Optimization of pulse discharge performance of lithium battery packs

First, optimize the battery material system

(1) Improvement of cathode materials

The cathode material has a significant impact on the pulse discharge performance of lithium battery packs. Different cathode materials have different crystal structures and electrochemical properties, which in turn affect the intercalation and deintercalation rates of lithium ions. For instance, cathode materials with a layered structure (such as lithium cobalt oxide) have a relatively high theoretical specific capacity, but during pulse discharge, their structural stability may be insufficient, resulting in rapid capacity attenuation.

The structural stability of the cathode material can be enhanced by modifying it with other elements (such as aluminium, magnesium, etc.). Doped elements can enter the lattice of the cathode material, change the lattice parameters, and increase the lattice energy of the material. Thus, it can better withstand the rapid intercalation and deintercalation of lithium ions during pulse discharge, reduce the possibility of structural collapse, and improve the performance of pulse discharge.

In addition, developing new cathode materials is also an important way to optimize the performance of pulse discharge. For instance, lithium-rich manganese-based cathode materials have a high specific capacity and good cycling performance. Under pulse discharge conditions, their multi-electron reaction mechanism can provide more lithium ions to participate in the reaction, which is expected to enhance the pulse discharge capacity of lithium battery packs.

(II) Optimization of anode materials

The anode material mainly affects the storage and release of lithium ions. Graphite anode materials have advantages such as low cost and good cycle performance. However, during pulse discharge, their relatively low lithium-ion diffusion coefficient may limit the pulse discharge performance.

Surface coating treatment of graphite anode materials is an effective optimization method. Coating the surface of graphite with a layer of amorphous carbon or metal oxides and other materials can improve its surface properties and increase the diffusion rate of lithium ions. For instance, coating amorphous carbon can enhance the conductivity of the graphite surface, reduce the diffusion resistance of lithium ions on the surface, and enable lithium ions to intercalate and deintercalate the graphite anode more quickly, thereby improving the performance of pulse discharge.

In addition, the development of new anode materials, such as silicon-based anode materials, is also a future development direction. Silicon-based anode materials have an extremely high theoretical specific capacity, but their volume changes significantly during charging and discharging. The modification of silicon-based anode materials through technical means such as nanoscale and composite can alleviate the problem of their volume change and improve their performance under pulsed discharge conditions.

(3) Adjustment of electrolyte formula

The electrolyte is the medium through which lithium ions transport between the positive and negative electrodes, and its performance directly affects the pulse discharge performance of lithium battery packs. Traditional electrolytes may have problems such as insufficient ionic conductivity and poor compatibility with electrode materials during pulse discharge.

The development of new electrolyte formulations can enhance ionic conductivity. For instance, by compounding solvents with high dielectric constant (such as ethylene carbonate) and low viscosity (such as dimethyl carbonate), the physical properties of the electrolyte can be optimized and the migration rate of lithium ions can be enhanced. Meanwhile, adding appropriate additives (such as film-forming additives, flame retardant additives, etc.) can improve the interface performance between the electrolyte and the electrode material, form a stable solid electrolyte interface film (SEI film), reduce interface resistance, and enhance pulse discharge performance.

Second, optimize the battery structure design

(1) Electrode structure design

Structural parameters such as the thickness, porosity and distribution of active substances of the electrode will affect the transport of lithium ions and the electrode reaction rate, and thereby influence the performance of pulse discharge.

Appropriately reducing the thickness of the electrode can shorten the diffusion path of lithium ions and increase the transport rate of lithium ions. During the pulse discharge process, lithium ions can diffuse more rapidly from the interior of the electrode to the surface to participate in the reaction, thereby enhancing the battery's pulse discharge capacity. However, if the electrode thickness is too thin, it may lead to a decrease in the energy density of the battery. Therefore, a trade-off needs to be made between the pulse discharge performance and the energy density.

Increasing the porosity of the electrode can enhance the wettability of the electrolyte and promote the transport of lithium ions. The porosity of the electrode can be controlled by optimizing the preparation process of the electrode (such as coating, drying, rolling, etc.). For instance, by adjusting the solid content and viscosity of the slurry during the coating process and controlling the rolling pressure and speed during the rolling process, an appropriate porosity can be achieved.

In addition, it is also very important to rationally design the distribution of active substances in the electrode. By adopting gradient distribution or core-shell structure and other methods, the electrode can have different active material contents and electrochemical performance at different positions, thereby enhancing the overall reaction rate and pulse discharge performance of the electrode.

(2) Optimization of battery pack connection methods

Lithium battery packs are usually composed of multiple individual cells connected in series or parallel. The connection method of the battery pack will affect its pulse discharge performance.

When connected in series, the internal resistance differences among individual batteries can lead to uneven voltage distribution. During the pulse discharge process, batteries with higher internal resistance may reach the discharge cut-off voltage earlier, thereby limiting the pulse discharge capacity of the entire battery pack. By optimizing the screening and assembly processes of batteries and reducing the internal resistance differences among individual batteries, the pulse discharge performance of series battery packs can be improved.

When connected in parallel, uneven current distribution between batteries may affect the performance of pulse discharge. The adoption of a balancing circuit can monitor and adjust the current of each parallel battery in real time, ensuring that the current is evenly distributed among the batteries, thereby enhancing the pulse discharge performance of the parallel battery pack. For instance, passive balancing circuits or active balancing circuits are adopted to achieve balancing between batteries through resistor discharge or energy transfer.

Third, optimize the battery management system (BMS) strategy

(1) Precise temperature management

Temperature has an important influence on the pulse discharge performance of lithium battery packs. In a low-temperature environment, the chemical reaction rate inside the battery slows down, and the diffusion coefficient of lithium ions decreases, resulting in a decline in pulse discharge performance. In high-temperature environments, the capacity attenuation of batteries accelerates and their safety is also affected.

The BMS can monitor the temperature of the battery pack in real time through a temperature sensor and adopt corresponding control strategies based on the temperature conditions. In a low-temperature environment, the BMS can activate the heating device to increase the temperature of the battery pack and bring it to the optimal operating temperature range. For instance, PTC heaters or liquid heating systems are adopted to heat the battery pack to between 10℃ and 30℃, thereby enhancing the performance of pulse discharge. In high-temperature environments, the BMS can activate cooling devices such as fans and liquid cooling systems to lower the temperature of the battery pack and prevent it from overheating.

(2) Intelligent charging and discharging control

A reasonable charge and discharge control strategy can improve the pulse discharge performance of lithium battery packs. During the charging process, a constant current - constant voltage charging method is adopted to prevent overcharging from causing damage to the battery. At the same time, control the size of the charging current to prevent excessive charging current from causing internal heating of the battery and affecting the pulse discharge performance.

During the discharge process, the BMS can dynamically adjust the discharge current based on the battery's SOC (State of Charge) and the requirements of pulse discharge. When the SOC of the battery is relatively high, a larger pulse discharge current can be allowed. When the SOC of the battery is low, limit the pulse discharge current to prevent over-discharge of the battery. In addition, BMS can also adopt a combined method of pulse charging and pulse discharging to activate the battery, thereby enhancing the battery's pulse discharge performance and cycle life.

(3) Fault Diagnosis and Protection

The BMS should be equipped with a complete fault diagnosis function, capable of promptly detecting abnormal conditions of the battery pack, such as short circuits, open circuits, and leakage. When a fault is detected, the BMS should immediately take protective measures, such as cutting off the connection between the battery and external devices, to prevent the fault from further expanding and affecting the pulse discharge performance and battery safety.

For instance, when a short circuit is detected inside the battery pack, the BMS can cut off the discharge circuit within tens of microseconds to prevent excessive short-circuit current from causing the battery to overheat, catch fire or even explode. Meanwhile, BMS can also record fault information, providing a basis for subsequent maintenance and fault analysis.