1. Why choose lithium battery?
At present, most power batteries are still lithium batteries. Of course, sodium-ion batteries are gradually beginning to be mass-produced, but they are not the main players yet.
(1) High energy density
Lithium batteries have a high energy density and can store relatively more electrical energy in a relatively small volume and weight.
(2) Good charge and discharge performance
Lithium batteries have higher charging and discharging efficiencies, and can utilize electrical energy more efficiently and reduce energy loss.
(3) Long life and stability
Lithium batteries typically have a long cycle life and a low self-discharge rate, and can maintain stable performance over a longer period of time, extending the service life of electric vehicles and reducing maintenance and replacement costs.
(4) Relatively safe and reliable
Modern lithium batteries are equipped with a variety of safety protection measures that can effectively prevent problems such as overcharging, over-discharging and short circuits, greatly reducing the risk of fire or explosion in electric vehicles.
2. Lithium battery voltage range
The nominal voltage of a single lithium-ion battery is usually between 3.6 V and 3.7 V. This voltage is the typical operating voltage range of lithium-ion batteries.
The voltage of a lithium battery changes during the charge and discharge process. A typical lithium-ion battery can reach a voltage of 4.2V when charged and can drop to around 2.5V when discharged. Exceeding or falling below these values may affect the performance, lifespan and even safety of the battery.
For large applications such as electric vehicles, multiple lithium battery cells need to be combined into battery packs to achieve the required voltage and capacity. The operating voltage of electric vehicle battery packs is generally between 300V and 400V, of course, there are higher voltages, which is to match the voltage requirements of the motor and meet the design and performance requirements of the vehicle.
However, the battery pack can achieve the required voltage and capacity by connecting multiple single cells in series and in parallel. Series connection can increase the voltage, while parallel connection increases the capacity.
3. Cell current
Current is an important parameter in battery cell design, affecting the safety, performance and service life of the battery. The maximum charge/discharge current refers to the maximum current that the battery is allowed to charge within a safe range. It is generally expressed as a multiple of the battery capacity (C-rate). For example, a 1C charging current means that the current is equal to the value of the battery capacity. For example, for a 2000mAh battery, a 1C charging current is 2A.
High charge/discharge currents can usually fill the battery faster, but if the maximum charge current for the battery design is exceeded, it may cause the battery to overheat or be damaged. Of course, many lithium batteries can provide instantaneous currents exceeding their rated maximum discharge current for a short period of time, but this is usually limited.
4. Battery capacity
The capacity of a lithium battery is an important indicator of its energy storage capacity, usually expressed in Ah (ampere-hour)/mAh. The cell capacity is defined as the total amount of charge that a battery or battery pack can supply under specific discharge conditions. In other words, it indicates how long the battery can continue to discharge at a specific discharge rate (usually C rate), or the total amount of electricity that can be stored in a complete charge/discharge cycle.
For example, 1Ah (ampere-hour) is a unit of capacity for a battery or battery pack, which means that the battery can supply 1 ampere of current in 1 hour, and can also discharge or store 1 ampere-hour of electricity in 1 hour. The capacity of the battery cell directly determines the amount of charge or energy that the battery can store. A battery with a larger capacity can support the use of the device for a longer period of time.
5. SOC of battery cell
The SOC (State of Charge) of a lithium battery chip refers to the percentage of charge in the current lithium battery, that is, the degree to which the lithium battery has been charged. SOC is crucial for lithium battery management because it directly affects the battery's service life and performance stability.
In practical applications, the battery management system adjusts the charging and discharging process according to the SOC to maximize the battery's efficiency and life. Therefore, accurately measuring and managing SOC is critical to the design and operation of various mobile devices and electric vehicles.
6. Internal resistance of battery cell
The internal resistance of a lithium battery chip refers to the resistance generated inside the battery when current passes through it. This internal resistance is determined by factors such as the battery's chemical structure, electrolyte, and electrode materials, and will change with the battery's charge and discharge process, temperature changes, and service life.
Typically aged or damaged batteries will usually show higher internal resistance; the internal resistance of a battery increases with increasing temperature because high temperatures cause the conductivity of the electrolyte to decrease, thereby increasing resistance; after many charge and discharge cycles, the internal structure of the battery may change, resulting in an increase in internal resistance.
Therefore, it seems that the internal resistance of a lithium battery chip is a complex parameter that is affected by many factors.
The DC internal resistance (DCIR) of a battery cell refers to the internal resistance of a lithium battery cell under specific conditions (usually at standard temperature and charging state). This parameter is usually measured in milliohms (mΩ) and indicates the resistance of the battery during DC discharge.
The DC internal resistance reflects the battery's ability to respond to high-power discharge. Lower DC internal resistance means that the battery can provide current more efficiently, reducing energy loss and battery temperature rise. The DC internal resistance is usually determined by applying a DC current under standard conditions and measuring the voltage drop caused by it, that is, [{DCIR} = \{Delta V}/{Delta I}] .
7. Battery charging and discharging efficiency
The charge and discharge efficiency of a battery cell refers to the energy conversion efficiency of the battery during the charge and discharge process, usually expressed as a percentage. General lithium-ion batteries can usually achieve a relatively high level of charge and discharge efficiency, generally above 90%. Of course, its charge and discharge efficiency is also affected by many factors:
During the charging and discharging process, chemical reactions occur inside the battery. The efficiency of these chemical reactions affects the energy conversion efficiency.
The resistance inside the battery will cause energy loss, which is released as heat. The size of the internal resistance is closely related to the design of the battery and the selection of materials. Low internal resistance can reduce losses and improve charging and discharging efficiency.
Temperature affects the efficiency of battery charging and discharging. Generally speaking, low temperatures reduce the battery's charging efficiency because the activity of the electrolyte is reduced. High temperatures may increase internal resistance and affect the efficiency of chemical reactions.
8. Self-discharge of battery cells
The self-discharge of a battery cell refers to the phenomenon that when there is no external circuit connection, the charge in the battery itself will gradually be lost, resulting in a decrease in battery power.
The self-discharge rate of lithium-ion batteries is usually relatively low, generally under room temperature conditions, the monthly self-discharge rate is about 1%. This means that if a fully charged lithium-ion battery is left for about a month, its power may decrease by about 1%. Of course, different battery cell designs and processes will also affect its self-discharge rate, but generally speaking, the higher the temperature, the faster the battery self-discharges. Therefore, batteries in high temperature environments will lose power faster than batteries in low temperature environments.
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