High-safety battery design method for inhibiting thermal runaway and thermal spread

Abstract

The invention discloses a high-safety battery design method for inhibiting thermal runaway and thermal spread, which is characterized in that a functional material with a certain thickness is coated on an exposed part of an anode current collector in a battery, and the functional material has a high resistance characteristic, so that an internal short circuit between the anode current collector and a cathode active material causes a battery discharge reaction. The safety of the battery can be improved, and thermal runaway and thermal spread of the battery are inhibited.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a high-safety battery design method for suppressing thermal runaway and thermal propagation. Background Art

[0002] The safety issue is one of the main obstacles to the further large-scale expansion of the market for lithium-ion batteries. The safety problem of lithium-ion batteries can be attributed to battery thermal runaway. Since the internal of lithium-ion batteries contains highly active and reactive substances such as organic electrolytes and lithium, the problem of battery thermal runaway has been difficult to solve. In scenarios such as electric vehicles and energy storage power stations, batteries are used after being assembled into modules. When a single battery undergoes thermal runaway, it is extremely easy to trigger the spread of battery thermal runaway, resulting in the escalation of disasters. Therefore, developing batteries that can suppress thermal runaway and its spread is expected to fundamentally solve the battery safety problem. Summary of the Invention

[0003] In view of this, the present invention provides a high-safety battery design method for suppressing thermal runaway and thermal propagation, which can improve battery safety and suppress battery thermal runaway and thermal propagation.

[0004] The technical solution adopted by the present invention is as follows:

[0005] A high-safety battery design method for suppressing thermal runaway and thermal propagation, wherein a functional material with a certain thickness is coated on the exposed part of the positive current collector inside the battery. The functional material has a high-resistance characteristic, so that an internal short circuit between the positive current collector and the negative active material triggers a battery discharge reaction.

[0006] Further, the thickness of the functional material is less than half of the vertical distance between adjacent positive current collectors.

[0007] Further, the determination method of the resistivity and coating thickness of the functional material is as follows:

[0008] Step 1, prepare one Battery I and several Battery II; the exposed part of the positive current collector inside Battery I is not coated with the functional material, and the exposed parts of the positive current collectors inside several Battery II are coated with functional materials with different resistivities and a thickness of D;

[0009] Step 2, heat Battery I by using a heating sheet to simulate the thermal runaway of a single battery;

[0010] Step 3, continuously heat Battery II with the same heating sheet as in Step 2, and observe whether Battery II undergoes thermal runaway; if thermal runaway occurs, replace Battery II with a functional material having a higher resistivity and re-conduct the thermal runaway triggering test. If thermal runaway does not occur, the resistivity of the functional material corresponding to this Battery II meets the requirements for suppressing thermal runaway; thus, the minimum resistivity and the maximum resistivity for suppressing thermal runaway are determined.

[0011] Further, when the coating thickness D changes, the resistivity range after the change is determined according to the inverse proportional relationship.

[0012] Further, the area occupied by the heating sheet is the same as the area of the largest surface of the battery.

[0013] Further, the heating power density of the heating sheet is 1 W / cm 2 .

[0014] Beneficial effects:

[0015] 1. The present invention utilizes the coated functional material to significantly increase the internal short-circuit resistance. The functional material has high-resistance characteristics, which promotes the transformation of the internal short circuit from triggering side reactions to triggering the battery discharge reaction. At this time, the lithium in the negative electrode active material is gradually consumed due to the battery discharge reaction, while the positive electrode active material is gradually intercalated with lithium due to the battery discharge reaction. Eventually, the battery will be in a fully discharged state, and the reaction activity of the positive and negative electrode active materials will be significantly reduced, and the battery safety will be greatly improved, and thermal runaway will also be suppressed accordingly. Thereby improving battery safety and suppressing battery thermal runaway and thermal spread.

[0016] 2. The method for determining the resistivity and coating thickness of the present invention can quickly select materials for the functional material.

[0017] 3. The heating power density of the heating sheet of the present invention is 1 W / cm 2 , which can ensure that the heating of the heating sheet triggers the battery to have thermal runaway, with high reliability. Description of the drawings

[0018] Figure 1 is a schematic diagram of a unit of the internal layered structure of the battery;

[0019] Figure 2 is a schematic diagram of the internal layered structure of the battery;

[0020] Figure 3 is a schematic diagram of the layered structure of the battery after the separator shrinks;

[0021] Figure 4 is a schematic diagram of the internal structure design of the battery using the design method of the present invention;

[0022] Figure 5 is a schematic diagram of the internal structure design of battery II in a specific implementation case;

[0023] Figure 6 is a schematic diagram of the temperature change curve of battery I;

[0024] Figure 7 is a schematic diagram of the temperature change curve of battery II with a resistivity of 5*10 -4 Ω·m for the functional material;

[0025] Figure 8 Schematic diagram of the temperature change curve of Battery II with a resistivity of 5×10 -3 Ω·m for the functional material;

[0026] Figure 9 Schematic diagram of the temperature change curve of Battery II with a resistivity of 5×10 -2 Ω·m for the functional material.

[0027] Among them, 1 - positive current collector, 2 - positive active material, 3 - separator, 4 - negative active material, 5 - negative current collector, 10 - exposed part, 11 - lower surface of the exposed part, 12 - upper surface of the negative active material, 20 - functional material. Specific implementation mode

[0028] The present invention will be described in detail below with reference to the accompanying drawings and by way of examples.

[0029] As Figure 1 , Figure 2 shown, in battery design, the areas occupied by the positive current collector 1 and the negative current collector 5 are generally larger than the areas occupied by the positive active material 2, the separator 3 and the negative active material 4, so as to extend the tabs of the battery from the positive current collector 1 and the negative current collector 5. Therefore, there will be an exposed part 10 on the positive current collector 1 where the active material is not coated. However, when the battery encounters thermal abuse, the separator 3 will shrink, melt or be damaged due to high temperature, and the battery will also expand and deform. At this time, the traditional battery structure design will cause the positive current collector 1 and the negative active material 4 to come into contact due to the deformation of the battery, thereby triggering an internal short circuit between the positive current collector and the negative active material (denoted as Al-an internal short circuit). This internal short circuit is the most serious one among the four typical internal short circuits of the battery and will promote the occurrence of thermal runaway. As Figure 3 shown, taking a unit of the internal layered structure of the battery as an example, at this time, the lower surface 11 of the exposed part of the positive current collector 1 will come into contact with the upper surface 12 of the negative active material, thereby triggering an Al-an internal short circuit.

[0030] Based on the above principle, the positive current collector 1 can be designed specifically. Therefore, the present invention provides a high-safety battery design method for suppressing thermal runaway and thermal spread. As Figure 4 shown, a functional material 20 with a certain thickness is coated on the exposed part 10 of the positive current collector 1 inside the battery. This functional material 20 has a high-resistance characteristic and is used to increase the resistance of the exposed part 10 of the positive current collector 1. When an Al-an internal short circuit occurs inside the battery, the coated functional material 20 can significantly increase the internal short circuit resistance at this time, so that the internal short circuit between the positive current collector 1 and the negative active material 4 triggers a side reaction and is transformed into triggering a battery discharge reaction, thereby improving the battery safety and suppressing the thermal runaway and thermal spread of the battery.

[0031] The key to the design or material selection of the functional material 20 (high-resistance material) lies in determining the resistance of the material. When the short-circuit resistance is too small, a large amount of Joule heat will be generated due to the short circuit within Al-an, leading to serious side reactions. At this time, lithium in the negative active material 4 participates in the side reaction and releases a large amount of heat, so it is extremely easy to trigger thermal runaway of the battery. When the short-circuit resistance is too large, the internal short-circuit loop is equivalent to being in an open state, and the lithium in the negative active material 4 will not be quickly consumed due to the internal short circuit. Therefore, the negative active material 4 remains in a highly active state. In this case, if the battery is continuously abused (such as the battery is heated and the temperature continues to rise), the negative active material 4 will eventually still participate in the side reaction and trigger thermal runaway. When the short-circuit resistance is regulated to an appropriate value by the functional material 20, the internal short circuit can trigger the battery discharge reaction. At this time, the lithium in the negative active material 4 is gradually consumed due to the battery discharge reaction, and the positive active material 2 is gradually intercalated with lithium due to the battery discharge reaction. Eventually, the battery will be in a fully discharged state, the reactivity of the positive and negative active materials is significantly reduced, the battery safety is greatly improved, and thermal runaway is thus inhibited. Based on the above principles, the functional material 20 with an appropriate resistance can effectively inhibit thermal runaway.

[0032] The resistance of the functional material 20 is proportional to its resistivity and coating thickness. Therefore, a method for determining the resistivity and coating thickness of the functional material 20 is proposed, and the steps are as follows:

[0033] Step 1, prepare one battery I and several battery II; the exposed part 10 of the positive current collector 1 inside the battery I is not coated with the functional material 20, and the exposed parts 10 of the positive current collectors 1 inside several battery II are coated with the functional material 20 with a thickness of D and different resistivities; the thickness D is less than half of the vertical distance between adjacent positive current collectors 1.

[0034] Step 2, heat the battery I by means of a heating sheet to simulate the thermal runaway of a single battery;

[0035] Specifically, the area occupied by the heating sheet is the same as the area occupied by the largest surface of the battery. To ensure that the heating of the heating sheet can trigger the battery to have thermal runaway, preferably, the heating power density of the heating sheet is 1W / cm 2 . Press the heating sheet tightly against the largest surface of the battery I, and use the selected heating sheet to heat the battery I to verify that the heating sheet can trigger the battery I to have thermal runaway.

[0036] Step 3: Continuously heat Battery II with the same heating sheet as in Step 2, and observe whether thermal runaway occurs in Battery II. If thermal runaway occurs, replace Battery II with a battery having a functional material 20 with a higher resistivity and restart the thermal runaway triggering test. If thermal runaway does not occur, the resistivity of the corresponding functional material 20 of this Battery II meets the requirements for suppressing thermal runaway. Thus, determine the minimum resistivity R min and the maximum resistivity R max of the functional material 20 that can suppress thermal runaway, and obtain the applicable range of the resistivity of the functional material 20 that can suppress thermal runaway.

[0037] Step 4: When the coating thickness D changes, determine the changed resistivity range according to the inverse proportional relationship.

[0038] The resistance of the internal short circuit of Battery Al-an can be calculated by the following formula:

[0039] R = D * ρ / S + Rc + Ro

[0040] In the formula, R is the internal short circuit resistance, D is the coating thickness of the functional material, ρ is the resistivity of the functional material, S is the contact area between the positive current collector 1 and the negative active material 4 during internal short circuit, Rc is the contact resistance, and Ro is other resistances. During internal short circuit, the positive current collector 1 and the negative active material 4 have substantial contact, the voltage drops suddenly, and intense physical and chemical reactions occur inside the battery. Compared with the resistance of the functional material, the contact resistance Rc can be ignored. Other resistances Ro mainly include the positive current collector resistance and the negative active material resistance. The positive current collector 1 is generally aluminum foil, and the negative active material 4 is generally graphite. Both have good conductivity and the resistance can also be ignored. Therefore, the internal short circuit resistance R is mainly determined by the resistance of the functional material. When the internal short circuit resistance is constant, it can be considered that the resistivity ρ of the functional material is inversely proportional to the coating thickness D. For example, when the coating thickness is changed to D / 2, the minimum applicable value of the resistivity becomes 2R min and the maximum applicable value becomes 2R max .

[0041] Specific implementation case:

[0042] Prepare one lithium-ion battery I of the lithium iron phosphate / graphite system and several Battery IIs. Among them, the positive current collector 1 inside Battery I is not coated with the functional material 20, while the positive current collector 1 inside Battery II is coated with the functional material 20 with a thickness of 5 μm and resistivities of 5 * 10 -4 Ω·m, 5 * 10 -3 Ω·m, 5 * 10 -2 Ω·m, etc. In this implementation case, the internal structure design of Battery II is as shown in Figure 5As shown, it should be noted that in this case, the exposed part 10 of the positive current collector 1 of battery II and the exposed part of the negative current collector 5 are on the same side. They can be on the same side or on two separate sides, which does not affect the implementation of this solution.

[0043] Heat battery I and battery II with a heating sheet having a heating power density of 1 W / cm 2 to obtain the battery temperature curve. From Figure 6 , Figure 7 , Figure 8 , Figure 9 , it can be seen that battery I, battery II with a resistivity of 5 * 10 -4 Ω·m, and battery II with a resistivity of 5 * 10 -2 Ω·m all experienced thermal runaway, while battery II with a resistivity of 5 * 10 -3 Ω·m did not experience thermal runaway, indicating that when the resistivity is 5 * 10 -3 Ω·m, it is within the applicable range. By disassembling and analyzing the battery II (with a resistivity of 5 * 10 -3 Ω·m) that did not experience thermal runaway, it was found that the main positive electrode material of the battery is LiFePO4, and the negative electrode is mainly un-lithiated graphite (C), which can further confirm that a discharge reaction occurs during the internal short circuit of the battery, and lithium in the negative electrode migrates to the positive electrode. Continuing to conduct thermal runaway trigger tests on battery II coated with functional materials 20 with different resistivities, and based on whether the battery experiences thermal runaway or not, it was finally obtained that for this type of battery when coated with a 5-μm-thick functional material 20, the minimum applicable value of the resistivity is approximately 1 * 10 -3 Ω·m, and the maximum applicable value is approximately 10 * 10 -3 Ω·m. Based on the acceptable resistivity applicable range of this type of battery, other suitable functional materials can also be selected. For example, silicon-based materials can be selected.

[0044] In summary, the above are only the preferred embodiments of the present invention and are not used to limit the protection scope of 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 high - safety battery design method for suppressing thermal runaway and thermal propagation, characterized in that, A functional material with a certain thickness is coated on the exposed part of the positive current collector inside the battery. The functional material has high-resistance characteristics, enabling an internal short circuit between the positive current collector and the negative active material to trigger the battery discharge reaction.

2. The high - safety battery design method for suppressing thermal runaway and thermal propagation as described in claim 1, characterized in that, The thickness of the functional material is less than half of the vertical distance between adjacent positive current collectors.

3. The high - safety battery design method for suppressing thermal runaway and thermal propagation as described in claim 1, characterized in that, The determination method of the resistivity and coating thickness of the functional material is as follows: Step 1: Prepare one Battery I and several Battery IIs. The exposed part of the positive current collector inside Battery I is not coated with the functional material, and the exposed parts of the positive current collectors inside several Battery IIs are coated with the functional material with different resistivities and a thickness of D. Step 2: Heat Battery I by using a heating sheet to simulate the thermal runaway of a single battery. Step 3: Continuously heat Battery II with the same heating sheet as in Step 2, and observe whether thermal runaway occurs in Battery II. If thermal runaway occurs, replace Battery II with the functional material having a higher resistivity and re-conduct the thermal runaway triggering test. If thermal runaway does not occur, the resistivity of the functional material corresponding to this Battery II meets the requirements for suppressing thermal runaway. Thus, determine the minimum resistivity and the maximum resistivity for suppressing thermal runaway.

4. The high - safety battery design method for suppressing thermal runaway and thermal propagation as described in claim 3, characterized in that, When the coating thickness D changes, determine the changed resistivity range according to the inverse proportion relationship.

5. The high - safety battery design method for suppressing thermal runaway and thermal propagation according to claim 3 or 4, characterized in that, The area occupied by the heating sheet is the same as the area of the largest surface of the battery.

6. The high - safety battery design method for suppressing thermal runaway and thermal propagation as described in claim 5, characterized in that, The heating power density of the heating sheet is 1 W / cm 2 .

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