CN117117085A

CN117117085A - Lithium ion battery

Info

Publication number: CN117117085A
Application number: CN202311377185.3A
Authority: CN
Inventors: 马超杰; 许久凌
Original assignee: China Innovation Aviation Technology Group Co ltd
Current assignee: China Innovation Aviation Technology Group Co ltd
Priority date: 2023-10-24
Filing date: 2023-10-24
Publication date: 2023-11-24
Anticipated expiration: 2043-10-24
Also published as: CN117117085B

Abstract

The application particularly discloses a lithium ion battery. The lithium ion battery comprises a pole piece, wherein the pole piece comprises a current collector and an active material layer; the ratio of the thickness d of the current collector to the length L of the active material layer satisfies 4.5X10 ^‑6 ≤d/L≤4×10 ^‑5 The length L of the active material layer is 200-1000mm; the ratio of the thickness t of the active material layer to the thickness d of the current collector satisfies 6.ltoreq.t/d.ltoreq.34. The application has the advantages of improving the energy density, the cycle performance and the electrochemical performance of the lithium ion battery.

Description

Lithium ion battery

Technical Field

The application relates to the technical field of lithium ion batteries, in particular to a lithium ion battery.

Background

Along with the continuous development of lithium ion batteries and the widening of application scenes thereof, how to improve the energy density, the safety and the integration and manufacturing efficiency of lithium batteries, and realizing energy conservation, emission reduction and cost saving are one of the hot problems of the current research.

After the pole piece in the lithium ion battery is adjusted to be longer, although the energy density of the lithium ion battery can be improved to a certain extent, the overcurrent requirement of the pole piece is increased at the moment, and the current collector in the pole piece bears the main overcurrent effect, so that after the length of the pole piece is increased, the overcurrent capacity of the current collector is correspondingly required to be improved, otherwise, the improvement of the cycle performance and the electrochemical performance of the lithium ion battery is not facilitated due to the increase of the voltage drop of the battery caused by the current collector. Therefore, it is desirable to provide a lithium ion battery that can achieve a combination of high energy density, excellent cycle performance and electrochemical performance.

Disclosure of Invention

In order to enable a lithium ion battery to have high energy density, excellent cycle performance and electrochemical performance, the application provides a lithium ion battery.

The application provides a lithium ion battery, which adopts the following technical scheme:

a lithium ion battery comprising a pole piece comprising a current collector and an active material layer; the ratio of the thickness d of the current collector to the length L of the active material layer satisfies 4.5X10 ^-6 ≤d/L≤4×10 ^-5 The length L of the active material layer is 200-1000mm; the ratio of the thickness t of the active material layer to the thickness d of the current collector satisfies 6.ltoreq.t/d.ltoreq.34.

At present, in order to improve the energy density of a lithium ion battery, the length of a pole piece in the lithium ion battery can be properly adjusted and increased to utilize more active materials to exert capacity, but as the length of the pole piece is increased, the internal resistance of the pole piece is correspondingly increased, although the internal resistance can be reduced by increasing the thickness of a current collector, the circulation and the electrochemical performance of the lithium ion battery are improved, after the thickness of the current collector is increased, the space for arranging an active material layer in a battery shell in a specific space is reduced, namely the total thickness of the active material layer in the lithium ion battery is reduced, so that the energy density of the lithium ion battery cannot be effectively improved.

According to the application, by controlling the ratio of the thickness of the current collector to the length of the active material layer, under the condition that the pole piece is longer, the overcurrent capacity of the current collector is ensured, the voltage drop of the lithium ion battery caused by larger internal resistance of the current collector is avoided, and the capacity and the cycle life of the lithium ion battery can be obviously improved; meanwhile, the thickness ratio of the active material layer to the current collector is controlled, so that the space capable of containing the active material is prevented from being reduced due to the overlarge thickness of the current collector under the same internal space of the battery, and the high energy density of the lithium ion battery is considered; meanwhile, the ratio of the thickness of the active material layer to the thickness of the current collector is controlled, so that the situation that the positive electrode plate and the negative electrode plate are gradually relaxed due to expansion and contraction of the electrode layer after being stored or in service for a period of time can be relieved, the rate of increasing the internal resistance of the lithium ion battery is delayed, and the cycle performance of the lithium battery is further improved.

When the ratio of the thickness of the current collector to the length of the active material layer is too low (less than 4.5x10 ^-6 ) The thickness of the current collector is smaller, the cross-sectional area of the corresponding current collector is reduced at the moment, and correspondingly, the internal resistance of the current collector is increased, so that the improvement of the cycle performance of the lithium battery is not facilitated; the thickness of the current collector is reduced, and under the condition that the pole piece is longer, the active material layer on the current collector is longer, and the edge of the pole piece is easy to bend and even break, so that the forming and processing difficulty of the pole piece is increased; and when the ratio of the thickness of the current collector to the length of the active material layer is too high (greater than 4×10 ^-5 ) At this time, although the increase in the thickness of the current collector can reduce the impedance of the current collector and thus the voltage drop of the battery caused by the current collector, the thickness of the active material layer in the lithium ion battery correspondingly decreases, so that the energy density of the lithium ion battery decreases, which is unfavorable for obtaining the lithium ion battery with excellent comprehensive performance. When the ratio of the thickness of the active material layer to the thickness of the current collector is too low (less than 6), the amount of active material that exerts capacity in the lithium battery decreases, and the energy density of the lithium battery decreases; when the ratio of the thickness of the active material layer to the thickness of the current collector is too high (greater than 34), on one hand, the wettability of the active material layer by the electrode liquid in the lithium battery is reduced, which is not beneficial to the exertion of the capacity of the lithium battery, but is not beneficial to the improvement of the energy density of the lithium battery, and on the other hand, the current collector is easy to crush in the roll forming of the pole piece.

Detailed Description

For a better understanding and implementation, the technical solutions of the present invention will be clearly and completely described below in connection with examples.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties to be obtained.

As used herein, "and/or" means one or all of the elements mentioned.

The use of "including" and "comprising" herein encompasses both the situation in which only the elements are mentioned and the situation in which other elements not mentioned are present in addition to the elements mentioned.

All percentages in the present invention are by weight unless otherwise indicated.

As used in this specification, the terms "a," "an," "the," and "the" are intended to include "at least one" or "one or more," unless otherwise specified. For example, "a component" refers to one or more components, and thus more than one component may be considered and possibly employed or used in the practice of the embodiments.

The lithium ion battery comprises a pole piece, wherein the pole piece comprises a current collector and an active material layer; the ratio of the thickness d of the current collector to the length L of the active material layer satisfies 4.5X10 ^-6 ≤d/L≤4×10 ^-5 The length L of the active material layer is 200-1000mm; the ratio of the thickness t of the active material layer to the thickness d of the current collector satisfies 6.ltoreq.t/d.ltoreq.34.

Preferably, the ratio of the internal resistance R of the current collector to the DCR value of the lithium ion battery satisfies 0.05-0.35R/DCR.

The impedance of the lithium battery is related to the current collector impedance, the electrolyte impedance, the ion impedance, the active material layer impedance and the like, and the ratio of the internal resistance of the current collector to the DCR value of the lithium battery is adjusted, so that the energy density of the lithium battery can be realized, the voltage drop of the lithium battery caused by the current collector part can be obviously reduced, and the cycle performance of the lithium battery can be improved.

Preferably, the electrode sheet includes a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer, and a negative electrode sheet including a negative electrode current collector and a negative electrode active material layer.

Preferably, when the length L1 of the positive electrode active material layer satisfies 200 mm.ltoreq.L1.ltoreq.400 mm, the thickness d1 of the positive electrode current collector satisfies 8 μm.ltoreq.d1.ltoreq.12 μm; when the length L1 of the positive electrode active material layer is more than 400mm, the thickness d1 of the positive electrode current collector is more than 12 mu m and less than or equal to 18 mu m; and/or, when the length L2 of the negative electrode active material layer is less than or equal to 200mm and less than or equal to L2 and less than or equal to 400mm, the thickness d2 of the negative electrode current collector is less than or equal to 4.5 mu m and less than or equal to d2 and less than or equal to 6 mu m; when the length L2 of the negative electrode active material layer satisfies L2 & gt400 mm, the thickness d2 of the negative electrode current collector satisfies 6 mu m & ltd 2 & ltoreq.12 mu m.

The lengths and the thicknesses of the active material layers and the current collectors of the positive plate and the negative plate are respectively adjusted, so that the respective internal resistances of the positive plate and the negative plate are reduced, the exertion of the active material capacity in the positive plate and the reduction of the internal resistance in the cycling process of the lithium battery are facilitated, and the lithium battery can have excellent electrochemical performance while having high energy density.

Preferably, the ratio of the thickness d1 of the positive electrode current collector to the length L1 of the positive electrode active material layer satisfies 8×10 ^-6 ≤d1/L1≤4×10 ^-5 And/or the ratio of the thickness d2 of the anode current collector to the length L2 of the anode active material layer satisfies 4.5×10 ^-6 ≤d2/L2≤2.25×10 ^-5 。

In a lithium ion battery, the length of a negative electrode plate is generally longer than that of a positive electrode plate, so that the problem that lithium is separated from a negative electrode due to the fact that the negative electrode plate cannot provide enough lithium intercalation positions after lithium ions in the positive electrode plate are separated is avoided; in addition, as the positive current collector is generally made of aluminum, the negative current collector is generally made of copper, and the conductivity of copper is better than that of aluminum, the thickness of the negative current collector is smaller, and the overcurrent requirement can be met; therefore, by adjusting the ratio of the thickness of the current collector and the length of the active material layer in the positive electrode plate and the negative electrode plate respectively to satisfy the above value ranges, the conditions of negative electrode lithium precipitation caused by too short of the negative electrode active material layer and battery energy reduction caused by too short of the positive electrode active material layer can be avoided, and the cycle performance of the lithium ion battery is obviously improved while the higher energy density is simultaneously considered.

Preferably, the ratio of the thickness t1 of the positive electrode active material layer to the thickness d1 of the positive electrode current collector satisfies 6.ltoreq.t1/d1.ltoreq.24, and/or the ratio of the thickness t2 of the negative electrode active material layer to the thickness d2 of the negative electrode current collector satisfies 13.ltoreq.t2/d2.ltoreq.34.

The ratio between the thickness of the active material layer and the thickness of the current collector is controlled to meet the value range, so that lithium ions in the positive plate can be completely separated out, lithium ion balance transfer between the positive plate and the negative plate is maintained, and the cycle performance of the lithium battery is improved.

Preferably, the thickness t1 of the positive electrode active material layer is 70 to 300 μm and/or the thickness t2 of the negative electrode active material layer is 80 to 210 μm.

By adjusting the thickness of the active material layer, on one hand, the negative influence on the energy density of the lithium battery when the thickness of the positive electrode active material layer is too thin is avoided, the contact resistance between the active material layer and the current collector is reduced, the partial pressure of the lithium battery caused by the current collector is reduced, and the cycle performance of the lithium battery is improved; on the other hand, the negative influence on the construction of the continuous ion transmission pore canal when the anode active material layer and the cathode active material layer are too thick is avoided, so that the electrochemical performance of the lithium battery is improved.

Preferably, the positive electrode sheet has a porosity of20% -40% and/or the porosity of the negative plate +.>25% -45%.

The lithium ion balance transfer between the positive plate and the negative plate can be realized by adjusting the porosity of the positive plate and the negative plate, and a transmission pore canal capable of fully infiltrating the positive active material layer and the negative active material layer is constructed, so that the cycle performance and the electrochemical performance of the lithium battery are obviously improved.

Preferably, the positive plate has an areal density m1 of 300-700g/m ² And/or the surface density m2 of the negative plate is 150-400g/m ² 。

The surface densities of the positive plate and the negative plate are adjusted to be maintained in the range, so that the capacity of the lithium ion battery can be exerted and the balance transmission of lithium ions between the positive plate and the negative plate can be realized; this is because, when the difference between the positive and negative electrode sheet surface densities is too small, which corresponds to too small positive electrode sheet surface density or too large negative electrode sheet surface density, in this case, the number of lithium ions that can be extracted from the positive electrode sheet becomes small, the capacity that the lithium ion battery can exert becomes small, and the process of lithium ions reaching the inside of the negative electrode active material layer from the negative electrode active material layer surface becomes slow due to the negative electrode sheet surface density being too large, and the phenomenon of lithium precipitation easily occurs on the negative electrode surface; when the difference between the surface densities of the positive and negative plates is too large, the surface density of the positive plate is too large or the surface density of the negative plate is too small, and in this case, although the quantity of lithium ions extracted from the positive plate is large, the negative plate does not have enough lithium intercalation positions, and lithium precipitation phenomenon also occurs, so that the improvement of the cycle performance and the energy density of the lithium battery is not facilitated.

Preferably, the lithium ion battery further comprises a shell and a battery cell, wherein the battery cell comprises the pole piece, and the battery cell is laminated; the shell comprises a first shell and a second shell, the second shell is provided with an opening, a flange structure is formed at the opening of the second shell, and the first shell is buckled with the opening of the second shell to form a cavity for accommodating the battery cell.

Preferably, the length L of the pole piece in the battery cell is 400-1000mm.

In the lithium battery with the structure, the length of the active material layer on the pole piece is longer, and the pole piece at the moment is more required to adjust the overcurrent capacity of the current collector so as to realize the effect of reducing the internal resistance of the pole piece.

Examples

Example 1

1. Preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 12 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 400mm, and the thickness t1 of the positive electrode active material layer was 180. Mu.m.

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 6 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 403mm, and the thickness t2 of the anode active material layer was 120. Mu.m.

3. Preparation of electrolyte

Ethylene Carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) are mixed according to the volume ratio of 1:1:1, mixing to obtain an organic solvent, and then drying the lithium salt LiPF sufficiently ₆ Dissolving in the mixed organic solvent to prepare the electrolyte with the concentration of 1 mol/L.

4. Preparation of lithium batteries

Sequentially stacking the positive plate, the isolating film and the negative plate, so that the isolating film is positioned between the positive plate and the negative plate to play a role of isolation, and the isolating film is a polyethylene film; and placing the bare cell in an outer packaging shell, drying, injecting electrolyte, and performing vacuum packaging, standing, formation, shaping and other procedures to obtain the lithium ion battery.

Example 2

The present embodiment differs from embodiment 1 in the preparation of the positive electrode sheet and the negative electrode sheet; the method comprises the following steps:

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 15 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 997mm, and the thickness t1 of the positive electrode active material layer was 225. Mu.m.

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 4.5 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 1000mm, and the thickness t2 of the anode active material layer was 90. Mu.m.

The remainder remained the same as in example 1.

Example 3

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 9 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 225mm, and the thickness t1 of the positive electrode active material layer was 135. Mu.m.

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 4.5 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 228mm, and the thickness t2 of the anode active material layer was 90. Mu.m. The remainder remained the same as in example 1.

Example 4

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 12 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 600mm, and the thickness t1 of the positive electrode active material layer was 180. Mu.m.

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 8 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 603mm, and the thickness t2 of the anode active material layer was 160. Mu.m.

The remainder remained the same as in example 1.

Example 5

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 18 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 600mm, and the thickness t1 of the positive electrode active material layer was 300. Mu.m.

2. Preparation of negative electrode sheet

The remainder remained the same as in example 1.

Example 6

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 6 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 600mm, and the thickness t1 of the positive electrode active material layer was 90. Mu.m.

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 6 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 603mm, and the thickness t2 of the anode active material layer was 120. Mu.m.

The remainder remained the same as in example 1.

Example 7

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of aluminum foil with the thickness d1 of 8 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 247mm, and the thickness t1 of the positive electrode active material layer was 120. Mu.m.

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 4.5 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 250mm, and the thickness t2 of the anode active material layer was 90. Mu.m.

The remainder remained the same as in example 1.

Example 8

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 18 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 600mm, and the thickness t1 of the positive electrode active material layer was 270. Mu.m.

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 12 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 603mm, and the thickness t2 of the anode active material layer was 120. Mu.m.

The remainder remained the same as in example 1.

Example 9

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 10 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 397mm, and the thickness t1 of the positive electrode active material layer was 150. Mu.m.

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 6 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 400mm, and the thickness t2 of the anode active material layer was 120. Mu.m.

The remainder remained the same as in example 1.

Example 10

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 12 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 597mm, and the thickness t1 of the positive electrode active material layer was 180. Mu.m.

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 8 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 600mm, and the thickness t2 of the anode active material layer was 120. Mu.m.

The remainder remained the same as in example 1.

Example 11

1. preparation of positive plate

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 5 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 600mm, and the thickness t2 of the anode active material layer was 100. Mu.m.

The remainder remained the same as in example 1.

Example 12

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 15 mu m, airing at room temperature, transferring to an oven for continuous drying, and then carrying out cold pressing and slitting to obtain an anode plate; the length L1 of the positive electrode active material layer was 997mm, and the thickness t1 of the positive electrode active material layer was 225. Mu.m.

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 4.5 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 1000mm, and the thickness t2 of the anode active material layer was 100. Mu.m.

The remainder remained the same as in example 1.

Example 13

1. preparation of positive plate

2. Preparation of negative electrode sheet

The remainder remained the same as in example 1.

Example 14

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 12 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 400mm, and the thickness t1 of the positive electrode active material layer was 72. Mu.m.

2. Preparation of negative electrode sheet

The remainder remained the same as in example 1.

Example 15

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 12 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 400mm, and the thickness t1 of the positive electrode active material layer was 288. Mu.m.

2. Preparation of negative electrode sheet

The remainder remained the same as in example 1.

Example 16

The present embodiment differs from embodiment 1 in the preparation of the positive electrode sheet and the negative electrode sheet; the method comprises the following steps: 1. preparation of positive plate

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 6 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 403mm, and the thickness t2 of the anode active material layer was 78. Mu.m. The remainder remained the same as in example 1.

Example 17

1. preparation of positive plate

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 6 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 403mm, and the thickness t2 of the anode active material layer was 204. Mu.m.

The remainder remained the same as in example 1.

Comparative example 1

This comparative example differs from example 1 in the preparation of the positive and negative electrode sheets; the method comprises the following steps:

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 3.2 mu m, airing at room temperature, transferring to an oven for continuous drying, and then carrying out cold pressing and slitting to obtain an anode plate; the length L1 of the positive electrode active material layer was 800mm, and the thickness t1 of the positive electrode active material layer was 48. Mu.m.

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 3.6 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 803mm, and the thickness t2 of the anode active material layer was 72. Mu.m.

The remainder remained the same as in example 1.

Comparative example 2

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 15 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 300mm, and the thickness t1 of the positive electrode active material layer was 225. Mu.m.

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 10 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 303mm, and the thickness t2 of the anode active material layer was 200. Mu.m.

The remainder remained the same as in example 1.

Comparative example 3

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 4 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 897mm, and the thickness t1 of the positive electrode active material layer was 60. Mu.m.

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 3.6 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 900mm, and the thickness t2 of the anode active material layer was 72. Mu.m.

The remainder remained the same as in example 1.

Comparative example 4

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 20 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 397mm, and the thickness t1 of the positive electrode active material layer was 300. Mu.m.

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 20 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 400mm, and the thickness t2 of the anode active material layer was 400. Mu.m.

The remainder remained the same as in example 1.

Comparative example 5

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 12 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 400mm, and the thickness t1 of the positive electrode active material layer was 456 μm.

2. Preparation of negative electrode sheet

The remainder remained the same as in example 1.

Comparative example 6

1. preparation of positive plate

Mixing the lithium iron phosphate anode active material with a conductive agent acetylene black and a binder PVDF according to a mass ratio of 97:1:2, mixing, adding a solvent NMP, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry; uniformly coating the anode slurry on two surfaces of an aluminum foil with the thickness d1 of 12 mu m, airing at room temperature, transferring to an oven for continuous drying, and then cold pressing and cutting to obtain an anode plate; the length L1 of the positive electrode active material layer was 400mm, and the thickness t1 of the positive electrode active material layer was 48. Mu.m.

2. Preparation of negative electrode sheet

The remainder remained the same as in example 1.

Comparative example 7

1. preparation of positive plate

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 6 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 403mm, and the thickness t2 of the anode active material layer was 84. Mu.m.

The remainder remained the same as in example 1.

Comparative example 8

1. preparation of positive plate

2. Preparation of negative electrode sheet

Graphite as a cathode active material, acetylene black as a conductive agent, CMC as a thickener and SBR as a binder according to the mass ratio of 96.4:1:1.2:1.4, mixing, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; uniformly coating the negative electrode slurry on two surfaces of a copper foil with the thickness d2 of 6 mu m to obtain a coated negative electrode plate, and rolling and slitting the coated negative electrode plate to obtain a negative electrode plate; the length L2 of the anode active material layer was 403mm, and the thickness t2 of the anode active material layer was 228. Mu.m.

The remainder remained the same as in example 1.

Detection method

1. Collector thickness test

The thickness of the current collector in the above examples and comparative examples was measured by the following specific measuring method: disassembling the lithium battery to obtain a positive plate and a negative plate, soaking in DMC at normal temperature for 60min, taking out, drying at 45 ℃, and testing the thickness of the positive and negative electrode lugs to obtain the thickness of the current collector. And measuring the thickness of the current collector at 20 different positions by adopting a ten-thousandth ruler, and taking an average value of 20 measured values to obtain the thickness value of the current collector.

2. Active material layer length measurement

The length test is carried out on the pole pieces in the embodiment and the comparative example, and the specific test method is as follows: and 3 times of pole piece length is tested by using a film ruler, and the 3 times of measured values are averaged to obtain the length value of the active substance layer.

3. Pole piece porosity test

The pole pieces in the above examples and comparative examples were subjected to porosity testing by the following specific test methods: cutting a pole piece into a wafer sample with the radius r of 6mm by using a pole piece punching machine, and simultaneously respectively measuring the thickness of the pole piece and the current collector by using a thickness gauge, wherein the thicknesses are h1 and h2 respectively; calculating the volume of the cut pole piece according to the formula, v =r ² （h1-h2）；

Weighing the mass of the pole piece sample by using a balance with the accuracy of 0.00001g, and marking the mass as g1;

Immersing the pole piece sample in a closed container with a certain volume of hexadecane for 1h (the volume of hexadecane in the closed solution is not required, but the required amount must be capable of ensuring that the pole piece is completely immersed therein); after immersing for 1h, taking out the pole piece by using tweezers, placing the pole piece on filter paper, sucking the pole piece to constant weight (generally, sucking the pole piece to constant weight for 1 h), and weighing the weight of the pole piece by using a balance, and marking the weight as g2;

calculating the porosity of the pole piece according to a formula=((g2-g1)//>)/v×100%，/>=0.7734g/cm3。

4. Polar plate surface Density test

The pole pieces in the above examples and comparative examples were subjected to an areal density test, which was carried out by: the method comprises the steps of sampling a pole piece by using a sampler, weighing the weight g1 of the sample, sampling a current collector by the same method, weighing the mass g2 of the current collector sample, calculating the sample area S prepared by the sampler, and obtaining the surface density of an active substance layer by using (g 1-g 2)/S.

5. Pole piece breaking strength test

The pole pieces in the above examples and comparative examples were subjected to breaking strength test by the following specific test methods: and (3) rolling the pole piece at the rolling speed of 15-20m/min under the rolling pressure of 70-100T, and observing the fracture condition of the pole piece.

6. Internal resistance R test of current collector

The lithium batteries in the above examples and comparative examples were subjected to a current collector internal resistance R test, and the specific test method was: internal resistance r=of current collector according to calculation formula of resistance lawL/S, wherein->And calculating the internal resistance values of the current collectors with different thicknesses for the conductivity of the current collector, wherein L is the length of the current collector, S is the cross-sectional area of the current collector.

7. DCR value test

The lithium batteries in the above examples and comparative examples were subjected to DCR test, and the specific test method was: at a certain temperature and SOC, a continuous charge or discharge time (usually 1-30 s) and a direct pulse current I (usually 1C) of a fixed magnitude are given, which is calculated by the voltage U1 at the end and U0 before the pulse, and the discharge dcr= (U0-U1)/I or the charge dcr= (U1-U0)/I.

8. Energy density testing

The lithium batteries in the above examples and comparative examples were subjected to energy density tests, and the specific test methods were: weighing the weight of the test battery, and recording as m; placing the battery in a clamp, applying 3000N force, charging to 4.3V at a constant current of 0.33C, standing for 30min, discharging to 2.5V at a constant current of 0.33C, standing for 30min, and continuously circulating for 3 times; the discharge capacity (in Ah) and energy E (three-turn average) were calculated, and the discharge energy density=e/m (in Wh/kg).

Table 1 table of various performance parameters of positive electrode sheet

Table 2 table of various Performance parameters of the negative electrode sheet

Table 3 lithium battery performance parameters

By combining examples 1-5, comparative examples 1-8 and tables 1-3, it can be seen that by controlling the ratio of the thickness of the current collector to the length of the active material layer and the ratio between the thickness of the active material layer and the thickness of the current collector in the lithium ion battery, the lithium ion battery can have excellent electrochemical performance and higher energy density, and the internal resistance DCR of the lithium battery can be reduced, thereby remarkably improving the cycle performance of the lithium battery; this is because in the lithium ion battery at this time, the voltage drop of the battery caused by the current collector under the condition that the electrode sheets are kept long can still be reduced to a state as low as possible, and it is advantageous to form an equilibrium state in which lithium ions stably exist to be transferred between the positive and negative electrode sheets. When the ratio d/L of the thickness d of the current collector to the length L of the active material layer is too large or too small, and the ratio t/d of the thickness t of the active material layer to the thickness d of the current collector is too large or too small, the cycle performance and the energy density of the lithium ion battery are obviously reduced, and the comprehensive performance of the lithium battery is not improved.

In combination with examples 1 to 6 and tables 1 to 3, it can be seen that when the thickness of the active material layer is greater than 400mm, the thicknesses of the positive electrode current collector and the negative electrode current collector should be correspondingly adjusted to reduce the internal resistance of the lithium battery, and in example 6, the thicknesses of the active material layers on the positive electrode sheet and the negative electrode sheet both exceed 400mm, but the thicknesses of the positive electrode current collector and the negative electrode current collector are not correspondingly adjusted, resulting in an increase in the internal resistance of the lithium battery in example 6 and a decrease in the energy density.

In combination with examples 1-5, 7-8 and tables 1-3, it can be seen that when the thicknesses of the positive electrode current collector and the negative electrode current collector are taken to the corresponding upper limit values, the DCR value of the lithium ion battery can be significantly reduced and the energy density of the lithium battery can be improved, and although the length of the positive electrode active material layer is not taken to the upper limit value at this time, the current collector is strong in overcurrent capacity, the capacity in the positive electrode active material layer can be effectively exerted, and the transfer of lithium ions between the positive and negative electrode sheets also tends to be balanced, so that the overall performance of the lithium ion battery can be significantly improved.

In combination with examples 1, 9 to 12 and tables 1 to 3, it can be seen that when the length of the positive electrode active material layer is increased, although the energy density of the lithium battery can be significantly improved, when the thickness of the positive electrode current collector or the negative electrode current collector is excessively thin, the cycle performance of the lithium battery is significantly reduced, and thus, it is necessary to consider that the length of the active material layer and the thickness of the current collector are within a proper range in order to make the overall performance of the lithium battery more excellent.

In combination with examples 1, 13 and tables 1 to 3, it can be seen that, as the porosity of the positive electrode sheet and the negative electrode sheet is reduced, the wettability of the electrolyte to the positive electrode active material layer and the negative electrode active material layer is poor, which is not beneficial to the effective exertion of the capacity of the positive electrode active material layer and the balance transfer of lithium ions between the positive electrode sheet and the negative electrode sheet, and at this time, even if the length of the electrode sheet active material layer is increased, the energy density of the battery cannot be significantly improved.

In combination with examples 1, 14-17 and tables 1-3, it can be seen that when the values of t1/d1 and t2/d2 are the upper limit value or the lower limit value, the DCR value of the lithium ion battery is smaller but the energy density is also low, and when the energy density of the lithium battery is higher, the DCR value is significantly improved, so that the lithium battery cannot have both excellent cycle performance and high energy density.

The present embodiment is only for explanation of the present application and is not to be construed as limiting the present application, and modifications to the present embodiment, which may not creatively contribute to the present application as required by those skilled in the art after reading the present specification, are all protected by patent laws within the scope of claims of the present application.

Claims

1. A lithium ion battery, characterized in that: the electrode comprises a pole piece, wherein the pole piece comprises a current collector and an active material layer; the ratio of the thickness d of the current collector to the length L of the active material layer satisfies 4.5X10 ^-6 ≤d/L≤4×10 ^-5 The length L of the active material layer is 200-1000mm; the ratio of the thickness t of the active material layer to the thickness d of the current collector satisfies 6.ltoreq.t/d.ltoreq.34.

2. A lithium ion battery according to claim 1, wherein: the ratio of the internal resistance R of the current collector to the DCR value of the lithium ion battery is more than or equal to 0.05 and less than or equal to 0.35.

3. A lithium ion battery according to claim 1, wherein: the pole piece comprises a positive pole piece and a negative pole piece, wherein the positive pole piece comprises a positive pole current collector and a positive pole active material layer, and the negative pole piece comprises a negative pole current collector and a negative pole active material layer.

4. A lithium ion battery according to claim 3, wherein: when the length L1 of the positive electrode active material layer is more than or equal to 200mm and less than or equal to L1 and less than or equal to 400mm, the thickness d1 of the positive electrode current collector is more than or equal to 8 mu m and less than or equal to d1 and less than or equal to 12 mu m; when the length L1 of the positive electrode active material layer is more than 400mm, the thickness d1 of the positive electrode current collector is more than 12 mu m and less than or equal to 18 mu m; and/or, when the length L2 of the negative electrode active material layer is less than or equal to 200mm and less than or equal to L2 and less than or equal to 400mm, the thickness d2 of the negative electrode current collector is less than or equal to 4.5 mu m and less than or equal to d2 and less than or equal to 6 mu m; when the length L2 of the negative electrode active material layer satisfies L2 & gt400 mm, the thickness d2 of the negative electrode current collector satisfies 6 mu m & ltd 2 & ltoreq.12 mu m.

5. A lithium ion battery according to claim 3, wherein: the ratio of the thickness d1 of the positive electrode current collector to the length L1 of the positive electrode active material layer satisfies 8×10 ^-6 ≤d1/L1≤4×10 ^-5 And/or the thickness d2 of the negative electrode current collector is equal to The ratio of the length L2 of the anode active material layer satisfies 4.5X10 ^-6 ≤d2/L2≤2.25×10 ^-5 。

6. A lithium ion battery according to claim 3, wherein: the ratio of the thickness t1 of the positive electrode active material layer to the thickness d1 of the positive electrode current collector satisfies 6.ltoreq.t1/d1.ltoreq.24, and/or the ratio of the thickness t2 of the negative electrode active material layer to the thickness d2 of the negative electrode current collector satisfies 13.ltoreq.t2/d2.ltoreq.34.

7. A lithium ion battery according to claim 3, wherein: the thickness t1 of the positive electrode active material layer is 70 to 300 μm, and/or the thickness t2 of the negative electrode active material layer is 80 to 210 μm.

8. A lithium ion battery according to claim 3, wherein: the porosity epsilon 1 of the positive plate is 20% -40%, and/or the porosity epsilon 2 of the negative plate is 25% -45%.

9. A lithium ion battery according to claim 3, wherein: the surface density m1 of the positive plate is 300-700g/m ² And/or the surface density m2 of the negative plate is 150-400g/m ² 。

10. A lithium ion battery according to any one of claims 1-9, wherein: the battery cell also comprises a shell and a battery cell, wherein the battery cell comprises the pole piece as claimed in claims 1-9, and the battery cell is laminated; the shell comprises a first shell and a second shell, the second shell is provided with an opening, a flange structure is formed at the opening of the second shell, and the first shell is buckled with the opening of the second shell to form a cavity for accommodating the battery cell.

11. A lithium ion battery according to claim 10, wherein: the length L of the pole piece in the battery cell is 400-1000mm.