Method for avoiding overcharge thermal runaway fire of square lithium iron phosphate battery and application of method

Abstract

The invention provides a method for avoiding overcharge thermal runaway fire of a square lithium iron phosphate battery and application of the method, and relates to the technical field of batteries. The invention provides a method for avoiding overcharge thermal runaway fire of a square lithium iron phosphate battery. The method comprises the following steps: a, calculating a torque force: T = k * A * D / (n * h); wherein T is torque force; n is the number of screws for fixing the clamp; k is the friction coefficient between the nut and the bearing surface; a is a torque coefficient; h is the thickness of the battery cell; d is the diameter of the screw; b, the clamps are arranged on the two sides of the square lithium iron phosphate battery, and then the clamps are fixed through bolts by applying torque force of 90% * T-110% * T to the nuts. According to the method provided by the invention, the torque force is quantified, and the expansion deformation of the battery cell in the overcharge process is inhibited by adopting the proper torque force, so that the risk of breakage and ignition at the tab of the battery cell is reduced, and the fire risk of the battery cell in single thermal runaway authentication is reduced.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a method for preventing a square lithium iron phosphate battery from overcharging, thermal runaway and catching fire, and an application thereof. Background Art

[0002] LFP battery thermal runaway will produce flammable gases such as hydrogen and methane. Once sparks appear in the battery during thermal runaway, it can easily cause a jet fire in the single battery. At present, GB-T-36276-2023 requires that the battery needs to trigger thermal runaway through heating combined with overcharging, and it is required not to catch fire or explode. At present, research on thermal runaway of LFP batteries mainly focuses on thermal runaway warning at the system level, but there is little work involved in how to reduce the risk of thermal runaway fire of single batteries from the source. Regarding square LFP batteries, there is a high probability of ignition in the single-cell thermal runaway test caused by overcharging, making it difficult to pass the requirements of GB-T-36276-2023 "Lithium-ion Batteries for Power Energy Storage".

[0003] In view of this, the present invention is proposed. Summary of the invention

[0004] The first object of the present invention is to provide a method for preventing a square lithium iron phosphate battery from overcharging, thermal runaway and catching fire, so as to solve the above-mentioned technical problems.

[0005] The second object of the present invention is to provide application of the above method in battery testing.

[0006] In order to achieve the above objectives, the following technical solutions are adopted:

[0007] In a first aspect, the present invention provides a method for preventing a square lithium iron phosphate battery from overcharging and thermal runaway and catching fire, comprising the following steps:

[0008] a. Calculate the torque:

[0009] T = k*A*D / (n*h);

[0010] Where, T is the torque force, in Nm; n is the number of screws of the fixing fixture; k is the friction coefficient between the nut and the supporting surface; A is the torque coefficient, which is 2.84*10^2, in Nm; h is the thickness of the battery cell, in m; D is the screw diameter, in m;

[0011] b. Place the clamps on both sides of the square lithium iron phosphate battery, and then bolt the clamps by applying a torque force of 90%*T to 110%*T to the nuts.

[0012] As a further technical solution, the square lithium iron phosphate battery includes a square soft-pack lithium iron phosphate battery and a square aluminum shell lithium iron phosphate battery.

[0013] As a further technical solution, the thickness of the battery core is 0.005-0.05m.

[0014] As a further technical solution, the screw diameter is 0.003-0.01m.

[0015] As a further technical solution, the number of the screws is at least 4.

[0016] As a further technical solution, after fixing, the screws are evenly distributed on the edge of the clamp.

[0017] As a further technical solution, a wrench is used to apply force to the nut.

[0018] As a further technical solution, the bolt fixing is performed by using screws and nuts.

[0019] In a second aspect, the present invention provides application of the above method in battery testing.

[0020] As a further technical solution, the test includes an overcharge thermal runaway test or a heating thermal runaway test.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The method for preventing square lithium iron phosphate batteries from overcharging and thermal runaway and catching fire provided by the present invention quantifies the torque force, and adopts appropriate torque force to suppress the expansion and deformation of the battery cell during the overcharging process, thereby reducing the risk of breakage and ignition at the battery cell tab, thereby reducing the fire risk of the battery cell in the thermal runaway certification of the single cell, and can guide the design of the battery module according to the pre-tightening force applied to the single cell, thereby facilitating the safe use of the battery at the customer application end. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 The test result of Test Example 1 in which 70%*T is applied to the nut;

[0025] Figure 2 The test result of Test Example 1 in which 130%*T is applied to the nut;

[0026] Figure 3 The test results of Test Example 1 with 100%*T applied to the nut;

[0027] Figure 4 The test result of Test Example 2 where 70%*T is applied to the nut;

[0028] Figure 5 The test result of Test Example 2 where 130%*T was applied to the nut;

[0029] Figure 6 The test results of Test Example 2 where 100%*T is applied to the nut;

[0030] Figure 7 The test results of Test Example 3 where 70%*T was applied to the nut;

[0031] Figure 8 The test result of Test Example 3 where 130%*T was applied to the nut;

[0032] Fig. 9 The test results of Test Example 3 were obtained by applying 100%*T to the nut. DETAILED DESCRIPTION

[0033] The embodiments of the present invention will be described in detail below in conjunction with the embodiments and examples, but it will be appreciated by those skilled in the art that the following embodiments and examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified, proceed according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0034] In a first aspect, the present invention provides a method for preventing a square lithium iron phosphate battery from overcharging and thermal runaway and catching fire, comprising the following steps:

[0035] a. Calculate the torque:

[0036] T = k*A*D / (n*h);

[0037] Where, T is the torque force, in Nm; n is the number of screws of the fixing fixture; k is the friction coefficient between the nut and the supporting surface; A is the torque coefficient, which is 2.84*10^2, in Nm; h is the thickness of the battery cell, in m; D is the screw diameter, in m;

[0038] b. Place the clamps on both sides of the square lithium iron phosphate battery, and then bolt the clamps by applying a torque force of 90%*T to 110%*T to the nuts (for example, but not limited to 90%*T, 95%*T, 100%*T, 105%*T or 110%*T).

[0039] The method for preventing square lithium iron phosphate batteries from overcharging and thermal runaway and catching fire provided by the present invention quantifies the torque force, and adopts appropriate torque force to suppress the expansion and deformation of the battery cell during the overcharging process, thereby reducing the risk of breakage and ignition at the battery cell tab, thereby reducing the fire risk of the battery cell in the thermal runaway certification of the single cell, and can guide the design of the battery module according to the pre-tightening force applied to the single cell, thereby facilitating the safe use of the battery at the customer application end.

[0040] In some optional embodiments, the square lithium iron phosphate battery includes a square soft-pack lithium iron phosphate battery and a square aluminum shell lithium iron phosphate battery.

[0041] In some optional embodiments, the thickness of the battery cell may be, for example, but not limited to, 0.005 m, 0.01 m or 0.05 m.

[0042] In some optional embodiments, the screw diameter may be, for example, but not limited to, 0.003 m, 0.005 m, 0.008 m or 0.01 m.

[0043] In some optional embodiments, the number of the screws is at least 4.

[0044] The present invention does not impose any specific limitation on the number of screws, for example, it can be 4, 6 or 8, and can be selected according to the size of the battery.

[0045] In some optional embodiments, after fixing, the screws are evenly distributed on the edge of the clamp.

[0046] Evenly distributed screws help to evenly distribute the force on the battery.

[0047] In some optional embodiments, a wrench is used to apply force to the nut.

[0048] In some optional embodiments, the bolt fixing is fixed by screws and nuts.

[0049] In a second aspect, the present invention provides application of the above method in battery testing.

[0050] The method for avoiding overcharging thermal runaway and fire of a square lithium iron phosphate battery provided by the present invention adopts a suitable torque force to suppress the expansion and deformation of the battery cell during the overcharging process, thereby reducing the risk of fracture and ignition at the battery cell tab, thereby reducing the fire risk of the battery cell in the thermal runaway certification of the single cell.

[0051] In some optional embodiments, the test includes an overcharge thermal runaway test or a heating thermal runaway test.

[0052] The present invention is further described below by means of specific examples and comparative examples. However, it should be understood that these examples are only used for more detailed description and should not be construed as limiting the present invention in any form.

[0053] Example 1

[0054] A method for preventing a square lithium iron phosphate battery from overcharging, thermal runaway and catching fire, comprising the following steps:

[0055] a. Calculate the torque:

[0056] T = k*A*D / (n*h);

[0057] Where, T is the torque force, in Nm; n is the number of screws of the fixing fixture; k is the friction coefficient between the nut and the supporting surface; A is the torque coefficient, which is 2.84*10^2, in Nm; h is the thickness of the battery cell, in m; D is the screw diameter, in m;

[0058] b. Place the clamps on both sides of the square lithium iron phosphate battery, and then bolt the clamps by applying a torque force of 90%*T to 110%*T to the nuts.

[0059] Test Example 1

[0060] The method of Example 1 is used to perform a thermal runaway test on the battery to be tested.

[0061] The battery to be tested is a square soft-pack lithium iron phosphate battery with a thickness of 0.01m.

[0062] The number of screws is: 4, the diameter is: 0.003m;

[0063] The friction coefficient between the nut and the supporting surface is: 0.15;

[0064] Then T = k*A*D / (n*h) = 0.15*2.84*10^2*0.003 / (4*0.01) = 3.195Nm;

[0065] The fixtures were placed on both sides of the square lithium iron phosphate battery, and then the fixtures were bolted by applying torques of 70%*T, 90%*T, 100%*T, 110%*T, and 130%*T to the nuts. Afterwards, a thermal runaway test was conducted, and the results were as follows: Figure 1-Figure 3 shown.

[0066] Figure 1 The test results of applying 70%*T to the nut show that using too little torque can cause the battery ear to break and ignite easily, causing a fire.

[0067] Figure 2The test results of applying 130%*T to the nut show that using excessive torque will cause the battery to catch fire or even explode and disintegrate.

[0068] Figure 3 The test results of applying 100%*T to the nut are shown in Figure 1. In addition, the test results of 90%*T and 110%*T are consistent with the test results of 100%*T. The results show that the torque force calculated by the method of the present invention is appropriate and can effectively avoid fire when the battery is under thermal runaway.

[0069] Test Example 2

[0070] The method of Example 1 is used to perform a thermal runaway test on the battery to be tested.

[0071] The battery to be tested is a square aluminum shell lithium iron phosphate battery with a thickness of 0.0365 μm.

[0072] The number of screws is: 6, the diameter is: 0.01m;

[0073] The friction coefficient between the nut and the supporting surface is: 0.15;

[0074] Then T = k*A*D / (n*h) = 0.15*2.84*10^2*0.01m* / (6*0.0365m) = 1.94N / m;

[0075] The fixtures were placed on both sides of the square aluminum shell lithium iron phosphate battery, and then the fixtures were bolted by applying torque forces of 70%*T, 90%*T, 100%*T, 110%*T, and 130%*T to the nuts. After that, a thermal runaway test was conducted, and the results were as follows: Figure 4-Figure 6 shown.

[0076] Figure 4 This is the test result of applying 70%*T to the nut.

[0077] Figure 5 This is the test result of applying 130%*T to the nut.

[0078] Figure 6 The test results of applying 100%*T to the nut are shown in Figure 1. In addition, the test results of 90%*T and 110%*T are consistent with the test results of 100%*T. The results show that the torque force calculated by the method of the present invention is appropriate and can effectively avoid fire when the battery is under thermal runaway.

[0079] Test Example 3

[0080] The method of Example 1 is used to perform a thermal runaway test on the battery to be tested.

[0081] The battery to be tested is a square soft-pack lithium iron phosphate battery with a thickness of 0.0113 μm.

[0082] The number of screws is: 4, the diameter is: 0.004m;

[0083] The friction coefficient between the nut and the supporting surface is: 0.15;

[0084] Then T = k*A*D / (n*h) = 0.15*2.84*10^2*0.004m* / (4*0.0113m) = 3.77N / m;

[0085] The fixtures were placed on both sides of the square soft-pack lithium iron phosphate battery, and then the fixtures were bolted by applying torque forces of 70%*T, 90%*T, 100%*T, 110%*T, and 130%*T to the nuts. After that, a thermal runaway test was conducted, and the results were as follows: Figure 7-Figure 9 shown.

[0086] Figure 7 This is the test result of applying 70%*T to the nut.

[0087] Figure 8 This is the test result of applying 130%*T to the nut.

[0088] Fig. 9 The test results of applying 100%*T to the nut are shown in Figure 1. In addition, the test results of 90%*T and 110%*T are consistent with the test results of 100%*T. The results show that the torque force calculated by the method of the present invention is appropriate and can effectively avoid fire when the battery is under thermal runaway.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preventing square lithium iron phosphate battery from overcharging, thermal runaway and fire, characterized in that: The following steps are involved: a. Calculate the torque: T = k*A*D / (n*h); Where, T is the torque force, in Nm; n is the number of screws of the fixing fixture; k is the friction coefficient between the nut and the supporting surface; A is the torque coefficient, which is 2.84*10^2, in Nm; h is the thickness of the battery cell, in m; D is the screw diameter, in m; b. Place the clamps on both sides of the square lithium iron phosphate battery, and then bolt the clamps by applying a torque force of 90%*T to 110%*T to the nuts.

2. The method according to claim 1, characterized in that The square lithium iron phosphate battery includes a square soft-pack lithium iron phosphate battery and a square aluminum shell lithium iron phosphate battery.

3. The method according to claim 1, characterized in that The thickness of the battery core is 0.005-0.05 μm.

4. The method according to claim 1, characterized in that The screw diameter is 0.003-0.01m.

5. The method according to claim 1, characterized in that The number of the screws is at least 4.

6. The method according to claim 1, characterized in that After fixing, the screws are evenly distributed around the edge of the clamp.

7. The method according to claim 1, characterized in that A wrench is used to apply force to the nut.

8. The method according to claim 1, characterized in that The bolt fixing is performed by using screws and nuts.

9. Use of the method according to any one of claims 1 to 8 in battery testing.

10. The use according to claim 9, characterized in that: The test includes an overcharge thermal runaway test or a heating thermal runaway test.

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