Bare battery cell, preparation method thereof, lithium ion battery and power device

Abstract

The invention provides a naked battery cell, a preparation method thereof, a lithium ion battery and a power device, and relates to the field of lithium batteries. The naked battery cell comprises a plurality of stacked pole pieces and tabs arranged on the pole pieces, the tabs are provided with welding and printing areas used for connecting the tabs, the central axis of each welding and printing area is parallel to the height direction of the naked battery cell, each welding and printing area is provided with a first welding and printing edge and a second welding and printing edge which are opposite to each other, and each tab is provided with a first tab edge and a second tab edge which are opposite to each other. The first welding printing edge and the first lug edge are positioned on one side of the vertical direction of the central axis and are spaced by a; the second welding printing edge and the second lug edge are positioned on the other side of the vertical direction of the central axis and are spaced by b; a and / or b are / is not 0, and the width of a connecting line of the lower end face of the welding printing area and the tab in the whole tab direction is c; and the naked battery cell meets the condition that (a + b) / c is more than or equal to 30% and less than or equal to 90 According to the invention, overcurrent can still be carried out under the condition that the tabs are broken, so that the quality reliability of the battery cell is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of lithium batteries, and in particular to a bare battery cell, a preparation method thereof, a lithium ion battery and a power device. Background Art

[0002] Since new energy vehicles, whether passenger cars or commercial vehicles, have higher and higher requirements for the dynamic performance of batteries, the development of lithium-ion batteries with high energy density, good fast charging performance, high safety and good battery pack consistency has become a hot topic of research today. Traditional lithium-ion batteries are connected to the main body of the battery and the top cover through adapters to form a complete electronic path. However, this method not only increases the complexity of the process, increases the cost of the battery, and increases the group margin of the battery, but also increases the ohmic internal resistance of the battery, resulting in a decrease in the electrochemical performance of the battery. Therefore, the researchers subtracted the design of the adapter from the existing battery design, which reduced the weight of the battery, simplified the process of preparing the battery, and saved the actual cost of the battery. Moreover, after ultrasonic pre-welding and laser welding soft connection, the internal resistance of the battery is reduced and the capacity of the battery is increased. However, after the laser welding soft connection process, a process of applying the ear protection glue will be added.

[0003] At present, the pole tabs are usually set as narrow pole tabs, and on the basis of the narrow pole tabs, full welding or incomplete welding is adopted during ultrasonic pre-welding. The stability of the connection between the ultrasonic pre-welding mark near the battery cell side and the pole tab after gluing is poor. In some harsh battery pack usage scenarios, the battery cell may become unstable due to collision, falling, etc., which affects the connection reliability of the connection between the ultrasonic pre-welding mark near the battery cell side and the pole tab after gluing, and then causes breakage.

[0004] The broken tab will affect the current that can be charged and discharged, causing some of the tabs to not be charged and discharged. After the cells are packed into groups, they will show low capacitance and large voltage difference in the entire battery pack, which will affect the energy efficiency of the entire battery pack. In particular, the broken tab inside a single cell may cause the entire battery pack to charge high and discharge low.

[0005] At present, the main methods to solve the problem of tab breakage include adding tab protection tape, or increasing the limit design of the tab and the battery cell to achieve a shock-absorbing effect to reduce the risk of tab breakage. However, it still cannot completely solve the problem of low internal capacity and large pressure difference in the battery pack caused by tab breakage.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The objects of the present invention include, for example, providing a bare battery cell, a preparation method thereof, a lithium-ion battery and a power device.

[0008] The embodiments of the present invention can be implemented as follows:

[0009] In a first aspect, the present invention provides a bare battery cell, comprising a plurality of stacked pole pieces and a pole ear arranged on each of the plurality of pole pieces, wherein a welding area is arranged on the pole ear, and the welding area is used for connecting the plurality of pole ears;

[0010] The central axis of the weld print area is parallel to the height direction of the bare battery core, the weld print area has a first weld print edge and a second weld print edge opposite to each other, the pole ear has a first pole ear edge and a second pole ear edge opposite to each other, the first weld print edge and the first pole ear edge are located on one side of the vertical direction of the central axis, and the second weld print edge and the second pole ear edge are located on the other side of the vertical direction of the central axis;

[0011] The distance between the first weld print edge and the first pole ear edge is a, the distance between the second weld print edge and the second pole ear edge is b, at least one of a and b is not 0, and the width of the connection line between the lower end surface of the weld print area and the pole ear in the width direction of the entire pole ear is c;

[0012] The bare battery cell satisfies: 30%≤(a+b) / c≤90%.

[0013] In an optional embodiment, the width of the pole piece is d, wherein 15%≤c / d≤45%.

[0014] In an optional embodiment, when the connection between the tab and the weld print area is broken, the current cross section of the tab based on the spacing a, b and the thickness w of the tab satisfies S≥xy / k, where S is in mm. 2 ; x is the capacity value of a single electrode of the bare cell, in Ah; y is the charge rate of a single electrode of the bare cell, in C; k is the safe overcurrent coefficient of the conductive layer of the current collector in the electrode, which is a constant, in A / mm 2 .

[0015] In an optional embodiment, the plurality of electrode sheets are negative electrode sheets, the conductive layer of the negative electrode sheet is a copper layer, and k=8A / mm 2 , S 负极 ≥xy / 8; or the plurality of electrodes are positive electrodes, the conductive layer of the positive electrode is an aluminum layer, k = 5A / mm 2 , S 正极 ≥xy / 5.

[0016] In an optional embodiment, the bare battery cell further includes a tab protection tape, which is connected to the pole piece and the tab at the same time, and the upper end surface of the tab protection tape is in contact with the lower end surface of the weld print area.

[0017] In an optional embodiment, the weld mark area is an ultrasonic pre-welding weld mark area.

[0018] In an optional embodiment, a laser welding soft connection weld mark area for connecting to an external shell is provided on the pole ear, and the laser welding soft connection weld mark area is located within the ultrasonic pre-welding weld mark area.

[0019] In a second aspect, the present invention provides a method for preparing a bare battery cell as described in any one of the above embodiments, comprising welding on the pole tab in a non-full welding manner to form a weld mark area for connecting a plurality of the pole tabs.

[0020] In a third aspect, the present invention provides a lithium-ion battery, comprising a bare cell as described in any one of the above embodiments.

[0021] In a fourth aspect, the present invention provides a power device comprising a lithium-ion battery as described in the above embodiment.

[0022] The beneficial effects of the embodiments of the present invention include, for example:

[0023] An embodiment of the present invention provides a battery cell structure, which limits the width of the welding area of ​​the pole tab, thereby ensuring the connection stability of the pole tab and still allowing current to flow when the pole tab is broken, thereby greatly improving the quality reliability of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 A schematic diagram of the structure of a battery cell provided in Example 1 of the present invention;

[0026] Figure 2 A schematic diagram of the structure of a battery cell provided in Example 2 of the present invention;

[0027] Figure 3 A schematic diagram of the structure of a comparative battery cell structure 1 provided in Comparative Example 1 of the present invention;

[0028] Figure 4 A schematic diagram of the structure of a comparative battery cell structure 2 provided in Comparative Example 2 of the present invention;

[0029] Figure 5The capacity retention rate statistics of Example 1-2 and Comparative Example 1-2 provided in the experimental examples of the present invention;

[0030] Figure 6 This is a statistical diagram comparing the DCR of different numbers of fracture layers of Examples 1-2 and Comparative Examples 1-2 provided as experimental examples of the present invention.

[0031] Icons: 100-bare cell; 110-pole piece; 120-pole ear; 1201-first pole ear edge; 1202-second pole ear edge; 121-weld mark area; 1211-first weld mark edge; 1212-second weld mark edge; 122-laser welding soft connection weld mark area; 123-prone breakage point; 130-pole ear protection tape; 141-first overcurrent path; 142-second overcurrent path; 143-third overcurrent path; 10-comparison cell structure one; 20-comparison cell structure two. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0033] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0035] In the description of the present invention, it should be noted that if the terms "upper", "lower", "inside", "outside", etc. appear to indicate an orientation or position relationship, they are based on the orientation or position relationship shown in the accompanying drawings, or are the orientation or position relationship in which the product of the invention is usually placed when used. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0036] In addition, the terms “first”, “second”, etc., if used, are merely used to distinguish between the descriptions and should not be understood as indicating or implying relative importance.

[0037] It should be noted that, in the absence of conflict, the features in the embodiments of the present invention may be combined with each other.

[0038] Please refer to Figure 1 The present embodiment provides a bare battery cell 100, which includes a pole piece 110, a pole ear 120 and a pole ear protection tape 130. The pole pieces 110 are multiple and stacked. Each of the multiple pole pieces 110 is provided with a pole ear 120, and the pole ear 120 is provided with a weld print area 121, which is used for connecting the multiple pole ears 120.

[0039] The central axis of the weld print area 121 is parallel to the height direction of the bare battery cell 100, the weld print area 121 has a first weld print edge 1211 and a second weld print edge 1212 relative to each other, the pole ear 120 has a first pole ear edge 1201 and a second pole ear edge 1202 relative to each other, the first weld print edge 1211 and the first pole ear edge 1201 are located on one side of the vertical direction of the central axis, and the second weld print edge 1212 and the second pole ear edge 1202 are located on the other side of the vertical direction of the central axis; the spacing between the first weld print edge 1211 and the first pole ear edge 1201 is a, the spacing between the second weld print edge 1212 and the second pole ear edge 1202 is b, at least one of a and b is not 0, and the width of the connecting line between the lower end surface of the weld print area 121 and the pole ear 120 in the width direction of the entire pole ear 120 is c.

[0040] The welding methods of the weld mark area 121 include two methods: "full welding" and "partial welding". In order to more clearly explain the welding method, the present invention sets "full welding" to mean welding from one side of the width direction of the pole ear 120 to the other side to achieve all welding in the width direction, that is, a / c=0 and b / c=0; "partial welding" means that the width direction is not fully welded, for example, it can be welded from the middle area of ​​one side of the width direction of the pole ear 120 to the middle area of ​​the other side, but both ends in the width direction are not welded; it can also be welded directly from the middle of the pole ear 120 to one side; as long as it is not completely welded in the width direction, it is considered "partial welding".

[0041] The welding method of "incomplete welding" includes two methods, namely "center welding" and "biased welding". Among them, "center welding" means that the widths reserved on both sides of the weld mark area 121 are the same, and the weld mark area 121 is located in the middle, that is, a=b, and a / c≥10%; "biased welding" means that the widths reserved on both sides of the weld mark area 121 are different, presenting an effect of biased welding to one side, that is, a≠b, and a / c≥0% or b / c≥0%; among them, when a or b is equal to 0, it is extreme biased welding.

[0042] In the present invention, the weld mark area 121 is welded in a non-full welding manner, the tab protection tape 130 is connected to the pole piece 110 and the tab 120 at the same time, and the upper end surface of the tab protection tape 130 contacts the lower end surface of the weld mark area 121, and the contact position is as shown in FIG. Figure 1 The position in the middle dotted line frame is the easy-to-break position 123. In the present invention, both the "center welding" and "bias welding" methods can well achieve that when the easy-to-break position 123 breaks, the tab 120 can still achieve flow through other paths, and the real capacity of the pole piece 110 can still be normally exerted, thereby improving the reliability and consistency of the product.

[0043] In order to achieve a better overcurrent effect, the bare battery cell 100 in the present invention satisfies: 30%≤(a+b) / c≤90%.

[0044] In the present invention, the area range of the weld mark area 121 is limited so that the weld mark area 121 of the bare battery cell 100 satisfies 30%≤(a+b) / c≤90%. At this time, the weld mark area 121 presents a state of not fully welded, so that when the connection position between the weld mark area 121 and the pole ear 120 after gluing is broken due to collision, falling, etc., part of the pole ear 120 is still connected to the pole piece 110, so that electron transmission can continue to be realized, the risk of low capacitance is reduced, the consistent reliability of each single pole piece 110 in the bare battery cell 100 is ensured, and the quality reliability of the product is improved.

[0045] In the present invention, the weld mark area 121 is an ultrasonic pre-welding weld mark area, and a laser welding soft connection weld mark area 122 for connecting to an external shell is provided on the tab 120, and the laser welding soft connection weld mark area 122 is located in the ultrasonic pre-welding weld mark area.

[0046] Furthermore, the present invention also defines the width of the pole piece 110 as d, wherein 15%≤c / d≤45%. The present invention defines the ratio of the width of the pole piece 110 to the width of the pole lug 120. The width of the pole lug 120 in the present invention is widened compared to the current conventional pole lug width, so that the range of the weld print area 121 can meet the connection and fixation of the pole lug 120, thereby ensuring the stability of the pole lug 120.

[0047] In the present invention, when the connection between the tab 120 and the weld print area 121 is broken, the current cross section of the tab based on the spacing a, b and the thickness w of the tab 120 satisfies S≥xy / k; wherein the unit of S is mm 2 ; x is the capacity value of a single pole piece 110 of the bare cell 100, in Ah; y is the charge rate of a single pole piece 110 of the bare cell 100, in C; k is the safe overcurrent coefficient of the conductive layer of the current collector in the pole piece, which is a constant, in A / mm 2 .

[0048] The safe overcurrent coefficient of the conductive layer of the current collector in the electrode is a fixed constant. For example, when multiple electrodes are negative electrodes and the conductive layer of the negative electrode is a copper layer, k = 8A / mm 2 , at this time, S负极 ≥xy / 8; when multiple electrodes are positive electrodes and the conductive layer of the positive electrode is an aluminum layer, k = 5A / mm 2 , at this time, S 正极 ≥xy / 5. By limiting the flow cross section of the conductive layer of the positive electrode and the negative electrode respectively, it is ensured that they have sufficient flow cross section.

[0049] In the present invention, after the positive or negative current collector is coated, baked, rolled, and slit, in the die-cutting or cutting process, a corresponding narrow or wide pole piece is obtained according to the designed size. The wide pole piece is the case where the ratio of the bottom width of a single pole piece to the width of the entire pole piece is ≥15%, and the narrow pole piece is the opposite. The negative pole piece prepared by the above process is assembled with the corresponding positive pole piece into a bare battery cell 100. The bare battery cell 100 is subjected to the ultrasonic pre-welding process and is selected to adopt a full welding, a non-full welding, or an extreme bias welding process, and then the shell is put into the shell, baked, and injected with liquid, and then it is left to stand at high temperature or at room temperature. The bare battery cell 100 undergoes the processes of formation, sealing, and capacity division, and the bare battery cell 100 product is prepared off the line. The design of the above-mentioned pole piece 120 is suitable for at least one of a laminated battery cell and a soft-pack battery cell.

[0050] Furthermore, the present invention provides a method for preparing a bare cell, which comprises welding on a pole tab 120 in a non-full welding manner to form a weld mark area 121 for connecting a plurality of pole tabs 120 .

[0051] The present invention provides a lithium-ion battery, which includes the bare battery cell 100, a housing, terminals and other structures.

[0052] In addition, the present invention provides a power device, which includes the above-mentioned lithium-ion battery. The power device includes but is not limited to mobile phones, computers, new energy vehicles, power tools, smart home devices, etc.

[0053] The present invention is further described below in conjunction with specific embodiments.

[0054] The present invention has a bare cell 100 with a capacity of 177Ah. The bare cell 100 includes two winding cores. The number of positive electrode sheets / negative electrode sheets of each winding core is 49 / 50 respectively. The capacity of a single negative electrode sheet is 1.77Ah, and the capacity of a single positive electrode sheet is 1.81Ah. The fast charging rate requirement is 2.1C. Different embodiments 1-2 and comparative examples 1-2 are designed. The specific designs and results are shown in Table 1 below:

[0055] Table 1. Statistics of design methods for different examples

[0056]

[0057] Among them, S 正 is the flow area of ​​the positive ear, S 负 is the flow area of ​​the negative electrode ear.

[0058] According to the above design, Examples 1-2 and Comparative Examples 1-2 are obtained, specifically:

[0059] Example 1

[0060] The present embodiment provides a bare cell 100, which includes a pole piece 110, a pole ear 120 and a pole ear protection tape 130. The pole ear 120 is connected to the pole piece 110. The pole ear 120 is provided with a welding area 121 for connecting the multi-layer pole ear 120 foil and a laser welding soft connection welding area 122 for connecting the external shell. In the present embodiment, the width d of the pole piece 110 is 300 mm, the width c of the connection line between the lower end surface of the welding area 121 and the pole ear 120 in the width direction of the entire pole ear 120 is 60 mm, and the pole ear 12 0 to the width of the pole piece 110 is 20%. The pole piece 120 of this embodiment is a wide pole piece, and the weld mark area 121 is welded in a welding method of not fully welding the center, wherein the width of the weld mark area 121 is 26 mm. At this time, the spacing a between the first weld mark edge 1211 and the first pole piece edge 1201 is 17 mm, and the spacing b between the second weld mark edge 1212 and the second pole piece edge 1202 is also 17 mm, (a+b) / c=56.7, satisfying the requirement of 30%≤(a+b) / c≤90%. The pole piece 110 and the pole piece 120 are connected to the pole piece 110 and the pole piece 120 at the same time.

[0061] In this embodiment, the conductive layer of the negative electrode is a copper layer, k = 8A / mm 2 , S 负极 ≥xy / 8; the conductive layer of the positive electrode is an aluminum layer, k = 5A / mm 2 , S 正极 ≥xy / 5.

[0062] In the case of wide tab design and no full welding and center welding in Example 1, the bare cell 100 is as follows Figure 1 As shown, the position where the ultrasonic pre-welding mark near the pole piece 110 is connected to the pole ear 120 after gluing is a breakable portion 123. Affected by the uneven stress after gluing, the pole ear 120 may be partially broken, but current can still be passed through the first current path 141 and the second current path 142.

[0063] Example 2

[0064] The present embodiment provides a bare cell 100, which includes a pole piece 110, a pole ear 120 and a pole ear protection tape 130. The pole ear 120 is connected to the pole piece 110. The pole ear 120 is provided with a weld print area 121 for connecting the multi-layer pole ear 120 and a laser welding soft connection weld print area 122 for connecting the external shell. In the present embodiment, the width d of the pole piece 110 is 300 mm, the width c of the connection line between the lower end surface of the weld print area 121 and the pole ear 120 in the width direction of the entire pole ear 120 is 60 mm, and the pole ear 12 0 to the width of the pole piece 110 is 20%. The pole piece 120 of this embodiment is a wide pole piece. The weld mark area 121 is welded in a welding mode of under-welding and extreme bias welding. The width of the weld mark area 121 is 30 mm. At this time, the spacing a between the first weld mark edge 1211 and the first pole piece edge 1201 is 0 mm, and the spacing b between the second weld mark edge 1212 and the second pole piece edge 1202 is 30 mm. (a+b) / c=50, which meets the requirement of 30%≤(a+b) / c≤90%. The pole piece 110 and the pole piece 120 are connected to the pole piece 110 and the pole piece 120 at the same time.

[0065] In Example 2, a unique wide tab design is used during ultrasonic pre-welding, and the welding is not fully welded but the welding is biased to an extreme, including but not limited to the biased welding design in a certain direction, such as Figure 2 As shown, it is also possible to achieve that even if the easily broken position of the tab 120 is broken, it can still pass through Figure 2 The third current flow path 143 is used for current flow, and the real capacity of the electrode 110 can still be normally exerted, thereby improving the reliability and consistency of the product.

[0066] Comparative Example 1

[0067] The present comparative example provides a comparative cell structure 20, which includes a pole piece 110, a pole ear 120 and a pole ear protection tape 130. The pole ear 120 is connected to the pole piece 110. The pole ear 120 is provided with a welding area 121 for connecting the multi-layer pole ear 120 foil and a laser welding soft connection welding area 122 for connecting the external shell. In this embodiment, the width d of the pole piece 110 is 300 mm, and the connection line between the lower end surface of the welding area 121 and the pole ear 120 is 10 mm in the width direction of the entire pole ear 120. The width c is 35 mm, and the ratio c / d of the width of the pole ear 120 to the width of the pole piece 110 is 11.7%. The pole ear 120 of the present embodiment is a narrow pole ear, and the weld mark area 121 is welded in a welding method of not fully welding and not extreme bias welding, wherein the unwelded area reserved on both sides of the weld mark area 121 is less than 10%, that is, a / c<10% and b / c<10%, which does not meet the requirement of 30%≤(a+b) / c≤90%, and the pole ear protection tape 130 is connected to the pole piece 110 and the pole ear 120 at the same time.

[0068] In comparative example 1, a narrow tab 120 design is adopted and whether or not the extreme bias welding is limited is not specified. Figure 3 As shown, when the tab 120 breaks, since the distance between the remaining two sides is too small, when the tab 120 breaks, the unwelded portion is also prone to break, resulting in no other current flow path, and the current flow capacity will be significantly reduced.

[0069] Comparative Example 2

[0070] The present comparative example provides a comparative battery cell structure 10, which includes a pole piece 110, a pole ear 120 and a pole ear protection tape 130, the pole ear 120 is connected to the pole piece of the pole piece 110, and the pole ear 120 is provided with a weld print area 121 for connecting the multi-layer pole ear 120 foil and a laser welding soft connection weld print area 122 for connecting the external shell. In this embodiment, the width d of the pole piece 110 is 300 mm, and the width c of the connection line between the lower end surface of the weld print area 121 and the pole ear 120 in the width direction of the entire pole ear 120 is 35 mm. The ratio c / d of the width of the pole ear 120 to the width of the pole piece 110 is 11.7%. The pole ear 120 of the present embodiment is a narrow pole ear, and the weld print area 121 is welded in a full welding manner, that is, a=0 and b=0, and the pole ear protection tape 130 is connected to the pole piece 110 and the pole ear 120 at the same time.

[0071] In comparative example 2, a narrow ear design is used and full welding is performed during ultrasonic welding. Figure 4 As shown; when the tab 120 is broken, there is no other current flow path, and the current flow capacity will be significantly reduced.

[0072] Experimental example

[0073] The battery cell structures provided in the above-mentioned embodiments 1-2 and comparative examples 1-2 are respectively assembled into battery cells, wherein the positive electrode main material is lithium iron phosphate, and the negative electrode is prepared by graphite to prepare the pole piece 110, and their electrochemical properties are tested. The pole pieces of each embodiment are designed with the same formula and compacted.

[0074] like Figure 5 As shown, by comparing the capacity retention rates of the four different cases, it can be seen that compared with Example 1-2 and Comparative Example 1-2, the cycle life is better, indicating that the design of the wide pole ear can make the connection area between the wide pole ear and the pole piece 110 larger, and the multi-layer pole ear foil can be ultrasonically pre-welded by a non-full welding method. The width of the pole ear 120 is greater than the width of the weld print area 121. Therefore, even if the pole ear 120 is partially broken (that is, the position where the weld print area 121 is connected to the pole ear 120 after glue is applied), the pole piece 110 can still pass current, effectively improving the quality reliability of the pole piece 110.

[0075] When the tab 120 is not broken, since the number of tabs 120 used for current flow remains unchanged and the areas of ultrasonic pre-welding and laser welding are constant, it is believed that the current flow capacity is the same. However, when the tabs 120 have different number of broken layers, the various electrical properties such as the current flow capacity show obvious differences. Considering that the existence of tabs 120 with different broken layers will greatly affect the internal resistance (DCR) of the pole piece 110, no distinction is made here between positive tabs and negative tabs. Figure 6 As shown, taking the DCR comparison of different broken layers of the negative ear (when not broken, when one layer is broken, when three layers are broken, and when five layers are broken) as an example, it can be seen from the comparison between Example 1-2 and Comparative Example 1-2 that the DCR of Comparative Example 1-2 has changed significantly before and after the break, especially with the increase in the number of broken layers, the DCR increases significantly. However, the DCR change of Example 1-2 before and after the break is not obvious, indicating that the wide ear design can have a large enough area on its surface for connecting the ear and the connecting parts, and can still pass the current when the ear is broken, which greatly improves the quality reliability of the pole piece 110.

[0076] Among them, compared with Example 2, Example 1 has a better cycle life, but a higher manufacturing cost, because in Example 2, when the welding is not fully completed and the welding is extremely biased, the unwelded tab 120 on the other side is in a free state, which is prone to the risk of wrinkling and edge collapse, while the tabs 120 on both sides of Example 1 that can be used for current flow are more evenly stressed, which can greatly reduce the risk. However, when attaching the corresponding tab protection tape 130, the adhesive attachment scheme in Example 2 is simpler and more operable than that in Example 1, so the cost of Example 1 will be higher.

[0077] From the results of the above embodiments, the design of widening the tab 120 can significantly improve the consistency and reliability of the product, mainly because under the background of a certain welding length, when part of the tab 120 is broken, the electrons can be effectively transmitted through the unwelded part of the tab 120, thereby being able to exert the real capacity of the pole piece 110 and improve the consistency of the capacity and voltage and other related electrical properties of the pole piece 110 product in the battery system. Therefore, in the present invention, widening the tab 120 design can improve the quality and reliability of the product to a certain extent.

[0078] In summary, an embodiment of the present invention provides a bare battery cell 100, which widens the pole ear 120 so that the ratio of the bottom width of the pole ear 120 to the pole piece width is ≥15%, and then ultrasonic pre-welding is performed by non-full welding. Even if the pole ear is broken, current can still be passed, thereby greatly improving the quality reliability of the pole piece 110.

[0079] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A bare battery cell, characterized in that: It comprises a plurality of stacked pole pieces (110) and a pole ear (120) arranged on each pole piece (110) of the plurality of pole pieces (110), wherein a weld print area (121) is arranged on the pole ear (120), and the weld print area (121) is used for connecting the plurality of pole ears (120); The central axis of the weld print area (121) is parallel to the height direction of the bare battery cell (100); the weld print area (121) has a first weld print edge (1211) and a second weld print edge (1212) opposite to each other; the pole ear (120) has a first pole ear edge (1201) and a second pole ear edge (1202) opposite to each other; the first weld print edge (1211) and the first pole ear edge (1201) are located on one side of the vertical direction of the central axis, and the second weld print edge (1212) and the second pole ear edge (1202) are located on the other side of the vertical direction of the central axis; The distance between the first weld print edge (1211) and the first pole ear edge (1201) is a, the distance between the second weld print edge (1212) and the second pole ear edge (1202) is b, at least one of a and b is not 0, and the width of the connection line between the lower end surface of the weld print area (121) and the pole ear (120) in the width direction of the entire pole ear (120) is c; The bare battery cell (100) satisfies: 30%≤(a+b) / c≤90%.

2. The bare battery cell according to claim 1, characterized in that: The width of the pole piece (110) is d, wherein 15%≤c / d≤45%.

3. The bare battery cell according to any one of claims 1 to 2, characterized in that: In the case where the connection between the pole tab (120) and the weld print area (121) is broken, the current cross section of the pole tab (120) based on the spacing a, b and the thickness w of the pole tab (120) satisfies S≥xy / k, where S is in mm 2 ; x is the capacity value of a single pole piece (110) of the bare battery cell (100), in Ah; y is the charging rate of a single pole piece (110) of the bare battery cell (100), in C; k is the safe overcurrent coefficient of the conductive layer of the current collector in the pole piece (110), which is a constant, in A / mm 2 .

4. The bare battery cell according to claim 3, characterized in that: The plurality of pole pieces (110) are negative pole pieces, the conductive layer of the negative pole piece is a copper layer, k=8A / mm 2 , S 负极 ≥xy / 8; or the plurality of electrodes (110) are positive electrodes, the conductive layer of the positive electrode is an aluminum layer, k=5A / mm 2 , S 正极 ≥xy / 5.

5. The bare battery cell according to claim 1, characterized in that: The bare battery cell (100) further comprises a tab protection tape (130), wherein the tab protection tape (130) is connected to both the pole piece (110) and the tab (120), and the upper end surface of the tab protection tape (130) is in contact with the lower end surface of the weld print area (121).

6. The bare battery cell according to claim 1, characterized in that: The weld mark area (121) is an ultrasonic pre-welding weld mark area.

7. The bare battery cell according to claim 6, characterized in that: The pole ear (120) is provided with a laser welding soft connection weld mark area (122) for connecting to an external shell, and the laser welding soft connection weld mark area (122) is located within the ultrasonic pre-welding weld mark area (121).

8. A method for preparing a bare battery cell according to any one of claims 1 to 7, characterized in that: The method comprises welding on the pole lug (120) in a non-full welding manner to form a weld mark area (121) for connecting a plurality of pole lugs (120).

9. A lithium ion battery, characterized in that: It comprises the bare battery core (100) as described in any one of claims 1 to 7.

10. A power device, characterized in that: It comprises the lithium ion battery as claimed in claim 9.

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