Lithium ion battery and gradient lithium ion battery negative pole piece thereof

Abstract

The invention provides a lithium ion battery and a gradient lithium ion battery negative pole piece thereof, and belongs to the technical field of lithium ion batteries. The negative pole piece of the lithium ion battery is provided with three active layers, namely an inner layer, a middle layer and an outer layer, the active component I of the inner layer, the active component II of the middle layer and the active component III of the outer layer are respectively and independently selected from any one of natural graphite, artificial graphite and porous carbon; the active component I of the inner layer, the active component II of the middle layer and the active component III of the outer layer are different. According to the gradient negative pole piece, the inner layer is made of natural graphite, the middle layer is made of artificial graphite, and the outer layer is made of a porous carbon material; and the outer layer uses low compaction, the inner layer uses high compaction, and the gradient negative pole piece design is beneficial to construction of ion and electron rapid channels, and when the gradient negative pole piece is applied to the lithium battery, the functions of high energy density and rapid charging are considered.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery and a gradient lithium ion battery negative electrode sheet. Background Art

[0002] Lithium-ion batteries are secondary battery systems that use two different lithium-intercalation compounds that can reversibly intercalate and deintercalate lithium ions as positive and negative electrodes. Due to their advantages such as high specific capacity, long cycle life, and low self-discharge, they are widely used in mobile phones, portable computers, camcorders, cameras, and other fields. Large-capacity lithium-ion batteries are already used in electric vehicles. In addition, the application of lithium-ion batteries is also expanding to fields such as artificial satellites, aerospace, and energy storage. Lithium-ion batteries may become one of the main power sources in the 21st century. However, there are still problems such as insufficient battery life and low energy density. With the rapid development of society, people are more pursuing lithium-ion batteries that combine high energy density and fast charging. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, the present invention proposes a lithium-ion battery negative electrode plate, a lithium-ion battery, and a method for preparing the same. In contrast to existing graphite materials, the present invention's negative electrode plate design utilizes natural graphite in the inner layer, artificial graphite in the middle layer, and a porous carbon material in the outer layer. Furthermore, the outer layer is compacted at low density, while the inner layer is compacted at high density. This gradient negative electrode plate design facilitates the formation of fast pathways for ions and electrons, enabling its application in lithium batteries to achieve both high energy density and fast charging.

[0004] The present invention provides a negative electrode plate for a lithium-ion battery, comprising a substrate and three active layers composited on the substrate: an inner layer, a middle layer, and an outer layer; the active ingredient I in the inner layer, the active ingredient II in the middle layer, and the active ingredient III in the outer layer are each independently selected from any one of natural graphite, artificial graphite, and porous carbon; the active ingredient I in the inner layer, the active ingredient II in the middle layer, and the active ingredient III in the outer layer are all different;

[0005] As a preferred technical solution, the surface density of the inner layer, middle layer and outer layer of the negative electrode plate is (preferably with a gradient surface density): the surface density of the inner layer accounts for 40% to 45% of the total surface density of the three layers; the surface density of the middle layer accounts for 40% to 45% of the total surface density of the three layers; the surface density of the outer layer accounts for 10% to 20% of the total surface density of the three layers.

[0006] As a preferred technical solution, the surface density of the inner layer is 127.2 to 143.1 g / m 2 .

[0007] As a preferred technical solution, the surface density of the middle layer is 127.2~143.1g / m 2 .

[0008] As a preferred technical solution, the surface density of the outer layer is 31.8 to 63.6 g / m 2 .

[0009] The gradient negative electrode sheet of the present invention is suitable for thick coating, and the total thickness of the three active layers is ≥200 μm, and the thickness of each layer depends on the surface density of each layer.

[0010] As a preferred technical solution, the components of the inner layer, middle layer and outer layer are independently selected from the following materials, calculated by weight percentage:

[0011] Natural graphite or artificial graphite or porous carbon: 96.5% to 97%;

[0012] Conductive carbon black 0.4% to 1.0%;

[0013] Sodium carboxymethyl cellulose 0.1% to 0.4%;

[0014] Styrene-butadiene rubber 0.3% to 0.5%;

[0015] Sodium polyacrylate 1.2%~1.7%.

[0016] As a preferred technical solution, the inner layer uses natural graphite, the middle layer uses artificial graphite, and the outer layer is a porous carbon material.

[0017] As a preferred technical solution, the characteristics of the porous carbon are: 2<specific surface area<4m 2 / g, 0.5<pore volume<1cm 3 / g.

[0018] As a preferred technical solution, the binder in the component raw materials can be selected from two or three of PAA sodium polyacrylate, CMC carboxymethyl cellulose, and SBR styrene-butadiene rubber.

[0019] The positive electrode of lithium-ion batteries is lithium iron phosphate positive electrode material.

[0020] The present invention also provides a method for preparing the negative electrode sheet of any of the above-mentioned lithium-ion batteries.

[0021] (1) Mixing the component raw materials of the inner layer to obtain an inner layer slurry; coating the inner layer slurry on a substrate (preferably copper foil) according to the surface density, drying, and rolling to obtain an electrode A;

[0022] (2) Mixing the component raw materials of the middle layer to obtain a middle layer slurry; applying the middle layer slurry to the pole piece A according to the surface density, drying, and rolling to obtain the pole piece B;

[0023] (3) Mixing the component raw materials of the outer layer to obtain an outer layer slurry; applying the outer layer slurry to the electrode B according to the surface density, drying, and rolling to obtain the negative electrode.

[0024] The present invention also provides a lithium-ion battery comprising any one of the above-mentioned negative electrode sheets.

[0025] The present invention uses a multi-layer gradient negative electrode sheet to replace the traditional negative electrode sheet, which can construct a fast channel for ions and electrons, achieve fast charging and high energy density, and thus achieve long cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 , schematic diagram of the gradient negative electrode sheet of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to specific examples, but they do not constitute any limitation to the present invention.

[0028] The sources of the instruments and materials used in the examples and comparative examples of the present invention are as follows:

[0029] Artificial graphite, Shangtai ST-174;

[0030] Conductive carbon black, super-high, Super-li;

[0031] Sodium polyacrylate, Indile, 136D;

[0032] Sodium carboxymethylcellulose, Daicel, BH2000;

[0033] Styrene butadiene rubber, Ruiong, 451B;

[0034] Porous carbon, Baisige, YTHC330, specific surface area 3.9m 2 / g, pore volume 0.9cm 3 / g;

[0035] Example 1

[0036] Preparation of gradient negative electrode sheet and lithium ion battery, including the following steps:

[0037] (1) According to the mass percentage, 96.5% of natural graphite, 1.0% of SP (conductive carbon black), 1.7% of PAA (sodium polyacrylate), 0.4% of CMC (sodium carboxymethyl cellulose), and 0.4% of SBR (styrene-butadiene rubber) were weighed and placed in a stirring tank in sequence, stirred for 4 h, and then slowly stirred (20 r / min) and vacuumed for defoaming for 30 min to obtain slurry A; slurry A was prepared at a surface density of 130 g / m 2 Coated on the bare copper foil, dried (85℃, 5min), according to 1.7~1.8g / cm 3 The compaction density is rolled to obtain pole piece A;

[0038] (2) According to the mass percentage, 96.5% of artificial graphite, 1.0% of SP, 1.7% of PAA, 0.4% of CMC, and 0.4% of SBR were weighed and placed in a stirring tank in sequence and stirred for 4 hours, then slowly stirred (20 r / min) and vacuumed for defoaming for 30 minutes to obtain slurry B; slurry B was prepared at a surface density of 130 g / m 2 Coated on the electrode A, dried (85℃, 5min), according to 1.4~1.7g / cm 3 The compaction density is further rolled to obtain pole piece B;

[0039] (3) According to the mass percentage, 96.5% of porous carbon, 1.0% of SP, 1.7% of PAA, 0.4% of CMC, and 0.4% of SBR were weighed and placed in a stirring tank in sequence and stirred for 4 hours, then slowly stirred (20 r / min) and vacuumed for defoaming for 30 minutes to obtain slurry C; slurry C was prepared at a surface density of 32 g / m 2 Coated on the electrode B, dried (85℃, 5min), according to 1.0~1.2g / cm 3 The compaction density was rolled to obtain the electrode C; the electrode C was cut and used as the negative electrode, and the negative electrode, separator (PP), electrolyte and lithium iron phosphate positive electrode were assembled into a lithium-ion full battery for cycle testing. The electrolyte was 1MLiPF6 + solvent EC:DEC:DMC=3:4:3 for cycle testing.

[0040] Comparative Example 1

[0041] The preparation of the negative electrode sheet and the lithium-ion battery includes the following steps:

[0042] (1) According to the mass percentage, 96.5% natural graphite, 1.0% SP, 1.7% PAA, 0.4% CMC, and 0.4% SBR were weighed and placed in a stirring tank in sequence and stirred for 4 hours, then slowly stirred (20 r / min) and vacuumed for defoaming for 30 minutes to obtain slurry A; slurry A was prepared at a surface density of 130 g / m 2 Coated on the bare copper foil, dried (85℃, 5min), according to 1.7~1.8g / cm 3 The compaction density is rolled to obtain pole piece A;

[0043] (2) According to the mass percentage, 96.5% natural graphite, 1.0% SP, 1.7% PAA, 0.4% CMC, and 0.4% SBR were weighed and placed in a stirring tank in sequence and stirred for 4 hours, then slowly stirred (20 r / min) and vacuumed for defoaming for 30 minutes to obtain slurry B; slurry B was prepared at a surface density of 130 g / m 2Coated on the electrode A, dried (85℃, 5min), according to 1.4~1.7g / cm 3 The compaction density is rolled to obtain pole piece B;

[0044] (3) According to the mass percentage, 96.5% of artificial graphite, 1.0% of SP, 1.7% of PAA, 0.4% of CMC, and 0.4% of SBR were weighed and placed in a stirring tank in sequence and stirred for 4 hours, then slowly stirred (20 r / min) and vacuumed for defoaming for 30 minutes to obtain slurry C; slurry C was prepared at a surface density of 32 g / m 2 The battery was coated on the electrode B, dried (85°C, 5 min), and then rolled at a compaction ratio of 1.0 to 1.2 to obtain the electrode C. The electrode C was cut and used as the negative electrode. The negative electrode, separator (PP), electrolyte and lithium iron phosphate positive electrode were assembled into a lithium-ion full battery for cycle testing. The electrolyte was 1MLiPF6 + solvent EC:DEC:DMC = 3:4:3 for cycle testing.

[0045] Comparative Example 2

[0046] The preparation of the negative electrode sheet and the lithium-ion battery includes the following steps:

[0047] (1) According to the mass percentage, 96.5% natural graphite, 1.0% SP, 1.7% PAA, 0.4% CMC, and 0.4% SBR were weighed and placed in a stirring tank in sequence and stirred for 4 hours, then slowly stirred (20 r / min) and vacuumed for defoaming for 30 minutes to obtain slurry A; slurry A was prepared at a surface density of 130 g / m 2 Coated on the bare copper foil, dried (85℃, 5min), according to 1.7~1.8g / cm 3 The compaction density is rolled to obtain pole piece A;

[0048] (2) According to the mass percentage, 96.5% of artificial graphite, 1.0% of SP, 1.7% of PAA, 0.4% of CMC, and 0.4% of SBR were weighed and placed in a stirring tank in sequence and stirred for 4 hours, then slowly stirred (20 r / min) and vacuumed for defoaming for 30 minutes to obtain slurry B; slurry B was prepared at a surface density of 130 g / m 2 Coated on the electrode A, dried (85℃, 5min), according to 1.4~1.7g / cm 3 The compaction density is rolled to obtain pole piece B;

[0049] (3) According to the mass percentage, 96.5% of artificial graphite, 1.0% of SP, 1.7% of PAA, 0.4% of CMC, and 0.4% of SBR were weighed and placed in a stirring tank in sequence and stirred for 4 hours, then slowly stirred (20 r / min) and vacuumed for defoaming for 30 minutes to obtain slurry C; slurry C was prepared at a surface density of 32 g / m 2 Coated on the electrode B, dried (85℃, 5min), according to 1.0~1.2g / cm 3 The compaction density was rolled to obtain the electrode C; the electrode C was cut and used as the negative electrode, and the negative electrode, separator (PP), electrolyte and lithium iron phosphate positive electrode were assembled into a lithium-ion full battery for cycle testing. The electrolyte was 1MLiPF6 + solvent EC:DEC:DMC=3:4:3 for cycle testing.

[0050] Comparative Example 3

[0051] The preparation of the negative electrode sheet and the lithium-ion battery includes the following steps:

[0052] (1) According to the mass percentage, 96.5% natural graphite, 1.0% SP, 1.7% PAA, 0.4% CMC, and 0.4% SBR were weighed and placed in a stirring tank in sequence and stirred for 4 hours, then slowly stirred (20 r / min) and vacuumed for defoaming for 30 minutes to obtain slurry A; slurry A was prepared at a surface density of 130 g / m 2 Coated on the bare copper foil, dried (85℃, 5min), according to 1.7~1.8g / cm 3 The compaction density is rolled to obtain pole piece A;

[0053] (2) According to the mass percentage, 96.5% natural graphite, 1.0% SP, 1.7% PAA, 0.4% CMC, and 0.4% SBR were weighed and placed in a stirring tank in sequence and stirred for 4 hours, then slowly stirred (20 r / min) and vacuumed for defoaming for 30 minutes to obtain slurry B; slurry B was prepared at a surface density of 130 g / m 2 Coated on the electrode A, dried (85℃, 5min), according to 1.4~1.7g / cm 3 The compaction density is rolled to obtain pole piece B;

[0054] (3) According to the mass percentage, 96.5% natural graphite, 1.0% SP, 1.7% PAA, 0.4% CMC, and 0.4% SBR were weighed and placed in a stirring tank in sequence and stirred for 4 hours, then slowly stirred (20 r / min) and vacuumed for defoaming for 30 minutes to obtain slurry C; slurry C was prepared at a surface density of 32 g / m 2Coated on the electrode B, dried (85℃, 5min), according to 1.0~1.2g / cm 3 The compaction density was rolled to obtain the electrode C; the electrode C was cut and used as the negative electrode, and the negative electrode, separator (PP), electrolyte and lithium iron phosphate positive electrode were assembled into a lithium-ion full battery for cycle testing. The electrolyte was 1MLiPF6 + solvent EC:DEC:DMC=3:4:3 for cycle testing.

[0055] Comparative Example 4

[0056] The preparation of the negative electrode sheet and the lithium-ion battery includes the following steps:

[0057] (1) According to the mass percentage, 96.5% artificial graphite, 1.0% SP, 1.7% PAA, 0.4% CMC, and 0.4% SBR were weighed and placed in a stirring tank in sequence and stirred for 4 hours, then slowly stirred (20 r / min) and vacuumed for defoaming for 30 minutes to obtain slurry A; slurry A was prepared at a surface density of 130 g / m 2 Apply on the bare copper foil, after drying, according to 1.7 ~ 1.8g / cm 3 The compaction density is rolled to obtain pole piece A;

[0058] (2) According to the mass percentage, 96.5% of artificial graphite, 1.0% of SP, 1.7% of PAA, 0.4% of CMC, and 0.4% of SBR were weighed and placed in a stirring tank in sequence and stirred for 4 hours, then slowly stirred (20 r / min) and vacuumed for defoaming for 30 minutes to obtain slurry B; slurry B was prepared at a surface density of 130 g / m 2 Coated on the electrode A, dried (85℃, 5min), according to 1.4~1.7g / cm 3 The compaction density is rolled to obtain pole piece B;

[0059] (3) According to the mass percentage, 96.5% of artificial graphite, 1.0% of SP, 1.7% of PAA, 0.4% of CMC, and 0.4% of SBR were weighed and placed in a stirring tank in sequence and stirred for 4 hours, then slowly stirred (20 r / min) and vacuumed for defoaming for 30 minutes to obtain slurry C; slurry C was prepared at a surface density of 32 g / m 2 Coated on the electrode B, dried (85℃, 5min), according to 1.0~1.2g / cm 3 The compaction density was rolled to obtain the electrode C; the electrode C was cut and used as the negative electrode, and the negative electrode, separator (PP), electrolyte and lithium iron phosphate positive electrode were assembled into a lithium-ion full battery for cycle testing. The electrolyte was 1MLiPF6 + solvent EC:DEC:DMC=3:4:3 for cycle testing.

[0060] Test Example 1

[0061] The lithium-ion full batteries assembled in Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Comparative Example 5 were subjected to electrical performance tests at 25 degrees Celsius and 1C / 1C cycles using BlueDian software. The test results are shown in Table 1.

[0062] Table 1

[0063]

[0064] Natural graphite has higher gram capacity and compaction, but natural graphite has higher compatibility requirements with the electrolyte and poor cycling performance; artificial graphite has advantages over natural graphite in rate and cycling performance, and porous carbon can provide a rapid ion transport channel, but has lower compaction. The present invention combines the advantages and disadvantages of the three to prepare a gradient negative electrode sheet and apply it to lithium-ion batteries.

[0065] The results in Table 1 show that compared with the negative electrode sheets of Comparative Examples 1-4, the lithium-ion battery using a multi-layer gradient negative electrode sheet in Example 1 of the present invention can construct fast channels for ions and electrons, achieve fast charging and high energy density, and thus realize long cycle.

[0066] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation of the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A lithium-ion battery negative electrode plate, characterized in that: The negative electrode plate comprises a substrate and three active layers: an inner layer, a middle layer and an outer layer; The active ingredient I of the inner layer, the active ingredient II of the middle layer, and the active ingredient III of the outer layer are each independently selected from any one of natural graphite, artificial graphite, and porous carbon; The active ingredient I in the inner layer, the active ingredient II in the middle layer and the active ingredient III in the outer layer are all different.

2. The negative electrode plate of a lithium-ion battery according to claim 1, characterized in that: areal density of the inner layer, middle layer and outer layer of the negative electrode sheet; The surface density of the inner layer accounts for 40% to 45% of the total surface density of the three layers; The surface density of the middle layer accounts for 40% to 45% of the total surface density of the three layers; The surface density of the outer layer accounts for 10 to 20% of the total surface density of the three layers.

3. The negative electrode plate of a lithium-ion battery according to claim 1 or 2, characterized in that: The surface density of the inner layer is 127.2 to 143.1 g / m 2 .

4. The negative electrode plate for a lithium-ion battery according to claim 1, 2 or 3, wherein: The surface density of the middle layer is 127.2 to 143.1 g / m 2 .

5. The negative electrode plate for a lithium-ion battery according to any one of claims 1 to 4, characterized in that: The surface density of the outer layer is 31.8 to 63.6 g / m 2 .

6. The negative electrode plate for a lithium-ion battery according to any one of claims 1 to 5, characterized in that: Calculated by weight percentage, the component raw materials of the inner layer, middle layer and outer layer independently include: Active ingredient: 96.5% to 97%, wherein the active ingredient is selected from natural graphite, artificial graphite or porous carbon; Conductive carbon black 0.4% to 1.0%; Sodium carboxymethyl cellulose 0.1% to 0.4%; Styrene-butadiene rubber 0.3% to 0.5%; Sodium polyacrylate 1.2%~1.7%.

7. The negative electrode plate for a lithium-ion battery according to any one of claims 1 to 6, characterized in that: 2m 2 / g<the specific surface area of the porous carbon<4m 2 / g,0.5cm 3 / g<the pore volume of the porous carbon<1cm 3 / g.

8. The method for preparing a negative electrode sheet for a lithium-ion battery according to any one of claims 1 to 7, characterized in that: (1) Mixing the component raw materials of the inner layer to obtain an inner layer slurry; applying the inner layer slurry to the substrate according to the surface density, drying, and rolling to obtain an electrode A; (2) Mixing the component raw materials of the middle layer to obtain a middle layer slurry; applying the middle layer slurry to the pole piece A according to the surface density, drying, and rolling to obtain the pole piece B; (3) Mixing the component raw materials of the outer layer to obtain an outer layer slurry; applying the outer layer slurry to the electrode B according to the surface density, drying, and rolling to obtain the negative electrode.

9. The preparation method according to claim 8, characterized in that In step (1), the compaction density of the inner layer is 1.7 to 1.8 g / cm 3 ; In step (2), the compaction density of the middle layer is 1.4 to 1.7 g / cm 3 ; In step (3), the compaction density of the outer layer is 1.0 to 1.2 g / cm 3 .

10. A lithium-ion battery comprising the negative electrode sheet of a lithium-ion battery according to any one of claims 1 to 7 or the negative electrode sheet of a lithium-ion battery obtained by the preparation method of any one of claims 8 or 9.

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