battery degradation is of significant importance for estimating the state of health. Loss of lithium inventory (LLI), loss of active materials of the negative electrodes (LAMNE), and loss of active materials of the positive electrodes (LAMPE) are three main degradation modes. This paper proposes an advanced model based on open circuit voltage and differential voltage (DV) fitting to diagnose and quantify the degradation modes of batteries at different stages, showing high fidelity. This physics-based model avoids solving many partial differential equations and is not computationally demanding. Using commercial batteries with NCA/SiC electrodes as a case study, the LLI, LAMPE, and LAMNE induced by battery cycling and storage at various temperatures, State-of-Charge, and charging/discharging rates are systematically identified and analyzed.</p

Mg-Ti-H thin films for smart solar collectors

Mg-Ti-H thin films are found to have very attractive optical properties: they absorb 87% of the solar radiation in the hydrogenated state and only 32% in the metallic state. Furthermore, in the absorbing state Mg-Ti-H has a low emissivity; at 400 K only 10% of blackbody radiation is emitted. The transition between both optical states is fast, robust, and reversible. The sum of these properties highlights the applicability of such materials as switchable smart coatings in solar collector

Dual Additives for Stabilizing Li Deposition and SEI Formation in Anode-Free Li-Metal Batteries

Anode-free Li-metal batteries are of significant interest to energy storage industries due to their intrinsically high energy. However, the accumulative Li dendrites and dead Li continuously consume active Li during cycling. That results in a short lifetime and low Coulombic efficiency of anode-free Li-metal batteries. Introducing effective electrolyte additives can improve the Li deposition homogeneity and solid electrolyte interphase (SEI) stability for anode-free Li-metal batteries. Herein, we reveal that introducing dual additives, composed of LiAsF6 and fluoroethylene carbonate, into a low-cost commercial carbonate electrolyte will boost the cycle life and average Coulombic efficiency of NMC||Cu anode-free Li-metal batteries. The NMC||Cu anode-free Li-metal batteries with the dual additives exhibit a capacity retention of about 75% after 50 cycles, much higher than those with bare electrolytes (35%). The average Coulombic efficiency of the NMC||Cu anode-free Li-metal batteries with additives can maintain 98.3% over 100 cycles. In contrast, the average Coulombic efficiency without additives rapidly decline to 97% after only 50 cycles. In situ Raman measurements reveal that the prepared dual additives facilitate denser and smoother Li morphology during Li deposition. The dual additives significantly suppress the Li dendrite growth, enabling stable SEI formation on anode and cathode surfaces. Our results provide a broad view of developing low-cost and high-effective functional electrolytes for high-energy and long-life anode-free Li-metal batteries.</p

A comparison between physics-based Li-ion battery models

Physics-based electrochemical battery models, such as the Doyle-Fuller-Newman (DFN) model, are valuable tools for simulating Li-ion battery behavior and understanding internal battery processes. However, the complexity and computational demands of such models limit their applicability for battery management systems and long-term aging simulations. Reduced-order models (ROMs), such as the Extended Single Particle Model (ESPM), Single Particle Model (SPM) and Polynomial and Padé approximations, here all referred to as simplifications, lead to faster computational speeds. Choosing the appropriate simplification method for a specific cell type and operating condition is a challenge. This study investigates the simulation accuracy and calculation speed of various simplifications for high-energy (HE) and high-power (HP) batteries at different current loading conditions and compares those to the full-order DFN model. The results indicate that among the ROMs, the ESPM consistently offers the best combination of high computational speed and relatively good accuracy in most conditions in comparison to the full-order DFN model. Among the approximations, higher-order polynomial approximation, third and fourth-order Padé approximation perform the best in terms of accuracy. The higher-order polynomial approximation shows an advantage in terms of computing speed, while the fourth-order Padé approximation achieves the highest overall accuracy among the different approximations.</p