Battery cell and preparation method thereof, module and lithium ion battery pack

Abstract

The invention provides a battery cell and a preparation method thereof, a module and a lithium ion battery pack, and belongs to the technical field of lithium ion battery packs. The battery cell comprises first pole groups and second pole groups, the energy density of the first pole groups is higher than that of the second pole groups, the safety performance of the second pole groups is higher than that of the first pole groups, and the first pole groups and the second pole groups are alternately arranged; and the adjacent first pole group and second pole group are connected in series. The battery cell has relatively high energy density and good safety performance, can realize high-voltage output, and is beneficial to reducing the number of battery cells of a low-power battery pack.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery packs, and in particular relates to a battery cell and a preparation method thereof, a module and a lithium-ion battery pack. Background Art

[0002] The existing power lithium-ion battery packs have the problem of not being able to balance energy density and safety. For example, when using a high energy density system such as a ternary cathode material, safety performance cannot be guaranteed, and when using a high safety performance system such as lithium iron phosphate, energy density cannot be met. Therefore, it is necessary to optimize the battery cell design based on the existing pure high energy density system and pure high safety system to achieve the goal of balancing energy density and safety performance. Summary of the invention

[0003] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the embodiments of the present invention provide a battery cell and a preparation method thereof, a module and a lithium-ion battery pack, so that the lithium-ion battery can have a high energy density while taking into account safety performance.

[0004] An embodiment of the present invention provides a battery cell, comprising: a first pole group and a second pole group, the energy density of the first pole group is higher than the energy density of the second pole group, the safety performance of the second pole group is higher than the safety performance of the first pole group, the first pole group and the second pole group are arranged alternately, and adjacent first pole groups and second pole groups are connected in series.

[0005] The advantages and technical effects of the battery cell of the embodiment of the present invention are as follows:

[0006] (1) The energy density of the first electrode group is higher than that of the second electrode group, and the safety performance of the second electrode group is higher than that of the first electrode group. After the first electrode group and the second electrode group are connected in series alternately, the obtained battery cell can simultaneously take into account high energy density and good safety performance;

[0007] (2) The battery cell of the embodiment of the present invention is obtained by connecting the electrode groups in series, so that high voltage output can be achieved, which is beneficial to reducing the number of battery cells in the low-power battery pack;

[0008] (3) The first electrode group and the second electrode group are arranged alternately, which can well balance the high energy density system and the high safety performance system, so that the battery cell of the embodiment of the present invention has good comprehensive performance.

[0009] In some embodiments, the first electrode group includes a first positive electrode sheet and a first negative electrode sheet, the first positive electrode sheet includes a first positive electrode active material, and the first negative electrode sheet includes a first negative electrode active material; the second electrode group includes a second positive electrode sheet and a second negative electrode sheet, the second positive electrode sheet includes a second positive electrode active material, and the second negative electrode sheet includes a second negative electrode active material; the first positive electrode active material and the second positive electrode active material include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium iron phosphate, lithium ferrous phosphate, lithium nickel oxide, lithium titanate, lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide and lithium iron manganese phosphate.

[0010] In some embodiments, the first negative electrode active material and the second negative electrode active material include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, lithium titanate, and silicon alloy materials.

[0011] In some embodiments, the first positive electrode active material is lithium nickel cobalt manganese oxide, and the first negative electrode active material is graphite; the second positive electrode active material is lithium nickel cobalt manganese oxide, and the second negative electrode active material is lithium titanate.

[0012] In some embodiments, the first positive electrode active material is lithium iron phosphate, and the first negative electrode active material is graphite; the second positive electrode active material is lithium nickel cobalt manganese oxide, and the second negative electrode active material is lithium titanate.

[0013] In some embodiments, the first positive electrode active material is lithium nickel cobalt manganese oxide, and the first negative electrode active material is graphite; the second positive electrode active material is lithium iron phosphate, and the second negative electrode active material is lithium titanate.

[0014] In some embodiments, the first positive electrode active material is lithium iron phosphate, and the first negative electrode active material is graphite; the second positive electrode active material is lithium iron phosphate, and the second negative electrode active material is lithium titanate.

[0015] In some embodiments, the first positive electrode active material is lithium nickel cobalt manganese oxide, and the first negative electrode active material is graphite; the second positive electrode active material is lithium iron phosphate, and the second negative electrode active material is graphite.

[0016] In some embodiments, the first positive electrode active material is lithium nickel cobalt manganese oxide, and the first negative electrode active material is lithium titanate; the second positive electrode active material is lithium iron phosphate, and the second negative electrode active material is lithium titanate.

[0017] In some embodiments, the first electrode group and the second electrode group have the same capacity.

[0018] In some embodiments, the number of the first pole group and the number of the second pole group are the same.

[0019] In some embodiments, a single first pole group and a single second pole group are connected in series.

[0020] An embodiment of the present invention also provides a method for preparing a battery cell, comprising the following steps: arranging the first pole group and the second pole group alternately, and connecting adjacent first pole groups and second pole groups in series, and then performing shell packaging, baking, liquid injection, chemical formation, aging and capacity division to form the battery cell.

[0021] The advantages and technical effects of the method for preparing the battery cell according to the embodiment of the present invention are as follows:

[0022] The preparation method of the embodiment of the present invention can make the battery cell have both high energy density and good safety performance by alternately connecting the first electrode group and the second electrode group in series, and can also achieve high voltage output, which is beneficial to reducing the number of battery cells in the low-power battery pack.

[0023] An embodiment of the present invention further provides a module, comprising the battery cell of the embodiment of the present invention.

[0024] The advantages and technical effects brought by the module of the embodiment of the present invention are: the module of the embodiment of the present invention can have both high energy density and good safety performance, and can achieve high voltage output, which is beneficial to reducing the number of battery cells in low-power battery packs.

[0025] An embodiment of the present invention further provides a lithium-ion battery pack, comprising the module of the embodiment of the present invention.

[0026] The advantages and technical effects brought by the lithium-ion battery pack of the embodiment of the present invention are: the lithium-ion battery pack of the embodiment of the present invention can have both high energy density and good safety performance, and can achieve high voltage output, which is beneficial to reducing the number of battery cells in the low-power battery pack. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic structural diagram of the first pole group of the battery cell of Example 1-6;

[0028] Figure 2 It is a schematic structural diagram of the second electrode group of the battery cell of Example 1-6;

[0029] Figure 3 It is a schematic diagram of the structure of the battery cell of Example 1-6;

[0030] Figure 4 It is a schematic structural diagram of the first electrode group of the battery cell of Comparative Examples 1-4;

[0031] Figure 5 It is a schematic structural diagram of the second electrode group of the battery cell of Comparative Examples 1-4;

[0032] Figure 6 It is a schematic diagram of the structure of the battery cell of Comparative Examples 1-4;

[0033] Explanation of the accompanying drawings: 1-positive electrode of the first electrode group; 2-negative electrode of the first electrode group; 3-positive electrode of the second electrode group; 4-negative electrode of the second electrode group; 5-positive electrode of the battery cell; 6-negative electrode of the battery cell; 7-third electrode. DETAILED DESCRIPTION

[0034] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0035] An embodiment of the present invention provides a battery cell, such as Figure 1-3 As shown, it includes: a first pole group and a second pole group, the energy density of the first pole group is higher than the energy density of the second pole group, the safety performance of the second pole group is higher than the safety performance of the first pole group, the first pole group and the second pole group are arranged alternately, and adjacent first pole groups and second pole groups are connected in series.

[0036] The energy density of the first pole group is higher than that of the second pole group, and the safety performance of the second pole group is higher than that of the first pole group. After the first pole group (high energy density system) and the second pole group (high safety performance system) are alternately connected in series, the battery cell of the embodiment of the present invention can have both high energy density and good safety performance. Compared with the high energy density battery cell (hereinafter referred to as the pure high energy density system) that uses all the first pole groups, although the battery cell of the embodiment of the present invention will lose a very small part of the energy density, the safety performance can be significantly improved; and compared with the high safety performance battery cell (hereinafter referred to as the pure high safety performance system) that uses all the second pole groups, although the safety performance of the battery cell of the embodiment of the present invention is slightly reduced, its energy density is significantly improved, that is, the energy density of the battery cell of the embodiment of the present invention is close to that of the pure high energy density system, and the safety performance is close to that of the pure high safety performance system. Therefore, it can be considered that the comprehensive performance of the battery cell of the embodiment of the present invention is superior to that of the pure high energy density system and the pure high safety performance system, and has a higher practical value.

[0037] In addition, since the first pole group and the second pole group in the battery cell of the embodiment of the present invention adopt a series design, the operating voltage of the battery cell of the embodiment of the present invention is significantly improved compared to the battery cell obtained by the parallel connection in the related art, and high-voltage output can be achieved, which is beneficial to reduce the number of battery cells in the low-power battery pack. It should be noted that the first pole group and the second pole group in the battery cell of the embodiment of the present invention cannot be designed in parallel, because the voltage use range of the first pole group and the second pole group is different. If they are connected in parallel, the loss of energy density is very large, and the design effect of taking into account both energy density and safety performance cannot be achieved. It can be understood that the first pole group and the second pole group are connected in series and arranged alternately, and the positive electrode of the first pole group can be connected to the negative electrode of the second pole group, or the negative electrode of the first pole group can be connected to the positive electrode of the second pole group.

[0038] It should be noted that the evaluation of the above-mentioned safety performance can be characterized by needle penetration, hot box and overcharge tests at the cell level, and by heat spread tests at the battery pack level.

[0039] The first electrode group includes a first positive electrode sheet and a first negative electrode sheet, the first positive electrode sheet includes a first positive electrode active material, and the first negative electrode sheet includes a first negative electrode active material; the second electrode group includes a second positive electrode sheet and a second negative electrode sheet, the second positive electrode sheet includes a second positive electrode active material, and the second negative electrode sheet includes a second negative electrode active material.

[0040] The battery cell of the embodiment of the present invention has no particular limitation on the specific types of the first positive electrode active material, the first negative electrode active material, the second positive electrode active material and the second negative electrode active material. Specifically, the first positive electrode active material and the second positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium iron phosphate, lithium ferrous phosphate, lithium nickel oxide, lithium titanate, lithium cobalt oxide, lithium manganate, lithium nickel manganese oxide and lithium manganese iron phosphate. The first negative electrode active material and the second negative electrode active material may include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, lithium titanate and silicon alloy materials.

[0041] It should be understood that in the battery cell of the embodiment of the present invention, when the first positive electrode active material is the same as the second positive electrode active material, the first negative electrode active material is different from the second negative electrode active material; similarly, when the first negative electrode active material is the same as the second negative electrode active material, the first positive electrode active material is different from the second positive electrode active material, so as to satisfy the requirement that the energy density of the first electrode group is higher than the energy density of the second electrode group, and the safety performance of the second electrode group is higher than the safety performance of the first electrode group.

[0042] In order to further improve the energy density and safety performance of the battery cell, the battery cell of the embodiment of the present invention is preferably a battery cell of the following types:

[0043] In some embodiments, the first positive electrode active material is lithium nickel cobalt manganese oxide, and the first negative electrode active material is graphite; the second positive electrode active material is lithium nickel cobalt manganese oxide, and the second negative electrode active material is lithium titanate. The energy density of the battery pack assembled from the battery cells can reach 210Wh / Kg, the thermal runaway test performs well, and the heat spread time is greater than 30min, indicating that the safety performance is good.

[0044] In some embodiments, the first positive electrode active material is lithium iron phosphate, the first negative electrode active material is graphite; the second positive electrode active material is lithium nickel cobalt manganese oxide, and the second negative electrode active material is lithium titanate. The energy density of the battery pack assembled from the battery cells can reach 179Wh / Kg, the thermal runaway test performance is excellent, and the heat spread time is greater than 1h, indicating excellent safety performance.

[0045] In some embodiments, the first positive electrode active material is lithium nickel cobalt manganese oxide, the first negative electrode active material is graphite; the second positive electrode active material is lithium iron phosphate, and the second negative electrode active material is lithium titanate. The energy density of the battery pack assembled from the battery cells can reach 192Wh / Kg, the thermal runaway test performance is excellent, and the heat spread time is greater than 1h, indicating excellent safety performance.

[0046] In some embodiments, the first positive electrode active material is lithium iron phosphate, the first negative electrode active material is graphite; the second positive electrode active material is lithium iron phosphate, and the second negative electrode active material is lithium titanate. The energy density of the battery pack assembled from the battery cells can reach 165Wh / Kg, the thermal runaway test performance is excellent, and the heat spread time is greater than 1h, indicating excellent safety performance.

[0047] In some embodiments, the first positive electrode active material is lithium nickel cobalt manganese oxide, and the first negative electrode active material is graphite; the second positive electrode active material is lithium iron phosphate, and the second negative electrode active material is graphite. The energy density of the battery pack assembled from the battery cells can reach 224Wh / Kg, and the thermal runaway test performance is excellent, and the heat spread time is greater than 1h, indicating excellent safety performance.

[0048] In some embodiments, the first positive electrode active material is lithium nickel cobalt manganese oxide, the first negative electrode active material is lithium titanate; the second positive electrode active material is lithium iron phosphate, and the second negative electrode active material is lithium titanate. The energy density of the battery pack assembled from the battery cells can reach 127Wh / Kg, the thermal runaway test performance is excellent, and the heat spread time is greater than 1h, indicating excellent safety performance.

[0049] In the battery cell of the embodiment of the present invention, the capacities of the first pole group and the second pole group may be the same or different. Preferably, in some embodiments, the capacities of the first pole group and the second pole group are the same. If the capacities of the first pole group and the second pole group are different, the overall capacity of the battery cell is determined by the pole group with the lower capacity of the first pole group and the second pole group, and the extra capacity of the other pole group with a relatively higher capacity will not actually play a role. Therefore, in order to avoid waste and increase costs, it is preferred that the capacities of the first pole group and the second pole group are the same.

[0050] In the battery cell of the embodiment of the present invention, the total number of the first pole group and the second pole group can be either an odd number or an even number, and the number of the first pole group and the second pole group can be the same or different. Preferably, in some embodiments, the number of the first pole group and the second pole group is the same, that is, the total number of the first pole group and the second pole group is an even number, which is conducive to improving the energy density and safety performance of the battery cell.

[0051] Preferably, in some embodiments, a single first electrode group and a single second electrode group are connected in series. In the design of electrode groups connected in series, if the number of electrode groups exceeds two, the design of the electrode tabs of the battery cell is very complicated, which is not conducive to simplifying the process.

[0052] In some embodiments, the first positive electrode plate may include a conductive agent, a binder, and a solvent in addition to the first positive electrode active material. Similarly, the second positive electrode plate may include a conductive agent, a binder, and a solvent in addition to the second positive electrode active material.

[0053] In some embodiments, the first negative electrode plate may include a conductive agent, a binder, and a solvent in addition to the first negative electrode active material, and may optionally include a thickener. Similarly, the second negative electrode plate may include a conductive agent, a binder, and a solvent in addition to the second negative electrode active material, and may optionally include a thickener.

[0054] In some embodiments, the first electrode group includes, in addition to the first positive electrode sheet and the first negative electrode sheet, a separator disposed between the first positive electrode sheet and the first negative electrode sheet. Similarly, the second electrode group includes, in addition to the second positive electrode sheet and the second negative electrode sheet, a separator disposed between the second positive electrode sheet and the second negative electrode sheet.

[0055] The cell of the embodiment of the present invention has no particular limitation on the separators in the first pole group and the second pole group, as long as they are materials with high porosity that allow lithium ions to pass through. In some embodiments, the separators in the first pole group and the second pole group can include at least one of PP, PE and non-woven fabric.

[0056] In some embodiments, the battery cell also includes an electrolyte. The battery cell of the embodiment of the present invention has no particular limitation on the electrolyte, as long as it can play the role of conducting ions between the positive and negative electrodes of the lithium-ion battery pack. The electrolyte includes a lithium salt and a solvent that can dissolve the lithium salt. Among them, the lithium salt may include lithium fluoride (LiF), lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LIFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium metaborate (LiBO2), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bis(trifluoromethylsulfonyl)imide (Li(SO2CF3)2). The solvent may include cyclic esters such as ethylene carbonate and propylene carbonate, and at least one of linear esters such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0057] The embodiment of the present invention also provides a method for preparing a battery cell, comprising the following steps: arranging the first electrode group and the second electrode group alternately, and connecting the adjacent first electrode group and the second electrode group in series, and then performing shell packaging, baking, liquid injection, chemical formation, aging and capacity division to form a battery cell. Specifically, the positive electrode of the first electrode group can be welded to the negative electrode of the second electrode group, or the negative electrode of the first electrode group can be welded to the positive electrode of the second electrode group, and the first electrode group and the second electrode group can be stacked to form a battery cell.

[0058] The preparation method of the embodiment of the present invention can make the battery cell have both high energy density and good safety performance by alternately connecting the first electrode group and the second electrode group in series, and can also achieve high voltage output, which is beneficial to reducing the number of battery cells in the low-power battery pack.

[0059] In some embodiments, the preparation method of the first electrode group includes the following steps: obtaining the first electrode group by winding or laminating in the order of first negative electrode sheet / separator / first positive electrode sheet / separator / first negative electrode sheet.

[0060] In some embodiments, the preparation method of the first positive electrode plate includes the following steps: mixing the first positive electrode active material, conductive agent, binder and solvent in a certain proportion, uniformly coating them on the surface of the aluminum foil substrate, and then baking, rolling and cutting to obtain the first positive electrode plate.

[0061] In some embodiments, the preparation method of the first negative electrode plate includes the following steps: mixing the first negative electrode active material, conductive agent, binder and solvent and optionally thickener in a certain proportion, uniformly coating the mixture on the surface of the copper foil substrate, and then baking, rolling and cutting to obtain the first negative electrode plate.

[0062] The preparation methods of the second positive electrode sheet, the second negative electrode sheet and the second electrode group may refer to the preparation methods of the first positive electrode sheet, the first negative electrode sheet and the first electrode group mentioned above.

[0063] The embodiment of the present invention further provides a module, including the battery cell of the embodiment of the present invention. The module of the embodiment of the present invention can have both high energy density and high safety performance, and can achieve high voltage output, which is conducive to reducing the number of battery cells in a low-power battery pack.

[0064] The embodiment of the present invention further provides a lithium-ion battery pack, including the battery cell of the embodiment of the present invention, or including the module of the embodiment of the present invention. The lithium-ion battery pack of the embodiment of the present invention can have both high energy density and high safety performance, and can achieve high voltage output, which is conducive to reducing the number of battery cells in the low-power battery pack.

[0065] The present invention is described in detail below with reference to the embodiments and the accompanying drawings.

[0066] Example 1

[0067] (1) Preparation of the first positive electrode sheet: The first positive electrode active material, lithium nickel cobalt manganese oxide (NCM811), the binder polyvinylidene fluoride (PVDF), and the conductive agent carbon black (SP) are homogenized in a weight ratio of 90:5:5, and the solvent N-methylpyrrolidone (NMP) is added to control the slurry viscosity to 6000-12000 mPa·s and the solid content to 60-75wt%. The slurry is then evenly coated on the surface of an aluminum foil with a thickness of 12 μm, and the first positive electrode sheet is obtained by drying.

[0068] (2) Preparation of the first negative electrode sheet: The first negative electrode active material artificial graphite, the binder styrene butadiene rubber (SBR), the thickener carboxymethyl cellulose (CMC), and the conductive agent carbon black (SP) are homogenized and mixed in a weight ratio of 95:2.5:1.5:1, and deionized water is added to control the slurry viscosity to 1000-5000 mPa·s and the solid content to 40-55wt%. The slurry is then evenly coated on the surface of a copper foil with a thickness of 6 μm, and the first negative electrode sheet is obtained by drying.

[0069] (3) Preparation of the second positive electrode sheet: The second positive electrode active material, lithium nickel cobalt manganese oxide (NCM811), the binder polyvinylidene fluoride (PVDF), and the conductive agent carbon black (SP) are homogenized in a weight ratio of 90:5:5, and the solvent N-methylpyrrolidone (NMP) is added to control the slurry viscosity to 6000-12000 mPa·s and the solid content to 60-75wt%. The slurry is then evenly coated on the surface of an aluminum foil with a thickness of 12 μm, and the second positive electrode sheet is obtained by drying.

[0070] (4) Preparation of the second negative electrode sheet: The second negative electrode active material lithium titanate (LTO), the binder styrene butadiene rubber (SBR), the thickener carboxymethyl cellulose (CMC), and the conductive agent carbon black (SP) are homogenized and mixed in a weight ratio of 95:2.5:1.5:1, and deionized water is added to control the slurry viscosity to 1000-5000 mPa·s and the solid content to 40-55wt%. The slurry is then evenly coated on the surface of a copper foil with a thickness of 6 μm, and the second negative electrode sheet is obtained by drying.

[0071] (5) Preparation of the first electrode group and the second electrode group: The first electrode group is prepared by stacking in the order of first negative electrode sheet / pp separator / first positive electrode sheet / pp separator / first negative electrode sheet; the second electrode group is prepared by stacking in the order of second negative electrode sheet / pp separator / second positive electrode sheet / pp separator / second negative electrode sheet; the capacities of the first electrode group and the second electrode group are controlled to be consistent by controlling the number of positive and negative electrode sheets.

[0072] (6) Preparation of battery cells: The prepared single first electrode group and single second electrode group are combined and welded in series, and then packaged into a shell, baked, injected with liquid, formed, aged and divided into different capacities to obtain a battery cell.

[0073] like Figure 1 As shown, in this embodiment, the first stage group includes a first electrode group positive electrode 1 and a first electrode group negative electrode 2; Figure 2 As shown, in this embodiment, the second stage group includes a second electrode group positive electrode 3 and a second electrode group negative electrode 4; Figure 3 As shown, the battery cell in this embodiment includes a battery cell positive electrode 5, a battery cell negative electrode 6 and a third electrode 7. The battery cell positive electrode 5 is the positive electrode 1 of the first electrode group, the battery cell negative electrode 6 is the negative electrode 4 of the second electrode group, and the third electrode 7 is a pole ear formed by welding the negative electrode 2 of the first electrode group and the positive electrode 3 of the second electrode group.

[0074] (7) Preparation of battery pack: Two battery cells are combined and welded in series to form a battery pack.

[0075] Example 2

[0076] The structure and preparation method of this embodiment are the same as those of Embodiment 1, except that: the first positive electrode active material is lithium iron phosphate (LFP), and the first negative electrode active material is artificial graphite; the second positive electrode active material is lithium nickel cobalt manganese oxide (NCM811), and the second negative electrode active material is lithium titanate (LTO).

[0077] Example 3

[0078] The structure and preparation method of this embodiment are the same as those of Embodiment 1, except that: the first positive electrode active material is lithium nickel cobalt manganese oxide (NCM811), and the first negative electrode active material is artificial graphite; the second positive electrode active material is lithium iron phosphate (LFP), and the second negative electrode active material is lithium titanate (LTO).

[0079] Example 4

[0080] The structure and preparation method of this embodiment are the same as those of Embodiment 1, except that: the first positive electrode active material is lithium iron phosphate (LFP), and the first negative electrode active material is artificial graphite; the second positive electrode active material is lithium iron phosphate (LFP), and the second negative electrode active material is lithium titanate (LTO).

[0081] Example 5

[0082] The structure and preparation method of this embodiment are the same as those of Embodiment 1, except that: the first positive electrode active material is lithium nickel cobalt manganese oxide (NCM811), and the first negative electrode active material is artificial graphite; the second positive electrode active material is lithium iron phosphate (LFP), and the second negative electrode active material is natural graphite.

[0083] Example 6

[0084] The structure and preparation method of this embodiment are the same as those of Embodiment 1, except that: the first positive electrode active material is lithium nickel cobalt manganese oxide (NCM811), and the first negative electrode active material is lithium titanate (LTO); the second positive electrode active material is lithium iron phosphate (LFP), and the second negative electrode active material is lithium titanate (LTO).

[0085] Comparative Example 1

[0086] The structure and preparation method of this comparative example are the same as those of Example 1, except that: the first positive electrode active material and the second positive electrode active material are both nickel cobalt manganese oxide (NCM811), and the first negative electrode active material and the second negative electrode active material are both artificial graphite; the first electrode group and the second electrode group are combined in parallel.

[0087] like Figure 4 As shown, in this comparative example, the first stage group includes a first pole group positive electrode 1 and a first pole group negative electrode 2; Figure 5 As shown, in this comparative example, the second stage group includes a second electrode group positive electrode 3 and a second electrode group negative electrode 4; Figure 6 As shown, the battery cell in this comparative example includes a battery cell positive electrode 5 and a battery cell negative electrode 6, the battery cell positive electrode 5 is a pole ear formed by welding the first pole group positive electrode 1 and the second pole group positive electrode 1, and the battery cell negative electrode 6 is a pole ear formed by welding the first pole group negative electrode 2 and the second pole group negative electrode 4.

[0088] Comparative Example 2

[0089] The structure and preparation method of this comparative example are the same as those of comparative example 1, except that the first positive electrode active material and the second positive electrode active material are lithium iron phosphate (LFP), and the first negative electrode active material and the second negative electrode active material are both artificial graphite.

[0090] Comparative Example 3

[0091] The structure and preparation method of this comparative example are the same as those of comparative example 1, except that the first positive electrode active material and the second positive electrode active material are both lithium nickel cobalt manganese oxide (NCM811), and the first negative electrode active material and the second negative electrode active material are both lithium titanate (LTO).

[0092] Comparative Example 4

[0093] The structure and preparation method of this comparative example are the same as those of comparative example 1, except that the first positive electrode active material and the second positive electrode active material are both lithium iron phosphate (LFP), and the first negative electrode active material and the second negative electrode active material are both lithium titanate (LTO).

[0094] The first electrode group and the second electrode group of the battery cells of Examples 1-6 and Comparative Examples 1-4 and their combination methods are shown in Table 1. It should be noted that the battery cells of Comparative Examples 1-4 can be obtained by connecting the electrode groups in series or in parallel. From the perspective of process technology, it is optimal to connect the electrode groups in parallel in Comparative Examples 1-4, and the effects of series connection and parallel connection are the same, which will not hinder the comparison with the effects of Examples 1-6. Therefore, Comparative Examples 1-4 choose to connect the electrode groups in parallel.

[0095] Performance Testing

[0096] (1) Capacity, voltage, energy and energy density test

[0097] Three battery packs of the same embodiment or comparative example were taken, and their capacity, voltage, energy and energy density were measured. The test conditions were: room temperature, 0.33C CCCV to the upper limit voltage, stand for 30 minutes, 0.33C DC to the lower limit voltage, and the upper limit voltage and the lower limit voltage are shown in Table 2. The capacity, voltage, energy and energy density test results of the battery packs of Examples 1-6 and Comparative Examples 1-4 are shown in Table 3.

[0098] (2) Thermal runaway and heat spread test

[0099] Two battery packs of the same embodiment or comparative example were taken for thermal runaway (hot box, needle puncture, overcharge) and heat spread tests. The specific test process is as follows:

[0100] ① Hot box: At room temperature, heat the 100% SOC fully charged battery cell at a heating rate of 5℃ / min to 200℃, and observe the state of thermal runaway of the battery cell;

[0101] ②Acupuncture: At room temperature, use a 3mm steel needle to pierce a 100% SOC fully charged battery cell at a speed of 1mm / s to observe the state of thermal runaway of the battery cell;

[0102] ③ Overcharge: At room temperature, charge a 100% SOC fully charged cell to 200% SOC at a charging current of 1C, and observe the state of thermal runaway of the cell;

[0103] ④ Heat spread: At room temperature, two 100% SOC full-level parallel sample cells are bound together, and one of the cells is pierced with a 3mm steel needle at a speed of 1mm / s. The state of thermal runaway in the other cell is observed, and the time interval from the occurrence of thermal runaway in the first cell to the occurrence of thermal runaway in the second cell is recorded, i.e., the heat spread time. The thermal runaway and heat spread test results of the battery packs of Examples 1-6 and Comparative Examples 1-4 are shown in Table 4.

[0104] Table 1. The first pole group, the second pole group and the combination mode of the battery cells of Examples 1-6 and Comparative Examples 1-4

[0105]

[0106] Table 2. Test conditions for capacity, voltage, energy and energy density of the battery packs of Examples 1-6 and Comparative Examples 1-4

[0107] Group Upper limit voltage Lower voltage limit Example 1 7.2V 4.3V Example 2 6.8V 4.0V Example 3 6.7V 4.0V Example 4 6.3V 3.7V Example 5 8.0V 5.3V Example 6 5.5V 3.0V Comparative Example 1 4.2V 2.8V Comparative Example 2 3.8V 2.5V Comparative Example 3 3.0V 1.5V Comparative Example 4 2.5V 1.2V

[0108] Table 3. Capacity, voltage, energy and energy density of the battery packs of Examples 1-6 and Comparative Examples 1-4

[0109]

[0110] Table 4 Thermal runaway and heat spread test results of battery packs of Examples 1-6 and Comparative Examples 1-4

[0111]

[0112] From the comparison of Example 1 and Comparative Example 1 and Comparative Example 3 in Table 3, the comparison of Example 2 and Comparative Example 2 and Comparative Example 3, the comparison of Example 3 and Comparative Example 1 and Comparative Example 4, the comparison of Example 4 and Comparative Example 2 and Comparative Example 4, the comparison of Example 5 and Comparative Example 1 and Comparative Example 2, and the comparison of Example 6 and Comparative Example 3 and Comparative Example 4, it can be seen that the battery cells of Examples 1-6 combine the advantages of high energy density and high safety characteristics. Compared with the corresponding comparative examples, in terms of energy density, although slightly lower than the pure high energy density system, it is much higher than the pure high safety system, that is, closer to the pure high energy density system. In addition, the capacity of the battery cells prepared by the series combination of Examples 1-6 is lower than the capacity of the battery cells prepared by the parallel combination of the corresponding comparative examples, but the voltage is relatively high, and high voltage output can be achieved.

[0113] From the comparison between Example 1 and Comparative Example 1 and Comparative Example 3, the comparison between Example 2 and Comparative Example 2 and Comparative Example 3, the comparison between Example 3 and Comparative Example 1 and Comparative Example 4, the comparison between Example 4 and Comparative Example 2 and Comparative Example 4, the comparison between Example 5 and Comparative Example 1 and Comparative Example 2, and the comparison between Example 6 and Comparative Example 3 and Comparative Example 4 in Table 4, it can be seen that the battery cells of Examples 1-6 combine the advantages of high energy density and high safety characteristic systems. Compared with the corresponding comparative examples, they are far superior to pure high energy density systems in terms of safety performance. In particular, the safety performance of Examples 2-6 basically reaches the safety performance of pure high safety systems such as Comparative Examples 2 and 4.

[0114] In summary, the embodiments of the present invention can greatly improve the safety performance without affecting the energy density by combining the high energy density system and the high safety system electrode groups in series, and at the same time can greatly improve the operating voltage of the battery cell, so the overall performance is excellent.

[0115] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0116] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A battery cell, characterized in that: include: A first pole group and a second pole group, wherein the energy density of the first pole group is higher than the energy density of the second pole group, the safety performance of the second pole group is higher than the safety performance of the first pole group, the first pole group and the second pole group are alternately arranged, and adjacent first pole groups and second pole groups are connected in series.

2. The battery cell according to claim 1, characterized in that: The first electrode group includes a first positive electrode sheet and a first negative electrode sheet, the first positive electrode sheet includes a first positive electrode active material, and the first negative electrode sheet includes a first negative electrode active material; the second electrode group includes a second positive electrode sheet and a second negative electrode sheet, the second positive electrode sheet includes a second positive electrode active material, and the second negative electrode sheet includes a second negative electrode active material; The first positive electrode active material and the second positive electrode active material include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium iron phosphate, lithium ferrous phosphate, lithium nickel oxide, lithium titanate, lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide and lithium iron manganese phosphate.

3. The battery cell according to claim 2, characterized in that: The first negative electrode active material and the second negative electrode active material include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, lithium titanate and silicon alloy materials.

4. The battery cell according to claim 3, characterized in that: The first positive electrode active material is lithium nickel cobalt manganese oxide, and the first negative electrode active material is graphite; the second positive electrode active material is lithium nickel cobalt manganese oxide, and the second negative electrode active material is lithium titanate.

5. The battery cell according to claim 3, characterized in that: The first positive electrode active material is lithium iron phosphate, and the first negative electrode active material is graphite; the second positive electrode active material is lithium nickel cobalt manganese oxide, and the second negative electrode active material is lithium titanate.

6. The battery cell according to claim 3, characterized in that: The first positive electrode active material is lithium nickel cobalt manganese oxide, and the first negative electrode active material is graphite; the second positive electrode active material is lithium iron phosphate, and the second negative electrode active material is lithium titanate.

7. The battery cell according to claim 3, characterized in that: The first positive electrode active material is lithium iron phosphate, and the first negative electrode active material is graphite; the second positive electrode active material is lithium iron phosphate, and the second negative electrode active material is lithium titanate.

8. The battery cell according to claim 3, characterized in that: The first positive electrode active material is lithium nickel cobalt manganese oxide, and the first negative electrode active material is graphite; the second positive electrode active material is lithium iron phosphate, and the second negative electrode active material is graphite.

9. The battery cell according to claim 3, characterized in that: The first positive electrode active material is lithium nickel cobalt manganese oxide, and the first negative electrode active material is lithium titanate; the second positive electrode active material is lithium iron phosphate, and the second negative electrode active material is lithium titanate.

10. The battery cell according to any one of claims 1 to 9, characterized in that: The first pole group and the second pole group have the same capacity; and / or the first pole group and the second pole group have the same number.

11. The battery cell according to any one of claims 1 to 9, characterized in that: The single first pole group and the single second pole group are connected in series.

12. The method for preparing a battery cell according to any one of claims 1 to 11, characterized in that: The method comprises the following steps: arranging the first pole group and the second pole group alternately, and connecting the adjacent first pole group and the second pole group in series, and then performing shell packaging, baking, liquid injection, chemical formation, aging and capacity division to form the battery cell.

13. A module, characterized in that: A battery cell comprising the battery cell described in any one of claims 1 to 11.

14. A lithium-ion battery pack, characterized in that: Includes the battery cell according to any one of claims 1 to 11, or includes the module according to claim 13.

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