BTMS Battery Thermal Management System

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Overview of BTMS battery thermal management system

The battery thermal management system (BTMS) is one of the main functions of the battery management system (BMS) (battery parameter monitoring, online fault diagnosis of battery state estimation, charging control, automatic equalization, thermal management, etc.). A closed-loop adjustment system is composed of heat-conducting medium, measurement and control unit and temperature control equipment, so that the power battery can work within a suitable temperature range to maintain its optimal use state and ensure the performance and life of the battery system.

The importance of BTMS battery thermal management system

The heat-related problems of batteries are the key factors that determine their performance, safety, life and cost.

1. Battery energy and power performance: When the temperature is low, the available capacity of the battery will rapidly decay. Charging the battery at a too low temperature (such as below 0°C) may cause instantaneous voltage overcharge, resulting in Internal short circuit.

2. Battery safety: Defects in the manufacturing process or improper operation during use may cause local overheating of the battery, which in turn causes a chain exothermic reaction, eventually causing serious thermal runaway events such as smoke, fire or even explosion.

3. Battery life: The optimum temperature for the battery is between 10°C and 30°C, too high or too low a temperature will cause the lifespan of the battery to attenuate. The large size of the power battery makes the ratio of its surface area to volume relatively smaller, and the internal heat of the battery is not easily dissipated, and problems such as uneven internal temperature and excessive local temperature rise are more likely to occur, thereby further accelerating battery attenuation and shortening battery life.

The battery thermal management system is to deal with the heat-related problems of the battery. The main functions include:

1. Heat dissipation: Effective heat dissipation is performed when the battery temperature is high to prevent thermal runaway accidents.

2. Preheating: Preheating is performed when the battery temperature is low to increase the battery temperature to ensure charging and discharging performance and safety at low temperatures.

3. Temperature equalization: reduce the temperature difference in the battery pack, suppress the formation of local hot spots, prevent the battery from decaying too quickly at high temperature locations, and improve the overall life of the battery pack.

BTMS battery thermal management system solutions

The battery thermal management system solutions are mainly divided into two categories: air cooling and liquid cooling, mainly focusing on preventing the battery from overheating.

1. Air cooling

This technology uses natural wind or a fan to install a cooling fan at one end of the battery pack, leaving ventilation holes at the other end to accelerate the flow of air between the gaps in the battery cells and take away the high heat generated when the cells work. The air cooling solution mainly considers the design of the battery system structure, the air duct, the location and power selection of the fan, and the control strategy of the fan. Air cooling uses low-temperature air as the medium and uses heat convection to reduce the battery temperature. It is divided into natural cooling and forced cooling (using fans, etc.).

In addition, another improved air-cooling solution is to add heat-conducting silicone pads on the top and bottom of the electrode terminal, so that the heat that is not easy to dissipate from the top and bottom is conducted to the metal shell for heat dissipation through the heat-conducting silica gel sheet. At the same time, the high electrical insulation of the silica gel sheet And anti-puncture performance has a good protection effect on the battery pack.

Advantages and disadvantages of air cooling

The main advantages of using gas as a heat transfer medium are: simple structure, light weight, effective ventilation when harmful gases are generated, low cost, and no risk of leakage. Weaknesses are: low heat transfer coefficient with the battery wall, slow cooling rate and low efficiency.

2. Liquid cooling

Liquid cooling technology uses liquid convection heat exchange to take away the heat generated by the battery and reduce the battery temperature. The working principle of the power battery liquid cooling solution is: the battery coolant is cooled through the refrigerant circuit, and the cooled battery coolant flows through the internal flow channel of the battery to take away the heat of the battery to achieve the purpose of cooling the battery.

The core components of the cooling circuit are the compressor, chiller and water pump. As the power source of the refrigerant circuit, the compressor is the source of cooling capacity of the entire system and determines the heat exchange capacity of the system. Chiller mainly plays a role in the heat exchange between the refrigerant and the coolant, and the amount of heat exchange directly determines the temperature of the coolant. The water pump determines the flow rate of the coolant and affects the heat exchange performance of the battery. The liquid cooling scheme design mainly considers the cooling pipeline, the flow rate, temperature and pressure drop of the inlet and outlet coolants. Control strategies for water pumps and vehicle air-conditioning compressors, etc.

Advantages and disadvantages of liquid cooling

The heat exchange coefficient between the contact wall with the battery is relatively large, and the cooling/heating speed is faster, which has a significant effect on reducing the maximum temperature and improving the consistency of the temperature field of the battery pack. At the same time, the volume of the thermal management system is relatively small. The form of the liquid cooling system is more flexible: the battery cells or modules can be immersed in the liquid, cooling channels can also be set between the battery modules or a cooling plate can be used at the bottom of the battery. When the battery is in direct contact with the liquid, the liquid must be insulated (such as mineral oil) to avoid short circuit.

At the same time, the solution system is heavy, complex in design, high in repair and maintenance costs, and there is a risk of liquid leakage. The airtightness requirements of the liquid cooling system are also high. There are requirements for mechanical strength, vibration resistance, and life.

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