Multilayer-coated negative electrode sheet and lithium ion battery

Abstract

The application provides a multi-layer coated negative electrode sheet and a lithium ion battery. Specifically, the application relates to a battery negative electrode sheet, which comprises a coating layer L1 close to a current collector, an intermediate coating layer L2 close to the coating layer L1, and an outermost coating layer L3. The coating layer L1, the coating layer L2 and the coating layer L3 all comprise negative electrode material single particles, negative electrode material secondary particles, a binder and a conductive agent. The battery negative electrode sheet can maximize the electrical performance and long-term performance of the negative electrode sheet under the condition that the total negative electrode formula remains unchanged.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium batteries, in particular, the present application relates to a multi-layer coated negative electrode sheet and a lithium ion battery. BACKGROUND

[0002] At present, the negative electrode material of lithium ion battery is mainly improved by reducing particle size and carbon coating to improve the fast charging performance of graphite, but the fast charging capacity of graphite material is difficult to improve greatly. Hard carbon, as a kind of amorphous carbon material with excellent fast charging performance, has problems such as processing difficulty, low compaction, voltage hysteresis, and low first efficiency. If only mechanical mixing of graphite and hard carbon is used, it is difficult to play the advantages of both. There are already some patents that use double-layer coating technology to coat double-layer negative electrode slurry on the negative electrode copper current collector, such as coating a first layer of graphite slurry first, and then coating a second layer of silicon-oxygen slurry or a second type of graphite slurry on the first layer of graphite. Generally speaking, the first layer of slurry is usually selected as a material with high compaction, high capacity, and high adhesion because it is in direct contact with the current collector. The second layer of slurry is usually selected as a material with good kinetics for the fast deintercalation of lithium ions. However, the multi-layer coating process is not yet mature, and therefore further exploration and research on the multi-layer coating process are still needed. SUMMARY

[0003] The inventors have found that the current lithium ion battery industry improves the multi-layer coating of the negative electrode sheet on the premise of ensuring high energy density. The improved multi-layer coating mainly targets the use of binders, the use of conductive agents, and the mixing of different single particles of negative electrode materials. Due to the floating of the negative electrode binder during coating, a large amount of binder needs to be added to ensure the adhesion of the negative electrode material to the current collector. With multi-layer coating, different contents of binders can be used in different coating layers, so that the total amount of the binder remains unchanged, and the DCR of the negative electrode sheet can still be improved. The results of the electrochemical performance test of the negative electrode conductive agent show that under the condition that the total content of the conductive agent remains unchanged, the electrode with a high content of conductive agent in the lower layer close to the current collector has better electrical performance. Therefore, reasonable control of the vertical distribution of the conductive agent is beneficial to improving the electrical performance of the electrode sheet. When multi-layer coating is used, the upper layer of the negative electrode uses a negative electrode with a higher proportion of secondary particles, and the lower layer uses a negative electrode with a lower proportion of secondary particles. By changing the distribution ratio of the total amount of single and secondary particles under the condition that the total amount of single and secondary particles remains unchanged, the charging performance can be optimized to the greatest extent. At present, the multi-layer coating process is not yet mature, and the double-layer coating on the market is more mature. However, the use of binders, conductive agents, and single and secondary particles lacks a reasonable proportion, and there is no good transition area between the upper and lower layers, resulting in large performance differences at the connection between different coating layers, which makes the long-term performance of the electrode sheet poor. The present application aims to provide a new multi-layer coated negative electrode sheet, which can maximize the electrical performance and long-term performance of the negative electrode sheet under the condition that the overall negative electrode formula remains unchanged.

[0004] In a first aspect, the present application provides a battery negative electrode sheet. According to an embodiment of the present application, the battery negative electrode sheet comprises:

[0005] a coating layer L1 close to the current collector,

[0006] an intermediate coating layer L2 close to the coating layer L1, and

[0007] an outermost coating layer L3,

[0008] The coating layer L1, the coating layer L2 and the coating layer L3 all contain negative electrode material single particles, negative electrode material secondary particles, a binder and a conductive agent. The battery negative electrode sheet can maximize the electrical performance and long-term performance of the negative electrode sheet while the total negative electrode formula remains unchanged.

[0009] According to an embodiment of the present application, the battery negative electrode sheet can further comprise at least one of the following additional technical features:

[0010] According to an embodiment of the present application, the negative electrode material in the negative electrode material single particles and the negative electrode material secondary particles is selected from artificial graphite, hard carbon or soft carbon.

[0011] According to an embodiment of the present application, the binder is selected from polyacrylic acid or synthetic rubber.

[0012] According to an embodiment of the present application, the conductive agent is selected from SP, carbon black, KS-6, carbon nanotubes or graphene.

[0013] According to an embodiment of the present application, the proportion of negative electrode single particles in the coating layer L1 is Gs1, the proportion of negative electrode material secondary particles in the coating layer L1 is Gd1, the proportion of the binder in the coating layer L1 is B1, the proportion of the conductive agent in the coating layer L1 is C1, the proportion of negative electrode material single particles in the coating layer L2 is Gs2, the proportion of negative electrode material secondary particles in the coating layer L2 is Gd2, the proportion of the binder in the coating layer L2 is B2, the proportion of the conductive agent in the coating layer L2 is C2, the proportion of negative electrode material single particles in the coating layer L3 is Gs3, the proportion of negative electrode material secondary particles in the coating layer L3 is Gd3, the proportion of the binder in the coating layer L3 is B3, and the proportion of the conductive agent in the coating layer L3 is C3, wherein Gs1+Gd1+B1+C1=100%, Gs2+Gd2+B2+C2=100%, and Gs3+Gd3+B3+C3=100%. d1 d2 d3

[0014] According to an embodiment of the present application, the D 10 , D 50 , and D 90 of the negative electrode material single particles in the coating layer L1 are respectively Ds 10 ​​​、Ds 50 、Ds 90 The secondary particles of the negative electrode material in the coating L1 have a D 10 D 50 D 90 Dd 10 、Dd 50 、Dd 90 The ratio of primary particles to secondary particles of the negative electrode material in the coating L1 is (Dd) 10 +Ds 10 ) / (Dd 90 +Ds 90 )=Gd1 / Gs1.

[0015] According to an embodiment of the present invention, the D of the single particles of the negative electrode material of the coating L2 is... 10 D 50 D 90 Ds 10 、Ds 50 、Ds 90 The D of the secondary particles of the negative electrode material in the coating L2 10 D 50 D 90 Dd 10 、Dd 50 、Dd 90 The ratio of primary particles to secondary particles of the negative electrode material in the coating L2 is ((Dd) 90 -Dd 10 )+(Ds 90 -Ds 10 )) / (Dd 50 +Ds 50 ) = Gd2 / Gs2.

[0016] According to an embodiment of the present invention, the D of the single particles of the negative electrode material of the coating L3 is... 10 D 50 D 90 Ds 10 、Ds 50 、Ds 90 The D of the secondary particles of the negative electrode material in the coating L3 10 D 50 D 90 Dd 10 、Dd 50 、Dd 90 The ratio of primary particles to secondary particles of the negative electrode material in the coating L3 is (Dd) 10 +Ds 10 ) / (Dd 90 +Ds 90) = Gs3 / Gd3.

[0017] According to an embodiment of the present application, the proportion of the binder is B1 = (1.1-1.3)B2 = (1.3-1.5)B3.

[0018] According to an embodiment of the present application, the proportion of the conductive agent is C1 = (1.1-1.3)C2 = (1.3-1.5)C3.

[0019] In another aspect of the present application, the present application also proposes a new type of multi-layer coated negative electrode sheet. According to an embodiment of the present application, the sheet has three coating layers in total, which are L1 coating layer close to the current collector, intermediate coating layer L2 immediately close to the L1 coating layer, and the outermost coating layer L3. The L1, L2, and L3 coating layers all contain negative electrode material (including artificial graphite, hard carbon, soft carbon, etc.) single particles, negative electrode material (including artificial graphite, hard carbon, soft carbon, etc.) secondary particles, binder (including SBR, polyacrylic acid (PAA), etc.), and conductive agent (including SP, carbon black, KS-6, carbon nanotube, graphene, etc.), as shown in the following table: Figure 1 .

[0020] According to an embodiment of the present application, the proportion of the negative electrode material single particles in the coating layer L1 is Gs1, the proportion of the negative electrode material secondary particles is Gd1, the proportion of the binder is B1, and the proportion of the conductive agent is C1. The proportion of the negative electrode material single particles in the L2 coating layer is Gs2, the proportion of the negative electrode material secondary particles is Gd2, the proportion of the binder is B2, and the proportion of the conductive agent is C2. The proportion of the negative electrode material single particles in the L3 coating layer is Gs3, the proportion of the negative electrode material secondary particles is Gd3, the proportion of the binder is B3, and the proportion of the conductive agent is C3. Wherein Gs1+Gd1+B1+C1 = 100%, Gs2+Gd2+B2+C2 = 100%, and Gs3+Gd3+B3+C3 = 100%. d1 d2 d3 .

[0021] According to an embodiment of the present application, the D 10 , D 50 , D 90 of the negative electrode material single particles is Ds 10 , Ds 50 , Ds 90 .The D 10 , D 50 , D 90 of the negative electrode material secondary particles is Dd 10 , Dd 50 , Dd 90 .

[0022] For the coating layer L1, the proportion of the negative electrode material single particles to the negative electrode material secondary particles is (Dd 10 ​+Ds 10 ) / (Dd 90 +Ds 90 )=Gd1 / Gs1.

[0023] For the single particle of the coating L2 negative material and the ratio of the secondary particles of the negative material is ((Dd 90 -Dd 10 )+(Ds 90 -Ds 10 )) / (Dd 50 +Ds 50 )=Gd2 / Gs2.

[0024] For the single particle of the coating L3 negative material and the ratio of the secondary particles of the negative material is (Dd 10 +Ds 10 ) / (Dd 90 +Ds 90 )=Gs3 / Gd3.

[0025] For the ratio of the three coating binders is B1=(1.1~1.3)B2=(1.3~1.5)B3.

[0026] For the ratio of the three coating conductive agents is C1=(1.1~1.3)C2=(1.3~1.5)C3.

[0027] According to the embodiment of the application, the slurries of the three coatings of the pole piece L1L2L3 are respectively prepared in a stirring tank, and the prepared slurries are coated on the negative current collector by using the extrusion spraying multi-layer coating technology. According to the embodiment of the application, the negative pole piece prepared by the method has greater adhesion and more stable adhesion effect, so that the yield of the pole piece in the pole piece process is higher than that of the ordinary pole piece.

[0028] In another aspect of the application, the application further provides a battery. According to the embodiment of the application, the battery comprises the battery negative pole piece described above.

[0029] According to the embodiment of the application, the battery negative pole piece described above takes into account the advantages of the double-layer coating in improving the fast-charging performance, and at the same time, improves the influence of the coating delamination on the long cycle of the battery cell. BRIEF DESCRIPTION OF DRAWINGS

[0030] The above and / or additional aspects and advantages of the application will become apparent and be readily understood from the following description, taken in connection with the accompanying drawings, in which:

[0031] Figure 1 is a schematic view of a multi-layer coated negative pole piece according to an embodiment of the application;

[0032] Reference numerals: 1 represents coating L1, 2 represents coating L2, 3 represents coating L3, 4 represents current collector, 5 represents negative electrode material single particle 6, negative electrode material secondary particle 7, conductive agent 8, binder. DETAILED DESCRIPTION

[0033] The examples described below by referring to the accompanying drawings are exemplary and are intended to serve for explaining the present application and cannot be understood as a limitation of the present application.

[0034] Example 1:

[0035] The particle size of the negative electrode artificial graphite single particle is selected as Ds 10 , Ds 50 , Ds 90 , and the particle size of the negative electrode artificial graphite secondary particle is Dd 10 , Dd 50 , Dd 90 . The proportion of the negative electrode particles of each coating satisfies L1: (Dd 10 + Ds 10 ) / (Dd 90 + Ds 90 ) = Gd1 / Gs1 = 0.3.

[0036] L2: ((Dd 90 -Dd 10 )+(Ds 90 -Ds 10 )) / (Dd 50 + Ds 50 ) = Gd2 / Gs2 = 1.2; L3: (Dd 10 + Ds 10 ) / (Dd 90 + Ds 90 ) = Gs3 / Gd3 = 0.3; the proportion of the binder satisfies B1 = 1.2B2 = 1.4B3; the proportion of the conductive agent satisfies C1 = 1.2C2 = 1.4C3. The proportion of the binder in the L1 coating is B1 = 1.4%, the proportion of the binder in the L2 coating is B2 = 1.16%, and the proportion of the binder in the L3 coating is B3 = 1.0%; the proportion of the conductive agent in the L1 coating is C1 = 1.4%, the proportion of the conductive agent in the L2 coating is C2 = 1.16%, and the proportion of the conductive agent in the L3 coating is C3 = 1.0%; the proportion of the single particle in the L1 coating is Gs1 = 74.84%, and the proportion of the secondary particle is Gd1 = 22.36%; the proportion of the single particle in the L2 coating is Gs2 = 43.96%, and the proportion of the secondary particle is Gd2 = 53.72%; the proportion of the single particle in the L3 coating is Gs3 = 22.54%, and the proportion of the secondary particle is Gd3 = 75.46%;

[0037] Comparative Example 1:

[0038] The negative electrode has only one coating layer, and the negative electrode artificial graphite particles are single and secondary particles mixed. The proportion of the binder is B = 1.19%, the proportion of the conductive agent is C = 1.19%, the proportion of the single particles is Gs = 47.11%, and the proportion of the secondary particles is Gd = 50.51%.

[0039] The total coating layer (L1+L2+L3) surface density of the example is equal to the surface density of the comparative example. Therefore, it can be known that the total amount of single particles, secondary particles, conductive agent and binder of the negative electrode of the example and the comparative example is consistent.

[0040] A ternary cell with a model number of 6575115 and a capacity of 6 Ah is prepared. The positive electrode sheet, the separator, the electrolyte and the like are conventional materials. The example uses a new type of coated negative electrode sheet, and the comparative example uses a conventional coated negative electrode sheet, and the remaining materials are the same. The performance of the example 1 and the comparative example 1 battery is tested, and the performance comparison is shown in the following table 1.

[0041] Table 1

[0042]

[0043] From the comparison of the example 1 and the comparative example 1, it can be seen that the battery made of the new type of negative electrode sheet of the application has better electrical performance and cycle than the battery made of the ordinary negative electrode sheet.

[0044] Example 2:

[0045] The particle size of the negative electrode artificial graphite single particle is Ds 10 , Ds 50 , and Ds 90 , and the particle size of the negative electrode artificial graphite secondary particle is Dd 10 , Dd 50 , and Dd 90 . The proportion of the negative electrode particles of each coating layer satisfies L1: (Dd 10 + Ds 10 ) / (Dd 90 + Ds 90 ) = Gd1 / Gs1 = 0.4;

[0046] L2: ((Dd 90 -Dd 10 ) + (Ds 90 -Ds 10 )) / (Dd 50 + Ds 50 ) = Gd2 / Gs2 = 0.93; L3: (Dd 10 + Ds 10 ) / (Dd 90 + Ds 90) = Gs3 / Gd3 = 0.4; the binder ratio satisfies B1 = 1.22B2 = 1.35B3; the conductive agent ratio satisfies C1 = 1.22C2 = 1.35C3. The binder ratio in the L1 coating is B1 = 1.35%, the binder ratio in the L2 coating is B2 = 1.22%, and the binder ratio in the L3 coating is B3 = 1.0%; the conductive agent ratio in the L1 coating is C1 = 1.35%, the conductive agent ratio in the L2 coating is C2 = 1.22%, and the conductive agent ratio in the L3 coating is C3 = 1.0%; the single particle ratio in the L1 coating is Gs1 = 69.05%, and the secondary particle ratio is Gd1 = 27.80%; the single particle ratio in the L2 coating is Gs2 = 50.55%, and the secondary particle ratio is Gd2 = 47.01%; the single particle ratio in the L3 coating is Gs3 = 28.00%, and the secondary particle ratio is Gd3 = 70.00%;

[0047] Comparative Example 2:

[0048] The negative electrode has only one coating, and the negative electrode artificial graphite particles are a mixture of single and secondary particles. The binder ratio is B = 1.19%, the conductive agent ratio is C = 1.19%, the single particle ratio is Gs = 49.35%, and the secondary particle ratio is Gs = 48.27%.

[0049] The total surface density of the coating (L1 + L2 + L3) of the example is equal to the surface density of the comparative example. Therefore, it can be known that the total amount of single particles, secondary particles, conductive agents, and binders of the negative electrode of the example and the comparative example is consistent.

[0050] A ternary cell with a model number of 6575115 and a capacity of 6 Ah is prepared. The positive electrode sheet, the separator, the electrolyte, and the like are conventional materials. The example uses a new type of coated negative electrode sheet, and the comparative example uses a conventional coated negative electrode sheet, and the remaining materials are the same. The performance of the batteries of Example 2 and Comparative Example 2 is tested, and the performance comparison is shown in Table 2 below.

[0051] Table 2

[0052]

[0053] From the comparison of Example 2 and Comparative Example 2, it can be seen that the battery made of the new type of negative electrode sheet of the present patent has a greater improvement in electrical performance and cycle than the battery made of the ordinary negative electrode sheet.

[0054] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are contained in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0055] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and the person skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A battery negative electrode sheet, characterized in that, The battery negative electrode includes: Coating L1 near the current collector, The intermediate coating L2 immediately adjacent to coating L1, and The outermost coating is L3. The coatings L1, L2 and L3 each contain single particles of negative electrode material, secondary particles of negative electrode material, binder and conductive agent. The proportion of negative electrode single particles in the coating L1 is G. s1 The proportion of secondary particles of the negative electrode material in the coating L1 is G. d1 The proportion of binder in coating L1 is B1, the proportion of conductive agent in coating L1 is C1, and the proportion of single particles of negative electrode material in coating L2 is G. s2 The proportion of secondary particles of the negative electrode material in the coating L2 is G. d2 The proportion of binder in coating L2 is B2, the proportion of conductive agent in coating L2 is C2, and the proportion of single particles of negative electrode material in coating L3 is G. s3 The proportion of secondary particles of the negative electrode material in the coating L3 is G. d3 The proportion of binder in coating L3 is B3, and the proportion of conductive agent in coating L3 is C3, wherein G s1 +G d1 +B1+C1=100%, G s2 +G d2 +B² + C² = 100%, G s3 +G d3 +B3+C3=100%; The D of the single particles of the negative electrode material in the coating L1 10 D 50 D 90 Ds 10 ’ 、Ds 50 ’ 、Ds 90 ’ The secondary particles of the negative electrode material in the coating L1 have a D 10 D 50 D 90 Dd 10 ’ 、Dd 50 ’ 、Dd 90 ’ The ratio of primary particles to secondary particles of the negative electrode material in the coating L1 is (Dd) 10 ’ +Ds 10 ’ ) / (Dd 90 ’ +Ds 90 ’ )=G d1 / G s1 ; The proportions of the adhesive are B1 = (1.1~1.3)B2 = (1.3~1.5)B3; The ratio of the conductive agent is C1=(1.1~1.3)C2=(1.3~1.5)C3.

2. The battery negative electrode sheet according to claim 1, characterized in that, The negative electrode material in the single particles and secondary particles of the negative electrode material is selected from artificial graphite, hard carbon, or soft carbon.

3. The battery negative electrode sheet according to claim 1, characterized in that, The adhesive is selected from polyacrylic acid or synthetic rubber.

4. The battery negative electrode sheet according to claim 1, characterized in that, The conductive agent is selected from KS-6, carbon black, carbon nanotubes, or graphene.

5. The battery negative electrode sheet according to claim 4, characterized in that, The carbon black is SP.

6. The battery negative electrode sheet according to claim 1, characterized in that, The D of the single particles of the negative electrode material in the coating L2 10 D 50 D 90 Ds 10 ’’ 、Ds 50 ’’ 、Ds 90 ’’ The D of the secondary particles of the negative electrode material in the coating L2 10 D 50 D 90 Dd 10 ’’ 、Dd 50’’ 、Dd 90 ’’ The ratio of primary particles to secondary particles of the negative electrode material in the coating L2 is (Dd) 90 ’’ -Dd 10 ’’ )+(Ds 90 ’’ -Ds 10 ’’ )) / (Dd 50 ’’ +Ds 50 ’’ )=G d2 / G s2 .

7. The battery negative electrode sheet according to claim 1, characterized in that, The D of the single particles of the negative electrode material in the coating L3 10 D 50 D 90 Ds 10 ’’’ 、Ds 50 ’’’ 、Ds 90 ’’’ The D of the secondary particles of the negative electrode material in the coating L3 10 D 50 D 90 Dd 10 ’’’ 、Dd 50 ’’’ 、Dd 90 ’’’ The ratio of primary particles to secondary particles of the negative electrode material in the coating L3 is (Dd) 10 ’’’ +Ds 10 ’’’ ) / (Dd 90 ’’’ +Ds 90 ’’’ )=G s3 / G d3 .

8. A battery, characterized in that, The battery includes the negative electrode sheet as described in any one of claims 1-7.

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