Lithium Power Battery Structure and Basic Information

Lithium power battery structure and basic information encompass vital components and essential details. At its core, a lithium power battery comprises electrodes, electrolytes, and a separator. The electrodes, typically made of lithium compounds, facilitate the flow of ions during charge and discharge cycles. Electrolytes serve as the medium for ion transport between electrodes, while the separator prevents short circuits by keeping electrodes apart. These batteries boast high energy density, long cycle life, and low self-discharge rates, making them ideal for various applications, from portable electronics to electric vehicles. Understanding their structure and characteristics is pivotal for optimizing performance and ensuring safety in their utilization.

The components of a lithium-ion battery are as follows

(1) Cathode: The active material is generally lithium manganese oxide or lithium cobalt oxide, nickel-cobalt-manganese oxide materials. Electric bicycles commonly use nickel-cobalt-manganese oxide (often referred to as ternary) or ternary with a small amount of lithium manganese oxide. Pure lithium manganese oxide and lithium iron phosphate have gradually faded out due to their large volume, poor performance, or high cost. The conducting electrode fluid utilizes electrolytic aluminum foil with a thickness of 10-20 micrometers.

(2) Separator: A specially formed polymer thin film with micro-porous structures that allow lithium ions to pass through freely while preventing the passage of electrons.

(3) Anode: The active material is graphite or carbon with a structure similar to graphite. The conducting collector fluid utilizes electrolytic copper foil with a thickness of 7-15 micrometers.

(4) Organic electrolyte: Solvents dissolved with lithium hexafluorophosphate carbonate esters, while polymers use gel-like electrolytes.

(5) Battery casing: It is divided into steel casing (rarely used in square shapes), aluminum casing, nickel-plated iron casing (used in cylindrical batteries), aluminum-plastic film (soft packaging), and battery caps, which also serve as the positive and negative terminals of the battery.

Introduction to Lithium-ion Batteries

1.State of Charge

The state of charge (SOC) refers to the available electrical energy within a battery, typically expressed as a percentage. As the available energy varies due to factors such as charging/discharging current, temperature, and aging effects, SOC can be defined in two ways: absolute SOC and relative SOC. Relative SOC typically ranges from 0% to 100%, where 100% represents full charge and 0% represents full discharge. Absolute SOC is a reference value calculated based on the designed fixed capacity of the battery at the time of manufacturing. A brand-new fully charged battery has an absolute SOC of 100%, while even when fully charged, an aged battery may not reach 100% SOC under different charging/discharging conditions.
The following graph illustrates the relationship between voltage and battery capacity at different discharge rates. Higher discharge rates result in lower battery capacity. Additionally, battery capacity decreases at lower temperatures.

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2.Maximum Charging Voltage

The maximum charging voltage is determined by the chemical composition and characteristics of the battery. For lithium batteries, the charging voltage typically ranges between 4.2V and 4.35V, though this may vary depending on the cathode and anode materials.

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3.Full Charge

A battery is considered fully charged when the voltage difference between the battery and the maximum charging voltage is less than 100mV, and the charging current decreases to C/10. The conditions for full charge may vary depending on the battery’s characteristics.

The graph below illustrates a typical charging characteristic curve for lithium batteries. When the battery voltage reaches the maximum charging voltage and the charging current decreases to C/10, the battery is considered fully charged.

4.Minimum discharge voltage

The minimum discharge voltage can be defined using the cutoff discharge voltage, which is typically the voltage when the state of charge is at 0%. This voltage value is not fixed but changes with load, temperature, degree of aging, or other factors.

5.Complete Discharge

When the battery voltage is less than or equal to the minimum discharge voltage, it can be considered as a complete discharge.

6.Charge and Discharge Rate

The charge and discharge rate is a representation of the charge and discharge current relative to the battery capacity. For example, if discharged at 1C for one hour, ideally, the battery would be completely discharged. Different charge and discharge rates result in different available capacities. Generally, the higher the charge and discharge rate, the smaller the available capacity.

7.Cycle Life

Cycle life refers to the number of complete charge and discharge cycles a battery can undergo, which can be estimated from the actual discharge capacity and design capacity. Each time the accumulated discharge capacity equals the design capacity, one cycle is counted. Typically, after 500 charge and discharge cycles, the fully charged battery capacity may decrease by approximately 10% to 20%.

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The self-discharge of all batteries increases with rising temperatures. Self-discharge is not typically a manufacturing defect but rather a characteristic of the battery itself. However, improper handling during the manufacturing process can also increase self-discharge. Generally, for every 10°C increase in temperature, the self-discharge rate doubles. Lithium-ion batteries typically have a self-discharge rate of about 1-2% per month, while various nickel-based batteries have a self-discharge rate of 10-15% per month.

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Basic Understanding of Lithium Power Batteries

Classification and technological development of power lithium-ion batteries

Relevant standards for German lithium-ion power batteries

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