Modified ternary cathode material, its modification method and lithium-ion battery

Abstract

The present invention relates to the field of lithium-ion batteries, and discloses a modified ternary cathode material and a method for modifying the ternary cathode material. The modified ternary cathode material has a ternary cathode material and a carbon coating layer covering the ternary cathode material; wherein, the carbon coating layer is obtained by sintering hydroxypropyl methylcellulose and polyethylene glycol. The modified ternary cathode material provided by the present invention has a dense carbon coating layer and stable cycle performance at normal and high temperatures.

Description

Technical Field

[0001] The invention relates to the field of lithium ion batteries, and in particular to a modified ternary positive electrode material and a modification method thereof, and a lithium ion battery. Background Art

[0002] Although the ternary cathode material LiNi x Co y Mn z O2(x+z+y=1) has many excellent electrochemical properties, but due to Ni 2+ With Li + The radius of the ternary lithium battery is similar, and the 3b position of the lithium ion layer is easily occupied by Ni 2+ Occupy, leading to Li + / Ni 2+ Mixed, resulting in irreversible structural transformation; in addition, under high voltage, the ternary lithium battery Ni 2+ It is easy to react with electrolyte to make LiNi x Co y Mn z O2 (x+z+y=1) transforms from a layered structure to a spinel structure and finally to a rock salt structure, which slows down the diffusion kinetics and directly affects the electrochemical properties of the material. In addition, the by-products on the surface of the ternary positive electrode material (such as Li2O / LiOH, etc.) are easily transformed into Li2CO3 under the action of water, and the SEI film formed on the cathode interface will affect the cycle performance of the battery.

[0003] Surface coating can solve these problems to a certain extent. The current coating method for positive electrode materials is solid phase coating, which is simple to operate and easy to use for large-scale industrial production. However, this method also has the problem of uneven coating. Uneven coating will expose part of the surface of the positive electrode material to the electrolyte. During the use of the battery, it will cause the above problems and be easily corroded by the hydrofluoric acid produced by the decomposition of the electrolyte, thus affecting the performance of the battery.

[0004] Therefore, it is necessary to provide a uniformly coated ternary positive electrode material. Summary of the invention

[0005] The purpose of the present invention is to overcome the problem of uneven coating in the simple solid phase coating in the prior art, and to provide a modified ternary positive electrode material and a modification method thereof and a lithium ion battery.

[0006] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a modified ternary positive electrode material, wherein the modified ternary positive electrode material has a ternary positive electrode material and a carbon coating layer coating the ternary positive electrode material; wherein the carbon coating layer is obtained by sintering hydroxypropyl methylcellulose and polyethylene glycol.

[0007] In the second aspect of the present invention, a method for modifying a ternary cathode material is provided. The method includes:

[0008] (1) Reacting the ternary cathode material with an aqueous mixed solution containing hydroxypropyl methylcellulose and polyethylene glycol to obtain a viscous material;

[0009] (2) Sintering the viscous material under a protective atmosphere to obtain a carbon-coated ternary cathode material;

[0010] Wherein, in the mixed solution, the molar ratio of hydroxypropyl methylcellulose to polyethylene glycol is 2 - 3:1 - 1.5.

[0011] In the third aspect of the present invention, a carbon-coated ternary cathode material prepared by the modification method of the present invention is provided.

[0012] In the fourth aspect of the present invention, a lithium-ion battery is provided. The positive electrode material of the lithium-ion battery includes the ternary cathode material of the present invention.

[0013] Through the above technical solutions, the modified ternary cathode material provided by the present invention has a uniformly coated carbon coating layer on the surface. The lithium-ion battery prepared has excellent normal and high-temperature cycle performance and a better capacity retention rate at 50 cycles. Description of the Drawings

[0014] Figure 1 is the SEM image of the modified ternary cathode material obtained in Example 1;

[0015] Figure 2 is the SEM image of the modified ternary cathode material obtained in Comparative Example 1;

[0016] Figure 3 is the transmission electron microscope image of the modified ternary cathode material obtained in Example 1;

[0017] Figure 4 is the transmission electron microscope image of the modified ternary cathode material obtained in Comparative Example 1;

[0018] Figure 5 is the comparison chart of the normal-temperature cycles of the modified ternary cathode materials obtained in Example 1 and Comparative Example 1.

[0019] Figure 6 is the comparison chart of the high-temperature cycles of the modified ternary cathode materials obtained in Example 1 and Comparative Example 1. Detailed Embodiments

[0020] The following detailed description of the specific embodiments of the present invention is provided with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0021] In the first aspect of the present invention, a modified ternary cathode material is provided. The modified ternary cathode material has a ternary cathode material and a carbon coating layer coating the ternary cathode material, and the carbon coating layer is obtained by sintering hydroxypropyl methylcellulose and polyethylene glycol.

[0022] In a preferred embodiment of the present invention, preferably, the layer thickness is 15 - 30 nm, and the weight ratio between the cathode material and the layer is 1:(500 - 5000).

[0023] In a preferred embodiment of the present invention, preferably, the composition of the ternary cathode material satisfies the general formula LiNi x Co y Mn z O2, where x + z + y = 1.

[0024] In a preferred embodiment of the present invention, preferably, the molar ratio of hydroxypropyl methylcellulose to polyethylene glycol is 2 - 3:1 - 1.5.

[0025] In the second aspect of the present invention, a method for modifying a ternary cathode material is provided. The method includes:

[0026] (1) Mixing the ternary cathode material with a mixed solution containing hydroxypropyl methylcellulose and polyethylene glycol to obtain a viscous material;

[0027] (2) Sintering the viscous material under a protective atmosphere to obtain a carbon-coated ternary cathode material;

[0028] wherein, the molar ratio of hydroxypropyl methylcellulose to polyethylene glycol in the mixed solution is 2 - 3:1 - 1.5.

[0029] In the present invention, it is specifically defined that hydroxypropyl methylcellulose and polyethylene glycol are used as carbon sources. After hydroxypropyl methylcellulose is dissolved in water, it has the ability to retain water and thicken, and after polyethylene glycol is dissolved in water, it has adhesiveness, which can make the carbon coating layer have a uniform surface. The prepared lithium-ion battery has excellent high and low temperature cycle performance and better 50-week capacity retention rate. Under the above molar ratio conditions of hydroxypropyl methylcellulose and polyethylene glycol, the prepared lithium-ion battery can have more excellent high and low temperature cycle performance.

[0030] In a preferred embodiment of the present invention, preferably, the concentration of hydroxypropyl methylcellulose in the mixed solution is 1 - 2 mol / L.

[0031] In a preferred embodiment of the present invention, preferably, the reaction conditions include: the reaction temperature is 60 - 80 °C, and the reaction time is 3 - 5 h.

[0032] In a preferred embodiment of the present invention, preferably, the solid content of the ternary cathode material and the mixed solution is 60-80 wt%, wherein the solid content is the solid content of the ternary cathode material and the mixed aqueous solution before reaction heating.

[0033] In a preferred embodiment of the present invention, preferably, the solid content of the viscous material is 70-80 wt%.

[0034] In the present invention, the solid content is the mass percentage of the remaining part after drying the mixed solution in the total amount.

[0035] In a preferred embodiment of the present invention, preferably, the protective atmosphere is nitrogen or argon.

[0036] In a preferred embodiment of the present invention, preferably, the sintering conditions include: the sintering temperature is 350°C - 400°C, and the sintering time is 6-7 h.

[0037] The third aspect of the present invention provides a carbon-coated ternary cathode material prepared by the modification method of the present invention.

[0038] The fourth aspect of the present invention provides a lithium-ion battery, wherein the positive electrode material of the lithium-ion battery includes the ternary cathode material of the present invention.

[0039] The present invention will be described in detail below through examples.

[0040] To make the present invention easier to understand, the present invention will be described in detail below in conjunction with examples. These examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Those not specified in the examples are carried out under conventional conditions or conditions recommended by the manufacturer. The raw materials involved in the examples are all commercially available products unless otherwise specified.

[0041] Performance evaluation

[0042] Electrochemical test

[0043] The ternary cathode material dried in an electrothermal blast drying oven for 2 h is mixed with conductive carbon black and PVDF in a certain mass ratio, and a certain amount of NMP is added as a dispersant during the mixing process. The mixed slurry is stirred evenly in a magnetic stirrer and then coated on an aluminum foil with a thickness of 0.016 mm. After the coated aluminum foil is dried at 120°C for 2 h and rolled, the positive electrode plate is obtained. Finally, the plate is punched into a circular piece with a diameter of 12 mm.

[0044] The test battery uses a CR2032 button battery. The battery assembly is carried out in an argon - protected glove box. A lithium sheet is used as the counter electrode, a polyethylene separator, and a 191104 type electrolyte (Beijing Research Institute of Chemical Reagents Co., Ltd.) are used. The electrochemical test voltage is 3.0 - 4.3V, 0.1CC / 0.1CD, the cycle test is 0.5CC / 0.5CD for 50 cycles, room temperature is at ambient temperature, and high temperature is 45°C.

[0045] Morphology characterization

[0046] The transmission electron microscope is the JSM - 6701F of FEI Company in the Netherlands.

[0047] Example 1

[0048] Hydroxypropyl methylcellulose and polyethylene glycol are dissolved in pure water at a molar ratio of 3:1.5 to prepare a stable mixed solution with a hydroxypropyl methylcellulose concentration of 1 mol / L. The ternary cathode material is mixed with the mixed solution at a solid content of 80 wt%. After mixing evenly, it is heated to 80°C and heated while stirring until a viscous material is formed. Finally, it is sintered for 6 h under a roasting process with a sintering temperature of 400°C and a sintering atmosphere of nitrogen.

[0049] The performance test results are as follows: The capacity retention rate at room temperature for 50 cycles is 96.8%, and the capacity retention rate at high temperature for 50 cycles is 97.5%.

[0050] Example 2

[0051] Hydroxypropyl methylcellulose and polyethylene glycol are dissolved in pure water at a molar ratio of 2:1.5 to prepare a stable mixed solution with a hydroxypropyl methylcellulose concentration of 1 mol / L. The ternary cathode material is mixed with the mixed solution at a solid content of 80 wt%. After mixing evenly, it is heated to 80°C and heated while stirring until a viscous material is formed. Finally, it is sintered for 6 h under a roasting process with a sintering temperature of 400°C and a sintering atmosphere of nitrogen.

[0052] Example 3

[0053] Hydroxypropyl methylcellulose and polyethylene glycol are dissolved in pure water at a molar ratio of 3:1 to prepare a stable mixed solution with a hydroxypropyl methylcellulose concentration of 1 mol / L. The ternary cathode material is mixed with the mixed solution at a solid content of 80 wt%. After mixing evenly, it is heated to 80°C and heated while stirring until a viscous material is formed. Finally, it is sintered for 6 h under a roasting process with a sintering temperature of 400°C and a sintering atmosphere of nitrogen.

[0054] Example 4

[0055] Dissolve hydroxypropyl methylcellulose and polyethylene glycol in pure water at a molar ratio of 2.5:1.5 to prepare a stable mixed solution with a hydroxypropyl methylcellulose concentration of 1 mol / L. Mix the ternary cathode material with the mixed solution at a solid content of 80 wt%, heat the mixture to 80 °C after mixing evenly, and heat while stirring until a viscous material is formed. Finally, sinter for 6 h under a roasting process with a sintering temperature of 400 °C and a sintering atmosphere of nitrogen.

[0056] Comparative Example 1

[0057] Dissolve anhydrous glucose and polyethylene glycol in pure water at a molar ratio of 3:1.5 to prepare a stable mixed solution with an anhydrous glucose concentration of 1 mol / L. Mix the ternary cathode material with the mixed solution at a solid content of 80 wt%, heat the mixture to 80 °C after mixing evenly, and heat while stirring until a viscous material is formed. Finally, sinter for 6 h under a roasting process with a sintering temperature of 400 °C and a sintering atmosphere of nitrogen.

[0058] The performance test results are as follows: the capacity retention rate after 50 cycles is. The capacity retention rate after 50 cycles at room temperature is 83.6%, and the capacity retention rate after 50 cycles at high temperature is 68.8%.

[0059] Comparative Example 2

[0060] Dissolve hydroxypropyl methylcellulose and polyethylene glycol in pure water at a molar ratio of 1.5:1.5 to prepare a stable mixed solution with a hydroxypropyl methylcellulose concentration of 1 mol / L. Mix the ternary cathode material with the mixed solution at a solid content of 80 wt%, heat the mixture to 80 °C after mixing evenly, and heat while stirring until a viscous material is formed. Finally, sinter for 6 h under a roasting process with a sintering temperature of 400 °C and a sintering atmosphere of nitrogen.

[0061] Comparative Example 3

[0062] Dissolve hydroxypropyl methylcellulose and polyethylene glycol in pure water at a molar ratio of 3:1.5 to prepare a stable mixed solution with a hydroxypropyl methylcellulose concentration of 1 mol / L. Mix the ternary cathode material with the mixed solution at a solid content of 80 wt%, heat the mixture to 80 °C after mixing evenly, and heat while stirring until a viscous material is formed. Finally, sinter for 6 h under a roasting process with a sintering temperature of 400 °C and a sintering atmosphere of air.

[0063] Comparative Example 4

[0064] Sinter the ternary cathode material for 6 h under a roasting process with a sintering temperature of 400 °C and a sintering atmosphere of nitrogen.

[0065] Figure 1 is the SEM image of the modified ternary cathode material prepared in Example 1. From Figure 1It can be seen that the gaps in the carbon coating layer are small and the compactness is better. Figure 2 is the SEM image of the modified ternary cathode material prepared in Comparative Example 1. Figure 2 It can be seen that the gaps in the carbon coating layer are large and the compactness is poor.

[0066] Figure 3 is the transmission electron microscope image of the ternary cathode material obtained in Example 1. Figure 4 is the transmission electron microscope image of the ternary cathode material obtained in Comparative Example 1. Figure 3 and 4 In 2 is the cathode material, and 1 is the carbon coating layer. Figure 3 It shows that a dense carbon coating layer is formed on the prepared modified ternary cathode material.

[0067] Figure 5 is the room temperature cycle comparison chart of the modified ternary cathode materials obtained in Example 1 and Comparative Example 1. Figure 6 is the high temperature cycle comparison chart of the modified ternary cathode materials obtained in Example 1 and Comparative Example 1. Figure 5 and Figure 6 It can be seen that the materials of the present invention have better room temperature and high temperature cycle performance.

[0068] From the performance test results, it can be seen that the modified ternary cathode material provided by the present invention has a carbon coating layer with high compactness; the lithium ion battery prepared with the modified ternary cathode material of the present invention has a high capacity retention rate, which further improves the comprehensive performance of the battery.

[0069] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Within the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any suitable combination of each specific technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A modified ternary cathode material, characterized in that, The modified ternary cathode material has a ternary cathode material and a carbon coating layer coating the ternary cathode material; the weight ratio between the ternary cathode material and the carbon coating layer is 1:500 - 5000; wherein, the carbon coating layer is obtained by sintering hydroxypropyl methylcellulose and polyethylene glycol; wherein, the modification method of the modified ternary cathode material includes: (1) Reacting the ternary cathode material with a mixed aqueous solution containing hydroxypropyl methylcellulose and polyethylene glycol to obtain a viscous material; wherein, the reaction temperature is 60 - 80 °C and the reaction time is 3 - 5 h; (2) Sintering the viscous material under a protective atmosphere to obtain a carbon-coated ternary cathode material; wherein, the sintering temperature is 350 - 400 °C; The molar ratio of hydroxypropyl methylcellulose to polyethylene glycol is (2 - 3):(1 - 1.5).

2. The modified ternary cathode material according to claim 1, wherein, The thickness of the carbon coating layer is 15 - 30 nm.

3. The modified ternary cathode material according to claim 1 or 2, wherein, The composition of the ternary cathode material satisfies the general formula LiNi x Co y Mn z O2, where x + z + y = 1.

4. A modification method for preparing the ternary cathode material according to claim 1, characterized in that, The method includes: (1) Reacting the ternary cathode material with a mixed aqueous solution containing hydroxypropyl methylcellulose and polyethylene glycol to obtain a viscous material; (2) Sintering the viscous material under a protective atmosphere to obtain a carbon-coated ternary cathode material; wherein, in the mixed aqueous solution, the molar ratio of hydroxypropyl methylcellulose to polyethylene glycol is (2 - 3):(1 - 1.5).

5. The modification method according to claim 4, wherein, In the mixed aqueous solution, the concentration of hydroxypropyl methylcellulose is 1 - 2 mol / L.

6. The modification method according to claim 4 or 5, wherein The solid content of the viscous material is 70 - 80 wt%; and / or, the protective atmosphere is nitrogen or argon.

7. The modification method according to claim 4 or 5, wherein The conditions for the sintering include: the sintering temperature is 350 - 400 °C and the sintering time is 6 - 7 h.

8. A lithium-ion battery, characterized in that, The cathode material of the lithium-ion battery includes the ternary cathode material according to any one of claims 1 - 3.

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