Method for modifying surface of positive electrode active material for lithium secondary battery and secondary battery manufactured therefrom

Abstract

The present invention relates to surface modification of a positive electrode active material of a secondary battery and, more particularly, to a method for suppressing an electrochemical side reaction between an electrolyte and a positive electrode active material by coating the positive electrode active material with an insulating polymer having insulating properties, and to a positive electrode active material and a lithium secondary battery prepared therefrom. According to the present invention, stability and lifespan characteristics of the lithium secondary battery can be improved.

Description

Method for surface modification of positive electrode active material for lithium secondary batteries and secondary batteries manufactured therefrom

[0001] The present invention relates to a cathode active material for a lithium-ion secondary battery, a method for surface modification of the cathode active material, and a battery. Specifically, the present invention seeks to improve the stability and lifespan characteristics of a lithium-ion secondary battery by applying a cathode active material coated with an insulating polymer.

[0002] Lithium-ion secondary batteries (LIBs) are a type of secondary battery system that boasts high energy density and superior performance. The LIB cathode electrode is largely composed of a layered cathode, a carbon-based conductive material, and a binder.

[0003] Lithium-ion secondary batteries (LIBs) experience electrochemical side reactions on the surface of the cathode during the initial charging process, which lead to the formation of CEI. Furthermore, these side reactions continue to occur during charge and discharge, leading to electrolyte decomposition. This significantly reduces the lithium-ion conductivity within the electrode. Furthermore, repeated charge and discharge cycles result in a rapid decline in battery life. The liquid electrolytes used in LIBs inevitably undergo redox reactions during charge and discharge, and the repetitive electrochemical decomposition of the electrolyte during charge and discharge degrades long-term battery life, necessitating appropriate control measures. Furthermore, this degradation in battery life can be exacerbated under high voltage and high temperature conditions.

[0004] Minimizing physical contact between the two materials is effective in suppressing electrolyte decomposition reactions originating from the cathode material surface. However, this poses the problem of surface coating difficulties due to surface impurities. To address these existing challenges, the development of novel materials capable of physically stabilizing the interface between the electrolyte and the conductive material, as well as suitable coating process technologies, is urgently needed.

[0005] In order to secure the stability of secondary batteries, a technology has been developed to control side reactions between positive active materials and electrolytes or electrode interface reactions, thereby coating the surface of positive active materials with metal oxides containing Mg, Al, Co, K, Na, or Ca. In particular, it is generally known that the surface of these positive active materials can be coated with oxides such as Al2O3, ZrO2, and AlPO4. However, these coating technologies do not cover the entire surface of the positive active material, but rather finely disperse it in the form of nano-sized particles.

[0006] The present invention provides a surface modification technology for a cathode active material to suppress electrochemical side reactions between the cathode active material and the electrolyte. The goal is to ultimately improve the stability and lifespan of lithium secondary batteries by minimizing contact between the cathode active material and the electrolyte, thereby suppressing electrochemical side reactions in the electrolyte that occur during charge and discharge.

[0007] In order to achieve the above object, the present invention provides a method for surface modification of a positive electrode active material of a lithium secondary battery, comprising the steps of dispersing a precursor of an insulating polymer in a solvent and then introducing a positive electrode active material; causing a solution reaction; and coating the surface of the positive electrode active material with an insulating polymer through a drying process.

[0008] Preferably, the precursor of the insulating polymer is added in an amount of 0.5 to 10 wt% with respect to the mass of the positive electrode active material.

[0009] Preferably, the positive electrode active material is LiCoO2 (lithium cobalt oxide, LCO), LiMn2O4 (lithium manganese oxide, LMO), Li(NiCoMnO2) (lithium nickel cobalt manganese oxide, NCM) or LiFePO2 (lithium iron oxide, LFP).

[0010] Preferably, the insulating polymer is formed by a condensation reaction of a silane precursor.

[0011] Preferably, the precursor of the insulating polymer is a silane precursor having at least one alkyl group on silicon (Si).

[0012] Preferably, the silane precursor comprises at least one of Tetraethyl orthosilicate (TEOS), Trimethoxy methylsilane (MTMS), Dimethoxydimethylsilane (DMDMS), and Vinyltrimethoxysilane (VTMS).

[0013] Preferably, the solvent may be anhydrous solvents such as benzene, toluene, xylene or alcohol.

[0014] Preferably, a polysiloxane coating layer is formed through the above coating step.

[0015] Preferably, in the solution reaction step, Si-OR of the silane precursor is changed to Si-OH through hydrolysis, and the Si-OH is changed to Si-O-Si- through a condensation reaction and coated on the surface of the positive electrode active material to form a polysiloxane coating layer.

[0016] Preferably, the hydrolysis and condensation reactions are carried out at room temperature to 200 o It proceeds in C.

[0017] Preferably, in the above solution reaction step, the reaction can proceed by adding a small amount of water, alcohol, or acid catalyst.

[0018] Preferably, the acid catalyst may include at least one of hydrochloric acid, acetic acid and nitric acid.

[0019] Preferably, the drying process is performed at room temperature ~ 150 o Performed under C conditions or vacuum conditions.

[0020] The present invention provides a positive electrode active material manufactured by the above method.

[0021] Preferably, the positive electrode active material includes an insulating polymer layer on its surface.

[0022] Preferably, the insulating polymer layer is a polysiloxane coating layer.

[0023] The present invention provides a lithium secondary battery including the positive electrode active material.

[0024] According to the present invention, by modifying the surface of the positive electrode active material, contact between the positive electrode active material and the electrolyte during the charge / discharge process of a lithium secondary battery is minimized, and electrochemical side reactions of the electrolyte occurring between them are effectively suppressed, thereby ultimately greatly improving the positive electrode safety of the battery.

[0025] Figure 1 is a schematic diagram of a method for modifying the surface of a positive electrode active material of the present invention.

[0026] Figure 2 shows the surface-modified positive electrode active material LiNi manufactured in the example. 0.8 Co 0.1 Mn 0.1 This is an SEM image of O2 (NCM811).

[0027] Figure 3 shows the evaluation results of a half cell using a positive electrode active material coated with VTMS.

[0028] Figure 4 is a cycle graph of a half cell using a positive electrode active material coated with VTMS.

[0029] The present invention provides a method for modifying the surface of a positive electrode active material of a secondary battery, a positive electrode active material coated with an insulating polymer, and a lithium ion secondary battery including the same.

[0030] The term 'surface modification' used in the present invention may be used with the term 'coating', and the two terms are used with the same meaning in the present invention.

[0031] As a method for modifying the surface of a positive electrode active material of a secondary battery, the present invention provides a method for modifying the surface of a positive electrode active material of a lithium secondary battery, comprising the steps of dispersing a precursor of an insulating polymer in a solvent and then introducing a positive electrode active material; causing a solution reaction; and coating the insulating polymer on the surface of the positive electrode active material through a drying process.

[0032] This is explained in more detail with reference to Fig. 1.

[0033] First, the precursor of the insulating polymer is dispersed in a solvent, and then the cathode active material is added. This is followed by a solution reaction process.

[0034] As the positive electrode active material, LiCoO2 (lithium cobalt oxide, LCO), LiMn2O4 (lithium manganese oxide, LMO), Li(NiCoMnO2) (lithium nickel cobalt manganese oxide, NCM), LiFePO2 (lithium iron oxide, LFP), etc. can be used, but are not limited thereto.

[0035] The precursor of the above insulating polymer is a material that is stable at 200°C or lower, or can be dissolved in a liquid state or the solvent, and is preferably a silane precursor having at least one alkyl group on silicon (Si). Specifically, TEOS (Tetraethyl orthosilicate), MTMS (Trimethoxy methylsilane), DMDMS (Dimethoxydimethylsilane), and VTMS (Vinyltrimethoxysilane) or silane compounds or polymers derived or synthesized therefrom may be used, but are not limited thereto. The silane precursor is preferably administered in an amount of 0.5 to 10 wt% relative to the mass of the positive electrode active material to improve the properties of the coating and active material.

[0036] The solvent may be any substance compatible with the precursor of the insulating polymer. Preferably, a solvent with a low volatility point and high vapor pressure is suitable. Specific examples include anhydrous solvents such as benzene, toluene, xylene, or alcohol.

[0037] The coating layer formed on the surface of the positive electrode active material through the above coating and drying process is a polysiloxane coating layer, and at this time, the Si-OR of the silane precursor reacts to Si-OH through hydrolysis, and then a silane polymer or compound in the form of Si-O-Si- is formed through a condensation reaction of the -OH group of Si-OH, which is coated on the surface of the positive electrode active material, thereby forming a polysiloxane coating layer or polysiloxane particle in various forms.

[0038] The above hydrolysis and condensation reactions occur at room temperature to 200 o It can be carried out in C, by adding a small amount of water or alcohol, or by adding an acid catalyst.

[0039] The above acid catalyst may include at least one of hydrochloric acid, acetic acid, and nitric acid.

[0040] After that, room temperature ~ 150 o The insulating polymer can be coated on the surface of the positive electrode active material to an appropriate thickness by removing the solvent through a drying process performed under C conditions or vacuum conditions. The drying process is a process in which the insulating polymer is coated and fixed on the surface of the positive electrode active material with a high surface area.

[0041] The thickness of the above polysiloxane coating layer can be controlled depending on the type of solvent, reaction temperature and time, addition of alcohol or addition of moisture, etc.

[0042] In the present invention, it is possible to modify the surface of a positive electrode active material with an insulating polymer through a mixing and drying process in a liquid phase. Furthermore, the properties of the positive electrode active material can be adjusted by controlling the thickness of the coating layer on the surface of the positive electrode active material.

[0043] The present invention provides a positive electrode active material whose surface has been modified as described above. The positive electrode active material includes an insulating polymer layer on its surface. This positive electrode active material can effectively reduce cell resistance, which increases due to repeated decomposition reactions between the electrolyte and the positive electrode active material during charge and discharge.

[0044] Accordingly, the present invention provides a lithium secondary battery comprising the positive electrode active material. By using a positive electrode active material coated with an insulating polymer, the overall performance of the lithium secondary battery can be comprehensively improved, and in particular, cycle life performance can be improved.

[0045]

[0046] The present invention is described in more detail through the following examples. However, the present invention should not be considered limited thereto.

[0047] Example

[0048] LiNi as positive electrode active material 0.8 Co 0.1 Mn 0.1 O2 (NCM811) was used, and the positive electrode active material surface modification process was performed with 1, 2.5, 5, and 10 wt% VTMS (Vinyltrimethoxysilane) based on its mass. Anhydrous EtOH or Anhydrous Toluene, which do not react with VTMS, were used as solvents.

[0049] The process proceeded as follows.

[0050]

[0051] Figure 2 shows the surface-modified positive electrode active material LiNi. 0.8 Co 0.1 Mn 0.1 This is an SEM image of O2 (NCM811).

[0052] When 2.5 wt% or more of VTMS was used, it was confirmed in the SEM image that a coating layer was formed on the surface of the positive electrode active material.

[0053]

[0054] physical property testing

[0055] To evaluate the performance of the surface-modified cathode active material, a 2032 coin half cell was fabricated. The cathode active material used in the evaluation was LiNi. 0.8 Co 0.1 Mn 0.1 O2(NCM811) (the positive electrode active material without VTMS coating (ref.) and the positive electrode active material surface-modified with VTMS prepared in the above example (5 wt%, 10 wt% and 5 wt% (toluene); where 5 wt% and 10 wt% are using only EtOH as a solvent, and 5 wt% (toluene) is using toluene as a solvent), the conductive material is super P, and the binder is PVDF. The materials were mixed in a ratio of 92:4:4 wt% to prepare a positive electrode slurry, and then 5.2 mg / cm was applied to an Al current collector. 2 The level was coated. The cell was manufactured using 1M LiPF6in EC / EMC=(v / v 1:2) + 2% VC as the electrolyte and Li metal as the cathode.

[0056]

[0057] Figure 3 shows the evaluation results of a half cell using a VTMS-coated cathode active material. The charge rate was fixed at 0.2 C-rate, and the evaluation was conducted by varying the discharge rate. At 5 C-rate discharge, the cell exhibited rate characteristics similar to those of the reference cell (non-VTMS-coated cathode active material). This indicates that, despite the presence of the polymer coating layer, the rate characteristics deteriorated only slightly due to reduced resistance.

[0058]

[0059] Figure 4 is a cycle graph of a half cell using a VTMS-coated cathode active material. This graph shows that the cell using a 5 wt% VTMS-coated cathode active material exhibited superior life characteristics to those in the ref. 100-cycle life evaluation. This suggests that controlling the contact between the cathode active material and the liquid electrolyte can significantly improve battery performance.

[0060]

[0061] The present invention is being filed with the support of the tasks described below.

[0062] - Assignment ID: 1415186499

[0063] - Assignment number: RS-2022-00155717

[0064] - Ministry name: Ministry of Trade, Industry and Energy

[0065] - Project Management (Professional) Agency Name: Korea Institute of Industrial Technology Planning and Evaluation

[0066] - Research Project Name: Development of Technology to Improve the Performance of Customized High-Power Capacitors (Supercapacitors) for Demand-Oriented Enterprises

[0067] - Research Project Name: Development of a High-Output Hybrid Lithium-Ion Capacitor for an Unmanned Logistics Transport System

[0068] - Project execution organization name: Lab2Market Co., Ltd.

[0069] Research period: April 1, 2022 - December 31, 2025

Claims

1. A step of dispersing a precursor of an insulating polymer in a solvent and then introducing a cathode active material; Step of reacting the solution; and A method for modifying the surface of a positive electrode active material for a lithium secondary battery, comprising a step of coating an insulating polymer on the surface of the positive electrode active material through a drying process.

2. In paragraph 1, A method for surface modification of a positive electrode active material for a lithium secondary battery, characterized in that the insulating polymer precursor is introduced in an amount of 0.5 to 10 wt% with respect to the mass of the positive electrode active material.

3. In paragraph 1, A method for surface modification of a lithium secondary battery cathode active material, characterized in that the cathode active material is LiCoO2 (lithium cobalt oxide, LCO), LiMn2O4 (lithium manganese oxide, LMO), Li(NiCoMnO2) (lithium nickel cobalt manganese oxide, NCM) or LiFePO2 (lithium iron oxide, LFP).

4. In paragraph 1, A method for surface modification of a lithium secondary battery cathode active material, characterized in that the insulating polymer is formed by a condensation reaction of a silane precursor.

5. In paragraph 1, A method for surface modification of a lithium secondary battery cathode active material, characterized in that the precursor of the insulating polymer is a silane-based precursor having at least one alkyl group on silicon (Si).

6. In paragraph 5, A method for surface modification of a lithium secondary battery cathode active material, characterized in that the silane precursor comprises at least one of TEOS (Tetraethyl orthosilicate), MTMS (Trimethoxy methylsilane), DMDMS (Dimethoxydimethylsilane), and VTMS (Vinyltrimethoxysilane).

7. In paragraph 1, A method for surface modification of a lithium secondary battery cathode active material, characterized in that the solvent is benzene, toluene, xylene or alcohol.

8. In paragraph 1, A method for modifying the surface of a lithium secondary battery cathode active material, characterized in that a polysiloxane coating layer is formed in the above coating step.

9. In paragraph 5, A method for surface modification of a positive electrode active material of a lithium secondary battery, characterized in that in the above solution reacting step, Si-OR of a silane precursor is changed to Si-OH through hydrolysis, and the Si-OH is changed to Si-O-Si- through a condensation reaction and is coated on the surface of the positive electrode active material to form a polysiloxane coating layer.

10. In paragraph 9, The above hydrolysis and condensation reactions are carried out at room temperature to 200 o A method for surface modification of a lithium secondary battery cathode active material, characterized in that it is performed in C.

11. In paragraph 1, A method for surface modification of a lithium secondary battery cathode active material, characterized in that in the above solution reacting step, a small amount of water, alcohol or acid catalyst is added to promote the reaction.

12. In paragraph 11, A method for surface modification of a lithium secondary battery cathode active material, characterized in that the acid catalyst comprises at least one of hydrochloric acid, acetic acid, and nitric acid.

13. In paragraph 1, The above drying process is performed at room temperature ~ 150 o A method for surface modification of a lithium secondary battery cathode active material, characterized in that it is performed under C conditions or vacuum conditions.

14. A positive electrode active material manufactured by any one of the methods of clauses 1 to 13.

15. In paragraph 14, A cathode active material characterized in that the cathode active material includes an insulating polymer layer on its surface.

16. In paragraph 15, A cathode active material, characterized in that the insulating polymer layer is a polysiloxane coating layer.

17. A lithium secondary battery characterized by including the positive electrode active material of clause 14.

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