LITHIUM-ION SECONDARY BATTERY AND PREPARATION METHOD THEREOF

Abstract

Provided are a lithium-ion battery and a preparation method therefor. The preparation method comprises the steps of connecting a plurality of cells in series and/or in parallel and then sealing to obtain a module, with the cells being jelly-rolls or stacking-rolls. According to the preparation method, the process is simple, and a battery housing shell and a module housing are combined into a whole, thereby greatly reducing the cost. Moreover, in the design of battery, the battery is internally provided with a heating sheet of graphene, etc., so as to overcome the low-temperature bottleneck of the lithium-ion battery. The standardized battery directly achieves integrated manufacturing from jelly-rolls or stacking-rolls into a module, has the characteristics of a low cost, a high energy density, a wide temperature range, high safety and a long service life, and omits the post-manufacturing procedure for the module so as to reduce the production cost.

Claims

1. A method for preparing a lithium-ion secondary battery, wherein the method comprises a step of obtaining a module by packaging a plurality of cells connected in series and/or in parallel, wherein the cells are stacking-rolls or jelly-rolls.

2. The method according to claim 1, wherein the method comprises the following steps: preparing cathode and anode electrode slurries: preparing cathode and anode electrode slurries from cathode and anode electrode materials; coating: coating cathode and anode electrode current collectors with the cathode and anode slurries, respectively; slitting: slitting the coated cathode and anode electrode current collectors to obtain electrode sheets; cutting: cutting the electrode sheets to make electrode tabs, so that the electrode sheets have protruding electrode tabs; lamination or winding: laminating or winding the cathode and anode electrode sheets to obtain cells in stacking-rolls or jelly-rolls; placing cells in unit compartments: placing the obtained stacks or jelly rolls in unit compartments which function to physically separate individual cells; and then connecting a plurality of cells in series and/or in parallel to form a module and sealing the module to obtain a lithium-ion secondary battery.

3. The method according to claim 2, wherein the cathode and anode electrode slurries comprise water or an organic solvent as the solvent.

4. The method according to claim 2, wherein the cathode and anode electrode slurries comprise an electrolyte solution as the solvent and no binder is added to the slurries.

5. The method according to claim 3, wherein the cathode electrode material is a conventional lithium-ion battery cathode electrode material, and the anode electrode material is a conventional lithium-ion battery anode electrode material.

6. The method according to claim 4, wherein the cathode electrode material is a conventional lithium-ion battery cathode electrode material, and the anode electrode material is a conventional lithium-ion battery anode electrode material.

7. The method according to claim 5, wherein the cathode electrode material is selected from the group consisting of one or more of lithium iron phosphate, NCM, lithium cobaltate, NCA, lithium manganate, and a quaternary cathode electrode material.

8. The method according to claim 6, wherein the cathode electrode material is one or a combination of more selected from the group consisting of lithium iron phosphate, NCM, lithium cobaltate, NCA, lithium manganate, and a quaternary cathode electrode material.

9. The method according to claim 5, wherein the anode electrode material is selected from the group consisting of one or more of graphite, a silicon-containing anode electrode material, and metallic lithium.

10. The method according to claim 6, wherein the anode electrode material is one or a combination of more selected from the group consisting of graphite, a silicon-containing anode electrode material, and metallic lithium.

11. The method according to claim 9, wherein the anode electrode material is one or a combination of more selected from the group consisting of graphite, silicon monoxide, nanoscale silicon, and lithium titanate.

12. The method according to claim 10, wherein the anode electrode material is one or a combination of more selected from the group consisting of graphite, silicon monoxide, nanoscale silicon, and lithium titanate.

13. The method according to claim 1, wherein the method further comprises a step of formation, wherein the cells are subjected to formation prior to module sealing, or the module is subjected to formation in series after module sealing.

14. The method according to claim 13, wherein for the formation of cells, the formation is performed on individual cells, or on cells connected in series.

15. The method according to claim 2, wherein formed or unformed cells are placed in the unit compartments in a bare state, or placed in the unit compartments after being packaged with a heat shrinkage film and flattened.

16. The method according to claim 3, wherein the method further comprises a step of calendering after the coating.

17. A lithium-ion secondary battery prepared by the method according to claim 1, wherein the lithium-ion secondary battery comprising: a plurality of cells, each being a jelly roll, a stacking roll, or a pouch cell; wherein each cell has a cathode electrode tab and an anode electrode tab at one end, the cathode electrode tabs and the anode electrode tabs of the plurality of cells are connected via connector so that the cells are connected in series and/or in parallel, and a total cathode terminal of the module and a total anode terminal of the module are formed; a plurality of separated components, each components for accommodating a single cell, the separated components physically separating individual cells and having an open structure on the upper side; and a housing and a cover plate, which, when assembled together, form an internal space for accommodating the plurality of separated components and the cells in the separated components, wherein the cover plate provides a connection part for the total cathode terminal of the module and a connection part for the total anode terminal of the module.

18. The lithium-ion secondary battery according to claim 17, wherein the separated component is a unit shell, a partitioning film, or a partitioning plate.

19. The lithium-ion secondary battery according to claim 17, wherein the energy density of lithium-ion secondary battery increases by 15%, volume utilization increases by 10% or more, impedance decreases by 10%, manufacturing period shortened, cost decreases by 20%, and cycle performance at room temperature increases by 20%, compared with conventional lithium-ion batteries.

20. The lithium-ion secondary battery according to claim 17, wherein the lithium-ion secondary battery is in a size the same as or half the size of a standard battery pack.

Description

DESCRIPTION OF THE DRAWINGS

[0079] FIG. 1 is a schematic diagram of the structure of a lithium-ion secondary battery according to an embodiment of the present disclosure.

[0080] FIG. 2 is a schematic diagram of the structure of another lithium-ion secondary battery according to an embodiment of the present disclosure.

[0081] FIG. 3 is an external appearance of a lithium-ion secondary battery according to an embodiment of the present disclosure.

[0082] FIG. 4 is a schematic diagram of the integrated unit compartments of a lithium-ion secondary battery according to an embodiment of the present disclosure.

[0083] FIG. 5 is a charge-discharge curve of a lithium-ion secondary battery according to an embodiment of the present disclosure.

[0084] FIG. 6 is a cycle performance curve of a lithium-ion secondary battery according to an embodiment of the present disclosure.

[0085] Main reference numbers in the drawings:

[0086] 1. Injection-molded top cover; 2. Connection hole; 3. injection hole; 4. cathode electrode connector; 5. cathode electrode tab; 6. anode electrode connector; 7. anode electrode tab; 8.

[0087] Unit shell; 9. Injection-molded housing; 10. Injection-molded cover plate; 11. Total cathode terminal of the module; 12. Total anode terminal of the module.

DETAILED DESCRIPTION OF THE INVENTION

[0088] In order to provide a better understanding of the technical features, objectives and beneficial effects of the present disclosure, detailed descriptions of the technical solutions of the present disclosure are provided hereinafter, but are not to be understood as limiting the practicable scope of the present disclosure.

Example 1

[0089] This example provides a lithium-ion secondary battery, as shown in FIG. 1, comprising: a plurality of cells, each cell being a jelly roll, a stack, or a pouch cell; wherein each cell has a cathode electrode tab 5 and an anode electrode tab 7 at one end, the cathode electrode tabs 5 and the anode electrode tabs 7 of the plurality of cells are connected via connector so that the cells are connected in series and/or in parallel, and a total cathode terminal of the module 11 and a total anode terminal of the module 12 are formed;

[0090] a plurality of unit shells 8, each for accommodating a single cell, the unit shells 8 physically separating individual cells and having an open structure on the upper side;

[0091] cathode electrode connector 4 as a conductive structure for connecting the cathode electrode tabs 5 of the cells;

[0092] anode electrode connector 6 as a conductive structure for connecting the anode electrode tabs 7 of the cells;

[0093] an injection-molded cover plate 10, as a structure for accommodating and fixing the cells, which forms, when assembled with the injection-molded housing, an internal space for accommodating the plurality of unit shells 8 and the cells therein, wherein a seal was formed between the injection-molded cover plate 10 and the open structure on the upper side of the unit shells 8, and the injection-molded cover plate 10 is provided with a connection part for the total cathode terminal of the module 11 and a connection part for the total anode terminal of the module 12;

[0094] an injection-molded housing 9, as the outermost shell having a protective and supporting function, for accommodating the plurality of unit shells 8; and

[0095] an injection-molded top cover 1, for covering the injection-molded cover plate 10 and packaging the housing.

[0096] Four jelly rolls are included. The jelly rolls were prepared from a plurality of small cells by a jelly-roll winding process. A cathode electrode tab 5 and an anode electrode tab 7 are provided at one end of a jelly roll. The cathode electrode tab 5 is connected to a cathode electrode connector 4, and the anode electrode tab 7 is connected to an anode electrode connector 6. The cathode electrode connector 4 and the anode electrode connector 6 may be in series and/or in parallel. For example, the anode electrode connector of a cell is connected to the cathode electrode connector of an adjacent cell, and the unconnected cathode electrode connector and the unconnected anode electrode connector serve as the connector for the total cathode electrode of the module and the total anode electrode of the module.

[0097] In this case, the cathode electrode connector 4 and the anode electrode connector 6 may be connected by bolts, and a connection hole can be provided in each of the cathode electrode connector 4 and the anode electrode connector 6 to allow a bolt or nut to pass through. Alternatively, the cathode electrode connector and the anode electrode connector can be connected by welding.

[0098] The jelly rolls may be replaced with stacks according to actual needs. A stack was prepared from a plurality small cells by a lamination process.

[0099] The four jelly rolls are placed respectively in four unit shells 8 that physically separate individual jelly rolls. The four jelly rolls are disposed in separate divisions to allow sealing, insulation, and blocking of ion transport channels for cells in series and/or in parallel. A unit shell 8 may be a single plastic shell, such as but not limited to a PET or PP hot melt sealing film, a PVC heat shrinkage film, or a PC, PP, or ABS-based injection-molded structure.

[0100] The separated component is preferably a partitioning plate, which may be a socket board directly inserted inside the injection-molded housing 9, dividing the inner cavity of the injection-molded housing 9 into a plurality of unit compartments. Alternatively, the partitioning plate is a partitioned structure formed by integrated molding with the housing, as shown in FIG. 4. When the separated component is a partitioning plate, no additional shell is needed to package the cells, and the packaging process from small cells to a module can be completed with only one housing, which greatly simplifies the process and saves the cost.

[0101] An injection-molded cover plate 10 is included to form a seal with the upper-side open structure of the unit shells 8. Connection holes 2 are provided in the injection-molded cover plate 10, and are used to connect external signal wires and also to achieve a seal connection between the injection-molded cover plate 10 and the cathode electrode Connector 4 and the anode electrode Connector 6.

[0102] The injection-molded cover plate 10 is in a seal connection with the cathode electrode connector 4 and the anode electrode connector 6 at one end of a jelly roll. The connection may be achieved by bolting. For example, a bolt or nut can pass through the connection hole 2 and be connected to the cathode electrode connector 4 and the anode electrode connector 6, and is sealed by injection molding at the same time.

[0103] In addition, the injection-molded cover plate 10 and the injection-molded housing 9 match each other to form a sealed structure. ultrasonic melt welding or laser welding can be used to ensure the sealing of the entire housing as well as the sealing of individual chambers (unit shells 8). The injection-molded cover plate 10 was integratedly molded with the cathode electrode connector 4 and the anode electrode connector 6, thereby avoiding the need for post-assembly (for integrated injection molding of nuts for bolt connection, the bolting process requires additional intermediate fixing parts, such as cathode and anode electrode connector, signal wires, and the like, and therefore requires subsequent processing and assembly to complete the module).

[0104] Also, injection holes 3 are provided in the injection-molded cover plate 10 for injecting liquid into the unit shell and degassing. An electrolyte solution may be injected according to actual needs. The number of injection holes 3 are the same as the number of unit shells, allowing separate contcalendering of the injection holes 3 and the corresponding unit shells 8. In addition, each injection hole 3 is equipped with a e injection hole sealing piece to achieve sealing of the module. After formation, the injection holes are sealed by the injection hole sealing piece, and the injection hole sealing piece is covered by the injection-molded cover plate 10. When the gas pressure inside the battery during use is too high, the injection hole sealing piece is flicked open to allow degassing through fine holes around the injection-molded cover plate, and after the degassing the injection hole sealing piece returns to its original state.

[0105] As shown in FIG. 2, on the injection-molded cover plate 10, a connection part for the total cathode terminal of the module 11 and a connection part for the total anode terminal of the module 12 are provided as the cathode and anode conductive structures of the entire module, and are connected to the cathode electrode connection piece and the anode electrode connection piece by welding, respectively.

[0106] An injection-molded housing 9 and an injection-molded top cover 1 are included, wherein the injection-molded housing 9 is used to accommodate the plurality of unit shells 8, and the injection-molded top cover 1 overlies the injection-molded cover plate 10 and is provided with an outlet for the total cathode terminal of the module 11 and an outlet for the total anode terminal of the module 12. The injection-molded top cover 1 may also be used to package the injection-molded housing 9, in which case the injection-molded top cover 1 and injection-molded housing 9 may be fixed and packaged by injection of glue to ensure the sealing of the module.

[0107] The injection-molded cover plate 10, the injection-molded top cover 1, and the injection-molded housing 9 are packaged by using a sealant, which may be accompanied by sealing with ultrasonic melt welding or laser welding at the same time. Connection holes 2 and other connectors and terminals are sealed with a sealant.

[0108] The battery shown in FIG. 3 can be directly used as a lithium-ion battery, or two or more lithium-ion battery modules shown in FIG. 3 may be assembled together to be used as a lithium-ion battery. Alternatively, one or more lithium-ion battery modules shown in FIG. 3 can be assembled with other lithium-ion battery modules to be used as a lithium-ion battery.

[0109] This example also provides use of a ½ size lead-acid battery case with four chambers (unit shells 8) provided in the case, and the designed capacity of the stack was 20 Ah. Parts of this example that are not described in detail here were those commonly used in the art. The specific method for preparation is as follows.

[0110] Preparing slurries. The cathode electrode of the example used 90% to 99% of lithium iron phosphate, and 1% to 10% of graphene and carbon tubes as a conductive agent, without binder; the anode electrode material used 92% to 99% of graphite and 1% to 8% of carbon black, without binder. The cathode and anode electrode slurries were prepared with an electrolyte solution in which 0.8 mol/L LiPF.sub.6 as the lithium salt was dissolved in EC:EMC:DMC=25:50:25. The solid content of the cathode electrode was 75% and the solid content of the anode electrode was 68%. As compared with a conventional process, the process for preparing slurries of this example did not use water or NMP as the solvent, thus saved the material cost, provided a high solid content and high viscosity of the slurries, and allowed preparation of electrode sheets with an area density of 100 to 1500 g/m.sup.2, while conventional slurries having a low solid content cannot provide a coated electrode sheet having such a high area density. And there was no need for drying and injection after coating, so that the entire manufacturing period was shortened and the manufacturing cost was reduced.

[0111] Coating after preparation of slurries. Coating was performed with a double-layer pressing coater. The current collector used was a mesh-like plate lattice. The thickness of the cathode electrode current collector was 8 μm, and the thickness of the anode electrode current collector was 8 μm. The shape of the mesh openings in the plate lattice may be triangular, square, rectangle, polygonal, or the like. The coated electrode sheets did not need drying or calendering.

[0112] Slitting and cutting. The coated and rolled electrode sheet was slit into small rolls, which were further cut by laser cutting or die cutting to finish with cut out tabs.

[0113] lamination. The number of layers of cathode and anode electrodes of a unit cell was selected according to the area density of the coated cathode and anode electrodes, and the number of layers stacked in this example was adapted to the thickness of the stack and the size of the cell case. The separator used in this example was a conventional separator for lithium-ion batteries, and had a thickness of 8 μm. The outer surface of the stack unit was wrapped with a heat shrinkage film. The cathode and anode electrodes of adjacent stacks were placed in opposite directions so that the cathode and anode electrodes of the four stacks were adjacent to each other.

[0114] Placing in shell and welding. The battery case had two terminals for the cathode and anode electrodes. At the cathode terminal of the battery case, the anode electrode of the outer stack and the cathode electrode of the inner adjacent stack were connected in series by welding, and at the anode terminal of the battery case, the cathode electrode of the outer stack and the anode electrode of the inner adjacent stack were connected in series by welding. The two unconnected cathode and anode electrodes of the stacks in the middle were connected in series by welding, and the cathode and anode electrodes of the outer stacks of the battery case were welded to cathode and anode electrode connectors, respectively. Preferably, the welding was cast welding after the cells were inverted, and the cast welding solder was molten metal, preferably molten tin metal. Signal wires were welded to the cathode terminal, the anode terminal, and the series connecting points of the battery case, and the connected signal wires allowed real-time monitoring of the voltage and temperature of the stacks. In this Example, the cover plate of the battery case and the body of the battery case were packaged with a sealant. Preferably, holes were reserved in the cover plate for the cathode and anode connectors to connect external circuits, and the holes can be sealed with a sealant.

[0115] Injection and formation. Liquid was injected via the four injection holes in the battery cover plate, and formation in series can be performed directly after assembly was completed, wherein the formation was performed by charging the stacks at a current of 0.01 to 0.5 C for 40 min to 5000 min to activate the stacks. After formation, the injection holes were closed by a rubber cap, and the rubber cap was covered by the cover plate. When the gas pressure inside the battery during use is too high, the cap is flicked open to allow degassing through fine holes around the cover plate, and after the degassing the cap returns to its original state.

[0116] Capacity grading. The welded and sealed battery was charged and discharged at a rate of 0.1 to 1 C to determine the battery capacity, and then the battery was adjusted to a SOC of 20% to 60%.

[0117] The lithium-ion secondary battery obtained in this example had a capacity at 0.33 C of 21.1 Ah, and the charge/discharge curve thereof is shown in FIG. 5. The voltage range of a normal single cell was 2.0 to 3.65. This example produced a module with cells connected in series, and the voltage range can be 8.0 to 14.4.

[0118] FIG. 6 shows the cycle performance of the battery of Example 1, and the number of cycles of the battery can reach 4000 at 25° C.

Example 2

[0119] This example used a lead-acid battery case, with four unit compartments provided inside the case, and the designed capacity of the cell was 40 Ah. Parts of this example that are not described in detail here were those commonly used in the art.

[0120] Preparing slurries. The cathode electrode components were 98 wt % of lithium iron phosphate, 1 wt % of graphene, and 1 wt % of PVDF, with NMP as a wetting agent, which were mixed by dry mixing or wet mixing. The solid content of the cathode electrode slurry was 65%. The anode electrode components were 96 wt % of graphite, 1 wt % of carbon black, and 3 wt % of CMC+SBR, using deionized water for the slurry, which were mixed by dry mixing or wet mixing. The solid content of the anode electrode slurry was 60%.

[0121] Coating. The above mixed cathode and anode electrode slurries were applied to the cathode and anode current collectors by press or contact coating. The cathode electrode current collector was made of an aluminum foil with a thickness of 3 to 25 microns, and the anode electrode current collector was made of a copper foil with a thickness of 3 to 25 microns. The coated area density was controlled at 100 to 600 g/m.sup.2 for the cathode electrode and 50 to 300 g/m.sup.2 for the anode electrode; the coating speed was controlled at 20 to 150 m/s, and the drying temperature was 70 to 140° C. The residual amount of NMP and water after drying was measured and controlled within 600 ppm.

[0122] Calendering. The coated cathode electrode sheet and anode electrode sheet were rolled, and the compacted density of the cathode electrode was controlled at 1.5 to 23.1 g/m.sup.2 and the compacted density of the anode electrode was controlled at 1.0 to 1.8 g/m.sup.2.

[0123] Slitting and cutting. The coated and rolled electrode sheet was slit into small rolls, which were further cut by laser cutting or die cutting to finish with cut out tabs.

[0124] Winding. The electrode sheets after cutting were made into stacks by winding. The thickness of the stacks was controlled at 93% to 98% of the thickness of the inner cavity.

[0125] Formation and placing in shell. The stacks were welded to electrode tabs coated with a heat seal adhesive, and then wrapped with a layer of a packaging film made of PET which was heat sealed on three sides. An electrolyte solution was injected through the opening on the other side and then the opening was sealed. After 12 to 80 h of impregnation, the cells were subjected to formation by charging the stacks at a current of 0.01 to 0.5 C for 40 min to 5000 min to activate the stacks. The stacks after formation were degassed, heat sealed again, and cut. The stacks were placed in the battery case by hand or a semi-automatic tool to complete the assembly.

[0126] Welding and sealing. The tabs of the stacks placed in the shell were connected to the connectors on the cover plate by laser welding, and then a structural adhesive was applied to the position where the battery cover plate contacted the battery case, and was cured by heating to achieve the sealing of the entire cover plate and the battery case. At the same time, laser welding completed the serial connection inside the entire battery. The voltage and temperature sensing wiring harnesses were fixed to the battery terminals by welding for signal collection.

[0127] Capacity grading. The welded and sealed battery was charged and discharged at a rate of 0.1 to 1 C to determine the battery capacity, and then adjusted to a SOC of 20% to 60%.

[0128] The lithium-ion secondary battery obtained in this example had a capacity at 0.33 C of 41 Ah, and the cycle performance was comparable to that of Example 1.

[0129] By simplifying the parts and components through integrated manufacturing, the method according to the present disclosure provides a lithium iron phosphate battery module having an energy density of more than 190 Wh/kg, much higher than the 160 Wh/kg of a conventional lithium iron phosphate module and the 50 Wh/kg of a lead-acid battery, improves volume utilization by at least 10% as compared to that of a lithium battery module, reduces impedance by about 10% as compared to that of a conventional module due to fewer connected parts, and reduces cost by about 20% to a level similar to that of a lead-acid battery. At the same time, the integrated manufacturing ensures consistency of the module stacks, and enables as high as 4000 cycles at room temperature, much higher than that of lead-acid to batteries, providing double advantages in terms of both performance and cost.