Because the aluminum-plastic film is light in weight and has high internal space utilization, soft-pack batteries are suitable for the development of batteries with larger energy density. However, metal casings are limited by internal space and generally have slightly lower energy density than soft-pack batteries. Safety: Because aluminum-shell batteries are protected by metal casings, their safety is higher, while soft-package batteries can only rely on the performance of the material itself to pass the safety test, which currently seems to be more difficult. In terms of process difficulty, because soft-pack batteries have many small pole pieces, they require high die-cutting equipment and are prone to large self-discharge and local micro-short circuits. At the same time, due to internal space limitations, there is less free electrolyte, and the cycle performance may be slightly lower. Difference. Rolled batteries are relatively better, with some margin, and are easy to realize automated production. In terms of cost, because rolled batteries require high welding of the shell, the cost is slightly higher, while soft-pack batteries do not involve lasers. Welding focuses on packaging and equipment investment is low.

　　Calculate the number of positive and negative electrodes and separator layers of the battery core based on the internal space of the battery. According to the development status of the industry, the relevant parameters of the material are all experimentally verified based on past testing experience. It is necessary to verify the compaction density and material performance. The performance of auxiliary materials (including verification of SBR, CMC, PVDF, conductive agents, etc.) is based on the development of platform models. The development of the final process also needs to be matched with the materials to derive the final control plan and process flow chart. In order to shorten the time, manufacturers now combine experimental verification and process development, but the risks are often relatively high. After all, the material system itself develops with the development of technology.

　　Each performance of each material has relevant testing standards. Certain performance indicators of the positive and negative electrodes are directly related to the performance indicators of the battery. However, there is currently no suitable model for forward electrochemical performance simulation. It is only based on existing Empirical data for patching.

　　Voltage (V) Open circuit voltage, as the name suggests, means that the battery is not connected to any external load or power supply, and the potential difference between the positive and negative electrodes of the battery is measured, which is the open circuit voltage of the battery. The working voltage corresponds to the open circuit voltage, that is, when the battery is connected to an external load or power supply, current flows through the battery, and the potential difference between the positive and negative electrodes is measured. Due to the existence of the internal resistance of the battery, the operating voltage is lower than the open circuit voltage when discharging (external load), and the operating voltage is higher than the open circuit voltage when charging (external power supply). Battery capacity (Ah) can hold or release the charge Q, Q=It, that is, battery capacity (Ah) = current (A) x discharge time (h), the unit is generally Ah (ampere hour) or mAh (milliamp hour) . For example, if the battery in the car is marked 16Ah, then when the working current is 1A, it can theoretically be used for 16 hours. Battery energy (Wh) The energy stored in the battery, in Wh (Watt-hour), energy (Wh) = voltage (V) × battery capacity (Ah). As shown in the picture below, it is a battery marked 3.7V/10000mAh, and its energy is 37Wh. If we connect 4 such batteries in series, it will form a battery pack with a voltage of 14.8V and a capacity of 10000mAh, although the battery capacity is not increased. , but the total energy did increase by 4 times.

　　After reviewing our high school knowledge, let’s take a look at some useful information... Energy density (Wh/L&Wh/kg) is the amount of energy released by a battery per unit volume or unit mass. If it is unit volume, it is volume energy density (Wh/L), which is simply called energy density in many places; if it is unit mass, it is mass energy density (Wh/kg), which is also called specific energy in many places. For example, if a lithium battery weighs 300g, has a rated voltage of 3.7V, and a capacity of 10Ah, its specific energy is 123Wh/kg. According to the "Energy Saving and New Energy Vehicle Technology Roadmap" released in 2016, we can have a rough idea of the development trend of power batteries. As shown in the figure below, by 2020, the specific energy of a pure electric vehicle battery cell will reach 350Wh/kg

　　Power density (W/L&W/kg) divides energy by time to obtain power, in W or kW. In the same way, power density refers to the power output of the battery per unit mass (also called specific power directly in some places) or unit volume, and the unit is W/kg or W/L. Specific power is an important indicator to evaluate whether the battery meets the acceleration performance of electric vehicles. What is the difference between specific energy and specific power? To give a vivid example: a power battery with a high specific energy is like a tortoise in the tortoise and the hare. It has good endurance and can work for a long time, ensuring a long cruising range of the car; a power battery with a high specific power is like a hare in the tortoise and the hare. It is fast and can provide high instantaneous current to ensure good acceleration performance of the car;

　　The following parameters are a bit convoluted... Battery discharge rate (C) Discharge rate refers to the current value required to discharge its rated capacity (Q) within a specified time. It is numerically equal to a multiple of the battery's rated capacity. That is: charge and discharge current (A) / rated capacity (Ah), the unit is generally C (abbreviation for C-rate), such as 0.5C, 1C, 5C, etc. For example, for a battery with a capacity of 24Ah: use 48A When discharging, the discharge rate is 2C. On the contrary, when discharging at 2C, the discharge current is 48A, and the discharge is completed in 0.5 hours; when charging at 12A, the charging rate is 0.5C. Conversely, when charging at 0.5C, the charging current is 12A, 2 Hours of charging; the charge and discharge rate of the battery determines how quickly we can store a certain amount of energy into the battery, or how quickly we can release the energy in the battery. State of charge (%) SOC, the full name is State of Charge, state of charge, also called remaining capacity, represents the ratio of the remaining capacity of the battery after discharge to its capacity in the fully charged state. Its value range is 0~1. When SOC=0, it means the battery is completely discharged. When SOC=1, it means the battery is fully charged. The battery management system (BMS) mainly ensures the efficient operation of the battery by managing SOC and making estimates, so it is the core of battery management. At present, SOC estimation mainly includes open circuit voltage method, ampere-hour measurement method, artificial neural network method, Kalman filter method, etc. We will explain it in detail later. Internal resistance Internal resistance refers to the resistance to current flowing through the interior of the battery when the battery is working. Including ohmic internal resistance and polarization internal resistance, among which: ohmic internal resistance includes the resistance of electrode materials, electrolytes, diaphragm resistors and various parts; polarization internal resistance includes electrochemical polarization resistance and concentration polarization resistance. Let the data speak. The figure below shows a battery discharge curve. The X-axis represents the discharge amount and the Y-axis represents the battery open circuit voltage. The ideal discharge state of the battery is the black curve, and the red curve is the true state when the internal resistance of the battery is taken into account.

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