Lithium iron phosphate short-knife battery cell without heat spreading and application of lithium iron phosphate short-knife battery cell

Abstract

The invention provides a lithium iron phosphate short-knife battery cell without heat spreading and application thereof, and relates to the technical field of lithium iron phosphate batteries. Specifically, the lithium iron phosphate short-knife battery cell does not contain an aerogel component, and meets three necessary conditions that the electrolyte comprises lithium bis (fluorosulfonyl) imide, the diaphragm is an aramid isolating membrane, and the gap between the battery cells is greater than 0.88 mm. According to the invention, by providing the LFP battery cell design covering the battery cell structure, the electrolyte and the diaphragm, no heat spreading among the lithium iron phosphate short-knife battery cells can be realized under the condition of no aerogel heat insulation component, and the thermal runaway condition is controlled in the independent battery cell, so that the serious safety problem is avoided, and the service life of the lithium iron phosphate short-knife battery cell is prolonged. Good practical prospects are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium iron phosphate batteries, and in particular to a lithium iron phosphate short-blade battery cell without heat spread and applications thereof. Background Art

[0002] Lithium iron phosphate batteries are widely used in energy storage equipment, electric vehicles, power tools or equipment due to their high energy density, long life and good charging performance. Lithium iron phosphate batteries also have advantages in safety performance. They show good thermal stability in high temperature environments and have natural overcharge protection characteristics. When thermal runaway or short circuit occurs, the gases generated are mainly oxygen and water, which are non-toxic and harmless, reducing the risk of fire and explosion. However, this does not mean that lithium iron phosphate batteries do not need to worry about safety issues. At present, lithium iron phosphate batteries still have problems such as increased internal pressure of the battery caused by short circuits, and even battery rupture or electrolyte leakage. At the same time, various industries have also put forward higher requirements for the safety performance of lithium iron phosphate batteries.

[0003] By adding an aerogel system to the lithium iron phosphate battery, it can achieve heat insulation and flame retardant effects to improve the overall safety performance of the battery. Aerogel itself has excellent fireproof and heat-insulating properties, so it can effectively block the transfer of heat between battery cells. Especially when the battery has thermal runaway, the aerogel system can significantly reduce the propagation speed of thermal runaway, reduce damage to the battery pack and the incidental destructive effects. However, some customers currently have very strict safety requirements. For lithium iron phosphate batteries with good safety performance, it is necessary to achieve no heat spread between adjacent cells without adding aerogel to completely eliminate major safety hazards. That is: within the operating temperature range of all lithium iron phosphate batteries (-30℃~60℃), after the target cell has thermal runaway, the adjacent cells will not have thermal runaway. At present, there is no lithium iron phosphate short knife cell that can meet the above safety requirements without aerogel.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The first purpose of the present invention is to provide a lithium iron phosphate short knife battery cell without heat spread, which is used to solve the technical problem that lithium iron phosphate batteries are difficult to achieve thermal runaway without heat spread in the absence of aerogel.

[0006] The second purpose of the present invention is to provide a detection method for the lithium iron phosphate short knife battery cell, specifically a method for inducing thermal runaway of the target battery cell and detecting whether thermal runaway occurs; avoiding the waste of testing resources caused by complex and changeable triggering methods.

[0007] The third object of the present invention is to provide a method for preparing the lithium iron phosphate short knife battery cell to adapt to the assembly processing of the short knife battery cell with a specific battery cell design.

[0008] A fourth object of the present invention is to provide a lithium ion battery.

[0009] A fifth object of the present invention is to provide an electrical device.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0011] A lithium iron phosphate short knife battery cell without heat spread, containing no aerogel component and satisfying the following characteristics (a) to (c):

[0012] (a) The electrolyte of the lithium iron phosphate short-blade battery cell includes lithium bis(fluorosulfonyl)imide;

[0013] (b) The diaphragm of the lithium iron phosphate short-blade battery cell is an aramid isolation membrane;

[0014] (c) The gap between each cell of the lithium iron phosphate short-blade battery cell is greater than 0.88 mm.

[0015] A method for detecting a lithium iron phosphate short-blade battery cell comprises the following steps:

[0016] Treating the target cell in the lithium iron phosphate short knife cell by a cold needle puncture method to detect whether the cell adjacent to the target cell has heat spread;

[0017] Among them, the acupuncture positions of the cold needle acupuncture method include a first point and a second point. The first point is an explosion-proof valve, and the second point is: in the length direction of the short knife battery core, 25mm to 50mm adjacent to the explosion-proof valve.

[0018] A method for preparing a lithium iron phosphate short-blade battery cell comprises the following steps performed in sequence:

[0019] Homogenization, coating, rolling, slitting, laser die-cutting, lamination, hot pressing, testing, flat welding of tabs, cutting of tabs, laser welding of negative cover and tabs, secondary testing, bending of negative tabs, installation of positive terminal plate, shelling, pressing and pre-spot welding of negative cover, laser welding of positive tabs and tabs, bending of positive tabs, pressing and pre-spot welding of positive cover, peripheral welding, tertiary testing, baking, quaternary testing, primary liquid injection, high temperature impregnation, pre-charging, secondary liquid injection, high temperature aging, standing at room temperature, DCR testing, sealing with glue nails, helium testing, capacity division, OCV1 testing, aging at room temperature, OCV2 / K value testing, quintuple testing, insulating film packaging, top patching, size measurement, thickness testing, insulation testing, appearance testing, sorting and warehousing.

[0020] A lithium-ion battery comprises the lithium iron phosphate short-blade battery cell.

[0021] An electrical device comprises the lithium iron phosphate short blade battery cell.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention provides an LFP battery cell design covering a battery cell structure, electrolyte and diaphragm, which can achieve no heat spread between the battery cells of the lithium iron phosphate short knife battery cell without an aerogel insulation component, and control the runaway within an independent battery cell when thermal runaway occurs, thus avoiding serious safety problems. The present invention further provides a safety performance test method for the short knife battery cell, mainly providing the operation steps related to the cold needle acupuncture method, and exploring and obtaining the best acupuncture position: that is, the temperature when the acupuncture causes thermal runaway is the lowest, and the heat transfer to the adjacent battery cell is the least. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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.

[0025] Figure 1 Provided is a temperature change curve diagram of battery cell No. 3 of Example 1 of the present invention, and a voltage change curve diagram of each battery cell;

[0026] Figure 2 A schematic diagram of the arrangement of the battery cells of Embodiment 1 of the present invention is provided;

[0027] Figure 3 A schematic diagram of the battery cell puncture test points of Example 1 of the present invention is provided. DETAILED DESCRIPTION

[0028] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but those skilled in the art will appreciate that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and 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 in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially. In addition, the terms "first", "second" and "third" are only used for descriptive purposes and cannot be interpreted as indicating or implying relative importance.

[0029] A first aspect of the present invention is to provide a lithium iron phosphate short-blade battery cell without heat spread.

[0030] The present invention aims to solve the problem that after any cell of a lithium iron phosphate battery system in any operating temperature range without aerogel experiences thermal runaway, the adjacent cells do not experience thermal runaway. Therefore, on the one hand, it is necessary to limit the lithium iron phosphate short-blade cell to not contain aerogel components, and on the other hand, it is also necessary to limit the electrolyte, diaphragm and short-blade cell structure. Specifically:

[0031] (a) The gap between each cell of the lithium iron phosphate short-blade battery cell is greater than 0.88 mm;

[0032] (b) The electrolyte of the lithium iron phosphate short-blade battery cell includes lithium bis(fluorosulfonyl)imide;

[0033] (c) The diaphragm of the lithium iron phosphate short knife battery cell is an aramid isolation membrane.

[0034] The short knife battery cell is a battery composed of multiple short knife-shaped battery cells arranged and combined. It is widely used in handheld electrical appliances, portable lighting tools and other scenarios due to its small size, light weight, high energy density and large discharge current. The existing short knife battery cells are long and thin. Therefore, when a battery cell has thermal runaway, the temperature of the battery cell is uneven. First, along the thickness direction, the heat will quickly spread to the surface of the battery cell due to its thin thickness, and transfer the heat to the adjacent battery cell. In addition, the spread speed along the length direction is slow, and usually only half of the length direction is short-circuited before heat spread occurs; therefore, when heat spread occurs, the temperature distribution on the surface of the battery cell is very uneven, and the heat is concentrated in the thickness direction and transferred to the adjacent battery cell, causing thermal runaway of the adjacent battery cell. By observing the battery cell module of the needle puncture test, it can be clearly seen that the temperature of the area far away from the needle puncture is low, the blue film is basically intact and not severely burned, but the area of ​​the needle puncture is severely damaged, which is enough to show that the temperature of the battery cell is very uneven.

[0035] In the present invention, the structural system of the short knife battery cell is optimized to achieve accelerated heat release when thermal runaway occurs in any battery cell, and the heat is released faster in the length direction of the battery cell and slower in the thickness direction. The heat is thereby released through the explosion-proof valve, and the thermal runaway is controlled to the target battery cell, rather than triggering thermal runaway of multiple batteries and causing greater safety hazards.

[0036] As a preferred implementation manner, the length of the short blade battery core is 300 mm to 600 mm, the thickness of the short blade battery core is less than 25 mm, and there are tabs at both ends of the short blade battery core.

[0037] In the present invention, the gap between each cell of the short knife battery cell is limited to ≥0.88mm. The larger the gap, the less likely it is for heat to spread, so a minimum value is provided, and the upper limit value is not controlled. It is understandable that when the air gap is larger, the heat transfer from the battery cell experiencing thermal runaway to the adjacent battery cell will be less. However, it is also necessary to comprehensively weigh the overall mechanical structure, charge and discharge performance, volume expansion and other factors of the short knife battery cell, and it is impossible to expand the gap between the batteries indefinitely. In the present invention, by limiting the gap between each single battery cell, the heat conduction between the batteries can be curbed to the greatest extent while satisfying the electrical and mechanical properties.

[0038] In the present invention, the thermal conductivity of the FSI electrolyte system is limited, that is, an electrolyte that can quickly spray heat is used; when thermal runaway occurs, the heat conduction speed of the electrode in the length direction can be accelerated, thereby accelerating the combustion speed in this direction, and achieving the effect of accelerating heat release, thereby preventing heat from being conducted to the non-thermal runaway battery cell.

[0039] As a preferred embodiment, in the electrolyte, the mass proportion of the lithium bis(fluorosulfonyl)imide (FSI) is 5% to 8%.

[0040] As a preferred embodiment, in addition to the lithium bis(fluorosulfonyl)imide, the electrolyte includes a solvent, a lithium salt and an additive;

[0041] The lithium salt accounts for 10% to 18% of the electrolyte by mass, and the lithium salt includes lithium hexafluorophosphate (LiPF 6 ) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0042] The mass proportion of the solvent in the electrolyte is 75% to 85%, and the solvent includes cyclic carbonates and chain esters; the cyclic carbonates include at least one of ethylene carbonate and propylene carbonate; the chain acid esters include at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, etc.

[0043] The mass proportion of the additive in the electrolyte is 4% to 10%, and the additive includes but is not limited to vinylene carbonate (VC), fluoroethylene carbonate (FEC) and vinyl sulfate.

[0044] As a preferred embodiment, the aramid isolation film includes a base film, a first coating layer and a third coating layer sequentially coated on a surface of one side of the base film, and a second coating layer coated on a surface of the other side of the base film.

[0045] Specifically, the properties and components of each coating include the following: the first coating is an oily coating, the first coating is an aramid coating, which can be understood as the first coating only including aramid, or including aramid and an oily solvent or dispersed component, etc. The second coating includes aramid and an adhesive material, the second coating is an oily coating, and the adhesive material includes one of PVDF or PMMA; the third coating is a water-based PVDF coating, which can be understood as the third coating including PVDF and a water solvent.

[0046] The aramid isolation membrane used in the present invention has a high membrane rupture temperature, which can effectively control the short circuit of the isolation membrane, slow down the heat transfer in the thickness direction, and thus improve the safety risk of overall thermal runaway of the short knife battery. For each coating of the aramid isolation membrane, those skilled in the art can prepare the isolation membrane on the surface of the base membrane by roller coating, spray coating, spot coating, etc., preferably roller coating.

[0047] As a preferred embodiment, the rupture temperature of the aramid isolation membrane is 250°C to 280°C, more preferably 260°C to 272°C.

[0048] As a preferred embodiment, the thickness of the aramid isolation film ranges from 9 μm to 18 μm, wherein the thickness of the base film ranges from 5 μm to 12 μm, the thickness of the first coating ranges from 2 μm to 3 μm, the thickness of the second coating ranges from 1 μm to 2 μm, and the thickness of the third coating is 1 μm.

[0049] As a preferred embodiment, the total aramid coating surface density of the aramid isolation membrane is 1.5 g / m 2 ~2.5g / m 2 .

[0050] It can be understood that the lithium iron phosphate short knife battery cell described in the present invention also includes a positive electrode and a negative electrode; the active material of the positive electrode is mainly lithium iron phosphate, and the positive electrode also includes necessary ingredients such as a conductive agent and a binder. Similarly, the negative electrode includes necessary components such as active ingredients and a binder, and the present invention does not impose any restrictions on the composition of the positive and negative electrodes.

[0051] A second aspect of the present invention is to provide a method for detecting the lithium iron phosphate short-blade battery cell as described in the first aspect.

[0052] The detection method includes the following steps: treating the target cell in the lithium iron phosphate short knife battery cell by the cold needle acupuncture method, and detecting whether the battery cell adjacent to the target cell has heat spread; wherein the acupuncture positions of the cold needle acupuncture method include a first point and a second point, the first point is the explosion-proof valve, and the second point is: in the length direction of the short knife battery cell, 25mm to 50mm adjacent to the explosion-proof valve.

[0053] The third aspect of the present invention is to provide a method for preparing the lithium iron phosphate short-blade battery cell as described in the first aspect, specifically comprising the following steps performed in sequence:

[0054] Homogenization, coating, rolling, slitting, laser die-cutting, lamination, hot pressing, testing, flat welding of tabs, cutting of tabs, laser welding of negative cover and tabs, secondary testing, bending of negative tabs, installation of positive terminal plate, shelling, pressing and pre-spot welding of negative cover, laser welding of positive tabs and tabs, bending of positive tabs, pressing and pre-spot welding of positive cover, peripheral welding, tertiary testing, baking, quaternary testing, primary liquid injection, high temperature impregnation, pre-charging, secondary liquid injection, high temperature aging, standing at room temperature, DCR testing, sealing with glue nails, helium testing, capacity division, OCV1 testing, aging at room temperature, OCV2 / K value testing, quintuple testing, insulating film packaging, top patching, size measurement, thickness testing, insulation testing, appearance testing, sorting and warehousing.

[0055] Specifically, the specific operations and functions performed in each process are as follows:

[0056] S1 Homogenization: Mix the raw materials such as the positive or negative electrode active material, conductive agent, binder and the solvent evenly to form a slurry.

[0057] S2 coating: evenly coating the homogenized slurry on the surface of the current collector.

[0058] S3 rolling: The coated electrode is rolled to increase the density and compaction of the electrode, thereby improving the capacity and cycle performance of the battery cell.

[0059] S4 cutting: Cut the rolled electrode sheets into predetermined sizes to obtain the electrode sheets required for a single battery cell.

[0060] S5 Laser Die Cutting: Use laser technology to precisely cut the pole piece to meet the shape and size requirements of the battery cell design.

[0061] S6 stacking: stack the positive electrode sheet, separator and negative electrode sheet together in a predetermined order to form the preliminary structure of the battery cell.

[0062] S7 hot pressing: The stacked cells are hot pressed to enhance the internal bonding strength and overall stability of the cells.

[0063] S8 detection: including hitpot and X-ray detection. The former performs high-voltage test on the battery cell to check whether the battery cell has internal short circuit or leakage. The latter uses X-ray technology to scan the battery cell to detect whether there are foreign objects or defects inside the battery cell.

[0064] S9 flat welding of the pole ear: connect the pole ear and the pole piece by flat welding to ensure that the connection between the pole ear and the pole piece is firm and reliable.

[0065] S10 Tab cutting: Cut the tabs after welding to meet the size requirements of the battery cell design.

[0066] S11 negative electrode cover and pole ear laser welding: Use laser welding technology to connect the negative electrode cover and the pole ear.

[0067] S12 secondary inspection: Perform the hitpot test again to ensure that the battery cell still maintains good electrical performance after welding.

[0068] S13 Negative electrode ear bending: Bend the negative electrode ear to adapt to the overall structure and installation requirements of the battery cell.

[0069] S14 positive terminal plate installation: Install the positive terminal plate and use Mylar for hot melting and gluing to enhance the sealing and stability of the battery cell.

[0070] S15 into the shell: put the battery cell into the battery shell as a whole.

[0071] S16 negative electrode cover plate press-fitting and pre-spot welding: The negative electrode cover plate is press-fitted onto the battery shell and pre-spot welded to achieve fixation.

[0072] S17 positive electrode tab and cover plate laser welding: Use laser welding technology to connect the positive electrode tab and cover plate.

[0073] S18 Positive electrode ear bending: Bend the positive electrode ear to adapt to the overall structure and installation requirements of the battery cell.

[0074] S19 Pressing and pre-spot welding of the positive electrode cover: Press the positive electrode cover onto the battery shell and perform pre-spot welding to fix it.

[0075] S20 peripheral welding: welding the periphery of the battery shell to enhance the sealing of the battery cell.

[0076] S21 triple test: Perform the third hitpot test to ensure that the battery cell still maintains good electrical performance after welding and assembly.

[0077] S22 Baking: The battery cells are baked to remove moisture and residual gas inside the battery cells.

[0078] S23 fourth test: Perform the fourth hitpot test to further ensure the electrical performance of the battery cell.

[0079] S24 primary injection: inject an appropriate amount of electrolyte into the battery cell.

[0080] S25 high temperature soaking: Leave the battery cell at high temperature for a period of time to allow the electrolyte to fully soak the active materials inside the battery cell.

[0081] S26 pre-charge: pre-charge the battery cell to activate the chemical reaction inside the battery cell.

[0082] S27 Secondary injection: According to the wetting condition of the battery cell, inject an appropriate amount of electrolyte into the battery cell again.

[0083] S28 High temperature aging: Leave the battery cell at high temperature for a period of time to accelerate the chemical reaction and aging process inside the battery cell.

[0084] S29 Leave the battery at room temperature for a period of time to stabilize its performance.

[0085] S30 DCR test: Measures the DC internal resistance of the battery cell to evaluate the conductivity of the battery cell.

[0086] S31 Glue nail sealing: Use glue nails to seal the battery cell.

[0087] S32 Helium test: Use helium to test the battery cells for leaks to ensure the sealing of the battery cells.

[0088] S33 Capacity test: Perform capacity test on battery cells to evaluate their energy storage capacity.

[0089] S34 OCV1 test: Measures the open circuit voltage of the battery cell to evaluate the voltage characteristics of the battery cell.

[0090] S35 room temperature aging: Leave the battery cell at room temperature for a period of time to further stabilize the performance of the battery cell.

[0091] S36 OCV2 / K value test: Measure the open circuit voltage (OCV2) of the battery cell again and calculate the K value (a parameter related to battery cell performance) to evaluate changes in battery cell performance.

[0092] S37 five tests: The second time uses X-ray technology to scan the battery cell to check whether there are defects or changes inside the battery cell; in addition, edge voltage detection is performed to measure the voltage at the edge of the battery cell to evaluate the voltage distribution and consistency of the battery cell.

[0093] S38 Insulation film packaging: Wrap the insulating film on the outside of the battery cell to enhance the insulation performance of the battery cell.

[0094] S39 Top patch: A label or logo is attached to the top of the battery cell.

[0095] S40 Dimensional measurement: Measure the dimensions of the battery cell to ensure that the battery cell meets the design requirements.

[0096] S41 Thickness Test: Measures the thickness of the battery cell under a specific pressure to assess the compaction and stability of the battery cell.

[0097] S42 Insulation test: Perform insulation test on the battery cell to ensure that the insulation performance of the battery cell meets the requirements.

[0098] S43 Appearance inspection: Check the appearance of the battery cell to ensure that the surface of the battery cell is free of damage and pollution.

[0099] S44 Sorting and warehousing: According to the test results and performance requirements, the battery cells are sorted and classified, and the qualified battery cells are placed in the warehouse for storage and standby.

[0100] A fourth aspect of the present invention is to provide a lithium-ion battery, comprising the lithium iron phosphate short blade battery cell as described in the first aspect.

[0101] It can be understood that the lithium-ion battery also includes necessary or non-essential functional elements or packaging components such as a protection circuit, a casing, a sealing structure, etc., and those skilled in the art can make arbitrarily selections and combinations thereof; when the lithium-ion battery contains at least one of the lithium iron phosphate short blade batteries, whether or not the lithium-ion battery also contains other types of batteries, it can be regarded as an embodiment of the present invention.

[0102] A fifth aspect of the present invention is to provide an electrical device, comprising the lithium iron phosphate short blade battery cell as described in the first aspect.

[0103] It can be understood that the electrical equipment can be any equipment or device that relies on electric energy to work or operate, including but not limited to new energy vehicles, building electrical equipment, industrial electrical appliances, household and agricultural electrical appliances, etc.; when the lithium-ion battery is included, any electrical equipment equipped with the lithium-ion battery can belong to an embodiment of the present invention.

[0104] Example 1

[0105] The electrode composition used in this embodiment is as follows: the positive electrode adopts LFP electrode (Yuneng Y9C), the negative electrode adopts graphite electrode (Shanshan 80% X9 / 20% CP9), the diaphragm includes 1μm oily aramid and PVDF mixed coating, 7μm polyethylene base film, 2μm pure aramid oily coating, 1μm water-based PVDF coating stacked in sequence, and the electrolyte includes 8wt.% FSI, 8wt.% LiPF6, 25wt.% EC, 30wt.% EMC, 24wt.% DMC, 0.8wt.% LiODFB, 2.5wt.% VC, 1.1wt.% FEC, and 0.6wt.% DTD.

[0106] The above-mentioned positive electrode, negative electrode, separator, electrolyte and electrode ear are assembled to obtain one of the independent battery cells; five battery cells are further assembled, sealed and formed to obtain the short knife battery cell sample of this embodiment, wherein the battery cell length is 590 mm and the gap between each battery cell is 0.95 mm.

[0107] Example 2

[0108] The method is basically the same as Example 1, except that the FSI concentration in the electrolyte is adjusted to 5 wt.%.

[0109] Comparative Example 1

[0110] The method is basically the same as Example 1, except that the FSI concentration in the electrolyte is adjusted to 4 wt.%.

[0111] Comparative Example 2

[0112] It is basically the same as Example 1, except that the diaphragm is replaced by: a 2 μm aramid and PVDF mixed oily coating, a 7 μm polyethylene-based film, and a 1 μm PVDF oily coating stacked in sequence.

[0113] Comparative Example 3

[0114] It is basically the same as Example 1, except that the diaphragm is replaced by: a 2 μm ceramic and PMMA water-based mixed coating, a 7 μm polyethylene-based film, and a 1 μm PVDF water-based coating stacked in sequence.

[0115] Table 1 below provides a comparison of the performance parameters of the diaphragms used in Example 1, Comparative Example 2 and Comparative Example 3.

[0116] Table 1

[0117]

[0118] Example 3

[0119] It is basically the same as Example 1, except that the gap between each battery cell is 0.88 mm.

[0120] Test Example 1

[0121] The lithium iron phosphate short blade battery cells prepared in the above embodiments and comparative examples were subjected to cold needle puncture safety performance test. The test was conducted according to the test method C5.3 in GB 38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles". The puncture equipment used a 5mm steel needle, a 45° cone angle, a puncture speed of 1mm / s, and an ambient temperature of 60°C. The results are shown in Table 2 below.

[0122] Table 2

[0123]

[0124] Test Example 2

[0125] For Example 1, the specific temperature results in Test Example 1 are as follows Figure 1 Among them, T1-3, T2-3, T3-3, T4-3, T positive electrode-3, and T negative electrode-3 correspond to the positions of cell 3, respectively, and the position of cell 3 (the first target cell) in the battery pack of Example 1 is as follows: Figure 2 As shown. Figure 1 In the figure, T1-3, T2-3, T3-3, T4-3, T positive pole-3, T negative pole-3 correspond to the left vertical axis, indicating the temperature sensing line at each position, and V1~V5 correspond to the right vertical axis, indicating Figure 2 The voltage change curve of cells 1 to 5. It should be noted that Figure 1 The colors of T1-3 and T4-3 are similar, so Figure 1 In the figure, “T1” and “T4” are additionally marked on the corresponding graph lines.

[0126] Further, through Figure 3 The specific positions of T1-3, T2-3, T3-3, T4-3, T positive electrode-3, and T negative electrode-3 in the No. 3 battery cell are explained, where the code "-3" means No. 3 battery, that is, Figure 3 In the 3# battery, T1, T2, T3, T4, T5, and T6 correspond to the puncture points of the battery respectively. Specifically, T1 and T2 are close to the explosion-proof valve, T3 and T4 are in the center of the large surface of the side of the battery cell, and T5 and T6 are far away from the explosion-proof valve.

[0127] Therefore, based on Figure 2 , Figure 3 The position diagram can clearly understand the positions of T1-3, T2-3, T3-3, T4-3, T positive pole-3, and T negative pole-3, and combine Figure 1 , you can know the temperature changes at each point and the voltage changes of each battery cell.

[0128] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A lithium iron phosphate short-blade battery cell without heat spread, characterized in that: The lithium iron phosphate short knife battery cell does not contain an aerogel component and meets the following characteristics (a) to (c): (a) The electrolyte of the lithium iron phosphate short-blade battery cell includes lithium bis(fluorosulfonyl)imide; (b) The diaphragm of the lithium iron phosphate short-blade battery cell is an aramid isolation membrane; (c) The gap between each cell of the lithium iron phosphate short-blade battery cell is greater than 0.88 mm.

2. The heat-spread-free lithium iron phosphate short-blade battery cell according to claim 1, characterized in that: The length of the short blade battery core is 300 mm to 600 mm, and the thickness of the short blade battery core is less than 25 mm.

3. The heat-spread-free lithium iron phosphate short-blade battery cell according to claim 1, characterized in that: The electrolyte also includes a solvent, a lithium salt and an additive; The mass ratio of the solvent, the lithium salt and the additive is (10% to 18%): (75% to 85%): (4% to 10%).

4. The heat-spread-free lithium iron phosphate short-blade battery cell according to claim 1, characterized in that: The mass proportion of the lithium bis(fluorosulfonyl)imide in the electrolyte is 5% to 8%.

5. The lithium iron phosphate short-blade battery cell without heat spread according to claim 1, characterized in that: The aramid isolation film comprises a base film, a first coating layer and a third coating layer sequentially coated on a surface of one side of the base film, and a second coating layer coated on a surface of the other side of the base film; The first coating is an oily coating, which is an aramid coating; the second coating includes aramid and an adhesive material, which is an oily coating, and the adhesive material includes one of PVDF and PMMA; the third coating is a water-based PVDF coating.

6. The lithium iron phosphate short-blade battery cell without heat spread according to claim 1, characterized in that: The rupture temperature of the aramid isolation membrane is 250°C to 280°C; And / or, the aramid coating surface density of the aramid isolation membrane is 1.5 g / m 2 ~2.5g / m 2 .

7. The method for detecting a lithium iron phosphate short-blade battery cell according to any one of claims 1 to 6, characterized in that: The detection method comprises the following steps: Treating the target cell in the lithium iron phosphate short knife cell by cold needle puncture method to detect whether the cell adjacent to the target cell has heat spread; Among them, the acupuncture positions of the cold needle acupuncture method include a first point and a second point. The first point is an explosion-proof valve, and the second point is: in the length direction of the short knife battery core, 25mm to 50mm adjacent to the explosion-proof valve.

8. The method for preparing a lithium iron phosphate short-blade battery cell according to any one of claims 1 to 6, characterized in that: The preparation method comprises the following steps performed in sequence: Homogenization, coating, rolling, slitting, laser die-cutting, lamination, hot pressing, testing, flat welding of tabs, cutting of tabs, laser welding of negative cover and tabs, secondary testing, bending of negative tabs, installation of positive terminal plate, shelling, pressing and pre-spot welding of negative cover, laser welding of positive tabs and tabs, bending of positive tabs, pressing and pre-spot welding of positive cover, peripheral welding, tertiary testing, baking, quaternary testing, primary liquid injection, high temperature impregnation, pre-charging, secondary liquid injection, high temperature aging, standing at room temperature, DCR testing, sealing with glue nails, helium testing, capacity division, OCV1 testing, aging at room temperature, OCV2 / K value testing, quintuple testing, insulating film packaging, top patching, size measurement, thickness testing, insulation testing, appearance testing, sorting and warehousing.

9. A lithium ion battery, characterized in that: It comprises the lithium iron phosphate short knife battery cell as described in any one of claims 1 to 6.

10. An electrical device, characterized in that: It comprises the lithium iron phosphate short knife battery cell as described in any one of claims 1 to 6.

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