Introduction
The ever-growing energy demand with the increasing population and rise in the economy has led to a rapid increase in the total energy demand globally.1,2 More than 80 % of the energy supplies come from carbon-rich non-renewable energy sources in the current situation.3 Battery technologies are being established rapidly due to its increasing demand in portable devices, stationary frameworks, and electric vehicles.4,5 Among present various battery technologies, Lead-Acid (PbA), Nickel-Metal Hydride (NiMH), Nickel-Cadmium (NiCd) and Lithium-ion (Li-ion) are the major chemistries towards different applications due to their specific characteristics related to energy density, power density, durability, and economic feasibility.6–8 Even though the growing popularity of Li-ion and NiMH batteries, the demand for PbA batteries grows proportionately due to their ease in availability, manufacturing, maintenance, reliability, recycling and cost.9 Lead acid battery demand is higher in large-scale applications such as renewable energy storage system, e.g., wind and solar technologies despite having lower energy density (< 50 Wh/kg). Lead acid battery market share is the largest for stationary energy storage system due to the development of innovative grid with Ca and Ti additives and electrodes with functioning carbon, Ga2O3 and Bi2O3 additives.10,11In the current scenario, leak-proof and maintenance-free Sealed Lead Acid batteries (SLAs) are used in multiple applications such as motorcycles, ATVs, home alarm systems, toys, backup systems, workout equipment and generators.12–14
Temperature plays a key role in the battery operation as it affects the cycle life, performance, and available capacity. The PbA battery system are designed to perform optimally at ambient temperature (25 °C) for performance, capacity and cyclability. However, they degrade faster when operated at higher than ambient conditions leading to shorter cycle life due to the degradation of electrode and grid materials.6 The oxidation and reduction rates increase significantly at both Pb anode and PbO2 cathode, leading to higher discharge capacity at elevated temperatures.7,12 Besides having a deleterious impact on the cycle life at elevated temperatures, several other impacts include self-discharge reactions, loss of electrolyte, active material shedding, grid corrosion, and loss of mechanical strength of the positive electrode (PbO2).15–17Shedding or loss of positive active mass particles into the electrolyte could also increase corrosion and macro defects on the lugs of the negative electrode.16,17 While operating at lower temperature, low electrolyte conductivity and active material results in reduced available capacity.6 To reduce the corrosion or degradation rate of the PbA battery, limiting the internal temperature to < 60 °C could minimize the electrolyte vaporization.18 The cell internal pressure should be in acceptable range for long term optimum performances. However, it was reported that charging efficiency and cyclability were improved under high internal pressure with the favorable crystal structure of the electrodes.16 Performance evaluation of the batteries at elevated temperatures and near-freezing temperature is critical for using these batteries for outdoor energy storage applications in hot and cold conditions.6
The adverse effect of temperature also includes reduced discharge capacity, increased internal resistance and self-discharge with increased duration at extreme temperatures. Typical PbA batteries undergo many charge/discharge cycles during their life time.10 Hence it is necessary to understand the complete cycling behavior of PbA battery in various operating conditions, including incomplete charging, slow discharging, extreme conditions such as temperature fluctuations, and vibrations that cause degradation of internal components leading to failure of the battery.
In this work, a systematic study was conducted to analyze the 2V/5Ah Enersys® Cyclon sealed lead-acid (SLA) cells cycled at -10, 0, 25 and 40 °C, to minimize the experimentation duration as these conditions are practical for vehicles used or stored in frozen tundra and arid desert climates. To evaluate these condition, electrochemical impedance spectroscopy (EIS) was carried out to evaluate internal resistance (ohmic and charge transfer) to explain the degradation mechanism of the battery. Further, electrode materials were extracted post cycling analysis for morphology characterization using X-ray diffraction (XRD), and Energy-dispersive X-ray spectroscopy analysis (EDX). SLA batteries were observed to degrade faster at higher temperatures (25 and 40°C). However, the degradation is minimal at lower temperatures (0 and -10 °C) due to less active material and slower kinetics. The impedance values, x-axis intercept of Nyquist plot was observed to increase with cycling at all the temperatures.