Lithium ion secondary battery

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a lithium ion secondary battery which comprises: a plurality of pole piece groups stacked in sequence, and along the stacking direction, the kinetic performance of the first pole piece group and the last pole piece group is the same, the kinetic performance of the pole piece groups located at the intermediate positions between the two is the same and is better than that of the first pole piece group and the last pole piece group; the pole piece groups with the same kinetic performance are collectively provided with a positive electrode tab; and all the pole piece groups are collectively provided with a negative electrode tab. It can be seen that when the battery cell is used, the middle part of the battery cell can be conveniently activated first, and after the activation is completed, the whole battery cell is used for charging and discharging work. Since the middle part is designed to have better heat dissipation performance, the novel battery cell structure provided by the application can well keep the SOC and the heat dissipation performance of the battery cell consistent, improve the safety and stability of the battery, and maximize the electrochemical capacity of the battery cell.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a lithium ion secondary battery. BACKGROUND

[0002] Lithium ion batteries are widely used in energy storage fields because of high energy density and long cycle performance. However, heat is inevitably generated during the use of lithium ion batteries. In the same battery cell, the heat generated at different positions during use is different, and the commonly used lithium ion soft package battery cell is assembled by using the same electrode material Z-shaped laminated structure, which leads to poor heat dissipation of the middle part of the lithium ion battery. Poor contact, thus forming lithium dendrites, will cause the battery to swell, bulge, accelerate the degradation of the battery, and the performance of the battery will decrease rapidly, and even explode to cause safety hazards.

[0003] In addition, due to the inconsistent internal and external heat dissipation of the lithium ion battery, there is a difference in the polarization of the internal and external battery, which brings harm to the battery, that is, the SOC of the entire battery is different, thereby significantly reducing the service life and discharge capacity of the battery. SUMMARY

[0004] The purpose of the present application is to provide a lithium ion secondary battery, which solves the technical problem that the heat dissipation of each part of the lithium ion battery is different in the prior art, causing the battery to swell, bulge, accelerate the degradation of the battery, and also leading to the SOC of the entire battery being different, thereby greatly reducing the service life and discharge capacity of the battery.

[0005] The present application provides a lithium ion secondary battery, comprising: a plurality of sheet groups stacked in sequence, and along the stacking direction, the kinetic performance of the first sheet group and the last sheet group is the same, the kinetic performance of the sheet group located at the middle position between the two is the same, and is better than the kinetic performance of the first sheet group and the last sheet group.

[0006] The sheet groups with the same kinetic performance are commonly provided with a positive tab; all the sheet groups are commonly provided with a negative tab.

[0007] In the above technical solution, further, the two positive tabs are located on the same side of the plurality of sheet groups, the negative tab is located on the opposite side of the plurality of sheet groups, and the positive tab and the negative tab of the sheet group located between the first sheet group and the last sheet group are subjected to 0.5C-1C charging and discharging twice, and then the two positive tabs and the negative tab are connected to complete the charging and discharging of the complete battery structure.

[0008] In any of the above technical solutions, further, the first pole piece group and the last pole piece group account for 1 / 3 to 1 / 4 of the total pole piece groups.

[0009] In any of the above technical solutions, further, the first pole piece group and the last pole piece group each include a plurality of first positive pole pieces and a plurality of first negative pole pieces, and the plurality of first positive pole pieces and the plurality of first negative pole pieces are alternately stacked together, and a first separator is arranged between any adjacent first positive pole piece and first negative pole piece;

[0010] Any first positive pole piece and any first negative pole piece are each provided with a first current collector;

[0011] All the first positive pole pieces are collectively provided with one positive pole tab.

[0012] In any of the above technical solutions, further, the active material of the first positive pole piece includes one or more of lithium iron phosphate, lithium nickel cobalt oxide, lithium nickel oxide, and lithium manganate, the binder of the first positive pole piece is a high molecular material, and the conductive agent of the first positive pole piece includes one or more of conductive carbon black, acetylene black, ketjen black, carbon nanotube, graphene oxide, and graphene;

[0013] The material of the first positive pole piece includes the following components in mass percentage: active material 70% to 99%, binder 0.5% to 12%, and conductive agent 0.5% to 18%;

[0014] The active material of the first negative pole piece is a porous carbon material, the binder of the first negative pole piece is a high molecular material, and the conductive agent of the first negative pole piece includes one or more of conductive carbon black, carbon nanotube, graphene oxide, or graphene;

[0015] The material of the first negative pole piece includes the following components in mass percentage: active material 90% to 97%, binder 2% to 5%, and conductive agent 1% to 5%.

[0016] In any of the above technical solutions, further, any of the pole piece groups between the first pole piece group and the last pole piece group each include a plurality of second positive pole pieces and a plurality of second negative pole pieces, and the plurality of second positive pole pieces and the plurality of second negative pole pieces are alternately stacked together, a second current collector is arranged between any adjacent second positive pole piece and second negative pole piece, and a graphene heat conduction layer is arranged between the second current collector and the second positive pole piece and the second negative pole piece;

[0017] At least the first end and the tail end are provided with a second separator along the stacking direction;

[0018] All the second positive pole pieces are collectively provided with one positive pole tab.

[0019] In any of the above technical solutions, further, the graphene heat-conducting layer is formed by graphene powder and a binder, and is coated on opposite sides of the second current collector.

[0020] In any of the above technical solutions, further, the active material of the second positive electrode sheet comprises one or more of lithium iron phosphate, lithium nickel cobalt oxide, lithium nickelate and lithium manganate, and has different particle sizes; the binder of the second positive electrode sheet is a high molecular material, and the conductive agent of the second positive electrode sheet comprises one or more of conductive carbon black, acetylene black, ketjen black, carbon nanotube, graphene oxide and graphene.

[0021] The material of the second positive electrode sheet comprises the following components in mass percentage: active material 70-99%, binder 0.5-12% and conductive agent 0.5-18%;

[0022] The active material of the second negative electrode sheet is a porous carbon material, the binder of the second negative electrode sheet is a high molecular material, and the conductive agent of the second negative electrode sheet comprises one or more of conductive carbon black, carbon nanotube, graphene oxide or graphene.

[0023] The material of the second negative electrode sheet comprises the following components in mass percentage: active material 90-97%, binder 2-5% and conductive agent 1-5%.

[0024] The application also provides a lithium ion secondary battery, comprising: a plurality of electrode sheet groups stacked in sequence, and the kinetic performance of the corresponding electrode sheet groups gradually increases from the two side portions to the central position; the electrode sheet groups with the same kinetic performance are collectively provided with a positive electrode tab; and all the electrode sheet groups are collectively provided with a negative electrode tab.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] In the lithium ion secondary battery provided by the application, electrode sheets with different kinetic performances are innovatively used to assemble the lithium ion battery, and the lithium ion battery is divided into an outer portion and a middle portion. Since the middle portion has the characteristics of slow heat dissipation and slow activation during use of the lithium ion battery, the application innovatively uses double positive electrode tabs to separate the outer portion and the middle portion of the lithium ion battery and respectively lead out, that is, one tab connects the outer portion of the lithium ion battery, and the other tab connects the middle portion of the lithium ion battery.

[0027] The middle part of the lithium ion battery can be activated conveniently when the lithium ion battery is used, and the whole lithium ion battery is used for charging and discharging after the activation is completed. Since the middle part is designed to have better heat dissipation performance, the new lithium ion battery structure provided by the application can well keep the SOC and heat dissipation performance of the lithium ion battery consistent, improve the safety and stability of the battery, and maximize the electrochemical capacity of the lithium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the specific embodiments or prior art of the present application, the drawings needed in the description of the specific embodiments or prior art will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0029] Figure 1 Structure diagram of a lithium ion secondary battery provided by an embodiment of the present application;

[0030] Figure 2 Another structure diagram of a lithium ion secondary battery provided by an embodiment of the present application;

[0031] Figure 3 Another structure diagram of a lithium ion secondary battery provided by an embodiment of the present application.

[0032] Reference signs:

[0033] 1-first diaphragm, 2-first current collector, 3-first positive plate, 4-first negative plate, 5-second positive plate, 6-graphene heat conduction layer, 7-second current collector, 8-second negative plate, 9-second diaphragm, 10-positive tab, 11-negative tab;

[0034] 100-A module, 200-B module, 300-C module. DETAILED DESCRIPTION

[0035] The technical solutions of the present application will be described in detail below in conjunction with the drawings. Obviously, the described embodiments are part of the embodiments of the present application, not all embodiments.

[0036] The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application.

[0037] All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the scope of the present application.

[0038] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0039] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0040] The following refers to Figures 1 to 3 A lithium ion secondary battery according to some embodiments of the present application is described.

[0041] Referring to Figures 1 to 3 As shown in the drawings, the embodiments of the present application provide a lithium ion secondary battery, comprising: a plurality of pole piece groups stacked in sequence, and along the stacking direction, the kinetic performance of the first pole piece group and the last pole piece group is the same, the kinetic performance of the pole piece group located at the middle position between them is the same, and is better than the kinetic performance of the first pole piece group and the last pole piece group (here, in order to facilitate the quick differentiation of the above modules, they are respectively named as follows: the first pole piece group is A module 100, the last pole piece group is C module 300, and the pole piece group between them is B module 200).

[0042] The pole piece groups with the same kinetic performance are collectively provided with a positive electrode lug 10; all the pole piece groups are collectively provided with a negative electrode lug 11.

[0043] Based on the structure described above, when using the lithium ion battery, the B module 200 can be activated first, and then the two positive tabs are used simultaneously to fully operate the battery. That is, after the B module 200 of the lithium ion battery assembly is fully activated, the A module 100 and the C module 300 of the lithium ion battery assembly are activated. Since the kinetic performance and heat dissipation performance of the B module 200 are better than those of the A module 100 and the C module 300, the SOC and the heat dissipation performance of the battery are well guaranteed during the entire battery operation, and the performance of the entire lithium ion battery is maximized.

[0044] It can be seen that, taking the lithium ion battery as a unit, the positive pole pieces with different kinetic performances are innovatively used to assemble the lithium ion battery, and the lithium ion battery is divided into an outer portion and a middle portion. Since the middle portion has the characteristics of slow heat dissipation and slow activation during use of the lithium ion battery, the lithium ion battery is innovatively separated by the double positive tabs, and the outer portion and the middle portion are respectively led out, that is, one tab connects the outer portion of the lithium ion battery, and the other tab connects the middle portion of the lithium ion battery.

[0045] When using the lithium ion battery, the middle portion of the lithium ion battery can be conveniently activated first, and then the entire lithium ion battery is used for charging and discharging. Since the middle portion has better heat dissipation performance, the new lithium ion battery structure provided by the application can well keep the SOC and the heat dissipation performance of the lithium ion battery consistent, improve the safety and stability of the battery, maximize the electrochemical capacity of the lithium ion battery, and the effect is more obvious especially in a low-temperature environment.

[0046] Of course, it is not limited to this, and the following structure can also be used:

[0047] The lithium ion secondary battery comprises: a plurality of pole piece groups stacked in sequence, and the kinetic performance of the corresponding pole piece groups gradually increases from the two side portions to the center position; the pole piece groups with the same kinetic performance are commonly provided with one positive tab 10; and all the pole piece groups are commonly provided with one negative tab 11.

[0048] According to the above description, in order to facilitate understanding, five modules are taken as examples, and they are A module 100, B module 200, C module 300, D module, and E module in turn. The A module 100 and the E module commonly use one first positive tab 10, the B module 200 and the D module commonly use one second positive tab 10, and the C module 300 itself uses one third positive tab 10. Among them, the kinetic performance of the C module 300 is the best, the kinetic performance of the B module 200 and the D module is the second, and the kinetic performance of the A module 100 and the E module is the worst.

[0049] For the convenience of understanding, four modules are taken as examples, and they are A module 100, B module 200, C module 300 and D module in turn, A module 100 and D module commonly adopt a first positive tab 10, B module 200 and C module 300 commonly adopt a second positive tab 10, and among them, the kinetic performance of B module 200 and C module 300 is the best, and the kinetic performance of A module 100 and D module is worse than that of B module 200 and C module 300.

[0050] Note: The kinetic performance mentioned above specifically refers to EIS and rate discharge performance (EIS-Rs, EIS-Rct, rate performance-0.8C vs 0.5C, rate performance-1C vs 0.5C and rate performance-2C vs 0.5C).

[0051] Further, preferably, the size of the two positive tabs 10 is 15mm*30mm respectively, and the size of the negative tab 11 is 20mm*60mm.

[0052] In this embodiment, preferably, as shown in Figure 1 The first and last pole piece groups account for 1 / 3-1 / 4 of the total pole piece groups, ensuring that the proportion of the middle module and the two side modules is coordinated, and improving the consistency of the whole battery operation.

[0053] In this embodiment, preferably, as shown in Figure 2 and Figure 3 The positive tab 10 is located on the same side of the plurality of pole piece groups, and the negative tab 11 is located on the opposite side of the plurality of pole piece groups, which is convenient for butt joint wiring and avoids wire harness confusion.

[0054] In this embodiment, preferably, as shown in Figure 1 The first and last pole piece groups each include a plurality of first positive pole pieces 3 and a plurality of first negative pole pieces 4, and the plurality of first positive pole pieces 3 and the plurality of first negative pole pieces 4 are alternately stacked together, and a first separator 1 is arranged between any adjacent first positive pole piece 3 and first negative pole piece 4;

[0055] Any first positive pole piece 3 and any first negative pole piece 4 are each provided with a first current collector 2;

[0056] All the second positive pole pieces 5 are commonly provided with a positive tab 10.

[0057] Further, preferably, the active material of the first positive pole piece 3 includes one or more of lithium iron phosphate, lithium nickel cobaltate, lithium nickelate and lithium manganate, the binder of the first positive pole piece 3 is a high molecular material, and the conductive agent of the first positive pole piece 3 includes one or more of conductive carbon black, acetylene black, ketjen black, carbon nanotube, graphene oxide and graphene;

[0058] The material of the first positive electrode sheet 3 comprises the following components in mass percentage: active material 70-99%, binder 0.5-12%, and conductive agent 0.5-18%;

[0059] The active material of the first negative electrode sheet 4 is a porous carbon material, the binder of the first negative electrode sheet 4 is a high molecular material, and the conductive agent of the first negative electrode sheet 4 comprises one or more of conductive carbon black, carbon nanotube, graphene oxide, or graphene;

[0060] The material of the first negative electrode sheet 4 comprises the following components in mass percentage: active material 90-97%, binder 2-5%, and conductive agent 1-5%.

[0061] In this embodiment, preferably, as shown in Figure 1 Any electrode sheet group between the first electrode sheet group and the last electrode sheet group comprises a plurality of second positive electrode sheets 5 and a plurality of second negative electrode sheets 8, and the plurality of second positive electrode sheets 5 and the plurality of second negative electrode sheets 8 are alternately stacked together, any adjacent second positive electrode sheet 5 and second negative electrode sheet 8 are provided with a second current collector 7, and the second current collector 7 is provided with a graphene heat conduction layer 6 between the second positive electrode sheet 5 and the second negative electrode sheet 8;

[0062] At least the head end and the tail end are provided with a second separator 9 along the stacking direction;

[0063] All the second positive electrode sheets 5 are also collectively provided with a positive electrode tab 10.

[0064] According to the above description, the graphene heat conduction layer 6 is coated on the second current collector 7 before the sheet is stacked, which mainly plays an auxiliary heat dissipation role.

[0065] Further, preferably, as shown in Figure 1 The graphene heat conduction layer 6 is formed by graphene powder and a binder, and is coated on the opposite two sides of the second current collector 7.

[0066] Further, preferably, as shown in Figure 1 The active material of the second positive electrode sheet 5 comprises one or more of lithium iron phosphate, lithium nickel cobalt oxide, lithium nickel oxide, and lithium manganate, and the particle sizes of the components are different; the binder of the second positive electrode sheet 5 is a high molecular material, and the conductive agent of the second positive electrode sheet 5 comprises one or more of conductive carbon black, acetylene black, ketjen black, carbon nanotube, graphene oxide, and graphene;

[0067] The material of the second positive electrode sheet 5 comprises the following components in mass percentage: active material 70-99%, binder 0.5-12%, and conductive agent 0.5-18%;

[0068] The active material of the second negative tab 8 is a porous carbon material, the binder of the second negative tab 8 is a high molecular material, and the conductive agent of the second negative tab 8 includes one or several of conductive carbon black, carbon nanotube, graphene oxide or graphene.

[0069] The material of the second negative tab 8 includes the following components in mass percentage: active material 90%-97%, binder 2%-5% and conductive agent 1%-5%.

[0070] The detailed parameter examples are given as follows in combination with the content of Example One:

[0071] Example One

[0072] The second positive tab 5 is formed of mixed materials of large lithium iron phosphate particles (D50 is 300-800 nm) and small lithium iron phosphate particles (D50 is 80-150 nm).

[0073] The manufacturing method of the second positive tab 5 is: the large lithium iron phosphate particles and the small lithium iron phosphate particles are added into a stirring barrel at a ratio of 1:1 for homogenization, and a conductive agent and a binder are added, wherein the active material: conductive agent: binder = 95%:2%:3% in mass percentage; the conductive agent is conductive carbon black, and the binder is PVDF.

[0074] Then, after coating (the surface density is 31 mg / cm 2 ), rolling and punching, the second positive tab 5 used in the middle part of the battery is prepared.

[0075] The material of the second negative tab 8 includes the following components in mass percentage: graphite (95%), conductive agent (2%) and binder (3%), wherein the conductive agent is conductive carbon black, and the binder is PVDF; the above-mentioned materials are homogenized, and then, after coating (the surface density is 31 mg / cm 2 ), rolling and punching, the second negative tab 8 used in the middle part of the battery is prepared.

[0076] It is noted that: the graphene heat conduction layer is formed by uniformly coating the slurry of the combination of graphene powder (2-5 um) + binder + NMP (wherein the graphene powder: binder = 80%:20% in mass percentage, and NMP is N-methyl pyrrolidone, which is a solvent, and is finally volatilized) on both sides of the second current collector 7, and the coating thickness is 5-8 um, and the graphene heat conduction layer is dried for use.

[0077] In addition to the positive tab used in the middle part of the battery, the positive tab used in the two side parts, i.e. the first positive tab 3, meets the following:

[0078] The first positive electrode sheet 3 used in the two side parts of the battery is prepared by homogenizing the active material, conductive agent and binder, coating, rolling and punching, wherein the active material is lithium iron phosphate particles, the conductive agent is conductive carbon black and the binder is PVDF, and the mass percentage of the active material, conductive agent and binder is 95%, 2% and 3% respectively.

[0079] The first negative electrode sheet 4 used in the two side parts of the battery is prepared by homogenizing the active material, conductive agent and binder, coating, rolling and punching, wherein the active material is graphite, the conductive agent is conductive carbon black and the binder is PVDF, and the mass percentage of the active material, conductive agent and binder is 95%, 2% and 3% respectively.

[0080] After the preparation of the electrode sheets, during the packaging and welding, the lithium ion battery two side areas (one side is 1 / 3 of the total number of positive electrode sheets) are led out together by using the same positive electrode tab (named as A tab) on one side of the lithium ion battery, and the middle positive electrode sheet (1 / 3 of the total number of positive electrode sheets) is led out by using another positive electrode tab (named as B tab), and both of the two positive electrode tabs are located on the same side. All the negative electrode sheets are led out by using the same negative electrode tab on the other side of the lithium ion battery. After the packaging, the soft package battery A is formed after baking, liquid injection and activation.

[0081] Example 2

[0082] The second positive electrode sheet 5 is formed by the mixed material of the lithium iron phosphate particles with large particle size (D50 is 300-800 nm) and the lithium iron phosphate particles with small particle size (D50 is 2000-3000 nm).

[0083] The preparation method of the second positive electrode sheet 5 is as follows: the lithium iron phosphate particles with large particle size and the lithium iron phosphate particles with small particle size are added into a stirring barrel in a ratio of 1:1 for homogenization, and the conductive agent and the binder are added, wherein the mass percentage of the active material, conductive agent and binder is 95%, 2% and 3% respectively, the conductive agent is conductive carbon black and the binder is PVDF.

[0084] Then, the second positive electrode sheet 5 used in the middle part of the battery is prepared after coating (the surface density is 31 mg / cm 2 ), rolling and punching.

[0085] The material of the second negative electrode sheet 8 includes the following components with the mass percentage of 95% of graphite, 2% of conductive agent and 3% of binder, the conductive agent is conductive carbon black and the binder is PVDF, and the material is homogenized, and then the second negative electrode sheet 8 used in the middle part of the battery is prepared after coating (the surface density is 31 mg / cm 2 ), rolling and punching.

[0086] And note: wherein the graphene heat-conducting layer for installation between the second current collector and the second positive electrode sheet and the second negative electrode sheet adopts a combination of graphene powder (2-5 um) + binder + NMP (wherein, according to the mass percentage, graphene powder: binder = 80%:20%, NMP is N-methyl pyrrolidone, which is a solvent, and is finally volatilized) to form a slurry, which is uniformly coated on both sides of the second current collector 7, with a coating thickness of 5-8 um, and is dried for use.

[0087] In addition to the positive electrode sheet used in the middle part of the battery, the positive electrode sheet used in the two side parts, i.e. the first positive electrode sheet 3, satisfies the following:

[0088] According to the mass percentage, active material: conductive agent: binder = 95%:2%:3%, wherein the active material is lithium iron phosphate particles, the conductive agent uses conductive carbon black, and the binder uses PVDF, the above-mentioned materials are uniformly slurried, and then the first positive electrode sheet 3 used in the two side parts of the battery is prepared after coating, rolling and punching.

[0089] The first negative electrode sheet 4 includes the following mass percentage of components: active material, i.e. graphite (95%), conductive agent (2%) and binder (3%), wherein the conductive agent uses conductive carbon black, and the binder uses PVDF, the above-mentioned materials are uniformly slurried, and then the first negative electrode sheet 4 used in the two side parts of the battery is prepared after coating, rolling and punching.

[0090] After the preparation of the electrode sheets, during the packaging and welding, the lithium ion battery two side areas (one side is 1 / 3 of the total number of positive electrode sheets) are led out together with the same positive electrode tab (named A tab) on one side of the lithium ion battery, and the middle positive electrode sheet (1 / 3 of the total number of positive electrode sheets) is led out with another positive electrode tab (named B tab), both of which are located on the same side. All the negative electrode sheets are led out with the same negative electrode tab on the other side of the lithium ion battery. After the packaging is completed, the soft package battery A is formed after baking, liquid injection and activation.

[0091] Example Three

[0092] The second positive electrode sheet 5 is formed by a mixed material of lithium iron phosphate particles with a larger particle size (D50 of 300-800 nm) and lithium iron phosphate particles with a smaller particle size (D50 of 80-150 nm).

[0093] The manufacturing method of the second positive electrode sheet 5 is: the larger lithium iron phosphate particles and the smaller lithium iron phosphate particles are added to the stirring barrel at a ratio of 1:1 for uniform slurry, and conductive agent and binder are added, wherein, according to the mass percentage, active material: conductive agent: binder = 92%:5%:3%; the conductive agent uses conductive carbon black, and the binder uses PVDF.

[0094] And then coating (areal density 31 mg / cm2 After rolling and punching, the second positive electrode sheet 5 for the middle part of the battery is prepared.

[0095] The material of the second negative electrode sheet 8 includes the following components in mass percentage: graphite (95%), conductive agent (2%), and binder (3%), wherein the conductive agent is conductive carbon black, and the binder is PVDF. The above materials are uniformly grinded, and then coated (the surface density is 31 mg / cm 2 After rolling and punching, the first negative electrode sheet 4 for the middle part of the battery is prepared.

[0096] Note that the graphene heat-conducting layer for mounting between the second current collector and the second positive electrode sheet and the second negative electrode sheet is formed by uniformly coating a slurry of graphene powder (2-5 um) + binder + NMP (wherein the mass percentage of graphene powder: binder = 80:20, and NMP is N-methyl pyrrolidone, which is a solvent, and is finally volatilized) on both sides of the second current collector 7, with a coating thickness of 5-8 um, and is dried for use.

[0097] In addition to the positive electrode sheet for the middle part of the battery, the positive electrode sheet for the two side parts, i.e., the first positive electrode sheet 3, satisfies the following:

[0098] The active material: conductive agent: binder = 95:2:3 in mass percentage, wherein the active material is lithium iron phosphate particles, the conductive agent is conductive carbon black, and the binder is PVDF. The above materials are uniformly grinded, and then coated, rolled, and punched to prepare the first positive electrode sheet 3 for the two side parts of the battery.

[0099] The first negative electrode sheet 4 includes the following components in mass percentage: active material, i.e., graphite (95%), conductive agent (2%), and binder (3%), wherein the conductive agent is conductive carbon black, and the binder is PVDF. The above materials are uniformly grinded, and then coated, rolled, and punched to prepare the first negative electrode sheet 4 for the two side parts of the battery.

[0100] After the preparation of the electrode sheets, during the packaging and welding, the lithium ion battery two side areas (one side is 1 / 3 of the total number of positive electrode sheets) are led out together by the same positive electrode tab (named A tab) on one side of the lithium ion battery, and the middle positive electrode sheet (1 / 3 of the total number of positive electrode sheets) is led out by another positive electrode tab (named B tab). Both positive electrode tabs are located on the same side. All negative electrode sheets are led out by the same negative electrode tab on the other side of the lithium ion battery. After the packaging is completed, the soft package battery A is formed after baking, liquid injection, and activation.

[0101] Comparative Example

[0102] The positive electrode sheet satisfies the following:

[0103] The active material: conductive agent: binder = 95%: 2%: 3% by mass, wherein the active material is lithium iron phosphate particles, the conductive agent is conductive carbon black, and the binder is PVDF. The above materials are homogenized, coated, rolled, and punched to form the first positive electrode sheet 3 used in the two side parts of the battery.

[0104] The negative electrode sheet includes the following components by mass: active material (graphite) (95%), conductive agent (2%), and binder (3%), wherein the conductive agent is conductive carbon black, and the binder is PVDF. The above materials are homogenized, coated, rolled, and punched to form the first negative electrode sheet 4 used in the two side parts of the battery.

[0105] The above positive electrode sheet and negative electrode sheet are stacked, packaged, baked, liquid injected, and activated to form the soft-pack conventional battery B1.

[0106] The batteries in the foregoing examples and comparative examples are tested for performance:

[0107] (1) Alternating current impedance (EIS) test and rate discharge performance test

[0108] Table 1 is the EIS test and rate discharge performance test results

[0109]

[0110] EIS-Rs is the ohmic resistance, and EIS-Rct is the contact resistance.

[0111] (2) Comprehensive performance test

[0112] The A batteries in Examples 1-3 are charged and discharged according to the following rules: when the lithium ion battery is in use, first charge and discharge the positive tab and negative tab 11 connected to the middle region at 0.5C-1C, then charge and discharge the complete lithium ion battery by connecting all the positive tabs 10 and negative tabs 11 at 10C for 10 cycles; the conventional battery B in the comparative example is charged and discharged at 1C for 10 cycles.

[0113] Table 2 is the 1C comprehensive test results at room temperature:

[0114]

[0115]

[0116] Performance test conclusion:

[0117] (1) From the EIS and rate discharge results, it can be concluded that the rate performance of the batteries assembled in Examples 1, 2 and 3 is better than that of the ordinary battery. Specifically, the EIS-Rct value of the conventional battery B is 20.6% higher than that of the battery A in Examples 1 to 3. In addition, in the rate discharge performance test, the high-rate capacity retention rate of the battery A in Examples 1 to 3 is higher than that of the conventional battery B.

[0118] (2) From the test results of the normal temperature 1C / 1C cycle, since the intermediate module of the battery A in Examples 1 to 3 is activated first for two weeks, and then the overall charging and discharging is performed, the climbing number of weeks is significantly reduced. This is due to the fact that the double positive electrode tabs activate the intermediate part (B module 200) first, which increases the consistency of the entire battery. At the same time, the maximum capacity of the charging and discharging of the battery A in Examples 1 to 3 is slightly higher than that of the conventional battery, which is also because the consistency of the charging and discharging state of the battery A in Examples 1 to 3 is higher, and more capacity can be discharged. As for the temperature rise, it can be seen that the temperature rise of the intermediate module (B module 200) of the battery A in Examples 1 to 3 is significantly close to that of the side modules (A, C module 300) of the battery, while the temperature rise of the intermediate module of the conventional battery is significantly greater than that of the two side modules.

[0119] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A lithium-ion secondary battery, characterized in that, The application relates to a lithium ion secondary battery. A plurality of polar piece groups are sequentially stacked, and the kinetic performance and heat dissipation performance of a first polar piece group and a last polar piece group are the same, the kinetic performance and heat dissipation performance of the polar piece groups located at the middle positions between the first polar piece group and the last polar piece group are the same and are better than the kinetic performance and heat dissipation performance of the first polar piece group and the last polar piece group, wherein the kinetic performance is EIS and rate discharge performance. The polar piece groups with the same kinetic performance are collectively provided with a positive electrode lug; and all the polar piece groups are collectively provided with a negative electrode lug. Any polar piece group located between the first polar piece group and the last polar piece group comprises a plurality of second positive polar pieces and a plurality of second negative polar pieces, and the plurality of second positive polar pieces and the plurality of second negative polar pieces are alternately stacked together, any adjacent second positive polar piece and second negative polar piece are provided with a second current collector, and a graphene heat conduction layer is arranged between the second current collector and the second positive polar piece and the second negative polar piece.

2. The lithium-ion secondary battery according to claim 1, characterized by The two positive electrode lugs are located on the same side of the plurality of polar piece groups, the negative electrode lug is located on the opposite side of the plurality of polar piece groups, and the positive electrode lug and the negative electrode lug of the polar piece groups located between the first polar piece group and the last polar piece group are subjected to 0.5C-1C charging and discharging twice, and then the two positive electrode lugs and the negative electrode lug are connected to complete the charging and discharging of the complete battery structure.

3. The lithium-ion secondary battery according to claim 1, characterized by The first polar piece group and the last polar piece group account for 1 / 3-1 / 4 of the total polar piece groups.

4. The lithium-ion secondary battery according to claim 1, characterized by The first polar piece group and the last polar piece group each comprise a plurality of first positive polar pieces and a plurality of first negative polar pieces, and the plurality of first positive polar pieces and the plurality of first negative polar pieces are alternately stacked together, and any adjacent first positive polar piece and first negative polar piece are provided with a first diaphragm. Any first positive polar piece and any first negative polar piece are provided with a first current collector. All the first positive polar pieces are collectively provided with a positive electrode lug.

5. The lithium-ion secondary battery according to claim 4, characterized by The active material of the first positive polar piece comprises one or more of lithium iron phosphate, lithium nickel cobalt oxide, lithium nickel oxide and lithium manganate, the binder of the first positive polar piece is a high molecular material, and the conductive agent of the first positive polar piece comprises one or more of conductive carbon black, acetylene black, ketjen black, carbon nanotube, graphene oxide and graphene. The material of the first positive polar piece comprises the following components in percentage by mass: 70-99% of active material, 0.5-12% of binder and 0.5-18% of conductive agent.

6. The lithium-ion secondary battery according to claim 4, characterized by The active material of the first negative polar piece is a porous carbon material, the binder of the first negative polar piece is a high molecular material, and the conductive agent of the first negative polar piece comprises one or more of conductive carbon black, carbon nanotube, graphene oxide or graphene. The material of the first negative polar piece comprises the following components in percentage by mass: 90-97% of active material, 2-5% of binder and 1-5% of conductive agent.

7. The lithium ion secondary battery according to claim 1, wherein At least the first end and the tail end are provided with a second diaphragm along the stacking direction. All the second positive sheets are collectively provided with one positive tab.

8. The lithium-ion secondary battery according to claim 7, characterized by The graphene heat-conducting layer is formed by graphene powder and a binder, and is coated on opposite sides of the second current collector.

9. The lithium-ion secondary battery according to claim 7, characterized by The active material of the second positive sheet includes one or more of lithium iron phosphate, lithium nickel cobalt oxide, lithium nickelate and lithium manganate, and has different particle sizes; the binder of the second positive sheet is a high molecular material, and the conductive agent of the second positive sheet includes one or more of conductive carbon black, acetylene black, ketjen black, carbon nanotube, graphene oxide and graphene; The material of the second positive sheet includes the following components in mass percentage: active material 70% to 99%, binder 0.5% to 12% and conductive agent 0.5% to 18%; The active material of the second negative sheet is a porous carbon material, the binder of the second negative sheet is a high molecular material, and the conductive agent of the second negative sheet includes one or more of conductive carbon black, carbon nanotube, graphene oxide or graphene; The material of the second negative sheet includes the following components in mass percentage: active material 90% to 97%, binder 2% to 5% and conductive agent 1% to 5%.

10. A lithium-ion secondary battery, characterized by comprising: Comprise: A plurality of sheet groups are sequentially stacked, and the dynamic performance of the corresponding sheet group is the same from the two sides to the center position, and gradually increases; the sheet groups with the same dynamic performance are collectively provided with one positive tab; all the sheet groups are collectively provided with one negative tab; wherein the dynamic performance is EIS and rate discharge performance; Any sheet group between the first sheet group and the last sheet group includes a plurality of second positive sheets and a plurality of second negative sheets, and the plurality of second positive sheets and the plurality of second negative sheets are alternately stacked together, any adjacent second positive sheet and second negative sheet are provided with a second current collector, and the second current collector is provided with a graphene heat-conducting layer between the second positive sheet and the second negative sheet; Along the stacking direction, the heat dissipation performance of the first sheet group and the last sheet group is the same, the heat dissipation performance of the sheet group at the middle position between them is the same, and is better than that of the first sheet group and the last sheet group.

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