CN114649500A - Negative pole piece, electrochemical device and electronic equipment - Google Patents

Abstract

The present application relates to the technical field of batteries, and particularly discloses a negative electrode pole piece, an electrochemical device and an electronic device, including a current collector and a negative electrode active material layer. The negative electrode active material layer is arranged on the current collector, the negative electrode active material layer includes a first active material layer and a second active material layer, the first active material layer is arranged on the current collector, the The first active material layer is located between the current collector and the second active material layer, wherein the porosity of the second active material layer is P ₂ , and the porosity of the first active material layer is P ₁ , the porosity P ₂ of the second active material layer satisfies: 20%≦P ₂ ≦26%, and 0.8≦P ₂ /P ₁ ≦1.6. In the above manner, the embodiments of the present application can reduce the capacitance and power loss on the electrode of the lithium ion battery.

Description

Negative pole piece, electrochemical device and electronic equipment

technical field

The present application relates to the field of battery technology, and in particular, to a negative electrode plate, an electrochemical device and an electronic device.

Background technique

At present, with the continuous advancement of science and technology, the application field of lithium-ion batteries has also expanded rapidly, from the initial portable mobile devices such as mobile phones and cameras to large electric devices with high power and high energy requirements such as electric bicycles and electric vehicles. Therefore, the requirements for the design and manufacturing process of lithium-ion batteries are getting higher and higher. Among them, the electrode material on the negative pole piece in the lithium ion battery reacts with the electrolyte at the solid-liquid phase interface to form a passivation layer covering the surface of the electrode material, and the passivation layer can be used for free insertion and extraction of lithium ions. , Therefore, the passivation layer is called a solid electrolyte interface film (solid electrolyte interface), referred to as SEI film.

In the process of realizing the present application, the inventors of the embodiments of the present application found that the SEI film formed on the negative electrode plate is prone to metal deposition, which leads to the blockage of the pores of the SEI film, and further causes the low capacity retention rate of the upper electrode of the lithium ion battery. And the power loss is serious, so that the cycle performance of the lithium ion battery is poor and the service life of the lithium ion battery is not long.

SUMMARY OF THE INVENTION

In view of the above problems, the embodiments of the present application provide a negative pole piece, an electrochemical device and an electronic device, which improve the low capacity retention rate of the upper electrode of the above-mentioned lithium ion battery, thereby resulting in poor cycle performance of the lithium ion battery and Lithium-ion batteries do not have a long service life.

According to an aspect of the embodiments of the present application, a negative electrode pole piece is provided, the negative electrode pole piece includes a current collector and a negative electrode active material layer, the negative electrode active material layer is disposed on the current collector, and the negative electrode active material layer It includes a first active material layer and a second active material layer, the first active material layer is arranged on the current collector, and the first active material layer is located between the current collector and the second active material layer The porosity of the second active material layer is P ₂ , the porosity of the first active material layer is P ₁ , and the porosity P ₂ of the second active material layer satisfies: 20%≤P ₂ ≤ 26%, and 0.8 ≤ P ₂ /P ₁ ≤ 1.6. In this way, the metal deposition of the SEI film formed on the negative pole piece can be reduced, so that the phenomenon that the pores of the SEI film are blocked.

In an optional manner, the porosity P ₂ of the second active material layer is greater than the porosity P ₁ of the first active material layer, and 1.1≦P ₂ /P ₁ ≦1.4. This setting can ensure that during the cycle of the battery, the porosity P2 of the _second active material layer is gradually reduced due to the continuous de-intercalation of lithium from the first active material layer/second active material layer on the negative pole piece. , and the porosity P1 of the _first active material layer gradually increases, which further improves the capacity retention rate on the battery electrode.

In an optional manner, the porosity P ₁ of the first active material layer satisfies: 16%≦P ₁ ≦24%.

In an optional manner, the first active material layer further includes a first active material, the second active material layer further includes a second active material, and the Dv50 of the second active material is greater than that of the first active material Dv50 of active material.

In an optional manner, the first active material and the second active material comprise graphite.

In an optional manner, the Dv50 of the second active material is greater than the Dv50 of the first active material.

In an optional manner, the Dv50 of the first active material ranges from 2.9 μm to 3.3 μm, and the Dv50 of the second active material ranges from 3.3 μm to 3.7 μm.

In an optional manner, along the thickness direction of the negative electrode pole piece, the thicknesses of the first active material layer and the second active material layer respectively account for 50% of the total thickness of the negative electrode active material layer.

According to another aspect of the embodiments of the present application, an electrochemical device is provided, and the electrochemical device includes the negative electrode plate as described above.

According to another aspect of the embodiments of the present application, there is provided an electronic device including the electrochemical device as described above.

The beneficial effects of the embodiments of the present application are: different from the situation in the prior art, the embodiments of the present application are provided with a current collector and a negative electrode active material layer, and the negative electrode active material layer is provided on the current collector. Wherein, the negative electrode active material layer includes a first active material layer and a second active material layer, the first active material layer is disposed on the current collector, and the second active material layer is disposed on the first active material layer on the material layer, and the first active material layer is located between the current collector and the second active material layer. In addition, the porosity of the second active material layer is P ₂ , the porosity of the first active material layer is P ₁ , and 0.8≦P ₂ /P ₁ ≦1.6. In this way, the SEI film formed by the first active material layer and the second active material layer can reduce metal deposition and block the pores of the SEI film, thereby reducing the capacitance and power loss on the electrode of the lithium ion battery, and improving the cycle performance of the lithium ion battery. and extend the life of lithium-ion batteries.

Description of drawings

In order to illustrate the specific embodiments of the present application or the technical solutions in the prior art more clearly, the following briefly introduces the drawings that are required to be used in the description of the specific embodiments or the prior art. Similar elements or parts are generally identified by similar reference numerals throughout the drawings. In the drawings, each element or section is not necessarily drawn to actual scale.

Fig. 1 is the overall structure side view of the negative pole piece of the embodiment of the present application;

2 is another side view of the overall structure of the negative pole piece of the embodiment of the present application;

Fig. 3 is the microstructure side view of the negative electrode pole piece of the embodiment of the present application;

Fig. 4 is another microstructure side view of the negative pole piece of the embodiment of the present application;

FIG. 5 is a schematic structural diagram of an electronic device according to an embodiment of the present application.

Detailed ways

In order to facilitate the understanding of the present application, the present application will be described in more detail below with reference to the accompanying drawings and specific embodiments. It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element, or one or more intervening elements may be present therebetween. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or one or more intervening elements may be present therebetween. The terms "vertical", "horizontal", "left", "right" and similar expressions used in this specification are for illustrative purposes only.

Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the technical field belonging to this application. The terms used in this specification are for the purpose of describing specific embodiments only, and are not used to limit the application. As used in this specification, the term "and/or" includes any and all combinations of one or more of the associated listed items.

In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict with each other.

Referring to FIG. 1 , the negative electrode pole piece 100 includes a current collector 101 and a negative electrode active material layer 102 . The current collector 101 has a first surface 1011 and a second surface 1012 opposite to the first surface 1011 , and the anode active material layer 102 is disposed on the first surface 1011 /second surface 1012 of the current collector 101 . The current collector 101 , the negative electrode active material layer 102 , and the case where the negative electrode active material layer 102 is located on the first surface 1011 of the current collector 101 will be specifically described below.

For the above-mentioned negative electrode active material layer 102 , as shown in FIGS. 1 and 2 , the negative electrode active material layer 102 includes a first active material layer 1021 and a second active material layer 1022 . The first active material layer 1021 is disposed on the current collector 101, the second active material layer 1022 is disposed on the first active material layer 1021, and the first active material layer 1021 is located on the current collector 101 and the second active material layer 1022 between. In addition, in order to reduce the metal deposition of the SEI film formed on the negative pole piece, thereby causing the phenomenon of blocking the pores of the SEI film, the porosity of the second active material layer 1022 is P2, the porosity of the first active material layer 1021 is P1, and 0.8≤P2/P1≤1.6. Optionally, the porosity P1 of the first active material layer 1021 satisfies: 16%≤P1≤24%. Optionally, the porosity P2 of the second active material layer 1022 satisfies: 20%≤P2≤26%.

It should be noted that: the pore is the particle spacing of the material, and the porosity P refers to the percentage of the pore volume in the material to the total volume of the material in its natural state. Among them, the porosity P of each layer can be tested by the following method: first, the pole piece is punched into a circular piece with a diameter of 10mm or 14mm, and the surface is flat without gaps, no powder drop, and the number of small discs is greater than 40 pieces. The thickness of the first active material layer and the second active material layer can be obtained from the cross section, and then the two layers of membranes with different porosity are cut according to the thickness of each layer, and then cleaned and dried with dimethyl carbonate, and then replaced by gas. The porosity of different membranes can be obtained by the method of testing.

In some embodiments, as shown in FIG. 3 , the porosity P ₂ of the second active material layer 1022 is greater than the porosity P ₁ of the first active material layer 1021 , and 1.1≦P ₂ /P ₁ ≦1.4. This arrangement can ensure that during the cycle of the battery, the porosity P ₂ of the second active material layer 1022 caused by the continuous de-intercalation of lithium from the first active material layer 1021/second active material layer 1022 on the negative electrode plate is reduced. The problems such as the gradual decrease and the gradual increase of the porosity P1 of the _first active material layer 1021 further improve the capacity retention rate on the battery electrode.

In some embodiments, both the first active material layer 1021 and the second active material layer 1022 include graphite. Optionally, the graphite in the first active material layer 1021 is selected from low-expansion graphite. The low expansion performance is compared with the graphite in the second active material layer 1022, that is, the expansion performance of the graphite in the first active material layer 1021 is lower than that of the graphite in the second active material layer 1022, The lower the expansion performance, the less likely it is to expand under the same conditions. This arrangement is beneficial to reduce the degree of peeling between the first active material layer 1021 on the negative electrode and the current collector 101, thereby improving the cycle stability of the battery.

In some embodiments, as shown in FIG. 4 , the Dv50 of the graphite of the second active material layer 1022 is greater than the Dv50 of the graphite of the first active material layer 1021 . Among them, Dv50 refers to the particle size of the particle size distribution based on the volume, starting from the small particle size and reaching 50% of the volume accumulation (which can be measured using a laser particle size tester). Optionally, the Dv50 of the graphite in the first active material layer 1021 ranges from 2.9 μm to 3.3 μm. Optionally, the Dv50 of the graphite in the second active material layer 1022 ranges from 3.3 μm to 3.7 μm.

In some embodiments, the thicknesses of the first active material layer 1021 and the second active material layer 1022 respectively account for 50% of the total thickness of the negative electrode active material layer 102 along the thickness direction of the negative electrode pole piece.

In addition, in order to facilitate readers to understand the technical effect brought by the performance of the negative pole piece in this technical solution, a comparative test is also carried out in the examples of this application, wherein the negative pole piece, the separator and the positive pole piece are wound in a way of winding Applied to the battery, 11 different negative pole pieces of the present application and 1 negative pole piece of the prior art are selected as the comparative example. Of course, the embodiments of the present application are not limited to this, and the test process is as follows:

Test method of battery discharge rate: at normal temperature (25 degrees Celsius), charge the battery with a constant current of 1.2C to 4.5V, and then charge the battery with a constant voltage of 4.5V to 0.1C, let it stand for 5 minutes, and then use Different rates (0.2C, 0.5C, 1C, 1.5C, 2C) were discharged to 3V at constant current, and the discharge capacity at different rates was recorded. Based on the 0.2C discharge capacity, the discharge capacity ratio at different rates was calculated.

Test method for battery expansion and capacity retention rate: under normal temperature (25 degrees Celsius), charge the battery with a constant current of 1.2C to 4.5V, and then charge the battery with a constant voltage of 4.5V to 0.1C, let it stand for 5 minutes, and then 1.0C constant current discharge to 3V, cycle 1000 cycles under this condition, record the capacity and cell thickness corresponding to 1000 cycles of 1C discharge, and calculate the capacity retention of 1000 cycles based on the discharge capacity of the first cycle and the initial thickness of the cell rate and thickness expansion.

The negative pole piece in the comparative example includes a current collector and a negative active material layer, and the negative active material layer in the comparative example is a single-layer active material layer, or, the two-layer active material layer in the comparative example (the first active material layer and the second active material layer). The porosity ratio range of the active material layer) is different from the porosity ratio range of the two active material layers in the present application.

Example 1

Preparation of positive electrode sheet: The positive active material lithium cobalt oxide, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride are dissolved in an organic solvent N-methylpyrrolidone (NMP) solution in a weight ratio of 97.6:1.3:1.1 In the process, a positive electrode slurry is formed by stirring. Using 9um aluminum foil as the positive electrode current collector, the positive electrode slurry was coated on the positive electrode current collector, the coating weight was 280mg/1540.25mm2, and the positive electrode pole piece was obtained after drying, cold pressing and slitting successively. The thickness is 96um, and the mass density of the active material layer is 4.23g/cm3.

Preparation of negative electrode pole piece: The negative electrode active material graphite, binder styrene-butadiene rubber and dispersant sodium carboxymethyl cellulose are dissolved in deionized water in a weight ratio of 97.8:1:1 to form a negative electrode slurry. Using 6um copper foil as the negative electrode current collector, first coat the first layer of negative electrode slurry on the negative electrode current collector with a coating weight of 80mg/1540.25mm ² to form the first active material layer, and then coat the first layer after drying. Two layers of negative electrode slurry, the weight of the second layer of negative electrode slurry is also 80mg/1540.25mm ² , to form a second active material layer, and then successively dried, cold pressed and cut to obtain a composite negative electrode piece. After cold pressing, the composite negative electrode The thickness of the sheet is 119 um, and the mass density of the active material layer is 1.74 g/cm ³ . The porosity of the second active material layer is different from that of the first active material layer, the porosity of the second active material layer is 20%, the porosity of the first active material layer is 24%, and the porosity ratio of the upper and lower active material layers is 0.8, the Dv50 of the first active material and the second active material are the same, and the Dv50 is 2.9 μm, and both the first active material and the second active material are graphite.

Preparation of isolation film: The isolation film substrate is polyethylene (PE) with a thickness of 8 μm, and 2 μm alumina ceramic layers are coated on both sides of the isolation film substrate, and finally, 2.5 μm alumina ceramic layers are coated on both sides of the coated ceramic layer. mg of binder polyvinylidene fluoride (PVDF), dried.

Preparation of electrolyte: in an environment with a water content of less than 10 ppm, mix lithium hexafluorophosphate with a non-aqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate ( PP): vinylene carbonate (VC) = 20:30:20:28:2, weight ratio) was formulated at a weight ratio of 8:92 to form an electrolyte.

Preparation of lithium ion battery: stack the positive pole piece, the separator and the negative pole piece in order, so that the separator is in the middle of the positive pole piece and the negative pole piece to play a role of isolation, and coil to obtain the electrode assembly. The electrode assembly is placed in the outer packaging aluminum-plastic film, and after dehydration at 80 °C, the above electrolyte is injected and packaged, and the lithium ion battery is obtained through the process of formation, degassing, and trimming.

Example 2

The difference from Example 1 is that the porosity of the second active material layer is 23%, the porosity of the first active material layer is 21%, and the porosity ratio of the upper and lower active material layers is 1.1; same.

Example 3

The difference from Example 1 is that the porosity of the second active material layer is 24%, the porosity of the first active material layer is 20%, and the porosity ratio of the upper and lower active material layers is 1.2; same.

Example 4

The difference from Example 1 is that the porosity of the second active material layer is 25%, the porosity of the first active material layer is 18%, and the porosity ratio of the upper and lower active material layers is 1.4; same.

Example 5

The difference from Example 1 is that the porosity of the second active material layer is 26%, the porosity of the first active material layer is 16%, and the porosity ratio of the upper and lower active material layers is 1.6; same.

Example 6

The difference from Example 1 is that the Dv50 of the second active material is 3.4 μm, and the rest are the same as Example 1.

Example 7

The difference from Example 2 is that the Dv50 of the second active material is 3.4 μm, and the rest is the same as Example 2.

Example 8

The difference from Example 3 is that the Dv50 of the second active material is 3.4 μm, and the rest is the same as Example 3.

Example 9

The difference from Example 4 is that the Dv50 of the second active material is 3.4 μm, and the rest is the same as Example 4.

Example 10

The difference from Example 5 is that the Dv50 of the second active material is 3.4 μm, and the rest are the same as in Example 5.

Example 11

The difference from Example 6 is that the porosity of the first active material layer and the porosity of the second active material layer are both 22%, the porosity ratio of the upper and lower active material layers is 1, and the rest is the same as Example 6.

Comparative Example 1

The difference from Example 1 is that the negative electrode pole piece is coated with a single layer, that is, the negative electrode active material layer is a single layer active material layer, and the negative electrode active material graphite, the binder styrene-butadiene rubber and the dispersant sodium carboxymethyl cellulose are coated. Dissolve in deionized water at a weight ratio of 97.8:1:1 to form a negative electrode slurry. Using copper foil as the negative electrode current collector, the negative electrode slurry was coated on the negative electrode current collector with a coating weight of 160mg/1540.25mm ² , and the negative electrode pole piece was obtained by drying, cold pressing and cutting successively. The sheet thickness is 119 um, the mass density of the active material layer is 4.23 g/cm ³ , the porosity of the single-layer active material layer is 22%, and the active material is graphite with Dv50 of 2.9 μm.

The test results are shown in the following table:

It can be seen from the test data in the table: Examples 1-11 and Comparative Example 1 show that the double-layer coating can significantly improve the cycle performance, and when the void ratio of the second active material layer and the first active material layer is between 1.1 and 1.4 When the rate performance of the battery is significantly improved, the optimal performance can be achieved. In the case where the porosity ratio of the second active material layer and the first active material layer is the same, by adjusting the Dv50 of the active material in the first active material layer and the second active material material layer, the active material in the second active material layer has the same porosity ratio. The Dv50 is greater than the Dv50 of the active material in the first active material layer, so that the discharge rate, capacity retention rate and swelling performance of the battery are further improved.

In the embodiment of the present application, the current collector 101 and the negative electrode active material layer 102 are provided, and the negative electrode active material layer 102 is provided on the current collector 101 . The anode active material layer 102 includes a first active material layer 1021 and a second active material layer 1022, the first active material layer 1021 is disposed on the current collector 101, and the second active material layer 1022 is disposed on the first active material layer 1021 , and the first active material layer 1021 is located between the current collector 101 and the second active material layer 1022 . In addition, the porosity of the second active material layer 1022 is P ₂ , the porosity of the first active material layer 1021 is P ₁ , and 0.8≦P ₂ /P ₁ ≦1.6. In this way, the SEI film formed by the first active material layer 1021 and the second active material layer 1022 can reduce metal deposition and reduce the blockage of the pores of the SEI film, thereby reducing the capacitance and power loss on the electrode of the lithium ion battery, and improving the performance of the lithium ion battery. Cycling performance and extending the life of Li-ion batteries.

The application also provides an embodiment of an electrochemical device, the electrochemical device includes a positive electrode piece, a separator, and the above-mentioned negative electrode piece, the separator is arranged between the positive electrode piece and the negative electrode piece, and the positive electrode The pole piece, the separator and the negative pole piece are wound or stacked in sequence. The function and structure of the negative pole piece can refer to the above-mentioned embodiments, and will not be repeated here. It can be understood that the electrochemical device can be a battery, and the negative electrode sheet can also be applied to other electronic products other than batteries.

The present application also provides an embodiment of an electronic device 2, as shown in FIG. 5, the electronic device includes the electrochemical device as described above, and the function and structure of the electrochemical device can refer to the above-mentioned embodiment, which is not repeated here. One more elaboration.

It should be noted that preferred embodiments of the present application are given in the description of the present application and the accompanying drawings. However, the present application can be implemented in many different forms, and is not limited to the embodiments described in the present specification. These embodiments are not intended as additional limitations to the content of the present application, and are provided for the purpose of making the understanding of the disclosure of the present application more thorough and complete. In addition, the above technical features continue to be combined with each other to form various embodiments not listed above, which are all regarded as the scope of the description of this application; further, for those of ordinary skill in the art, they can be improved or transformed according to the above descriptions , and all these improvements and transformations should belong to the protection scope of the appended claims of this application.

Claims (9)

1. a negative pole piece, comprising: a current collector and a negative electrode active material layer, the negative electrode active material layer is arranged on the current collector, it is characterized in that, The negative electrode active material layer includes a first active material layer and a second active material layer, the first active material layer is disposed on the current collector, and the first active material layer is located on the current collector and the current collector Between the second active material layers, wherein the porosity of the second active material layer is P ₂ , the porosity of the first active material layer is P ₁ , and the porosity of the second active material layer is P ₂ Satisfaction: ₂₀ %≤P2≤26%, and _0.8≤P2 / _P1≤1.6 . 2 . The negative electrode sheet according to claim 1 , wherein the porosity P ₂ of the second active material layer is greater than the porosity P ₁ of the first active material layer, and 1.1≦P ₂ /P ₁ ≦1.4. 3 . The negative pole piece according to claim 1 , wherein the porosity P1 of the first active material layer satisfies: 16%≦P1≦24%. 4 . 4. The negative pole piece according to claim 1, characterized in that, The first active material layer further includes a first active material, the second active material layer further includes a second active material, and the Dv50 of the second active material is greater than the Dv50 of the first active material. 5. The negative pole piece according to claim 4, characterized in that, The first active material and the second active material include graphite. 6 . The negative pole piece according to claim 4 , wherein the Dv50 of the first active material ranges from 2.9 μm to 3.3 μm, and the Dv50 of the second active material ranges from 3.3 μm to 3.7 μm. 7 . 7. The negative pole piece according to claim 1, characterized in that, Along the thickness direction of the negative electrode pole piece, the thicknesses of the first active material layer and the second active material layer respectively account for 50% of the total thickness of the negative electrode active material layer. 8 . An electrochemical device, characterized in that, comprising the negative electrode plate according to any one of claims 1 to 7 . 9. An electronic device, comprising the electrochemical device of claim 8.

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