Lithium-ion power battery pack constant temperature thermal management system

Abstract

The invention relates to a constant-temperature thermal management system for a lithium-ion power battery pack. The thermal management system comprises the lithium-ion power battery pack which comprises a battery box, a plurality of single lithium batteries, a heating sheet, an electronic refrigerating sheet and a fan, a power input change-over switch which comprises two interfaces connected to an external power supply and an internal power supply, a direct current (DC) / alternating current (AC) variable-frequency inversion controller which is used for outputting power inputted by the power input change-over switch to the refrigerating sheet or the heating sheet after voltage and frequency conversion, a voltage acquisition module for acquiring the voltage of the inputted power and the output voltage of the voltage DC / AC variable-frequency inversion controller, a temperature acquisition module for acquiring the temperature of the single lithium batteries, and a master controller which is used for controlling the heating sheet or the electronic refrigerating sheet to heat or refrigerate the single lithium batteries according to the temperature of the single lithium batteries. The thermal management system disclosed by the invention is applicable to the constant-temperature control of the single lithium batteries or is capable of controlling the temperature of the single lithium batteries within a reasonable temperature range.

Description

technical field [0001] The application relates to a thermal management device for a lithium-ion battery pack, in particular to a high-voltage variable frequency constant temperature thermal management system for a lithium-ion power battery of a pure electric vehicle Background technique [0002] Lithium-ion batteries are the most likely to be applied to electric vehicles on a large scale at this stage, with the best cost performance and broad application prospects. However, lithium-ion batteries need to operate normally within a certain temperature range, and temperature is an important parameter that affects the performance of lithium batteries. When many lithium batteries are grouped, if the temperature is not balanced, the uniformity of the battery will be poor, which will lead to the difference in the electrochemical performance of the single battery, which will cause the battery to have the risk of overshoot and overdischarge, shorten the life of the energy storage syst...

AI Technical Summary

Problems solved by technology

When many lithium batteries are grouped, if the temperature is not balanced, the uniformity of the battery will be poor, which will cause the difference in the electrochemical performance of the single battery, which will cause the battery to have the risk of overcharging and overdischarging, shorten the life of the energy storage system, and cause electric shock. Car mileage drops

It cannot be charged at low temperature or can only be charged with a very small current. It is very inconvenient to use in winter or in severe cold areas, which seriously affects the application and promotion of electric vehicles.

This is because at low temperature (such as -20°C), the internal resistance of lithium-ion batteries increases sharply by 5-100 times compared with room temperature (such as 25°C), and the voltage quickly reaches the upper limit during normal charging, and the chargeable power is very small. At the same time, there is a hidden danger of lithium dendrite precipitation on the negative electrode. When the lithium dendrite grows to a certain extent, it will pierce the separator and cause a short circuit inside the battery, causing fire or explosion accidents.

The deep-seated reasons are caused by two parts. One is that the conductivity of the organic electrolyte used in lithium-ion batteries is greatly reduced at low temperatures. Adjusting the composition of the solvent components will improve part of it, such as increasing the proportion of PC components, etc., but it will affect the battery as a whole. The performance is adversely affected, the degree of adjustment is limited, and the problem cannot be fundamentally solved; the second is that the lithium-ion battery positive and negative electrode materials themselves are at low temperature, and the transfer resistance of lithium ions at the material interface and the diffusion resistance inside the material are greatly increased. ; Improvement methods include nano-processing of materials to reduce interface resistance, using positive electrode materials such as lithium manganate, hard carbon and other negative electrode materials to reduce internal diffusion resistance, and have achieved certain improvements, but compared with room temperature, the safe charging current is still smaller 2-5 times, at the same time, it will bring a series of problems such as increased manufacturing costs and reduced energy density. On the contrary, if it exceeds 55 °C, it will also be dangerous, and it is necessary to dissipate heat from the battery

[0003] At present, the existing battery pack thermal management system generally only has natural air cooling, so the cooling effect is not obvious, and the constant temperature control effect cannot be achieved; the heating is heated by a PTC heating element, and the traditional method is to diffuse the heat through a fan. The pack plays an overall heating effect, but the temperature uniformity of the whole battery pack is not high, the internal heat distribution is uneven, and the internal temperature difference is too large, and the traditional heating control is to connect the voltage source directly to the PTC heating element to realize the work of the PTC heating element and stop, energy utilization is not high

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