Square aluminum-cased lithium iron phosphate battery

Abstract

The present application discloses a square aluminum-cased lithium iron phosphate battery. The battery comprises a case, an electrode assembly and an electrolyte, wherein the electrode assembly is located in the case and connected to poles at the top of the case, and the electrolyte is located in the case; the electrode assembly has at least 500 layers of electrode sheets; each layer of electrode sheet comprises a positive electrode sheet, a separator and a negative electrode sheet; and a mounting portion for mounting a heat exchange tube is provided on each pole, and the size of the poles needs to be matched with the thickness of the electrode assembly. According to the battery, the capacity of the battery is improved by increasing the number of electrode sheets. Additionally, the mounting portion for mounting the heat exchange tube is provided on each battery pole, enabling heat exchange with an external cooling device by means of the heat exchange tube, so as to cool the electrode assembly, thereby avoiding the problem of battery swelling or even thermal runaway caused by insufficient heat dissipation when the number of stacked sheets of the electrode assembly increases.

Description

A square aluminum shell lithium iron phosphate battery Technical Field

[0001] The present application belongs to the field of batteries, and specifically relates to a square aluminum shell lithium iron phosphate battery. Background Art

[0002] Common lithium-ion batteries are divided into button batteries, square batteries and cylindrical batteries according to their appearance.

[0003] The electrode components in the square battery are arranged in the order of positive electrode-diaphragm-negative electrode, assembled using a stacking or winding process, and then encapsulated in a square aluminum shell.

[0004] With the continuous development of science and technology, the market demand for batteries with high safety and large capacity is growing stronger. Therefore, how to ensure battery safety while increasing battery capacity has become a technical hotspot in the battery field.

[0005] To increase the capacity of a prismatic aluminum-cased lithium iron phosphate battery, the number of winding layers or stacking layers of the electrode sheets in the electrode assembly needs to be increased. However, the temperature of the electrode assembly continues to rise during battery operation. In particular, the temperature of the electrode sheets in the center of the assembly cannot be effectively controlled, which can cause continuous heating and increased internal pressure within the battery, leading to battery bulging, failure, and even thermal runaway. Summary of the Invention

[0006] In order to solve the problem that the capacity of existing square aluminum shell lithium iron phosphate batteries cannot be increased, the present application provides a square aluminum shell lithium iron phosphate battery.

[0007] The battery includes a shell, an electrode assembly and an electrolyte; the electrode assembly is located in the shell and connected to the pole on the top of the shell, and the electrolyte is located in the shell; the number of pole pieces in the electrode assembly is ≥500 layers; each layer of pole pieces includes a positive pole piece, a diaphragm, and a negative pole piece; the pole piece is provided with a mounting portion for installing a heat exchange tube, and the size of the pole piece must be compatible with the thickness of the electrode assembly.

[0008] The battery capacity is increased by increasing the number of pole pieces. Most importantly, a mounting portion for a heat exchange tube is provided on the battery pole. The heat exchange tube is used to exchange heat with an external refrigeration device to cool the electrode assembly, thereby avoiding the problem of battery swelling or even thermal runaway caused by the inability to transfer heat due to the increase in the number of pole piece layers in the electrode assembly.

[0009] Furthermore, the mounting portion is a groove provided on the pole, and a liquid cooling pipe or a cored heat pipe is mounted on the groove to connect to an external refrigeration device, thereby achieving a temperature reduction treatment for the electrode assembly of the battery.

[0010] Furthermore, the shell includes an upper cover, a cylinder and a lower cover; the upper and lower ends of the cylinder are open; the upper cover and the lower cover are fixed to the open ends of the cylinder by welding;

[0011] The upper cover comprises a cover body, a positive pole and a negative pole; the positive pole and the negative pole are fixedly insulated on the cover body; and an explosion relief membrane is provided on the cover body.

[0012] Furthermore, the cylinder body and the lower cover are integrally formed.

[0013] Furthermore, at least one first reinforcing rib is provided on the outer surface of the side wall in the width and thickness directions of the cylinder body. The provision of the first reinforcing rib can increase the strength of the cylinder body and reduce the impact of shell expansion on battery performance.

[0014] Furthermore, the first reinforcing rib is a hollow structure. The first reinforcing rib of the hollow structure not only increases the strength of the cylinder, but also the hollow structure can be used as a cooling channel, which can further enhance the ability to cool the electrode assembly in the battery.

[0015] Furthermore, at least two second reinforcing ribs are provided on the cover plate body of the upper cover and the lower cover. The provision of the second reinforcing ribs can increase the strength of the upper cover and the lower cover and reduce the impact of shell expansion on battery performance.

[0016] Furthermore, the positive electrode active material gram capacity of the above electrode assembly is 145 mAh / g, the negative electrode active material gram capacity is 350 mAh / g, the positive electrode collector thickness is 12 μm, the negative electrode collector thickness is 6 μm, and the positive electrode sheet density is 32 g / m 2 , negative electrode sheet density 53.5g / m 2 The positive electrode sheet size is 164mm×186mm, the negative electrode sheet size is 167×190mm; the diaphragm thickness is 16um, the diaphragm size is 169mm×195mm; the shell width is 174mm±1mm; the height is: 204±1mm; the thickness is ≥145mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG1 is a schematic diagram of a battery structure without the first and second reinforcing ribs;

[0018] FIG2 is a schematic diagram of a battery structure with a first reinforcing rib and a second reinforcing rib;

[0019] FIG3 is a second schematic diagram of a battery structure provided with a first reinforcing rib and a second reinforcing rib;

[0020] Figure 4 is a schematic structural diagram of the upper cover;

[0021] FIG5 is a schematic diagram of the structure after the upper cover and the electrode assembly are connected;

[0022] FIG6 is a capacity deviation value curve diagram.

[0023] The figures are marked as follows: 1-shell, 11-upper cover, 110-cover body, 111-positive pole, 112-negative pole, 113-explosion-proof membrane, 12-cylinder, 13-lower cover, 14-first reinforcing rib, 15-second reinforcing rib, 2-pole, 3-mounting part, 4-through hole, 5-groove, 6-electrode assembly. DETAILED DESCRIPTION

[0024] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in the embodiments. Obviously, the embodiments described are only some embodiments, not all embodiments. Based on the following embodiments, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0025] At the same time, it should be noted that the terms "top, bottom, inner, and outer" used herein to indicate orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the technical solution. Furthermore, the terms "first, second, or third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0026] Unless otherwise specified or limited, the terms "mounted, connected, and connected" in this application should be understood broadly. For example, they can refer to fixed, removable, or integral connections. They can also refer to mechanical, electrical, or direct connections, indirect connections through an intermediary, or internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in this application.

[0027] The basic idea of ​​the present application is: by making the number of square lithium iron phosphate battery pole pieces greater than 500 layers, the capacity of a single square lithium iron phosphate battery can be greatly improved. At the same time, a mounting portion for installing a heat exchange tube is provided on the battery pole. Heat exchange is carried out between the heat exchange tube and an external refrigeration device to cool the electrode assembly, thereby avoiding the problem that the heat of the pole pieces located in the middle area cannot be transferred out after the number of electrode assemblies increases, causing the battery to swell or even produce thermal runaway. In addition, when making the square aluminum shell lithium iron phosphate battery, a heat exchange tube can be installed on the square aluminum shell lithium iron phosphate battery pole before liquid injection, and the heat exchange tube is used to heat the electrode assembly to control the water content of the electrode assembly and avoid damage to the battery caused by hydrofluoric acid generated after water contacts the electrolyte. Compared with the traditional vacuum baking method, this dehydration method does not require a special vacuum baking box, reduces the production cost of large-capacity batteries, and improves the production efficiency of large-capacity batteries.

[0028] The following is a more detailed introduction to the square lithium iron phosphate battery of the present application through a specific embodiment:

[0029] As shown in Figures 1 and 5, the square lithium iron phosphate battery includes a shell 1, an electrode assembly 6 and an electrolyte; the electrode assembly is located in the shell and connected to the pole 2 on the top of the shell, and the electrolyte is located in the shell; the electrode assembly 6 has 500 layers of pole pieces, and each layer of pole pieces in the electrode assembly includes a positive pole piece, a diaphragm, and a negative pole piece, and the electrode assembly is made by a lamination process or a winding process; an installation portion 3 for installing a heat exchange tube is provided on the pole 2, and the size of the pole 2 needs to be compatible with the thickness of the electrode assembly 6.

[0030] The purpose of the size of the pole 2 being adapted to the thickness of the electrode assembly 6 is to ensure reliable electrical connection between the pole and the electrode assembly. Therefore, the pole of the battery is usually rectangular or racetrack-shaped.

[0031] The basic parameters of the square lithium iron phosphate battery in this embodiment are shown in the following table:

[0032] Among them, the active material: conductive agent: binder in the positive electrode is 97:0.5:2.5; the active material: conductive agent: binder in the negative electrode is 96:0.8:3.2; the positive electrode solvent is NMP, and the negative electrode solvent is water.

[0033] Battery capacity = single positive electrode capacity × number of electrode layers;

[0034] Single-piece positive electrode capacity = positive electrode sheet size × positive electrode sheet surface density × positive electrode active material gram capacity;

[0035] In this embodiment, the capacity of a single positive electrode sheet = 164mm × 186mm × 32g / m2 × 145mAh / g = 1.41Ah;

[0036] Battery capacity = 1.41Ah × 500 = 705Ah.

[0037] If the above parameters remain unchanged and only the number of electrodes is reduced to 200 layers, the capacity of the battery will drop to 1.41Ah×200=282Ah.

[0038] As shown in Figure 6, the capacity deviation curves of 500 commonly used 280Ah single square lithium iron phosphate batteries and 500 2800Ah single square lithium iron phosphate batteries show that the larger the nominal capacity, the smaller the deviation between the actual capacities of the batteries (i.e., the flatter the deviation curve). Therefore, the following conclusion can be drawn: by increasing the number of electrode layers of the electrode assembly (i.e., increasing the capacity of the battery), the capacity difference of each square lithium iron phosphate battery can be reduced. When a battery module is composed of multiple square lithium iron phosphate batteries, the probability of grouping each square lithium iron phosphate battery when capacity separation and sorting is performed can be increased. Even when the capacity of the square lithium iron phosphate battery is large enough (i.e., the capacity difference is very small), the step of capacity separation and sorting can be omitted, thereby improving the work efficiency when assembling the battery module.

[0039] Moreover, since the capacity of each square lithium iron phosphate battery in the battery module is highly consistent, the impact of poor consistency on the cycle life of the battery module can also be reduced.

[0040] Capacity deviation value = (battery actual capacity / nominal capacity) × 100%;

[0041] The installation part of the heat exchange tube in this application has two forms:

[0042] Method 1, as shown in Figure 2, a through hole 4 is opened on the pole 2, and the through hole 4 is arranged perpendicular to the axial direction of the pole 2; the aperture size of the through hole 4 needs to ensure that the heat exchange tube is tightly clamped therein to ensure installation stability while ensuring the heat transfer effect between the heat exchange tube and the pole.

[0043] Method 2, as shown in FIG3 , a groove 5 is provided on the top or side wall of the pole 2 ; the width of the groove 5 needs to ensure that the heat exchange tube is tightly clamped therein to ensure installation stability while also ensuring heat transfer between the heat exchange tube and the pole.

[0044] Compared with method 1, the processing of the groove 5 is easier and the precision is easier to ensure. Moreover, when the heat exchange tube is made of metal materials such as copper tubes or heat pipes, it is easier to ensure that the heat exchange tube is in close contact with the groove wall than the through hole (that is, the heat exchange tube can be squeezed into the groove from the groove opening through external tooling, and the two can be in close contact); therefore, method 2 is preferred as the installation part of the heat exchange tube.

[0045] As shown in Figures 2 and 3, the shell 1 of the present application includes an upper cover 11, a cylinder 12 and a lower cover 13; the upper and lower ends of the cylinder 12 are open; the upper cover 11 and the lower cover 13 are fixed to the open ends of the cylinder 12 by welding; as shown in Figure 4, the upper cover 11 includes a cover body 110, a positive pole 111 and a negative pole 112; the positive pole 111 and the negative pole 112 are fixed and insulated on the cover body 110; an explosion-proof membrane 113 is provided on the cover body 110.

[0046] Preferably, in order to facilitate processing and manufacturing, the cylinder 12 and the lower cover 13 can be integrally formed by extrusion.

[0047] Preferably, in order to improve the strength of the shell and reduce the impact of shell expansion on battery performance, in the present application, at least one first reinforcing rib 14 is provided on the outer surface of the side wall in the width and thickness directions of the cylinder 12, and at least two second reinforcing ribs 15 are provided on the upper cover and the lower cover.

[0048] More preferably, the first reinforcing rib 14 is a hollow structure. The first reinforcing rib of the hollow structure not only increases the strength of the cylinder, but also the hollow structure can be used as a cooling channel, which can further enhance the ability to cool the electrode assembly in the battery.

Claims

1. A square aluminum shell lithium iron phosphate battery, characterized in that: comprising a shell, an electrode assembly and an electrolyte; The electrode assembly is located in the shell and connected to the pole at the top of the shell, and the electrolyte is located in the shell; The number of electrode sheets in the electrode assembly is ≥500 layers; each layer of electrode sheets includes a positive electrode sheet, a separator, and a negative electrode sheet; The pole is provided with a mounting portion for mounting a heat exchange tube, and the size of the pole must be compatible with the thickness of the electrode assembly.

2. The square aluminum shell lithium iron phosphate battery according to claim 1, characterized in that: The mounting portion is a groove arranged on the pole.

3. The square aluminum shell lithium iron phosphate battery according to claim 2, characterized in that: The shell comprises an upper cover, a cylinder and a lower cover; the upper and lower ends of the cylinder are open; The upper cover and the lower cover are fixed to the two openings of the cylinder by welding; The upper cover comprises a cover body, a positive pole and a negative pole; the positive pole and the negative pole are fixedly insulated on the cover body; and an explosion-proof film is arranged on the cover body.

4. The square aluminum shell lithium iron phosphate battery according to claim 3, characterized in that: The cylinder body and the lower cover are integrally formed.

5. The square aluminum shell lithium iron phosphate battery according to claim 4, characterized in that: At least one first reinforcing rib is disposed on the outer surface of the side wall in the width and thickness directions of the cylinder.

6. The square aluminum shell lithium iron phosphate battery according to claim 5, characterized in that: The first reinforcing rib is a hollow structure.

7. The square aluminum shell lithium iron phosphate battery according to claim 6, characterized in that: There are at least two second reinforcing ribs on the cover plate body of the upper cover and on the lower cover.

8. The square aluminum shell lithium iron phosphate battery according to any one of claims 1 to 7, characterized in that: The gram capacity of the positive electrode active material in the electrode assembly is 145mAh / g, the gram capacity of the negative electrode active material is 350mAh / g, the thickness of the positive electrode collector is 12um, the thickness of the negative electrode collector is 6um, and the surface density of the positive electrode is 32g / m 2 , negative electrode surface density 53.5g / m 2 The positive electrode sheet size is 164mm×186mm, the negative electrode sheet size is 167×190mm, the diaphragm thickness is 16um, and the diaphragm size is 169mm×195mm; the width of the shell is 174mm±1mm; the height is: 204±1mm; the thickness is ≥145mm.

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