A battery and a method for preparing the same

Abstract

The present invention belongs to the technical field of battery preparation, and specifically relates to a battery and a preparation method thereof. The battery comprises a positive electrode plate and a negative electrode plate, the positive electrode plate comprises a first current collector and a first active layer; the first active layer comprises a first coating and a second coating sequentially coated on the first current collector; the negative electrode plate comprises a second current collector and a second active layer; the second active layer comprises a third coating and a fourth coating coated on the second current collector; the components of the first coating comprise lithium nickel cobalt manganese oxide and lithium iron manganese phosphate; the components of the second coating comprise lithium iron manganese phosphate; the components of the third coating comprise graphite and silicon dioxide; the components of the fourth coating comprise lithium titanate and graphite. The current collector of the positive electrode plate is first coated with a composite system of lithium nickel cobalt manganese oxide and lithium iron manganese phosphate, and then coated with a lithium iron manganese phosphate system, which avoids the defects of lithium nickel cobalt manganese oxide and diaphragm being directly in contact with each other and the diaphragm being oxidized and the poor safety performance of lithium nickel cobalt manganese oxide, and improves the cycle life and safety performance of the battery cell.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery preparation, and in particular relates to a battery and a preparation method thereof. Background Art

[0002] The new energy electric vehicles currently popular in the market mainly use lithium-ion batteries. Lithium-ion batteries also have problems such as range anxiety, long charging time and safety in use.

[0003] For the positive electrode, the use of high-gram capacity positive electrode active materials, such as high-nickel ternary materials, can increase the energy density of the battery and solve the problems of mileage anxiety and long charging time. However, the crystal structure stability of high-gram capacity positive electrode active materials is poor, and thermal runaway may occur during use, causing safety problems. When fully charged, the high-nickel ternary positive electrode material has a high oxidation potential and is oxidizing to PP and PE separators, which will reduce the service life and safety performance of the battery cell. Lithium manganese iron phosphate has a high voltage platform and good safety, a stable crystal structure, but poor rate performance and low gram capacity, making it unsuitable as the preferred material for fast charging and long-range models.

[0004] For the negative electrode, the potential of graphite and silicon negative electrodes to lithium is relatively low. Using graphite or silicon negative electrodes can increase the charging and discharging voltage platform of the battery cell and increase the output voltage of the lithium-ion battery. However, lithium deposition is prone to occur at the negative electrode during fast charging. As the number of cycles increases, the lithium metal at the negative electrode will form dendrites that pierce the diaphragm, causing a short circuit inside the battery cell and causing safety problems. Lithium titanate has a high potential to lithium and can avoid lithium deposition, but it will reduce the output voltage of the battery cell, and the specific capacity of lithium titanate is low, thereby reducing the energy density of the battery cell.

[0005] Therefore, how to overcome the problems of short service life, low safety performance, poor rate performance and low gram capacity of lithium-ion batteries in the prior art caused by the positive electrode materials; and lithium plating at the negative electrode during charging. As the number of cycles increases, the lithium metal at the negative electrode forms dendrites that pierce the diaphragm, causing a short circuit inside the battery cell, causing safety problems. Summary of the invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the prior art batteries caused by the positive electrode materials, such as short service life of the battery cells, low safety performance, poor rate performance and low gram capacity; and lithium deposition at the negative electrode during charging. As the number of cycles increases, the lithium metal at the negative electrode forms dendrites that pierce the diaphragm, causing internal short circuits in the battery cells, resulting in safety problems, etc., thereby providing a battery and a preparation method thereof.

[0007] To this end, the present invention provides the following technical solutions.

[0008] The present invention provides a battery, comprising a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet comprises a first current collector and a first active layer; the first active layer comprises a first coating layer and a second coating layer sequentially coated on the first current collector;

[0009] The negative electrode plate includes a second current collector and a second active layer; the second active layer includes a third coating layer and a fourth coating layer sequentially coated on the second current collector;

[0010] The components of the first coating include lithium nickel cobalt manganese oxide and lithium manganese iron phosphate;

[0011] The components of the second coating layer include lithium iron manganese phosphate;

[0012] The components of the third coating layer include graphite and silicon oxide;

[0013] Components of the fourth coating layer include lithium titanate and graphite.

[0014] The thickness of the first coating is 20-200 μm;

[0015] Preferably, the second coating has a thickness of 1-5 μm.

[0016] The thickness of the third coating is 20-200 μm;

[0017] Preferably, the fourth coating has a thickness of 10-50 μm.

[0018] The battery satisfies at least one of (1) to (4):

[0019] (1) The components of the first coating layer further include at least one of a binder and a conductive agent;

[0020] Preferably, the mass ratio of the binder, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide and the conductive agent is (0.8-2):(20-50):(50-75):(1-2);

[0021] (2) the second coating layer further comprises at least one of a binder and a conductive agent;

[0022] Preferably, the mass ratio of the binder, lithium manganese iron phosphate and the conductive agent is (0.8-2):(93-97):(1.5-2);

[0023] (3) The components of the third coating layer further include at least one of a binder, a thickener and a conductive agent;

[0024] Preferably, the mass ratio of the binder, thickener, graphite, silicon dioxide and conductive agent is (1.7-2.0):(1.2-1.5):(90-95):(0-5):(1-3);

[0025] (4) The fourth coating layer further comprises at least one of a binder, a thickener and a conductive agent;

[0026] Preferably, the mass ratio of the binder, thickener, graphite, lithium titanate and conductive agent is (1.7-2.0):(1.2-1.5):(90-95):(2-8):(1-3).

[0027] The battery further includes a separator, which is disposed between the positive electrode sheet and the negative electrode sheet.

[0028] The diaphragm comprises a glue coating layer and a ceramic layer which are bonded together.

[0029] The components of the coating layer include at least PVDF;

[0030] Preferably, the components of the ceramic layer include at least PVDF and boehmite;

[0031] Preferably, the components of the ceramic layer include PVDF and boehmite in a mass ratio of (7-17):(83-93).

[0032] The present invention also provides a method for preparing the above-mentioned battery, comprising the following steps:

[0033] Preparation of positive electrode sheet: preparing a slurry containing lithium nickel cobalt manganese oxide and lithium iron manganese phosphate, and coating it on the current collector to form a first coating; preparing a slurry containing lithium iron manganese phosphate, and coating it on the first coating to form a second coating;

[0034] Preparation of negative electrode sheet: preparing a slurry containing graphite and silicon oxide, and coating it on the current collector to form a third coating; preparing a slurry containing lithium titanate and graphite, and coating it on the third coating to form a fourth coating.

[0035] The preparation method further comprises the step of assembling the separator with the positive electrode sheet and the negative electrode sheet.

[0036] The positive electrode plate is bonded to the adhesive layer of the diaphragm;

[0037] And / or, the negative electrode plate is bonded to the ceramic layer of the separator.

[0038] The technical solution of the present invention has the following advantages:

[0039] 1. The battery provided by the present invention comprises a positive electrode plate and a negative electrode plate, the positive electrode plate comprises a first current collector and a first active layer; the first active layer comprises a first coating layer and a second coating layer sequentially coated on the first current collector; the negative electrode plate comprises a second current collector and a second active layer; the second active layer comprises a third coating layer and a fourth coating layer sequentially coated on the second current collector; the components of the first coating layer comprise lithium nickel cobalt manganese oxide and lithium iron manganese phosphate; the components of the second coating layer comprise lithium iron manganese phosphate; the components of the third coating layer comprise graphite and silicon dioxide; the components of the fourth coating layer comprise lithium titanate and graphite. The current collector of the positive electrode plate of the battery is first coated with a composite system of lithium nickel cobalt manganese oxide and lithium iron manganese phosphate, and then coated with a lithium iron manganese phosphate system, thereby avoiding the defects of lithium nickel cobalt manganese oxide and diaphragm being directly in contact with each other, thereby oxidizing the diaphragm and the poor safety performance of lithium nickel cobalt manganese oxide, and improving the cycle life and safety performance of the battery cell.

[0040] The negative electrode of the battery is first coated with a composite system of graphite and silicon oxide, and then coated with a composite system of graphite and lithium titanate, which reduces the interface impedance between lithium titanate and the current collector. The high potential of lithium titanate to lithium reduces the risk of lithium precipitation during fast charging of the battery cell, while lithium titanate and silicon oxide can improve the fast charging capability of the negative electrode.

[0041] The invention can significantly improve the cycle life and safety of the battery through the cooperation of the positive electrode sheet and the negative electrode sheet, reduce the problems of rapid charging and lithium deposition, and the battery can also pass the needle puncture test.

[0042] 2. The lithium-ion battery provided by the present invention can change the energy density of the battery cell by adjusting the proportion of lithium nickel cobalt manganese oxide active material in the positive electrode first coating and the proportion of silicon oxide in the negative electrode third coating; as the content of lithium nickel cobalt manganese oxide and silicon oxide in the coating increases, the energy density can be improved. The use of a mixed system of lithium nickel cobalt manganese oxide and lithium iron manganese phosphate in the first coating can also reduce the cost of the battery cell.

[0043] The diaphragm of the present invention comprises a glue coating layer, a ceramic layer and a PE base film which are laminated to each other, and can ensure that the interface between the positive and negative electrode sheets can be in good contact without defects. DETAILED DESCRIPTION

[0044] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0045] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0046] Example 1

[0047] This embodiment provides a battery, including a positive electrode sheet, a negative electrode sheet and a separator; wherein:

[0048] The positive electrode sheet includes a current collector aluminum foil and a first active layer, and the first active layer is coated on both sides of the current collector; the first active layer includes a first coating layer and a second coating layer sequentially coated on the current collector; the thickness of the first coating layer is 100 μm, and the first coating layer includes a binder PVDF, lithium iron manganese phosphate, lithium nickel cobalt manganese oxide and a conductive agent SP in a mass ratio of 2:30:66:2; the thickness of the second coating layer is 5 μm, and the second coating layer includes a binder PVDF, lithium iron manganese phosphate and a conductive agent SP in a mass ratio of 2:96:2.

[0049] The negative electrode sheet includes a current collector copper foil and a second active layer, and the second active layer is coated on both sides of the current collector; the second active layer includes a third coating layer and a fourth coating layer sequentially coated on the current collector; the thickness of the third coating layer is 105 μm, and the third coating layer includes a binder SBR, a thickener CMC, graphite, silicon dioxide and a conductive agent SP in a mass ratio of 2:1.2:93:2.8:1; the thickness of the fourth coating layer is 20 μm, and the fourth coating layer includes a binder SBR, a thickener CMC, graphite, lithium titanate and a conductive agent SP in a mass ratio of 1.7:1.2:94:2.1:1.

[0050] The diaphragm includes a PVDF coating layer with a thickness of 3 μm and a ceramic layer with a thickness of 2 μm. The mass ratio of PVDF and boehmite in the ceramic layer is 12:88. The coating layer and the ceramic membrane are laminated together; the coating layer is laminated to the positive electrode plate, and the ceramic layer is laminated to the negative electrode plate.

[0051] This embodiment also provides a method for preparing the above-mentioned battery, comprising the following steps:

[0052] A binder, lithium nickel cobalt manganese oxide, lithium iron manganese phosphate and a conductive agent are mixed to form a slurry, which is applied on the current collector by an extrusion coater, and coated on both sides to form a first coating layer; a binder, lithium iron manganese phosphate and a conductive agent are mixed to form a slurry, which is applied on the first coating layer by gravure printing to form a second coating layer, and coated on both sides to obtain a positive electrode sheet.

[0053] A binder, a thickener, graphite, silicon dioxide and a conductive agent are mixed to form a slurry, which is applied on the current collector on both sides to form a third coating layer; lithium titanate, graphite, a thickener, a binder and a conductive agent are mixed to form a slurry, which is applied on the third coating layer on both sides to form a fourth coating layer to obtain a negative electrode sheet.

[0054] The positive electrode sheet, the negative electrode sheet and the diaphragm are assembled into an electrode group. During the assembly, the positive electrode sheet is bonded to the adhesive layer of the diaphragm, and the negative electrode sheet is bonded to the ceramic layer of the diaphragm. After the electrode group is assembled, the diaphragm tail is used to wind the electrode group for one week, and the diaphragm tail is fastened with tape; and then an aluminum-plastic film is used for packaging to obtain a battery.

[0055] Example 2

[0056] This embodiment provides a battery, including a positive electrode sheet, a negative electrode sheet and a separator; wherein:

[0057] The positive electrode plate includes a current collector aluminum foil and a first active layer, and the first active layer is coated on both sides of the current collector; the first active layer includes a first coating layer and a second coating layer coated on the current collector in sequence; the thickness of the first coating layer is 150 μm, and the first coating layer includes a binder PVDF, lithium iron manganese phosphate, lithium nickel cobalt manganese oxide and a conductive agent SP in a mass ratio of 2:40:56:2; the thickness of the second coating layer is 5 μm, and the second coating layer includes PVDF, lithium iron manganese phosphate and SP in a mass ratio of 1.5:96:2.

[0058] The negative electrode sheet includes a copper foil and a second active layer, and the second active layer is coated on both sides of the current collector; the second active layer includes a third coating layer and a fourth coating layer sequentially coated on the current collector; the thickness of the third coating layer is 155 μm, and the third coating layer includes SBR, CMC, graphite, silicon oxide and SP in a mass ratio of 2:1.2:93:2.8:1; the thickness of the fourth coating layer is 20 μm, and the fourth coating layer includes SBR, CMC, graphite, lithium titanate and SP in a mass ratio of 1.7:1.2:94:2.1:1.

[0059] The diaphragm includes a 3μm thick adhesive layer and a 2μm thick ceramic layer. The adhesive layer and the ceramic layer are the same as those in Example 1. The adhesive layer and the ceramic membrane are bonded together; wherein the adhesive layer is bonded to the positive electrode plate, and the ceramic layer is bonded to the negative electrode plate.

[0060] This embodiment also provides a method for preparing the above-mentioned battery, comprising the following steps:

[0061] The binder PVDF, lithium iron manganese phosphate, lithium nickel cobalt manganese oxide and the conductive agent SP are mixed to form a slurry, which is applied on the current collector by an extrusion coater, and double-sided coating is performed to form a first coating layer; the binder PVDF, lithium iron manganese phosphate and the conductive agent SP are mixed to form a slurry, which is applied on the first coating layer by gravure printing to form a second coating layer, and double-sided coating is performed to obtain a positive electrode sheet.

[0062] The binder SBR, the thickener CMC, the graphite, the silicon oxide and the conductive agent SP are mixed to form a slurry, which is applied on the current collector on both sides to form a third coating layer; the lithium titanate, the graphite, the SBR, the CMC and the conductive agent SP are mixed to form a slurry, which is applied on the third coating layer on both sides to form a fourth coating layer to obtain a negative electrode sheet.

[0063] The positive electrode sheet, the negative electrode sheet and the diaphragm are assembled into an electrode group. During the assembly, the positive electrode sheet is bonded to the adhesive layer of the diaphragm, and the negative electrode sheet is bonded to the ceramic layer of the diaphragm. After the electrode group is assembled, the diaphragm tail is used to wind the electrode group for one week, and the diaphragm tail is fastened with tape. Then, an aluminum-plastic film is used for packaging to obtain a lithium-ion battery.

[0064] Example 3

[0065] This embodiment provides a battery, including a positive electrode sheet, a negative electrode sheet and a separator; wherein:

[0066] The positive electrode sheet includes a current collector aluminum foil and a first active layer, and the first active layer is coated on both sides of the current collector; the first active layer includes a first coating layer and a second coating layer sequentially coated on the current collector; the thickness of the first coating layer is 170 μm, and the first coating layer includes a PVDF binder, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, and a conductive agent SP in a mass ratio of 2:25:71:2; the thickness of the second coating layer is 5 μm, and the second coating layer includes a binder PVDF, lithium manganese iron phosphate, and a conductive agent SP in a mass ratio of 2:96:2.

[0067] The negative electrode sheet includes a current collector copper foil and a second active layer, and the second active layer is coated on both sides of the current collector; the second active layer includes a third coating layer and a fourth coating layer sequentially coated on the current collector; the thickness of the third coating layer is 155 μm, and the third coating layer includes SBR, CMC, graphite, silicon oxide and SP in a mass ratio of 2:1.2:93:2.8:1; the thickness of the fourth coating layer is 20 μm, and the fourth coating layer includes a binder SBR, a thickener CMC, graphite, lithium titanate and a conductive agent SP in a mass ratio of 1.7:1.2:93:3.1:1.

[0068] The diaphragm includes a 3μm thick adhesive layer and a 2μm thick ceramic layer. The adhesive layer and the ceramic layer are the same as those in Example 1. The adhesive layer and the ceramic membrane are bonded together; wherein the adhesive layer is bonded to the positive electrode plate, and the ceramic layer is bonded to the negative electrode plate.

[0069] This embodiment also provides a method for preparing the above-mentioned battery, comprising the following steps:

[0070] A binder, lithium iron manganese phosphate, lithium nickel cobalt manganese oxide and a conductive agent are mixed to form a slurry, which is applied on the current collector by an extrusion coater, and double-sided coating is performed to form a first coating layer; a binder, lithium iron manganese phosphate and a conductive agent are mixed to form a slurry, which is applied on the first coating layer by gravure printing to form a second coating layer, and double-sided coating is performed to obtain a positive electrode sheet.

[0071] A binder, a thickener, graphite, silicon dioxide and a conductive agent are mixed to form a slurry, which is applied on the current collector on both sides to form a third coating layer; lithium titanate, graphite, a PAA binder, a thickener and a conductive agent are mixed to form a slurry, which is applied on the third coating layer on both sides to form a fourth coating layer to obtain a negative electrode sheet.

[0072] The positive electrode sheet, the negative electrode sheet and the diaphragm are assembled into an electrode group. During the assembly, the positive electrode sheet is bonded to the adhesive layer of the diaphragm, and the negative electrode sheet is bonded to the ceramic layer of the diaphragm. After the electrode group is assembled, the diaphragm tail is used to wind the electrode group for one week, and the diaphragm tail is fastened with tape; and then an aluminum-plastic film is used for packaging to obtain a battery.

[0073] Comparative Example 1

[0074] This comparative example provides a battery, including a positive electrode plate, a negative electrode plate and a separator; the difference from Example 1 is that the negative electrode plate is different, and the negative electrode plate of this comparative example is pure artificial graphite.

[0075] Comparative Example 2

[0076] This comparative example provides a battery, including a positive electrode plate, a negative electrode plate and a separator; the difference from Example 1 is that the positive electrode plate is different. The positive electrode plate of this comparative example is lithium nickel cobalt manganese oxide and does not contain lithium manganese iron phosphate. The rest is the same as Example 1.

[0077] Test example

[0078] This test example provides a performance test method for the batteries provided in each embodiment and comparative example, as follows:

[0079]

[0080]

[0081]

[0082] Acupuncture test: refer to national standard GB / T-31485.

[0083]

[0084]

[0085] It can be seen from the above experimental results that after changing the negative electrode or positive electrode of Comparative Example 1-2, the energy density of the battery cannot be improved or cannot pass the puncture test. The negative electrode of Comparative Example 1 is artificial graphite, and the negative electrode of Example 1 is first coated with a graphite and silicon oxide composite system, and then coated with a graphite and lithium titanate composite system, which helps to reduce the interface impedance and improve the energy density. The positive electrode in Comparative Example 2 uses a single nickel cobalt manganese oxide lithium, which causes the battery to fail the puncture test. The present invention uses a nickel cobalt manganese oxide and lithium iron manganese phosphate composite system, which helps to improve the safety of the battery and pass the puncture test.

[0086] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A battery comprising a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet, characterized in that: The positive electrode plate comprises a first current collector and a first active layer; the first active layer comprises a first coating layer and a second coating layer sequentially coated on the first current collector; The negative electrode plate comprises a second current collector and a second active layer; the second active layer comprises a third coating layer and a fourth coating layer sequentially coated on the second current collector; The thickness of the first coating is 20-200 μm; the components of the first coating include a binder, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide and a conductive agent in a mass ratio of (0.8-2):(20-50):(50-75):(1-2); The components of the second coating layer include a binder, lithium manganese iron phosphate and a conductive agent in a mass ratio of (0.8-2):(93-97):(1.5-2); the thickness of the second coating layer is 1-5 μm; The components of the third coating include a binder, a thickener, graphite, silicon dioxide and a conductive agent in a mass ratio of (1.7-2.0):(1.2-1.5):(90-95):(2.8-5):(1-3); the thickness of the third coating is 20-105 μm or 155-200 μm; The components of the fourth coating include a binder, a thickener, graphite, lithium titanate and a conductive agent in a mass ratio of (1.7-2.0):(1.2-1.5):(90-95):(2-8):(1-3), and the thickness of the fourth coating is 10-50 μm.

2. A method for preparing a battery as claimed in claim 1, characterized in that: The following steps are involved: Preparation of positive electrode sheet: preparing a slurry containing lithium nickel cobalt manganese oxide and lithium iron manganese phosphate, and coating it on the current collector to form a first coating; preparing a slurry containing lithium iron manganese phosphate, and coating it on the first coating to form a second coating; Preparation of negative electrode sheet: preparing a slurry containing graphite and silicon oxide, and coating it on the current collector to form a third coating; A slurry containing lithium titanate and graphite is prepared and coated on the third coating layer to form a fourth coating layer.

3. The preparation method according to claim 2, characterized in that: The method also includes the step of assembling the separator with the positive electrode sheet and the negative electrode sheet.

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