CN112670670B - Diaphragm for lithium ion battery and preparation method of quick-charging type lithium ion battery - Google Patents
Diaphragm for lithium ion battery and preparation method of quick-charging type lithium ion battery Download PDFInfo
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Abstract
The invention relates to a diaphragm for a lithium ion battery and a preparation method of a quick-charging type lithium ion battery. The diaphragm for the lithium ion battery comprises a diaphragm substrate and a continuous graphite layer positioned on one side surface of the diaphragm substrate, wherein the graphite layer is provided with a plurality of island-shaped structures arranged at intervals, the graphite layer comprises a binder and graphite particles, and the particle size distribution of the graphite particles is that D50 is between 1 and 8 mu m. When the quick-charging lithium ion battery is prepared, one surface of the diaphragm, which is provided with the graphite layer, is attached to the negative pole piece, and the prepared battery core is subjected to hot-pressing compounding under certain pressure and temperature, so that the negative pole piece and the diaphragm are compounded. The technology of the invention can directly achieve the same effect as a double-layer coating process on the pole piece produced by the prior process through a simple hot-pressing composite process, and has no influence on the production capacity and the processing cost.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a diaphragm for a lithium ion battery and a preparation method of a quick-charging type lithium ion battery.
Background
In order to improve the quick charge performance of the ion battery, improvement has been mainly made in terms of a negative electrode containing graphite. In addition, the surface of the current quick-charging electrode is frequently exposedPhenomenon of lithium deposition, in the case where the main cause of lithium deposition is high rate, li is due to polarization + The graphite layer can not be rapidly embedded, so that the lithium precipitation phenomenon is easy to occur on the surface of the negative pole piece. The dynamic performance can be improved by reducing the particle size of graphite and increasing the content of amorphous carbon on the surface, thereby reducing polarization and achieving the improvement of rate capability. However, the power type graphite has the disadvantages of low first efficiency and low gram capacity. Therefore, the energy density is lowered by using such a negative electrode entirely.
In order to overcome the problems, the conventional method generally adopts a double-layer coating method to prepare a negative electrode, wherein the bottom layer is coated with large-particle graphite, and the surface layer is coated with power type graphite. However, when the double-layer coating technology is adopted, a special coating die head needs to be customized, the manufacturing cost is high, and the requirements on the process parameters of coating are strict. If the coating speed needs to be strictly controlled, the problems of narrow processing temperature range, difficult switching between different graphite particles, and the like exist at the same time. The defects reduce the production capacity and improve the processing cost.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a diaphragm for a lithium ion battery and a preparation method of a quick-charging lithium ion battery.
The first object of the invention is to provide a diaphragm for a lithium ion battery, which comprises a diaphragm substrate and a continuous graphite layer positioned on one side surface of the diaphragm substrate, wherein the graphite layer has a plurality of island-shaped structures arranged at intervals, the graphite layer comprises a binder and graphite particles, and the particle size distribution of the graphite particles is D50 between 1 and 8 mu m.
Preferably, the distribution of the graphite particles is between D50 and 5 μm.
Further, the thickness of the graphite layer is 4 to 20 μm, and when the graphite particle size distribution D50 is 3 μm, the optimum thickness is 6 μm. The graphite particles can be sprayed on the surface of the diaphragm substrate by adopting a spraying mode.
Furthermore, the binder accounts for 1-5% of the total weight of the graphite layer, and the graphite particles account for 95-99% of the total weight of the graphite layer. In the graphite layer, graphite particles are uniformly distributed in the binder.
Further, the binder comprises one or more of PVDF (polytetrafluoroethylene), CMC/SBR (sodium carboxymethylcellulose/styrene butadiene rubber), PAA (polyacrylic acid) and PVA. Preferably, the binder is PVDF.
Furthermore, the lithium ion battery separator can also comprise a conductive agent, and the conductive agent accounts for less than 5% of the total weight of the graphite layer.
Further, the conductive agent is selected from carbon black, carbon nanotubes, graphene, and the like.
Furthermore, the diaphragm for the lithium ion battery also comprises a dispersing auxiliary agent, wherein the dispersing auxiliary agent accounts for less than 2% of the total weight of the graphite layer.
Further, PVA (polyvinyl alcohol) is used as the dispersion aid.
Further, the material of the diaphragm substrate is selected from one or more of PE, PP and PI.
Further, the thickness of the diaphragm substrate is 5-20 microns.
The second purpose of the invention is to provide a preparation method of a quick-charging lithium ion battery, which comprises the following steps:
(1) Preparing the diaphragm for the lithium ion battery;
(2) Attaching a graphite layer of a diaphragm for a lithium ion battery to a negative pole piece, and selecting proper pressure (1-20 ton/mm) according to the content of a binder in the graphite layer, the diaphragm material and the requirements of different hot-pressed stripping forces 2 ) And hot-pressing and compounding under the pressure and at the temperature of 70-95 ℃ to compound the negative pole piece and the diaphragm.
Further, in the step (2), the negative electrode plate includes a negative electrode active material, and the negative electrode active material is attached to the graphite layer.
Further, the negative electrode active material is selected from a single graphite-containing material or a composite system containing silicon carbon, LTO and the like.
Further, the negative electrode active material is graphite, and the particle size of the graphite is larger than the particle size of the graphite particles in the coating layer. In general, the particle size of the graphite selected for the negative electrode active material is 10 to 30 μm. The process of the invention can achieve the structure that the negative pole piece has the tightly combined double-layer graphite material.
The invention coats a small particle of graphite material on the negative electrode surface of the diaphragm, thereby maintaining a certain energy density of the battery and improving the multiplying power and the cycle performance of the battery.
At the normal temperature of 25 ℃, the rechargeable battery with the SOC of 0 percent to 80 percent within 48 minutes or the charging rate of more than 1C is generally regarded as a quick-charging lithium ion battery.
By the scheme, the invention at least has the following advantages:
the diaphragm for the lithium ion battery adopts the graphite layer containing the small-particle functional graphite particles, fully utilizes the advantage of ultrahigh multiplying power of the small-particle graphite particles, greatly improves the phenomenon of lithium precipitation on the surface of the quick-charge electrode, and improves the cycle, multiplying power performance and safety performance of the quick-charge lithium ion battery.
In the preparation process of the quick-charging lithium ion battery, the diaphragm and the negative pole piece for the lithium ion battery are compounded by adopting a hot-pressing compounding process, so that the effect of negative double-layer coating that small-particle power graphite particles on the diaphragm are tightly combined with negative active matters on the original negative pole piece is achieved, and the quick-charging lithium ion battery with ultrahigh power performance is prepared. The method of combining the diaphragm and the hot-pressing composite process realizes the double-layer coating effect, and has the advantages of simple coating process, uniform coating and high operability compared with the original method of simultaneously coating double layers of graphite with different particle sizes on the surface of the negative electrode. Meanwhile, the effect of tight combination of the diaphragm and the negative pole piece is achieved, so that the dynamics is improved from two aspects, and the power performance of the quick-charging lithium ion battery is greatly improved.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following description is made with reference to the preferred embodiments of the present invention and the accompanying detailed drawings.
Drawings
FIG. 1 is a schematic illustration of the attachment of a separator containing a layer of small-grained graphite to a negative electrode;
description of reference numerals:
1-a separator substrate; 2-power type graphite material; 3-large-particle artificial graphite; 4-copper foil.
Detailed Description
The following examples are given to further illustrate the embodiments of the present invention. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
Comparative example 1
A commercial 20 μm thick material is a PPPP separator.
Example 1
A diaphragm containing a small-particle graphite layer is prepared by the following steps:
specifically, selecting the power type graphite material 2, namely graphite a: d50 is 3 μm, the particle size distribution is 1-5 μm, and after PVDF and water are prepared into a solution. The surface of the diaphragm substrate 1 with the thickness of 20 mu m is uniformly sprayed by adopting a spraying mode so as to form a continuous graphite layer on one side surface of the diaphragm substrate 1, and the graphite layer has a plurality of island-shaped structures distributed at intervals. Wherein, in the graphite layer, the mass fractions of the power type graphite material 2 and PVDF in the total mass of the graphite layer are 95% and 5% in sequence. The diaphragm substrate 1 is made of a PP diaphragm, and the thickness of the graphite layer is 8 mu m.
Examples 2 to 6
A diaphragm containing a small-particle graphite layer is prepared by the following steps:
preparing a power type graphite material (graphite a: D50 is 3 mu m, the particle size distribution is 1-5 mu m or graphite b: D50 is 6 mu m, the particle size distribution is 2-10 mu m), PVDF, a conductive agent SuperP and water into a solution a or a solution b, and uniformly spraying the solution a or the solution b on the surface of a diaphragm with the thickness of 20 mu m by adopting a spraying mode so as to form a continuous graphite layer on one side surface of the diaphragm, wherein the graphite layer is provided with a plurality of island-shaped structures which are distributed at intervals. Wherein in the graphite layer, the mass fractions of the power type graphite material, PVDF and the conductive agent in the total mass of the graphite layer are 95%, 3% and 2% in sequence. The diaphragm material is PP diaphragm. The thickness of the graphite layer is shown in table 1.
TABLE 1 separator coating thickness and corresponding cathode table
The diaphragm of the embodiment is used for preparing the quick-charging lithium ion battery, and the steps are as follows:
by adopting the design of a 1Ah soft package battery, the positive electrode material is a ternary 622 material, the negative electrode comprises a copper foil 4 and a negative electrode active layer positioned on the surface of one side of the copper foil 4, wherein the negative electrode active layer comprises large-particle artificial graphite 3 (the particle size is D50 mu m).
And the lithium ion battery is assembled by using the diaphragm of the comparative example 1 according to a conventional method.
In the lamination process, one surface of the diaphragm matrix 1 with the graphite layer is tightly attached to the negative active layer (figure 1), and then the hot pressing forming process is adopted, and 8 tons/mm of pressure is applied 2 And heating at 80 ℃ for 60 seconds to tightly combine the diaphragm matrix 1 with the negative electrode, thereby achieving the double-layer coating effect.
The normal temperature cycle life of the lithium ion battery prepared above was tested. The cycle performance shows the improvement of the quick charge performance of the lithium ion battery by comparing the cycle life of two different charges under the same discharge condition (CC 1C-2.5V).
The first charging mode is as follows: charging: CC/CV 0.5C to 4.3V,0.05C cut-off, SOC0-80% Charge time 96min.
And a second charging mode: quick charging: 2C,9min-1.5C,8min-1C, 18min-0.5C-4.3V, 0.05C cut-off and SOC0-80% charging time of 35min. The results are shown in table 2:
TABLE 2 Electrical Properties of different lithium ion batteries
As can be seen from table 2, in examples 1 to 6, compared with comparative example 1, the improvement on normal-temperature normal charging is not obvious, the fast-charging cycle performance is remarkably improved, and the performance is improved by adding the conductive agent (examples 1 and 3). Further, the influence of graphite size and coating thickness was analyzed as follows:
(1) Thickness of graphite layer
Graphite a: when D50 is 3 μm and the particle size distribution is 2 to 10 μm, the electrical properties of the lithium ion battery are improved and then reduced in comparative examples 2 to 4 with the increase in coating thickness (4 μm, 8 μm, 20 μm). The best performance is achieved when the thickness is 8 μm, i.e. the graphite layer thickness is about 2.5 times (3 × 2.5=8.5 μm) the D50 value of graphite a.
B, graphite b: the D50 is 6 μm, and when the particle size distribution is 2-10 μm, the thinner the coating thickness is, the more excellent the battery performance is.
(2) Influence of graphite particle size
Comparing example 4 with example 6, the electrical properties of the small particle graphite selected in the coating are better than those of the large particle graphite selected in the coating at the same thickness of 20 μm.
In order to improve the rate capability of a high-energy density quick-charging system, the prior art is a double-layer coating process. The invention develops a technology for coating a power type graphite material on the surface of a diaphragm, fully utilizes the good power of the graphite with small particle size, inhibits the high-rate lithium precipitation performance, greatly expands the performance window of charging under high rate, further reduces the charging time and maintains the excellent cycle performance. Meanwhile, the method has the characteristics of simple process and high manufacturability.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, it should be noted that, for those skilled in the art, many modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (8)
1. A separator for a lithium ion battery, characterized in that: the diaphragm comprises a diaphragm base body and a continuous graphite layer positioned on the surface of the diaphragm base body, wherein the graphite layer is provided with a plurality of island-shaped structures arranged at intervals, the graphite layer comprises a binder and graphite particles, and the particle size distribution of the graphite particles is that D50 is between 1 and 8 mu m; the binder comprises one or more of PVDF, CMC/SBR, PAA and PVA; the material of the diaphragm substrate is selected from one or more of PE, PP and PI;
in the process of preparing the lithium ion battery, the diaphragm for the lithium ion battery is tightly compounded with the negative pole piece in a hot-pressing compounding manner.
2. The separator for a lithium ion battery according to claim 1, characterized in that: the thickness of the graphite layer is 4-20 μm.
3. The separator for a lithium ion battery according to claim 1, characterized in that: the binder accounts for 1-5% of the total weight of the graphite layer, and the graphite particles account for 95-99% of the total weight of the graphite layer.
4. The separator for a lithium ion battery according to claim 1, characterized in that: the graphite layer also comprises a conductive agent, wherein the conductive agent accounts for less than 5% of the total weight of the graphite layer.
5. A preparation method of a quick-charging type lithium ion battery is characterized by comprising the following steps:
(1) Preparing the separator for a lithium ion battery according to any one of claims 1 to 4;
(2) Attaching the graphite layer of the diaphragm for the lithium ion battery to a negative pole piece at 1-20ton/mm 2 And carrying out hot-pressing compounding at the temperature of 70-95 ℃ under pressure so as to enable the negative pole piece and the diaphragm to be tightly compounded.
6. The production method according to claim 5, characterized in that: the negative pole piece comprises a negative active material, and the negative active material is attached to the graphite layer.
7. The method of manufacturing according to claim 6, characterized in that: the negative active material comprises one or more of graphite, silicon carbon and LTO.
8. The method of claim 7, wherein: the particle diameter of graphite in the negative electrode active material is larger than the average particle diameter of graphite particles used in the graphite layer.
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| CN114824660A (en) * | 2022-03-14 | 2022-07-29 | 郑州英诺贝森能源科技有限公司 | Ceramic microporous diaphragm for lithium ion battery and preparation method thereof |
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| CN103380525A (en) * | 2011-02-14 | 2013-10-30 | 株式会社神户制钢所 | Fuel cell separator |
| CN106558664A (en) * | 2015-09-25 | 2017-04-05 | 比亚迪股份有限公司 | A kind of diaphragm for lithium ion battery and preparation method thereof and lithium ion battery |
| CN110233241A (en) * | 2019-07-08 | 2019-09-13 | 无锡市明杨新能源有限公司 | Fast charging type lithium ion battery |
| CN111403705A (en) * | 2020-03-19 | 2020-07-10 | 风帆有限责任公司 | Negative electrode material of high-power lithium battery, preparation method and lithium battery |
| CN111600066A (en) * | 2020-06-29 | 2020-08-28 | 天津市捷威动力工业有限公司 | Quick-charging type high-energy-density lithium ion battery |
| CN111987344A (en) * | 2020-10-09 | 2020-11-24 | 昆山宝创新能源科技有限公司 | Quick-charging lithium ion battery |
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- 2020-12-24 CN CN202011553285.3A patent/CN112670670B/en active Active
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103380525A (en) * | 2011-02-14 | 2013-10-30 | 株式会社神户制钢所 | Fuel cell separator |
| CN106558664A (en) * | 2015-09-25 | 2017-04-05 | 比亚迪股份有限公司 | A kind of diaphragm for lithium ion battery and preparation method thereof and lithium ion battery |
| CN110233241A (en) * | 2019-07-08 | 2019-09-13 | 无锡市明杨新能源有限公司 | Fast charging type lithium ion battery |
| CN111403705A (en) * | 2020-03-19 | 2020-07-10 | 风帆有限责任公司 | Negative electrode material of high-power lithium battery, preparation method and lithium battery |
| CN111600066A (en) * | 2020-06-29 | 2020-08-28 | 天津市捷威动力工业有限公司 | Quick-charging type high-energy-density lithium ion battery |
| CN111987344A (en) * | 2020-10-09 | 2020-11-24 | 昆山宝创新能源科技有限公司 | Quick-charging lithium ion battery |
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