A lithium-ion battery pack based on phase change heat storage protection and its preparation method

Abstract

The present invention belongs to the field of new energy, and particularly relates to a lithium-ion battery pack based on phase change heat storage protection and a preparation method thereof. The battery pack includes a housing and at least two soft-pack lithium-ion batteries disposed in the housing, and a heat-absorbing material and a shaping material are filled around the soft-pack lithium-ion batteries. The lithium-ion battery pack of the present invention uses a soft-pack lithium-ion battery as the core, and a heat-absorbing material and a shaping material are filled between the soft-pack lithium-ion battery and the outer shell to achieve the phase change heat absorption and temperature control effect during the temperature rise process of the lithium-ion battery pack. Above the phase change temperature, each soft-pack battery monomer can conduct convective heat transfer to ensure the temperature uniformity of the lithium-ion battery pack.

Description

Technical Field

[0001] The present invention relates to the field of new energy technologies, and particularly to a lithium-ion battery pack. The present invention realizes the internal filling and reinforcement of the lithium-ion battery pack by adopting a phase change material with a multi-layer structure, and improves the thermal stability of the lithium-ion battery pack. Background Art

[0002] With the rapid consumption of fossil energy, more and more countries have started to research new energy technologies, among which the lithium-ion battery technology is most favored by the market. Lithium-ion batteries occupy a major position in the new energy market due to their extremely high energy density and high number of rechargeable cycles.

[0003] Lithium-ion batteries can be divided into lithium manganate, lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt manganate (commonly known as ternary), lithium iron phosphate, and lithium titanate lithium-ion batteries according to the difference in their anode materials. Pure lithium iron phosphate and lithium manganate are restricted to a certain extent in the application of new energy vehicles due to their large volume, while the ternary cathode material of lithium nickel cobalt manganate has a relatively high specific capacity and cycle stability. Therefore, at present, most electric vehicles use ternary lithium-ion batteries, and high-energy-density large ternary lithium-ion batteries are preferentially applied. However, the higher the energy density of ternary lithium-ion batteries, the worse their thermal stability. Developing a lithium-ion battery pack with good thermal stability is the main research and development goal at present.

[0004] According to the statistics of the National Fire and Rescue Bureau, in 2021, a total of nearly 18,000 fire accidents caused by electric vehicles and their battery failures were reported, and the fires caused by lithium batteries were mainly due to thermal runaway of the battery igniting the battery and its accessories.

[0005] How to effectively control the heat generation of lithium-ion batteries can be achieved through BMS battery management or by improving the electrode materials and separator materials of lithium-ion batteries. However, these all require major modifications to the existing lithium-ion battery production line. If certain improvements can be made in the battery pack, then it is possible to quickly launch lithium-ion battery products that meet the thermal stability safety requirements using the existing lithium-ion production line, which is of great significance for accelerating the popularization and application of new energy technologies. Summary of the Invention

[0006] The purpose of the present invention is to provide a new lithium-ion battery pack packaging structure that can improve the thermal stability of the lithium-ion battery pack in view of the thermal stability risk of the existing lithium-ion batteries.

[0007] In order to achieve the above invention purpose, the following technical solutions are provided:

[0008] A lithium-ion battery pack includes a housing and at least two soft-pack lithium-ion batteries disposed in the housing, and a heat-absorbing material and a shaping material are filled around the soft-pack lithium-ion batteries.

[0009] The lithium-ion battery pack of the present invention uses a soft-pack lithium-ion battery as the core, and heat-absorbing material and shaping material are filled between the soft-pack lithium-ion battery and the outer shell. Preferably, the heat-absorbing material is a phase-change material, so as to realize the function of controlling temperature by phase-change heat absorption during the temperature rise of the lithium-ion battery pack. When the temperature of the lithium-ion battery pack rises during discharge or charge, the heat-absorbing material can absorb a large amount of heat, so that the overall temperature of the soft-pack lithium-ion battery inside the lithium-ion battery pack remains relatively stable, thereby effectively avoiding thermal runaway of the soft-pack lithium-ion battery inside the battery pack. The heat-absorbing material is structurally fixed by using spaced shaping materials to prevent the heat-absorbing material from softening or hardening after absorbing heat and causing instability of the internal structure of the battery pack. Through the cooperation of the heat-absorbing material and the shaping material, the stability of the overall structure and temperature stability are realized, which is different from simply applying the heat-absorbing material, which is prone to structural instability due to lack of sufficient support between the soft-pack lithium-ion batteries after absorbing heat.

[0010] Furthermore, the heat-absorbing material is a phase-change material. When the phase-change material is around the phase-change temperature, it can absorb a large amount of heat through phase change, and better control the overall temperature stability of the battery pack.

[0011] Furthermore, the shaping material wraps the phase-change material. The shaping material and the phase-change material wrap each other, which is beneficial to heat absorption and temperature control, and can also keep the overall structure stable.

[0012] Furthermore, the phase-change material and the shaping material are arranged alternately in layers. Preferably, the height of each layer is 1-20 mm, more preferably 1-8 mm. The colloidal setting of the phase-change material and the shaping material in each layer better maintains the structural stability, and at the same time, the phase-change material is evenly dispersed to better realize the function of preventing thermal runaway. Preferably, the thickness of each layer of the phase-change material is 1-10 mm, for example, the thickness can be 2, 3, 5, 7, 8 mm, etc.; the thickness of each layer of the shaping material is 1-6 mm, for example, the thickness can be 1, 2, 3, 4, 5 mm, etc., preferably 1-2 mm. Preferably, the layered distribution of the phase-change material is perpendicular to the soft-pack lithium-ion battery, which better realizes the heat exchange between multiple soft-pack lithium-ion batteries and controls the temperature uniformity.

[0013] The layered phase-change material can form a continuous phase after phase-changing into a liquid state, which is better for convective heat transfer, achieves the effect of optimizing and improving the temperature uniformity of the battery pack, and is beneficial to realizing the convective heat transfer of the low-temperature part on the outer periphery of the battery pack. That is, after reaching the phase-change temperature, the overall heat exchange capacity is enhanced, the higher the temperature, the better the heat exchange capacity, the more it can enhance heat dissipation and prevent local thermal runaway. The layered distribution can also enable the explosion-proof valve to form a continuous explosion-proof protection for the inside of the battery pack. Even if the local pressure rises in the central part of the battery pack, it can be convectively depressurized through the continuous phase-change material, and the same explosion-proof effect can be achieved with fewer explosion-proof devices.

[0014] Furthermore, the shaping material is a soft material. Preferably, the shaping material forms a continuous phase to prevent the distribution state between layers from changing after the phase change material undergoes multiple phase transitions during repeated use, and to control the phase change material to always maintain the same content in each layer.

[0015] Preferably, the shaping material wraps the phase change material. Preferably, the shaping material is silicone potting adhesive, and the silicone potting adhesive is distributed to form a continuous thin sheet state. The silicone potting adhesive has good high and low temperature resistance, heat conduction and flame retardancy, and also has an elastic buffering effect, which can effectively prevent / cut off the chain reaction of lithium battery thermal runaway and better improve the safety of power batteries. More preferably, the silicone brand silicone rubber of this invention is applied. For example, silicone 4926 type silicone potting adhesive.

[0016] Preferably, the shaping material wraps the phase change material to form multiple micro-units, and the volume of the phase change material in each micro-unit is 1-50 mL, such as the single micro-unit volume of 2, 3, 5, 10, 15, 20, 30 mL. The volumes of each micro-unit can be the same or different.

[0017] Furthermore, the phase change material is a polymer phase change material. Preferably, the polymer phase change material is at least one of paraffin wax, straight-chain alkanes, fatty alcohols, polyols, layered perovskites, and polymer-based polymers. The polymer phase change material has good stability and excellent heat absorption effect.

[0018] Furthermore, the phase change material is a composite phase change heat storage material.

[0019] Furthermore, the phase change temperature of the phase change material is 30-60 °C.

[0020] Preferably, the phase change material is paraffin wax, and the paraffin wax used is paraffin wax with a phase change temperature of 32-55 degrees Celsius (melting point). For example, it can be 35, 40, 45, 50 degrees Celsius.

[0021] Furthermore, a temperature sensor is provided in the phase change material.

[0022] Furthermore, there are multiple temperature sensors. The multiple temperature sensors are dispersedly distributed inside the battery pack to monitor the overall temperature stability of the lithium battery pack. Preferably, the multiple temperature sensors are evenly dispersed. Preferably, there are at least two or at least three temperature sensors.

[0023] Furthermore, the temperature sensor is arranged in the micro-unit of the phase change material.

[0024] Furthermore, the shaping material is at least one of thermoplastic polymer materials and thermosetting polymer materials. Preferably, the shaping material is at least one of silicone and epoxy resin.

[0025] Furthermore, the phase change material is filled between multiple soft-pack lithium-ion batteries, and at the same time, the phase change material is filled between the soft-pack lithium-ion battery and the housing.

[0026] Preferably, the proportion of the phase change material located between the soft-pack lithium-ion battery and the housing is > 50 - 80%. There are relatively large pores between the soft-pack lithium-ion battery and the housing, and it is the main area for heat accumulation and dissipation of the lithium-ion battery. Filling the phase change material mainly in this part is more conducive to improving the heat dissipation and temperature control effects.

[0027] Furthermore, a pressure relief valve is provided on the housing. Preferably, the pressure relief valve is a one-way valve.

[0028] Furthermore, the material of the housing is foam metal, and the pores of the foam metal are filled with a phase change material. The foam metal has a small density, good heat insulation performance, and can absorb electromagnetic waves, which is beneficial to improving the overall environmental weather resistance of the battery pack and is more conducive to the stability of the system.

[0029] At the same time, the foam metal also has a better impact energy absorption effect, and can maintain the safety and reliability of the battery pack under accidental impact or shock.

[0030] Furthermore, the soft-pack lithium-ion battery can be any one or a mixture of two or more of ternary lithium-ion batteries (nickel-cobalt-manganese lithium batteries, nickel-cobalt-aluminum lithium batteries), lithium iron phosphate batteries, lithium iron manganese phosphate batteries, etc.

[0031] The present invention also provides a preparation method for the above lithium-ion battery pack, including the following steps:

[0032] S1. Install the soft-pack lithium-ion battery into the housing, arrange the intervals between the soft-pack lithium-ion batteries, and the distance between the soft-pack lithium-ion battery and the housing.

[0033] S2. Alternately inject the phase change material and the shaping material into the housing; after each injection of the phase change material or the shaping material, adjust the temperature to solidify the phase change material or the shaping material, and then inject the next layer of material after the previous layer of the phase change material or the shaping material has solidified.

[0034] S3. After the injection of the phase change material and the shaping material is completed, install the tab and seal the housing to obtain the lithium-ion battery pack.

[0035] Furthermore, when injecting the phase change material and the shaping material, use an injection needle to insert to the filling height for injection. Preferably, there are multiple injection needles, and the multiple injection needles inject synchronously. Preferably, the heights of the multiple injection needles are equal.

[0036] Further, an isolation interval control framework is provided between adjacent soft-pack lithium-ion batteries, and the isolation interval control framework is higher than the height of the injection needle. After each layer of phase change material or shaping material is completed, the height of the injection needle is increased, and at the same time, the isolation interval framework is raised until the isolation interval control framework is separated from the housing.

[0037] Further, the phase change material is degassed before injection to improve the uniformity of the phase change material and prevent the influence of air mixing on the structural stability of the phase change material.

[0038] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows:

[0039] 1. In the lithium-ion battery pack of the present invention, the phase change material and the shaping material are arranged at intervals, realizing stable interval control of the soft-pack lithium-ion batteries in the battery pack, and uniformly improving the thermal stability of the lithium-ion batteries. When the temperature of a certain lithium-ion battery in the battery pack rises to the phase change temperature, the phase change material undergoes a phase change transformation, absorbing the heat emitted by the lithium-ion battery and avoiding thermal runaway.

[0040] 2. After the phase change material in the lithium-ion battery pack of the present invention undergoes a phase change transformation, it has a certain fluidity. When it is necessary to heat the lithium-ion battery to a certain temperature, it can better assist in heat convection among the individual cells in the lithium-ion battery pack, ensuring better temperature uniformity in heating the lithium-ion battery pack, and significantly improving the control of the preheating temperature uniformity of power-type lithium-ion batteries.

[0041] 3. In the preferred embodiment of the present invention, the lithium-ion battery pack can use a temperature sensor in cooperation with the phase change material to achieve more accurate temperature monitoring and realize the overall temperature consistency control of the battery pack. And in the preferred embodiment, the housing is made of foam metal to assist in the thermal stability of the battery pack. The thickness of the housing can be increased to enhance the structural toughness, while better controlling the weight of the housing. That is, under the same housing weight, higher structural strength can be achieved, and it can help the overall battery pack exchange heat with the environment, avoiding the risk of thermal runaway caused by internal heat accumulation in the battery pack. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic cross-sectional and longitudinal-sectional structure diagram of a lithium-ion battery pack (pouring one layer of paraffin and one layer of silica gel).

[0043] Figure 2 is a schematic external structure diagram of the overall lithium-ion battery pack.

[0044] Figure 3 is a schematic cross-sectional structure diagram of the lithium-ion battery pack with soft-pack batteries placed (without pouring paraffin and silica gel).

[0045] Figure 4It is a schematic structural diagram of a lithium-ion battery pack after pouring a layer of paraffin and silica gel.

[0046] Figure 5 It is a three-dimensional structural schematic diagram of a lithium-ion battery pack provided with paraffin, silica gel pouring, as well as sensors and a cover plate.

[0047] Icon: 1 - Battery housing, 11 - Explosion-proof valve, 2 - Soft-pack battery, 21 - Tab, 31 - Paraffin, 32 - Silica gel, 4 - Sensor, 5 - Cover plate. Specific implementation manners

[0048] The present invention will be described in detail below with reference to the accompanying drawings.

[0049] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0050] Embodiment 1

[0051] As Figure 1 shown, a lithium-ion battery pack includes six soft-pack lithium-ion batteries, with a 1-mm gap reserved between the soft-pack batteries, and a heat-absorbing material and a shaping material are filled in layers in the gap. The heat-absorbing material and the shaping material are filled alternately at intervals until close to the top of the housing. The tabs of the soft-pack batteries are arranged at the upper part of the soft-pack lithium-ion batteries. The top of the housing has a cover plate, and holes through which the tabs pass are arranged on the cover plate. After all the tabs of the soft-pack lithium-ion batteries pass through the cover plate, they are respectively connected in parallel or connected in series in sequence according to the anode and the cathode to form the total tab structure of the battery pack.

[0052] Embodiment 2

[0053] The structure of the lithium-ion battery pack in this embodiment is similar to that in Embodiment 1, where the heat-absorbing material is paraffin and the shaping material is silica gel. The phase change temperature of the paraffin is 40 degrees Celsius. The silicone sealant of type Guibao 4926 is used in this embodiment. Of course, those skilled in the art can select two-component silica gel according to the actual situation. The paraffin and the silica gel are arranged alternately in layers, with a total of 18 layers. Two temperature sensors are arranged in the paraffin layer in the middle. The two temperature sensors are respectively arranged at positions close to both sides of the battery pack, and the temperature sensors are all arranged in the paraffin layer.

[0054] Furthermore, the phase change material can also adopt paraffin with a phase change temperature of 42 or 44 degrees Celsius. For example, paraffin of models 44, 46, etc. can be adopted.

[0055] Furthermore, the silicone sealant is replaced with epoxy resin.

[0056] Embodiment 3

[0057] The battery pack structure of this embodiment is similar to that of Embodiment 2. The paraffin wax used herein is paraffin wax with a phase change temperature of 40 °C, and it is separated into multiple layers by Guibao 4926 silicone potting adhesive. The thickness of the paraffin wax layer is 2 - 8 mm, and the thickness of the silicone layer is 1.5 mm. Battery packs with different paraffin wax layer thicknesses are prepared and baked 30 cm above a flame. The temperature increase rate inside the battery pack is read through a temperature sensor. The results are shown in the following table.

[0058]

[0059] The test results show that there are certain differences in the temperature increase rate for different paraffin wax layer thicknesses. A thicker paraffin wax layer can effectively inhibit the temperature rise. However, on the other hand, an overly thick paraffin wax layer will also occupy the space of the silicone potting adhesive, thus affecting the overall structural strength of the module. Therefore, it is more beneficial to control the paraffin wax layer thickness within 5 - 10 mm.

[0060] Embodiment 4

[0061] As Figure 1 shown, the lithium-ion battery pack includes six soft-pack lithium-ion batteries. After arranging the soft-pack batteries in place, a frame-shaped tooling is used to separate each soft-pack lithium-ion battery, leaving a 1 mm gap between the soft-pack batteries and a 2 mm gap between the soft-pack batteries and the housing.

[0062] Paraffin wax with a phase change temperature of 44 °C and Guibao 4926 silicone potting adhesive are alternately injected layer by layer. Among them, the paraffin wax is heated to 55 °C to melt, vacuum degassed for 30 min, and then injected. After each layer of the injected raw material solidifies, the next layer of material is injected. The thickness of each layer of paraffin wax is controlled at 4 mm, and the thickness of the silicone potting adhesive is 1 mm. Before injecting each layer of raw material, the frame-shaped tooling is lifted a certain height to avoid contact or conflict between the frame-shaped tooling and the injected material.

[0063] When injecting to a medium height, three temperature sensors are buried in the paraffin wax layer and the leads of the temperature sensors are led out, and then paraffin wax or silicone potting adhesive is alternately injected layer by layer until reaching the top of the battery pack.

[0064] Install the cover plate of the housing and connect the tabs of the soft-pack lithium-ion batteries.

[0065] Furthermore, a pressure relief valve is installed on the cover plate, and the pressure relief valve is a water-blocking one-way valve.

[0066] Furthermore, the housing of the battery pack is made of foam metal, and 60# paraffin wax (melting point about 60 °C) is filled in the pores of the foam metal. By filling a paraffin wax material with a higher melting point in the foam metal, it plays a further protective role. When the temperature is lower than the change temperature of the internal phase change material, the heat conduction rate from the outside to the inside of the battery pack is lower, and the performance in the stable state under normal environment is better.

[0067] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery pack, characterized in that, It includes a housing and at least two soft-pack lithium-ion batteries disposed in the housing, and a heat-absorbing phase change material and a shaping material are filled around the soft-pack lithium-ion batteries; The shaping material is a soft material, and the shaping material wraps the heat-absorbing phase change material; The heat-absorbing phase change material and the shaping material are alternately arranged in layers, and the height of each layer is 1-20 mm; The material of the housing is foam metal, and the pores of the foam metal are filled with a phase change material; The lithium-ion battery pack is obtained by the following preparation method: S1. Install the soft-pack lithium-ion batteries in the housing, arrange the intervals between the soft-pack lithium-ion batteries and the distance between the soft-pack lithium-ion batteries and the housing; S2. Inject the phase change material and the shaping material into the housing alternately; after each injection of the phase change material or the shaping material, adjust the temperature to make the phase change material or the shaping material solidify, and wait for the previous layer of the phase change material or the shaping material to solidify before injecting the next layer of material; S3. After the injection of the phase change material and the shaping material is completed, install the electrode tabs and seal the housing to obtain the lithium-ion battery pack.

2. The lithium-ion battery pack according to claim 1, characterized in that, The phase change material is a polymer phase change material.

3. The lithium-ion battery pack according to claim 2, wherein The polymer phase change material is at least one of paraffin, straight-chain alkane, fatty alcohol, polyol, layered perovskite, and polymer-based polymer.

4. The lithium-ion battery pack according to claim 3, wherein, The phase change temperature of the phase change material is 30-60 °C.

5. The lithium-ion battery pack according to claim 1, characterized in that, A pressure relief valve is provided on the housing; the pressure relief valve is a one-way valve.

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