Solid-state battery composite positive electrode material and preparation method and application thereof

Abstract

The invention relates to a solid-state battery composite positive electrode material and a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing a ternary positive electrode material and graphene to obtain a graphene-coated positive electrode material; and (2) carrying out ball-milling mixing on sulfide electrolyte and the graphene-coated positive electrode material obtained in the step (1) to obtain the solid-state battery composite positive electrode material. According to the preparation method provided by the invention, the surface of the ternary positive electrode material is firstly coated with the graphene, and then the coating of the solid electrolyte is carried out, so that the interface state of the ternary positive electrode material and the sulfide electrolyte is improved, the interface impedance is reduced, and the charge-discharge capacity of the solid-state lithium ion battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, relates to a cathode material, and particularly relates to a solid-state battery composite cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion batteries are used as power sources in electronic devices such as mobile phones and personal computers due to their advantages such as high working voltage, high energy density, and long cycle time. In recent years, with the development of electronic technology, people's requirements for power storage devices have become increasingly high. The safety performance and existing energy density of currently widely used liquid lithium-ion batteries are difficult to further meet the requirements of larger-scale commercial applications. Therefore, researchers have proposed a solution strategy of using non-flammable solid electrolytes to replace liquid electrolytes, which is beneficial to improving the safety of batteries.

[0003] The NCM ternary cathode material has the advantages of high energy density, low cost, and environmental friendliness, and has currently been proven to have great practical application and commercial value. At the same time, sulfide solid electrolytes have high ionic conductivity and relatively soft mechanical properties, and also have high promotion and application value. However, the interfacial instability between the NCM ternary cathode material and the sulfide solid electrolyte limits the further development of all-solid-state lithium batteries composed of them. Therefore, researchers are committed to finding a method for constructing a stable interfacial structure to improve the interfacial stability and overall battery performance of all-solid-state lithium batteries composed of the NCM ternary cathode material and sulfide electrolytes. In addition, there are also a series of problems caused by chemical and electrochemical side reactions between the NCM ternary cathode and the sulfide electrolyte.

[0004] Therefore, studying the interfacial problems between the NCM cathode material and the sulfide solid electrolyte and finding a suitable solution is the key to improving the performance of all-solid-state lithium batteries. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a solid-state battery composite cathode material, a preparation method thereof, and an application thereof. The preparation method improves the interfacial state between the ternary cathode material and the sulfide solid electrolyte, reduces the interfacial impedance, and improves the charge and discharge capacity of the solid-state lithium-ion battery.

[0006] To achieve the purpose of this invention, the following technical solutions are adopted:

[0007] In the first aspect, the present invention provides a preparation method of a solid-state battery composite cathode material, and the preparation method includes the following steps:

[0008] (1) Mix the ternary cathode material with graphene to obtain a graphene-coated cathode material;

[0009] (2) Ball-mill and mix the sulfide electrolyte with the graphene-coated cathode material described in step (1) to obtain the solid-state battery composite cathode material.

[0010] The preparation method provided by the present invention first coats graphene on the surface of the ternary cathode material and then coats the solid-state electrolyte, improving the interfacial state between the ternary cathode material and the sulfide solid-state electrolyte; moreover, during the process of coating the sulfide electrolyte and the ternary cathode material by ball-milling and mixing, through repeated extrusion, deformation, fracture, and welding, the solid-solid contact area between the ternary cathode material and the sulfide electrolyte is increased, thereby improving the interface, reducing the interfacial impedance, and increasing the charge and discharge capacity of the solid-state lithium-ion battery.

[0011] Preferably, the ternary cathode material in step (1) is an NCM cathode material.

[0012] Preferably, the mass ratio of the ternary cathode material to graphene in step (1) is 380:1 - 420:1.

[0013] Preferably, the sulfide electrolyte in step (2) includes Li 2 S, Li 3 PS 4 、Li 6 PS 5 Cl or Li 7 Ge 3 PS 12 Any one or a combination of at least two of them.

[0014] Preferably, the mass ratio of the sulfide electrolyte in step (2) to the ternary cathode material in step (1) is 1.4:1 - 1.6:1.

[0015] Preferably, the rotation speed of the ball-milling and mixing in step (2) is 100 r / min - 500 r / min.

[0016] Preferably, the time of the ball-milling and mixing in step (2) is 4 h - 20 h.

[0017] Preferably, the mixing method in step (1) includes ultrasonic stirring.

[0018] Preferably, the time of the ultrasonic stirring is 1 h - 3 h.

[0019] In the second aspect, the present invention provides a solid-state battery composite cathode material, which is prepared by the preparation method described in the first aspect.

[0020] In the third aspect, the present invention provides a solid-state lithium-ion battery, which includes the solid-state battery composite cathode material described in the second aspect.

[0021] The numerical ranges described in the present invention include not only the point values exemplified above, but also any point values between the above numerical ranges that are not exemplified. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the described ranges.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The preparation method provided by the present invention first coats graphene on the surface of the ternary cathode material, and then coats the solid electrolyte, which improves the interfacial state between the ternary cathode material and the sulfide solid electrolyte, reduces the interfacial impedance, and increases the charge and discharge capacity of the solid-state lithium-ion battery. Specific Embodiments

[0024] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the described embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0025] An embodiment of the present invention provides a preparation method of a solid-state battery composite cathode material, and the preparation method includes the following steps:

[0026] (1) Mix the ternary cathode material and graphene to obtain a graphene-coated cathode material;

[0027] (2) Ball-mill and mix the sulfide electrolyte and the graphene-coated cathode material obtained in step (1) to obtain the solid-state battery composite cathode material.

[0028] The preparation method provided by the present invention first coats graphene on the surface of the ternary cathode material, and then coats the solid electrolyte, which improves the interfacial state between the ternary cathode material and the sulfide solid electrolyte; moreover, during the process of coating the sulfide electrolyte and the ternary cathode material by ball-milling and mixing, through repeated extrusion, deformation, fracture and welding, the solid-solid contact area between the ternary cathode material and the sulfide electrolyte is increased, thereby improving the interface, reducing the interfacial impedance, and increasing the charge and discharge capacity of the solid-state lithium-ion battery.

[0029] In some embodiments, the ternary cathode material in step (1) is an NCM cathode material.

[0030] Optionally, the chemical formula of the NCM cathode material is LiNi x Co y Mn z O 2 , where 0 < x < 1, 0 < y < 1, 0 < z < 1 and x + y + z = 1.

[0031] As a preferred technical solution, the NCM cathode material is LiNi0.8 Co 0.1 Mn 0.1 O 2 .

[0032] Graphene coating can improve the electronic conductivity and structural stability of the ternary positive electrode material, but too much graphene will hinder the diffusion of lithium ions and cause capacity loss; while too little graphene will result in limited protection effect and cannot effectively improve the interface state between the ternary positive electrode material and the sulfide electrolyte.

[0033] In some embodiments, the mass ratio of the ternary positive electrode material to graphene in step (1) is 380:1-420:1, for example, it can be 380:1, 390:1, 400:1, 410:1 or 420:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] In certain embodiments, the sulfide electrolyte in step (2) includes Li 2 S. Li 3 PS 4 , Li 6 PS 5 Cl or Li 7 Ge 3 PS 12 Any one or a combination of at least two of the following, typical but non-limiting combinations include Li 2 S and Li 3 PS 4 The combination of Li 3 PS 4 With Li 6 PS 5 Combination of Cl, Li 6 PS 5 Cl and Li 7 Ge 3 PS 12 The combination of Li 2 S. Li 3 PS 4 With Li 6 PS 5 Combination of Cl, or Li 2 S. Li 3 PS 4 , Li 6 PS 5 Cl and Li 7 Ge 3 PS 12 combination.

[0035] Excessive use of the sulfide electrolyte will result in an overly thick coating layer, thereby reducing the electronic conductivity and lengthening the diffusion path of lithium ions; while if the amount of the sulfide electrolyte is too low, an effective sulfide electrolyte coating cannot be formed.

[0036] In certain embodiments, the mass ratio of the sulfide electrolyte described in step (2) to the ternary cathode material described in step (1) is 1.4:1 - 1.6:1. For example, it can be 1.4:1, 1.5:1, or 1.6:1, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0037] In certain embodiments, the rotation speed of the ball milling and mixing in step (2) is 100 r / min - 500 r / min. For example, it can be 100 r / min, 200 r / min, 300 r / min, 400 r / min, or 500 r / min, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0038] In certain embodiments, the time of the ball milling and mixing in step (2) is 4 h - 20 h. For example, it can be 4 h, 5 h, 8 h, 10 h, 12 h, 15 h, 18 h, or 20 h, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0039] In certain embodiments, the mixing method described in step (1) includes ultrasonic stirring.

[0040] In certain embodiments, the time of the ultrasonic stirring is 1 h - 3 h. For example, it can be 1 h, 1.5 h, 2 h, 2.5 h, or 3 h, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0041] In certain embodiments, a dispersant is added during the ultrasonic stirring.

[0042] The present invention does not limit the solid content during ultrasonic stirring, the power of ultrasonic stirring, the stirring speed, and the specific type of the dispersant, as long as the uniform coating of graphene on the ternary cathode material can be achieved. When the uniform coating of graphene can be achieved only by ultrasonic stirring, the dispersant may not be used.

[0043] Exemplarily, the dispersant includes polyisobutylene succinic acid polyamine ester (PIBSI).

[0044] An embodiment of the present invention provides a solid-state battery composite cathode material, which is prepared by the preparation method described in any of the embodiments.

[0045] An embodiment of the present invention provides a solid-state lithium-ion battery, and the solid-state lithium-ion battery includes the solid-state battery composite cathode material described in any embodiment.

[0046] Example 1

[0047] This example provides a preparation method of a solid-state battery composite cathode material, and the preparation method includes the following steps:

[0048] (1) Mix the ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O 2 with graphene, stir ultrasonically for 1.5 h, filter and dry to obtain the graphene-coated cathode material; wherein, the mass ratio of LiNi 0.8 Co 0.1 Mn 0.1 O 2 to graphene is 400:1;

[0049] (2) Ball-mill and mix the sulfide electrolyte Li 2 S with the graphene-coated cathode material described in step (1) at a rotation speed of 300 r / min for 10 h to obtain the solid-state battery composite cathode material; wherein, the dosage of the sulfide electrolyte Li 2 S and the mass ratio of the ternary cathode material in step (1) is 1.5:1.

[0050] Example 2

[0051] This example provides a preparation method of a solid-state battery composite cathode material, and the preparation method includes the following steps:

[0052] (1) Mix the ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O 2 with graphene, stir ultrasonically for 1 h, filter and dry to obtain the graphene-coated cathode material; wherein, the mass ratio of LiNi 0.8 Co 0.1 Mn 0.1 O 2 to graphene is 380:1;

[0053] (2) Ball-mill and mix the sulfide electrolyte Li 2 S with the graphene-coated cathode material described in step (1) at a rotation speed of 100 r / min for 20 h to obtain the solid-state battery composite cathode material; wherein, the dosage of the sulfide electrolyte Li 2 S and the mass ratio of the ternary cathode material in step (1) is 1.4:1.

[0054] Example 3

[0055] This example provides a method for preparing a composite cathode material for a solid-state battery. The preparation method includes the following steps:

[0056] (1) Mix the ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O 2 with graphene, stir ultrasonically for 3 h, filter and dry to obtain a graphene-coated cathode material; wherein, the mass ratio of LiNi 0.8 Co 0.1 Mn 0.1 O 2 to graphene is 420:1;

[0057] (2) Ball-mill the mixed sulfide electrolyte Li 2 S and the graphene-coated cathode material obtained in step (1) at a speed of 500 r / min for 4 h to obtain the composite cathode material for the solid-state battery; wherein, the dosage of the sulfide electrolyte Li 2 S and the mass ratio of the ternary cathode material in step (1) is 1.6:1.

[0058] Example 4

[0059] This example provides a method for preparing a composite cathode material for a solid-state battery. Except that the sulfide electrolyte is replaced with an equal mass of Li 3 PS 4 , the rest are the same as in Example 1.

[0060] Example 5

[0061] This example provides a method for preparing a composite cathode material for a solid-state battery. Except that the sulfide electrolyte is replaced with an equal mass of Li 6 PS 5 Cl, the rest are the same as in Example 1.

[0062] Example 6

[0063] This example provides a method for preparing a composite cathode material for a solid-state battery. Except that the sulfide electrolyte is replaced with an equal mass of Li 7 Ge 3 PS 12 , the rest are the same as in Example 1.

[0064] Example 7

[0065] This example provides a method for preparing a composite cathode material for a solid-state battery. Except that the speed of ball-milling and mixing in step (2) is 50 rpm, the rest are the same as in Example 1.

[0066] Example 8

[0067] This example provides a method for preparing a composite cathode material for a solid-state battery. Except that the rotation speed of ball milling and mixing in step (2) is 600 rpm, the rest are the same as in Example 1.

[0068] Example 9

[0069] This example provides a method for preparing a composite cathode material for a solid-state battery. Except that the mass ratio of the ternary cathode material to graphene is 350:1, the rest are the same as in Example 1.

[0070] Example 10

[0071] This example provides a method for preparing a composite cathode material for a solid-state battery. Except that the mass ratio of the ternary cathode material to graphene is 450:1, the rest are the same as in Example 1.

[0072] Comparative Example 1

[0073] This comparative example provides a method for preparing a composite cathode material for a solid-state battery. The preparation method includes the following steps:

[0074] Ball-mill and mix the ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O 2 with graphene and the sulfide electrolyte Li 2 S at a rotation speed of 300 r / min in a planetary ball mill for 10 h to obtain a composite cathode material for a solid-state battery; wherein, the mass ratio of LiNi 0.8 Co 0.1 Mn 0.1 O 2 to graphene is 400:1, and the dosage of the sulfide electrolyte Li 2 S is 1.5:1 based on the mass of the ternary cathode material.

[0075] Comparative Example 2

[0076] This example provides a method for preparing a composite cathode material for a solid-state battery. The preparation method includes the following steps:

[0077] (1) Ball-mill and mix the ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O 2 with the sulfide electrolyte Li 2 S for 10 h in a planetary ball mill to obtain a sulfide-coated cathode material; the sulfide electrolyte Li 2The mass ratio of S to the ternary cathode material is 1.5:1;

[0078] (2) Mix the sulfide-coated cathode material with graphene, stir ultrasonically for 1.5 h, filter and dry to obtain the solid-state battery composite cathode material; among them, the mass ratio of the ternary cathode material to graphene is 400:1.

[0079] Performance characterization

[0080] Prepare the solid-state battery composite cathode materials provided in the above examples and comparative examples into solid-state lithium-ion batteries:

[0081] (1) Prepare the positive electrode sheet by dry method

[0082] Mix the solid-state battery composite cathode material, the sulfide electrolyte Li 3 PS 4 , the additive Li[(FSO 2 )(CF 3 SO 2 )N], and the conductive agent VGCF evenly according to the mass ratio of 70:24:5:1, disperse on the surface of the aluminum foil, and press at 100 °C and 250 MPa for 2 min to obtain the positive electrode sheet;

[0083] (2) Prepare the solid-state electrolyte membrane

[0084] Press the sulfide electrolyte Li 3 PS 4 at 100 °C and 250 MPa for 2 min to obtain the solid-state electrolyte membrane;

[0085] (3) Prepare the negative electrode sheet

[0086] Attach a lithium sheet with a thickness of 25 μm to the surface of the copper foil and slice it to obtain the negative electrode sheet;

[0087] (4) Prepare the solid-state lithium-ion battery

[0088] Align the centers of the positive electrode sheet, the solid-state electrolyte membrane, and the negative electrode sheet, then stack them in sequence, and cold-press at room temperature and 250 MPa for 2 min to obtain the cell unit. Cold-press 10 layers of cell units and place them in the outer package for encapsulation to obtain the solid-state lithium-ion battery.

[0089] Perform cyclic tests on the obtained solid-state lithium-ion batteries in the working voltage range of 2.8 V - 4.2 V by means of constant current charge and discharge. The test current is 0.1 C, the test temperature is 25 °C, and the test content includes the initial specific capacity and the capacity retention rate after 200 cycles. The obtained results are shown in Table 1.

[0090] Table 1

[0091]

[0092]

[0093] As can be seen from Table 1, the solid-state battery composite cathode material provided by the present invention has a discharge capacity of more than 196.4 mAh / g and a cycle capacity retention rate of more than 97.9%.

[0094] As can be seen from the comparison between Example 7, Example 8 and Example 1, the rotation speed of ball milling mixing affects the electrochemical performance of the finally obtained solid-state battery composite cathode material. As a preferred technical solution, it is necessary to control the rotation speed of ball milling mixing at 100 r / min - 500 r / min.

[0095] As can be seen from the comparison between Example 9, Example 10 and Example 1, the amount of graphene also affects the electrochemical performance of the finally obtained solid-state battery composite cathode material. As a preferred technical solution, it is necessary to make the mass ratio of the ternary cathode material to graphene be 380:1 - 420:1.

[0096] As can be seen from the comparison between Comparative Example 1 and Example 1, directly mixing graphene, sulfide electrolyte and ternary cathode material results in a decline in the electrochemical performance of the obtained solid-state battery composite cathode material, which is not as good as the technical solution in the present invention of first mixing the ternary cathode material and graphene and then mixing with the sulfide electrolyte.

[0097] As can be seen from the comparison between Comparative Example 2 and Example 1, first wrapping the sulfide electrolyte and then coating graphene will also cause a decline in the electrochemical performance of the obtained solid-state battery composite cathode material.

[0098] In summary, the preparation method provided by the present invention first coats graphene on the surface of the ternary cathode material and then coats the solid electrolyte, which improves the interfacial state between the ternary cathode material and the sulfide solid electrolyte, reduces the interfacial impedance, and increases the charge and discharge capacity of the solid-state lithium-ion battery.

[0099] The applicant declares that the above description is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing a solid-state battery composite positive electrode material, characterized in that: The preparation method comprises the following steps: (1) mixing a ternary cathode material and graphene to obtain a graphene-coated cathode material; (2) ball milling the mixed sulfide electrolyte and the graphene-coated positive electrode material of step (1) to obtain the solid-state battery composite positive electrode material.

2. The preparation method according to claim 1, characterized in that: The ternary positive electrode material in step (1) is NCM positive electrode material.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the ternary positive electrode material to graphene in step (1) is 380:1-420:

1.

4. The preparation method according to claim 1, characterized in that: The sulfide electrolyte in step (2) includes Li2S, Li3PS4, Li6PS5Cl or Li7Ge3PS 12 Any one or a combination of at least two of the following.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the sulfide electrolyte in step (2) to the ternary cathode material in step (1) is 1.4:1-1.6:

1.

6. The preparation method according to claim 1, characterized in that: The rotation speed of the ball milling mixing in step (2) is 100 r / min-500 r / min; And / or, the ball milling mixing time in step (2) is 4h-20h.

7. The preparation method according to claim 1, characterized in that: The mixing method in step (1) includes ultrasonic stirring.

8. The preparation method according to claim 7, characterized in that: The ultrasonic stirring time is 1h-3h.

9. A solid-state battery composite positive electrode material, characterized in that: The solid-state battery composite positive electrode material is prepared by the preparation method described in any one of claims 1 to 8.

10. A solid-state lithium-ion battery, characterized in that: The solid-state lithium-ion battery comprises the solid-state battery composite positive electrode material according to claim 9.

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