Secondary battery including a positive electrode material containing an irreversible additive and method for manufacturing the same

Abstract

A secondary battery according to an embodiment of the present invention is a secondary battery including a positive electrode in which a positive electrode material is coated on a positive electrode current collector, wherein the positive electrode material includes an irreversible additive and a positive electrode active material, and the irreversible additive includes lithium nickel oxide (LNO) having a trigonal crystal structure in a working range of 3.0 V to 4.0 V in the secondary battery.

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of Korean Patent Application Nos. 10 - 2020 - 0106090, filed on August 24, 2020, and 10 - 2021 - 0110819, filed on August 23, 2021, with the Korean Intellectual Property Office, the entire disclosures of which are incorporated herein by reference in their entireties.

[0003] The present invention relates to a positive electrode material including an irreversible additive, a secondary battery including the positive electrode material, and a method for manufacturing the same. Background Art

[0004] Due to the rapid increase in the use of fossil fuels, the demand for alternative or clean energy sources is continuously increasing, and the most actively studied field is the field of power generation and power storage using electrochemistry.

[0005] Currently, secondary batteries are representative examples of electrochemical devices that utilize this electrochemical energy, and their range of use has a tendency to gradually expand.

[0006] Recently, with the technological development and increasing demand for mobile devices such as laptop computers, mobile phones, and cameras, the demand for secondary batteries as an energy source has increased rapidly. Among these secondary batteries, many studies have been conducted on lithium secondary batteries with high energy density, long cycle life, and low self - discharge rate, and they have been commercialized and widely used.

[0007] In addition, as people's attention to environmental issues has increased, there has been more and more research on electric vehicles, hybrid electric vehicles, etc., which can replace vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are a major cause of air pollution. Although nickel - metal hydride secondary batteries are mainly used as power sources for electric vehicles and hybrid electric vehicles, research on the use of lithium secondary batteries with high energy density is actively underway, and some of them are in the commercialization stage.

[0008] Carbon materials are mainly used as negative electrode active materials for such lithium secondary batteries, and lithium transition metal composite oxides are used as positive electrode active materials for lithium secondary batteries. Among them, in addition to lithium cobalt composite metal oxides such as LiCoO2, which have a high working voltage and excellent capacity characteristics, various lithium transition metal oxides such as LiNiO2, LiMnO2, LiMn2O4, or LiFePO4 have been developed.

[0009] On the other hand, since Li ions are consumed during the initial charge and discharge process, an SEI (solid electrolyte interface) layer is formed and irreversibility occurs at the positive and negative electrodes. As a result, the energy density decreases, and there is a problem that the theoretically designed amount cannot be fully utilized.

[0010] To solve these problems, irreversible additives can be added to the positive electrode material to supplement lithium ions. However, the commonly used irreversible additive Li2NiO2 has an orthorhombic crystal structure and belongs to the Immm space group. However, the problem with the above material is that it undergoes three stages of structural changes within the working voltage range after the initial charge of the secondary battery, leading to the generation of impurities or gases.

[0011] Specifically, the above material maintains an orthorhombic crystal structure in the range of 3.0V to 3.5V, but due to the insertion and extraction of Li, the material undergoes three crystal structure changes to become a trigonal system at 3.5V to 4.0V and a monoclinic system at 3.5V to 4.25V. In particular, when the irreversible additive (Li2NiO2) with an orthorhombic crystal structure causes the crystal structure to transform into a trigonal system, unpredictable by-products and excessive gases are generated. In addition, there is also a problem of reduced structural stability due to the change in crystal structure. Summary of the Invention

[0012] Technical problem

[0013] The present invention aims to solve the above problems, and an object of the present invention is to provide an irreversible additive that minimizes the generation of impurities or gases within the working voltage range of a secondary battery and has high structural stability.

[0014] Another object of the present invention is to provide a positive electrode material for a secondary battery containing the irreversible additive, a secondary battery containing the positive electrode material and having excellent electrochemical performance, and a manufacturing method thereof.

[0015] Technical solution

[0016] According to an embodiment of the present invention, there is provided a secondary battery including a positive electrode in which a positive electrode material is coated on a positive electrode current collector, wherein the positive electrode material includes an irreversible additive and a positive electrode active material, and wherein the irreversible additive includes lithium nickel oxide (LNO) having a trigonal crystal structure within a working range of 3.0V to 4.0V in the secondary battery.

[0017] The lithium nickel oxide (LNO) having a trigonal crystal structure can be transformed into a monoclinic crystal structure within a working range of greater than 4.0V and 4.25V or less in the secondary battery.

[0018] Among irreversible additives, the space group of lithium nickel oxide (LNO) with a trigonal crystal structure can belong to P3-m1, and the space group of lithium nickel oxide (LNO) with a monoclinic crystal structure can belong to C2 / m.

[0019] The irreversible additive with a trigonal crystal structure can have a lattice with γ = 120.00°.

[0020] In the positive electrode material, the content of the irreversible additive relative to the total weight of the positive electrode material is 0.1% by weight to 10% by weight.

[0021] The positive electrode active material may include an oxide represented by Chemical Formula 2 below:

[0022] Li(Ni a Co b Mn c )O2 (2)

[0023] In the above formula, 0 < a < 1, 0 < b < 1, 0 < c < 1, and a + b + c = 1.

[0024] The secondary battery may have a structure in which an electrode assembly and an electrolytic solution are placed together in a battery case, and the electrode assembly includes: a positive electrode; a negative electrode in which a negative electrode material containing a negative electrode active material is coated on a negative electrode current collector; and a separator disposed between the positive electrode and the negative electrode.

[0025] According to another embodiment of the present invention, there is provided a method for manufacturing a secondary battery, the secondary battery including a positive electrode on which a positive electrode material is coated on a positive electrode current collector, and the method includes the following steps:

[0026] Coating a positive electrode composition on a positive electrode current collector to manufacture a positive electrode, the positive electrode composition being a mixture of a positive electrode material, a conductive material, and a binder;

[0027] Manufacturing a secondary battery including the positive electrode; and

[0028] Activating the secondary battery at a C rate of 0.01 to 0.05,

[0029] wherein the positive electrode material includes an irreversible additive and a positive electrode active material.

[0030] The method for manufacturing a secondary battery according to another embodiment of the present invention further includes, after the activation step: charging and discharging the secondary battery at least twice at a C rate of 0.05 to 0.15.

[0031] Before the activation step, the irreversible additive may include lithium nickel oxide (LNO) having an orthorhombic crystal structure, and after the activation step, the lithium nickel oxide included in the irreversible additive may have a trigonal crystal structure within the operating range of 3.0 V to 4.0 V in the secondary battery.

[0032] The lithium nickel oxide (LNO) may have a monoclinic crystal structure within the operating range of above 4.0 V and below 4.25 V in the secondary battery.

[0033] In the irreversible additive, the space group of the lithium nickel oxide (LNO) having an orthorhombic crystal structure may belong to Immm, the space group of the lithium nickel oxide (LNO) having a trigonal crystal structure may belong to P3-m1, and the space group of the lithium nickel oxide (LNO) having a monoclinic crystal structure may belong to C2 / m.

[0034] In the irreversible additive, the lithium nickel oxide having an orthorhombic crystal structure may have a lattice, and the lithium nickel oxide having a trigonal crystal structure may have a lattice with γ = 120.00°.

[0035] Beneficial effect

[0036] The positive electrode material including the irreversible additive, the secondary battery including the positive electrode material, and a method for manufacturing the same according to the present invention can significantly reduce the problem of generating impurities or gases due to the possible insertion and extraction of excessive lithium ions within the operating voltage range of the secondary battery, because the irreversible additive has a trigonal crystal structure within the operating range of 3.0 V to 4.0 V in the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A diagram showing the crystal structure of lithium nickel oxide (LNO) as an irreversible additive according to an embodiment of the present invention;

[0038] Figure 2 A diagram showing the charge curve of a comparative example according to Experimental Example 1;

[0039] Figure 3 A diagram showing the XRD measurement results of a comparative example according to Experimental Example 1;

[0040] Figure 4 A diagram showing the charge-discharge curve of an example according to Experimental Example 1;

[0041] Figure 5 A diagram showing the XRD measurement results of an example according to Experimental Example 1. DETAILED DESCRIPTION

[0042] In the following, various embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement them. The present invention can be modified in various different ways and is not limited to the embodiments set forth herein.

[0043] A positive electrode material containing an irreversible additive, a secondary battery containing the positive electrode material, and a method for manufacturing the same according to an embodiment of the present invention will be described.

[0044] Conventionally, as an irreversible additive, a lithium raw material and a nickel raw material are mixed and then heat-treated to produce lithium nickel oxide (LNO, Li2NiO2) as an oxide.

[0045] When ordinary raw materials are mixed and heat-treated in this way, the oxide is made into a material having an orthorhombic crystal structure, which is the most stable form. Therefore, conventionally, an oxide having an orthorhombic crystal structure is added as an irreversible additive.

[0046] Figure 1 is a diagram showing the crystal structure of lithium nickel oxide (LNO), which is an irreversible additive according to an embodiment of the present invention. Figure 1 (a) shows the orthorhombic structure of lithium nickel oxide (LNO), and Figure 1 (b) shows the trigonal structure of lithium nickel oxide (LNO).

[0047] More specifically, referring to Figure 1 , in the case where lithium nickel oxide (LNO) is used as an irreversible additive, generally three stages of structural changes occur within the available voltage operating range after the initial charge. At this time, lithium nickel oxide (LNO) has an orthorhombic crystal structure in the range of 3.0V to 3.5V, a trigonal crystal structure in the range of 3.5V to 4.0V, and a monoclinic crystal structure in the range of 3.5V to 4.25V.

[0048] Here, when lithium nickel oxide (LNO, Li2NiO2) contains two lithium ions, lithium nickel oxide (LNO, Li2NiO2) can have an orthorhombic structure as shown in Figure 1 (a) and has a high structural stability. However, the lithium ions contained in lithium nickel oxide (LNO, Li2NiO2) can be deintercalated in the range above 3.5V. Therefore, when the number of lithium ions contained in lithium nickel oxide (LNO, Li2NiO2) becomes 1, as shown in Figure 1(As shown in (b), it can transform into a trigonal crystal structure. Additionally, when the insertion and extraction of lithium ions deepen within a range exceeding 4.0V and the number of lithium ions thus becomes less than 1, it becomes a monoclinic crystal structure. Here, the number of lithium ions contained in the chemical formula of lithium nickel oxide (LNO, Li2NiO2) varies depending on the crystal structure, but for the sake of convenience in explanation, it is expressed as lithium nickel oxide (LNO) without considering the crystal structure.)

[0049] However, within such an available voltage range, as the structure changes in each stage, lithium nickel oxide (LNO) has problems related to the following: the progress of side reactions and the generation of gases / impurities. More specifically, the trigonal crystal structure and monoclinic crystal structure of the inserted and extracted lithium ions have incomplete chemical formulas, thereby reducing the structural stability. In addition, since lithium ions are inserted and extracted from lithium nickel oxide (LNO), elements that cannot combine with the electrolyte can cause side reactions or can generate gases or impurities. In particular, lithium nickel oxide (LNO) is expected to have a very large activation energy in the process of changing from a relatively stable orthorhombic structure to a relatively unstable trigonal crystal structure. At this time, the progress of side reactions or the generation of gases / impurities will also be relatively large.)

[0050] Therefore, because the initial crystal structure corresponds to the orthorhombic structure, conventional lithium nickel oxide (LNO) still has problems related to the following: the progress of side reactions or the generation of gases / impurities within the available voltage range.)

[0051] In contrast, in the lithium nickel oxide (LNO) of the present invention, the initial crystal structure corresponds to the trigonal crystal structure within the available voltage range, thereby omitting the stage of changing from the orthorhombic structure to the trigonal crystal structure. In addition, it has the advantage of being able to reduce side reactions or the generation of gases / impurities during the stage of changing from the orthorhombic structure to the trigonal crystal structure.)

[0052] According to an embodiment of the present invention, lithium nickel oxide (LNO) used as an irreversible additive can have an initial crystal structure as a trigonal crystal structure, so that it can reversibly maintain the trigonal crystal structure and monoclinic crystal structure according to the voltage within the operating voltage range of the secondary battery. Therefore, the irreversible additive according to this embodiment changes the number of stages to be less than the number of stages of general structural changes. Therefore, as the structural changes proceed in each stage, it has the advantage of being able to minimize the progress of side reactions or the generation of gases / impurities.)

[0053] The secondary battery according to an embodiment of the present invention is a secondary battery including a positive electrode in which a positive electrode material is coated on a positive electrode current collector, wherein the positive electrode material includes an irreversible additive and a positive electrode active material.)

[0054] Hereinafter, the irreversible additive will be mainly described.)

[0055] The irreversible additive according to an embodiment of the present invention comprises lithium nickel oxide (LNO) having a trigonal crystal structure. More specifically, the irreversible additive may comprise lithium nickel oxide having a trigonal crystal structure in a working range of 3.0 V to 4.0 V in a secondary battery.

[0056] In particular, different from conventional lithium nickel oxide (LNO) having an orthorhombic crystal structure in the range of 3.0 V to 3.5 V, the lithium nickel oxide (LNO) contained in the irreversible additive may have a trigonal crystal structure even in the range of 3.0 V to 3.5 V.

[0057] In other words, the irreversible additive according to the present embodiment may not comprise lithium nickel oxide (LNO) having an orthorhombic crystal structure in the range of 3.0 V to 4.0 V. More specifically, the irreversible additive according to the present embodiment may not comprise lithium nickel oxide (LNO) having an orthorhombic crystal structure in the range of 3.0 V to 3.5 V.

[0058] Therefore, the irreversible additive according to the present embodiment does not contain lithium nickel oxide (LNO) having an orthorhombic crystal structure in the range of 3.0 V to 4.0 V, and thus has the advantage of being able to effectively reduce the occurrence of side reactions or the generation of gases / impurities caused by the transformation of lithium nickel oxide (LNO) from an orthorhombic crystal structure to a trigonal crystal structure.

[0059] The lithium nickel oxide (LNO) having a trigonal crystal structure may have a space group of P3-m1. At this time, the lithium nickel oxide (LNO) having a trigonal crystal structure may have and a lattice with γ = 120.00°.

[0060] In addition, the lithium nickel oxide having a trigonal crystal structure contained in the irreversible additive according to an embodiment of the present disclosure may be lithium nickel oxide (LNO) having an orthorhombic crystal structure activated at a rate of 0.01 C to 0.05 C and whose crystal structure can be transformed from an orthorhombic system to a trigonal system.

[0061] Here, the space group of the lithium nickel oxide (LNO) having an orthorhombic crystal structure may belong to Immm. At this time, the lithium nickel oxide having an orthorhombic crystal structure may have and a lattice.

[0062] More specifically, lithium nickel oxide (LNO) with an orthorhombic crystal structure can be activated at a C-rate ranging from 0.01C to 0.05C. More preferably, lithium nickel oxide (LNO) with an orthorhombic crystal structure can be activated at a C-rate ranging from 0.015C to 0.035C. As an example, lithium nickel oxide (LNO) with an orthorhombic crystal structure can be activated at a C-rate ranging from 0.02C to 0.03C. Herein, activation can refer to charging and discharging at a predetermined C-rate. In addition, activation can refer to charging or discharging at a predetermined C-rate.

[0063] When lithium nickel oxide (LNO) with an orthorhombic crystal structure is activated at a C-rate that is too high outside the above range, it is less likely for lithium nickel oxide (LNO) with an orthorhombic crystal structure to transform into a trigonal crystal structure. Therefore, during the three-stage structural change of conventional lithium nickel oxide (LNO), it can be related to the occurrence of side reactions or the generation of gases / impurities. In addition, when the C-rate is too high, excessive gases may be generated due to overreaction. On the contrary, when lithium nickel oxide (LNO) with an orthorhombic crystal structure is activated at a C-rate that is too low outside the above range, the productivity may decrease.

[0064] In addition, the irreversible additive contains lithium nickel oxide with a trigonal crystal structure, where the lithium nickel oxide with a trigonal crystal structure can transform into a monoclinic crystal structure within the operating range of greater than 4.0V and less than 4.25V in a secondary battery. In addition, the lithium nickel oxide contained in the irreversible additive has a trigonal crystal structure or a monoclinic crystal structure within the operating range of the secondary battery and can undergo reversible transformation according to the operating range of the secondary battery. In addition, when the lithium nickel oxide contained in the irreversible additive has a monoclinic crystal structure, it can belong to the space group of C2 / m.

[0065] Therefore, the lithium nickel oxide contained in the irreversible additive can omit one stage of changing the crystal structure within the operating voltage range because the initial crystal structure within the operating voltage range is a trigonal crystal structure. Therefore, collateral problems such as the generation of impurities or gases caused by the insertion and extraction of excessive lithium ions can be minimized.

[0066] Hereinafter, the positive electrode material will be mainly described.

[0067] The positive electrode active material contained in the positive electrode material can include, for example, LiCoO2, LiNiO2, LiMnO2, LiMn2O2, Li(Ni a Co b Mn c )O2 (0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), LiNi 1-d Co d O2, LiCo1-d Mn d O2, LiNi 1-d Mn d O2(0 ≤ d < 1), Li(Ni a Co b Mn c )O4(0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), LiMn 2-e Ni e O4, LiMn 2-e Co e O4(0 < e < 2), LiCoPO4, LiFePO4, etc. Any one of them alone or a mixture of two or more can be used.

[0068] Among them, specifically, the positive electrode active material may include an oxide represented by the following Chemical Formula 2.

[0069] Li(Ni a Co b Mn c )O2 (2)

[0070] In the above formula, 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1.

[0071] Within the operating voltage range of the secondary battery, while Li ions are deintercalated and intercalated, the crystal structure of the oxide of Chemical Formula 2 easily changes from the hexagonal system to the monoclinic system. Therefore, since the oxide can have a structure similar to that of the irreversible additive of the present invention within the operating range, the irreversible additive according to the present invention can be used more effectively.

[0072] More specifically, the content of the oxide represented by Chemical Formula 2 can be 80% by weight or more based on the total weight of the positive electrode active material.

[0073] The content of the irreversible additive can be 0.1% by weight to 10% by weight based on the total weight of the positive electrode material. More preferably, the content of the irreversible additive can be 1% by weight to 8% by weight based on the total weight of the positive electrode material. In one example, the content of the irreversible additive can be 2% by weight to 5% by weight based on the total weight of the positive electrode material.

[0074] When the content of the irreversible additive is lower than the above range, the positive electrode efficiency compensation effect caused by adding the irreversible additive cannot be obtained. When the content of the irreversible additive is greater than the above range, problems such as electrode volume expansion and shortened life may be caused due to the generation of impurities or gases.

[0075] In addition to the positive electrode active material and the irreversible additive, the positive electrode material may further include a conductive material, a binder, and a filler.

[0076] The conductive material is used to impart conductivity to the electrode, and there is no particular limitation on the use of the conductive material as long as it does not cause chemical changes in the battery to be constructed and has electron conductivity.

[0077] The binder serves to improve the adhesion between the positive electrode active material particles and the adhesion strength between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene rubber (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber or various copolymers thereof, and any one of them alone or a mixture of two or more thereof can be used.

[0078] There is no particular limitation on the positive electrode current collector as long as it has conductivity and does not cause chemical changes to the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon; or aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, etc. can be used.

[0079] On the other hand, the secondary battery can have a structure in which the electrode assembly and the electrolyte are placed together in a battery case, and the electrode assembly includes: a positive electrode; a negative electrode, in which a negative electrode material containing a negative electrode active material is coated on a negative electrode current collector; and a separator disposed between the positive electrode and the negative electrode. Specifically, the secondary battery can be a lithium secondary battery.

[0080] The negative electrode can also be manufactured in a form in which a negative electrode material containing a negative electrode active material is coated on a negative electrode current collector, and the negative electrode material can also contain the conductive material, the binder, and the negative electrode active material as described above.

[0081] There is no particular limitation on the negative electrode current collector as long as it has high conductivity and does not cause chemical changes to the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon; copper or stainless steel whose surface is treated with carbon, nickel, titanium, silver, etc.; aluminum - cadmium alloy, etc. can be used.

[0082] The separator separates the negative electrode and the positive electrode and provides a channel for the movement of lithium ions. Any separator can be used without particular limitation as long as it is generally used as a separator in a lithium secondary battery. In particular, a separator having excellent water retention ability for the electrolyte and at the same time having low resistance to the migration of electrolyte ions is preferred.

[0083] The lithium secondary battery according to the present invention as described above can be used as a power source in the following devices: portable devices such as mobile phones, laptop computers, digital cameras; and electric vehicles such as hybrid electric vehicles (HEVs).

[0084] According to another embodiment of the present invention, there is provided a method for manufacturing a secondary battery including a positive electrode in which a positive electrode material is coated on a positive electrode current collector, the method including the steps of:

[0085] Coating a positive electrode composition on the positive electrode current collector to manufacture a positive electrode, the positive electrode composition being a mixture of the positive electrode material, a conductive material, and a binder; and

[0086] Manufacturing a secondary battery including the positive electrode, wherein the positive electrode material includes an irreversible additive and a positive electrode active material.

[0087] First, lithium nickel oxide (LNO) contained in the irreversible additive is prepared by mixing a lithium raw material, a nickel raw material, and a titanium raw material at a molar ratio of 1:1 and subjecting the mixture to heat treatment.

[0088] The heat treatment is carried out at 650°C to 800°C for 10 to 24 hours in an air atmosphere. In the case of a wet process, a drying process may also be included. More preferably, the heat treatment can be carried out in a nitrogen (N2) atmosphere. More preferably, the heat treatment can be carried out at 650°C to 750°C for 16 to 20 hours. As an example, the heat treatment can be carried out at 680°C for 18 hours. The heat treatment should be carried out within the above temperature and time ranges so that the reaction between the lithium raw material, the nickel raw material, and the titanium raw material can occur sufficiently and the unreacted materials can be minimized.

[0089] As the lithium raw material, lithium-containing oxides, sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or hydroxyoxides, etc. can be used, and specific examples thereof include Li2O, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, etc. Any one of them or a mixture of two or more of them can be used.

[0090] As the nickel raw material, nickel-containing oxides, sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or hydroxyoxides, etc. can be used, and specific examples thereof include NiO, Ni(NO3)2, LiNO2, NiSO4, Ni(OH)2, etc. Any one of them or a mixture of two or more of them can be used.

[0091] In addition, the method for manufacturing a secondary battery according to the present embodiment includes, after the step of manufacturing the secondary battery: activating the secondary battery at a C-rate of 0.01 to 0.05. More specifically, the secondary battery can be activated at a C-rate of 0.015C to 0.035C. As an example, the secondary battery can be activated at a C-rate of 0.02C to 0.03C. Here, activation can refer to charging and discharging at a predetermined C-rate. In addition, activation can refer to charging or discharging at a predetermined C-rate.

[0092] In addition, the method for manufacturing a secondary battery according to the present embodiment may further include, after the activation step: performing at least two charge and discharge cycles on the secondary battery at a C-rate of 0.05 to 0.15. More specifically, the charge and discharge of the secondary battery can be performed at a C-rate of 0.07C to 0.13C. As an example, the charge and discharge of the secondary battery can be performed at a C-rate of 0.09C to 0.11C.

[0093] When the activation step and the charge / discharge steps of activation or charge / discharge are performed at a C-rate that is too high outside the above range, the lithium nickel oxide (LNO) having an orthorhombic crystal structure contained in the secondary battery may not be converted into a trigonal crystal structure. When the steps of activation or charge / discharge are performed at a C-rate that is too low, the productivity may decrease.

[0094] Therefore, in the method for manufacturing a secondary battery according to the present embodiment, after the step of manufacturing the secondary battery, the activation step and / or the charge / discharge step can be performed. Thus, the irreversible additive contained in the secondary battery can include lithium nickel oxide that can be reversibly converted into a trigonal crystal structure or a monoclinic crystal structure within the working range (3.0V to 4.25V) of the secondary battery.

[0095] More specifically, in the method for manufacturing a secondary battery according to the present embodiment, before the activation step and / or the charge / discharge step, the irreversible additive contains lithium nickel oxide (LNO) having an orthorhombic crystal structure. After the activation step and / or the charge / discharge step, the lithium nickel oxide contained in the irreversible additive can have a trigonal crystal structure within the working range of 3.0V to 4.0V in the secondary battery. In addition, when the working range of the secondary battery is greater than 4.0V and below 4.25V, the lithium nickel oxide (LNO) may have a monoclinic crystal structure.

[0096] In other words, in the method for manufacturing a secondary battery according to the present embodiment, after the activation step and / or the charge / discharge step, it is not necessary to include lithium nickel oxide having a trigonal crystal structure within the working range (3.0V to 4.25V) of the secondary battery.

[0097] That is, in the method for manufacturing a secondary battery according to the present embodiment, after the activation step and / or the charge / discharge step, the lithium nickel oxide contained in the irreversible additive can minimize collateral problems such as the generation of impurities or gases caused by the deintercalation of excessive lithium ions, because the step of transforming from an orthorhombic crystal structure to a trigonal crystal structure during the crystal structure change stage can be omitted within the operating voltage range.

[0098] Hereinafter, the experimental contents in the above-described examples of the present invention and comparative examples for comparison will be described.

[0099] 22.9 g of Li2O and 30 g of NiO (molar ratio 1:1) were mixed and heat-treated at 685 °C for 18 hours in an N2 atmosphere, and then the resulting reaction product was cooled to obtain lithium nickel oxide (LNO).

[0100] Specifically, the irreversible additives prepared in Comparative Example 1 and Example 1, LiNi 0.4 Mn 0.3 Co 0.3 O2, a carbon black conductive material, and a PVdF binder were mixed in an N-methylpyrrolidone solvent at a weight ratio of 4.6:87.9:3.5:4 to prepare a positive electrode paste. The paste was coated on an aluminum current collector, and then dried and calendered to prepare a positive electrode. By using the obtained lithium nickel oxide (LNO) as the irreversible additive, a positive electrode and a lithium secondary battery were prepared by the following method.

[0101] Specifically, lithium nickel oxide (LNO) as the irreversible additive, LiNi 0.4 Mn 0.3 Co 0.3 O2, a carbon black conductive material, and a PVdF binder were mixed in an N-methylpyrrolidone solvent at a weight ratio of 4.6:87.9:3.5:4 to prepare a positive electrode paste. The paste was coated on an aluminum current collector, and then dried and calendered to prepare a positive electrode.

[0102] In addition, MCMB (mesophase carbon microbeads) as the negative electrode active material, a carbon black conductive material, and a PVdF binder were mixed in an N-methylpyrrolidone solvent at a weight ratio of 90:5:5 to prepare a composition for forming a negative electrode, and then the composition was coated on a copper current collector to prepare a negative electrode, and the MCMB was artificial graphite mixed with 10 wt% SiO.

[0103] A porous polyethylene separator was inserted between the positive electrode and the negative electrode prepared as described above to fabricate an electrode assembly. The electrode assembly was placed in a case, and then an electrolyte was injected into the case to fabricate a lithium secondary battery. At this time, an electrolytic solution was prepared by dissolving 1.15 M lithium hexafluorophosphate (LiPF6) in an organic solvent composed of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (EC / DMC / EMC, mixing volume ratio = 3 / 4 / 3).

[0104] Comparative example

[0105] The fabricated secondary battery was charged and discharged three times at a C-rate of 0.1.

[0106] Example

[0107] The fabricated secondary battery was activated at a C-rate of 0.025, and then charged and discharged twice at a C-rate of 0.1.

[0108] Experimental example - XRD analysis

[0109] The secondary batteries charged and discharged in the above comparative examples and examples were analyzed by ex-situ XRD, and the results are shown in Figures 1 to 4 . The XRD analysis was measured using a Bruker XRD D4 device, and using a Cu source target, the experiment was carried out within 10° to 80° at a step size of 0.02.

[0110] Referring to Figure 2 and Figure 3 , it was confirmed that when the secondary battery of the comparative example was charged at 30% SOC, 60% SOC, and 90% SOC, the LNO(101) peak and the LNO(002) peak were detected simultaneously. In particular, it was confirmed that when charging was carried out at 30% SOC, the available voltage range corresponded to the range of 3.0 V to 3.5 V, and the LNO 101 peak and the LNO 002 peak were detected simultaneously. In addition, it was confirmed that even when charging was carried out at 60% SOC and 90% SOC respectively, the available voltage ranges corresponded to the ranges of 3.0 V to 4.0 V and 3.0 V to 4.25 V, whereby the LNO(101) peak and the LNO(002) peak were detected simultaneously.

[0111] Therefore, it can be confirmed that when charge and discharge are performed at a rate of 0.1C as in the comparative example, the structure of at least a part of lithium nickel oxide (LNO) as an irreversible additive does not change and has an orthorhombic structure. In addition, at least a part of lithium nickel oxide (LNO) within the available voltage range has an orthorhombic crystal structure, such that lithium nickel oxide (LNO) having an orthorhombic crystal structure can be changed into a trigonal crystal structure or a monoclinic crystal structure. During this structural change process, the secondary battery of the comparative example is expected to be accompanied by the progress of side reactions or the generation of gas / impurities.

[0112] Reference Figure 4 and Figure 5 , it can be confirmed that the secondary battery of the example is activated at a rate of 0.025C, and then XRD analysis is performed according to the voltage change during two charge and discharge processes at a rate of 0.1C, and the LNO(101) peak and the LNO(002) peak disappear through the two charge / discharge processes.

[0113] In particular, it can be confirmed that the LNO(101) peak and the LNO(002) peak are detected simultaneously during one charge / discharge process. However, it can be confirmed that the LNO 101 peak and the LNO 002 peak are not detected during two charge / discharge processes.

[0114] Therefore, it can be confirmed that, different from the comparative example, the example is activated at a rate of 0.025C before two charge / discharge processes, whereby the crystal structure of lithium nickel oxide (LNO) as an irreversible additive has changed into a trigonal crystal structure. This indicates that the example activates lithium nickel oxide (LNO) at a relatively slow C rate and, compared with the conventional charge / discharge process, activates lithium nickel oxide (LNO) within the voltage range of 3.5V to 4.0V for a relatively longer time, making it change into a trigonal crystal structure, so that lithium nickel oxide (LNO) can change into a trigonal crystal structure.

[0115] Therefore, the irreversible additive according to the example contains lithium nickel oxide having a trigonal crystal structure within the available voltage range, and the lithium nickel oxide contained in the irreversible additive changes with a smaller number of stages compared to the number of stages of general structural changes, so that the progress of side reactions or the generation of gas / impurities can be minimized as the structural change of each stage proceeds.

[0116] Although the present invention has been shown and described with reference to preferred embodiments, the scope of the present invention is not limited thereto, and various variations and improvements made by those skilled in the art using the basic concepts of the present invention defined in the appended claims also fall within the gist and scope of the present invention.

Claims

1. A secondary battery, the secondary battery comprising a positive electrode in which a positive electrode material is coated on a positive electrode current collector, wherein the positive electrode material comprises an irreversible additive and a positive electrode active material, and wherein the irreversible additive is composed of lithium nickel oxide (LNO) having a trigonal crystal structure in a working range of 3.0 V to 4.0 V in the secondary battery, wherein in the positive electrode material, the content of the irreversible additive is 1 wt% to 10 wt% based on the total weight of the positive electrode material.

2. The secondary battery according to claim 1, wherein the lithium nickel oxide (LNO) having a trigonal crystal structure is transformed into a monoclinic crystal structure in a working range greater than 4.0 V and less than or equal to 4.25 V in the secondary battery.

3. The secondary battery according to claim 2, wherein in the irreversible additive, the space group of the lithium nickel oxide (LNO) having a trigonal crystal structure belongs to P3-m1, and the space group of the lithium nickel oxide (LNO) having a monoclinic crystal structure belongs to C2 / m.

4. The secondary battery according to claim 3, wherein the irreversible additive having a trigonal crystal structure has a lattice with γ = 120.00°.

5. The secondary battery according to claim 1, wherein the positive electrode active material comprises an oxide represented by Chemical Formula 2 below: Li(Ni a Co b Mn c )O2(2) In the above formula, 0 < a < 1, 0 < b < 1, 0 < c < 1, and a + b + c = 1.

6. The secondary battery according to claim 5, wherein the secondary battery has a structure in which an electrode assembly and an electrolyte are placed together in a battery case, the electrode assembly comprising: the positive electrode; a negative electrode in which a negative electrode material containing a negative electrode active material is coated on a negative electrode current collector; and a separator disposed between the positive electrode and the negative electrode.

7. A method of manufacturing a secondary battery, the secondary battery comprising a positive electrode in which a positive electrode material is coated on a positive electrode current collector, the method comprising the following steps: Coating a positive electrode composition on the positive electrode current collector to manufacture a positive electrode, the positive electrode composition being a mixture of the positive electrode material, a conductive material, and a binder; Manufacturing the secondary battery containing the positive electrode; Activating the secondary battery at a C rate of 0.01 to 0.05; and After the activation, charging and discharging the secondary battery at least twice at a C rate of 0.05 to 0.15, wherein the positive electrode material comprises an irreversible additive and a positive electrode active material, wherein in the positive electrode material, the content of the irreversible additive is 1 wt% to 10 wt% based on the total weight of the positive electrode material, wherein: Before the activation, the irreversible additive comprises lithium nickel oxide (LNO) having an orthorhombic crystal structure, and After charging and discharging the secondary battery at least twice, the lithium nickel oxide contained in the irreversible additive has a trigonal crystal structure in a working range of 3.0 V to 4.0 V in the secondary battery.

8. The method of manufacturing a secondary battery according to claim 7, wherein: The lithium nickel oxide (LNO) has a monoclinic crystal structure in a working range greater than 4.0 V and less than or equal to 4.25 V in the secondary battery.

9. The method of manufacturing a secondary battery according to claim 7, wherein, In the irreversible additive, The space group of lithium nickel oxide (LNO) with an orthorhombic crystal structure belongs to Immm, the space group of lithium nickel oxide (LNO) with a trigonal crystal structure belongs to P3-m1, and the space group of lithium nickel oxide (LNO) with a monoclinic crystal structure belongs to C2 / m.

10. The method for manufacturing a secondary battery according to claim 9, wherein: Among the irreversible additives, the lithium nickel oxide having an orthorhombic crystal structure has a lattice, and The lithium nickel oxide having a trigonal crystal structure has a lattice with γ = 120.00°.

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