Understanding the Self-charge and discharge mechanism ...

Understanding the Self-charge and Discharge Mechanism

Lithium-ion batteries are rechargeable batteries that utilize lithium ions for energy storage. Compared to other rechargeable batteries, they boast a low self-discharge rate, typically losing around 5% of their charge each month. This characteristic allows them to remain dormant for extended periods without significant energy loss. The charge and discharge processes in lithium-ion batteries are primarily governed by the movement of lithium ions between the anode and cathode. During charging, lithium ions migrate from the anode to the cathode, storing energy. Conversely, during discharge, the ions move back to the anode, releasing energy. This cycle can be repeated multiple times. The charging and discharging rates of lithium-ion batteries are influenced by several factors, such as the type of electrolyte, the size and composition of the electrodes, and the operating temperature. Additionally, the design of the battery, including the arrangement of electrodes, plays a critical role. Overall, the charge and discharge processes of lithium-ion batteries are complex and can be influenced by various factors. Nevertheless, their high energy density and low self-discharge rates keep them popular for numerous applications.

Visit Sunplus to learn more.

Self-charge and Discharge Mechanism of a Lithium-Ion Battery

Importance of Self-discharge

The self-discharge rate of lithium-ion batteries is crucial for maintaining long-term performance. Self-discharge is a natural phenomenon that occurs even when batteries are not in use. Typically, a lithium-ion battery self-discharges at about 5% per month, depending on its type and temperature. This rate can be minimized by keeping the storage voltage above the minimum threshold and storing the battery in cooler environments. Managing self-discharge helps maintain charge capacity over time, contributing to a longer lifespan.

Self-discharge Mechanism

Self-discharge refers to the gradual loss of stored electrical energy in a battery, even when not actively used. This phenomenon arises from various factors, including chemical reactions, leakage, and temperature variations. To mitigate self-discharge rates, techniques such as using lower temperatures and special coatings can be employed.

Effects of Self-discharge on Storage Batteries

Self-discharge in storage batteries leads to charge loss over time, impacting battery performance and potentially shortening lifespan. This loss can result from internal chemical reactions, environmental influences, and other factors. It diminishes battery capacity and performance, possibly leading to premature failure. Although proper storage and maintenance can minimize self-discharge, it cannot be entirely eliminated.

Distinction Between Chemical and Physical Self-discharge

Chemical self-discharge occurs due to electrochemical reactions that reduce a battery's voltage over time. These reactions happen when the battery's chemicals interact with the electrolyte, creating different substances. Physical self-discharge arises from heat, vibration, or mechanical actions that lower the terminal voltage. Exposure to high temperatures accelerates this process by increasing the movement of ionic charge carriers, leading to quicker voltage loss.

Self-discharge Testing

Self-discharge tests are conducted to evaluate the rate at which a battery loses its charge over time. This information is essential for assessing capacity, reliability, and performance. In this test, the battery is disconnected from an electrical circuit, and the voltage is monitored over a defined period. A steady voltage decline indicates normal discharge behavior; if this decline is not as expected, it may suggest battery faults or a shorter lifespan.

Types of Self-discharge Tests

Self-discharge tests measure how quickly a battery loses its charge without a load. They assess battery health, capacity, and expected lifespan. The common types of self-discharge tests include:

• Continuous self-discharge test
• Intermittent self-discharge test
• Short-term self-discharge test
• Long-term self-discharge test
• Vibration self-discharge test
• Submersion self-discharge test
• High-temperature self-discharge test
• Low-temperature self-discharge test

Factors Affecting Self-discharge and Control Points

Are you interested in learning more about Low self-discharge rate low voltage lithium battery services? Contact us today for an expert consultation!

• The internal resistance of the battery directly influences the self-discharge rate as it affects the draw of current from the battery. Higher internal resistance correlates with lower self-discharge rates.

Control point: Choose a battery with lower internal resistance.

• Temperature significantly impacts the electrochemical reactions within the battery, influencing the self-discharge rate. Higher temperatures result in increased self-discharge.

Control point: Maintain the battery at optimal temperatures.

• The state of charge affects the self-discharge rate—lower states lead to higher rates of self-discharge.

Control point: Keep the battery's state of charge at an optimal level.

• Age affects self-discharge rates—the older the battery, the higher the self-discharge rate.

Control point: Regular maintenance and timely battery replacement after its life cycle.

What is the Discharge Rate and Self-discharge Rate of Lithium ...

Battery Discharge Rate

The discharge rate refers to the current required for a battery to deliver its rated capacity within a specified period, expressed as a multiple of the battery's rated capacity (denoted as C). Generally, rates of 0.2-2C represent capacity lithium batteries (LCR), while rates above 2C represent power lithium batteries (LNR/LMR).

High-rate batteries primarily refer to lithium batteries, which function through the movement of lithium ions between the positive and negative electrodes. During the charging and discharging processes, Li+ ions are inserted and extracted between electrodes: during charging, Li+ is drawn from the positive electrode and embedded into the negative electrode via the electrolyte; during discharging, this process reverses. Batteries with lithium-containing materials as electrodes exemplify modern high-performance batteries.

Lithium batteries fall into categories of high-rate batteries and lithium-ion batteries. Presently, lithium-ion batteries are prevalent in mobile phones and laptops, often misconstrued as high-rate batteries. In reality, true high-rate batteries are seldom used in everyday electronic products due to their inherent risks.

Lithium-ion batteries exhibit high energy density and uniform high output voltage. With a low self-discharge rate (above 2% per month for quality batteries), they possess no memory effect and operate efficiently across a wide temperature range (-20°C to 60°C). Their excellent cycle performance and rapid charging capabilities achieve up to 100% charging efficiency and high output power. Furthermore, these batteries contain no toxic materials and are recognized as environmentally friendly.

Battery Self-Discharge Rate

The self-discharge rate, or charge retention capacity, reflects a battery's ability to retain stored charge under specific conditions when in an open circuit state. It is influenced by manufacturing processes, materials, and storage conditions. Self-discharge is a critical parameter in evaluating battery performance.

Given that it is impossible to achieve perfect purity in battery raw materials, impurities inevitably contribute to self-discharge phenomena.

The voltage drop in lithium power batteries is recorded in millivolts per day (mV/day). Well-performing lithium batteries should exhibit a voltage drop of less than 2mV daily.

Self-discharge can also be represented in terms of the K value, indicating the voltage drop over a specified time (mV/h). For quality lithium batteries, the K value typically remains within 0.08mV/h and can be calculated using the equation: K = (V1 - V2) / ΔT, where V1 is the battery voltage before one hour and V2 is the voltage afterward.

Self-discharge rate as a percentage represents the capacity decrease in lithium batteries over specified time periods: Y% = (C1 - C2) / C1 × 100, where Y% signifies the self-discharge rate, C1 denotes the battery capacity before storage, C2 indicates capacity after storage, and T stands for storage duration, usually noted in days, weeks, months, or years.

Lithium power batteries often experience voltage drops during use or storage, largely attributed to self-discharge within their cells.

Contact us to discuss your requirements regarding low voltage lithium battery China. Our experienced sales team can assist you in identifying the best options for your needs.