Ternary cathode materials and their preparation methods, cathode sheets, secondary batteries and electronic devices

Abstract

This application provides a ternary cathode material, its preparation method, a cathode sheet, a secondary battery, and an electronic device. The ternary cathode material includes a ternary cathode material matrix containing doped regions, wherein the doped regions include aluminum-rich doped regions doped within the bulk phase of the ternary cathode material matrix and titanium-rich doped regions doped on the surface layer of the ternary cathode material matrix. The ternary cathode material provided by this application can improve the structural stability and cycle performance of secondary batteries.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a ternary cathode material and its preparation method, cathode sheet, secondary battery and electronic device. Background Technology

[0002] Lithium-ion batteries, as a representative of rechargeable batteries, have advantages such as high operating voltage, high energy density, good safety, and no memory effect, and have achieved great success in portable electronic devices, electric vehicles, and hybrid vehicles. Currently, in traditional rechargeable batteries, ternary materials such as nickel-cobalt-manganese are widely used as cathode materials due to their advantages such as high capacity and energy density. However, rechargeable batteries containing ternary cathode materials such as nickel-cobalt-manganese have poor structural stability and cycle performance during deep charge-discharge. Summary of the Invention

[0003] Based on this, this application provides a ternary cathode material and its preparation method, cathode sheet, secondary battery and electronic device, aiming to improve the structural stability and cycle performance of secondary batteries.

[0004] The first aspect of this application provides a ternary cathode material, comprising:

[0005] A ternary cathode material matrix containing doped regions, wherein the doped regions include aluminum-rich doped regions distributed within the bulk phase of the ternary cathode material matrix and titanium-rich doped regions distributed on the surface of the ternary cathode material matrix.

[0006] According to any embodiment of the first aspect of this application, the ternary cathode material matrix further includes a transition region located between the aluminum-rich doped region and the titanium-rich doped region, and a eutectic structure formed by Li-Ti-Al-O is distributed in the transition region.

[0007] According to any embodiment of the first aspect of this application, the ternary cathode material satisfies at least one of the following conditions (1) to (3):

[0008] (1) The average particle size of the ternary cathode material is 4μm to 20μm;

[0009] (2) Based on the total mass of the ternary cathode material, the mass percentage of aluminum in the aluminum-rich doped region is 0.01% to 10%;

[0010] (3) Based on the total mass of the ternary cathode material, the mass percentage of titanium in the titanium-rich doped region is 0.01% to 10%.

[0011] According to any embodiment of the first aspect of this application, the molecular formula of the ternary cathode material matrix is ​​LiNi. x Co y Mn1-x-y O2, where 0.33 ≤ x < 0.95, 0.05 <y≤0.77,0≤z<1。

[0012] The second aspect of this application provides a method for preparing a ternary cathode material, comprising:

[0013] Provides ternary cathode precursors and sols containing MAX-type compound dopants;

[0014] A pre-doped material is prepared by mixing a ternary cathode precursor, a sol containing a MAX-type compound dopant, and a lithium salt.

[0015] The pre-doped material is subjected to segmented sintering to form doped regions in the ternary cathode material matrix. The doped regions include aluminum-rich doped regions distributed in the bulk phase of the ternary cathode material matrix and titanium-rich doped regions distributed on the surface of the ternary cathode material matrix.

[0016] According to any embodiment of the second aspect of this application, the segmented sintering process of the pre-doped material includes:

[0017] The pre-doped material is subjected to a first sintering treatment at 400℃~500℃, preferably 450℃~500℃, for 3h~5h, preferably 3.5h~4.5h, to obtain the first sintered material;

[0018] The first sintering material is subjected to a second sintering treatment at 700℃~1000℃, preferably 750℃~950℃, for 10h~20h, preferably 12h~18h, to obtain a ternary cathode material.

[0019] According to any embodiment of the second aspect of this application, the mixing treatment of the ternary cathode precursor, the sol containing a MAX-type compound dopant, and the lithium salt includes:

[0020] The ternary cathode precursor is brought into contact with and mixed evenly with a sol containing a MAX-type compound dopant to obtain a mixture;

[0021] After drying, the mixture is uniformly mixed with lithium salt.

[0022] According to any embodiment of the second aspect of this application, the ternary cathode precursor satisfies at least one of the following conditions (1) to (2):

[0023] (1) The molecular formula of the ternary cathode precursor is Ni x Co y Mn 1-x-y (OH)₂, of which 0.33 <x<0.95,0.05<y<0.77;

[0024] (2) The average particle size of the ternary cathode precursor is 4μm to 20μm.

[0025] According to any embodiment of the second aspect of this application, the preparation method satisfies at least one of the following conditions (1) to (3):

[0026] (1) Lithium salts include one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate and lithium chloride;

[0027] (2) The mass ratio of the ternary cathode precursor to the MAX-type compound dopant is 1:(0.0005~0.05);

[0028] (3) The molar ratio of lithium element in lithium salt to alloy element in ternary cathode precursor is 1:(1.0~1.1).

[0029] According to any embodiment of the second aspect of this application, a sol containing a MAX-type compound dopant is provided, comprising:

[0030] Particles containing MAX-type compound dopants are brought into contact with and mixed with a dispersant in a pure aqueous solution to obtain a mixture;

[0031] The mixture was ball-milled to reduce the average particle size of particles containing MAX-type compound dopants to 20 nm to 200 nm.

[0032] According to any embodiment of the second aspect of this application, the preparation method satisfies at least one of the following conditions (1) to (4):

[0033] (1) The mass ratio of the particles containing the MAX-type compound dopant to the dispersant is 1:(0.01~1.5);

[0034] (2) The solid content of the sol containing MAX-type compound dopants is 5% to 50%;

[0035] (3) The molecular formula of the MAX-type compound dopant is Ti m AlC n , of which 0 <m<5,0<n<5;

[0036] (4) The dispersant includes one or more of the following: hexadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, hexadecylpyridine chloride, sodium benzenesulfonate, lauroylglutamic acid, and diethanolamide.

[0037] The third aspect of this application provides a positive electrode sheet, including the ternary positive electrode material provided in the first aspect of this application or the ternary positive electrode material prepared according to the preparation method provided in the second aspect of this application.

[0038] The fourth aspect of this application provides a secondary battery, including the positive electrode provided in the third aspect of this application.

[0039] The fifth aspect of this application provides an electronic device including the secondary battery provided in the fourth aspect of this application.

[0040] The electronic device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery.

[0041] The ternary cathode material provided in this application includes a doped region composed of an aluminum-rich doped region formed in the bulk phase and a titanium-rich doped region formed on the surface. This doped region has the following advantages: (1) The Al element provided by the aluminum-rich doped region in the bulk phase of the ternary cathode material can form a strong Al-O bond in the bulk phase, which can effectively stabilize the lattice structure of the material during the deep charge-discharge cycle of the secondary battery, suppress the structural collapse during the cycle, improve the stability of the material's crystal structure, and thus effectively improve the structural stability of the secondary battery and enhance its cycle performance; (2) The Ti element provided by the titanium-rich doped region on the surface of the ternary cathode material can form a Ti 4+ / Ti 3+ (2) The carrier concentration is increased, which effectively improves the electronic / ionic conductivity of the micro-region on the surface of the material, thereby improving the rate performance of the material and the secondary battery; (3) The Ti element provided by the titanium-rich doped region on the surface of the ternary cathode material can form Ti-O bonds, thereby reducing the activity of oxygen atoms on the surface, inhibiting the surface structure reconstruction caused by the migration of oxygen atoms, inhibiting the lattice distortion of the surface, further improving the stability of the material crystal structure, and improving the structural stability and cycle performance of the secondary battery; (4) The doped region formed in the ternary cathode material will form an interface region between the aluminum-rich doped region in the bulk phase and the titanium-rich doped region on the surface. Al and Ti elements are present in the interface region at the same time, which can give full play to the synergistic effect of Al and Ti elements on improving the material crystal structure, forming a "super-stable region" that is more conducive to the stability of the crystal structure, thereby further improving the structural stability and cycle performance of the secondary battery. Attached Figure Description

[0042] Figure 1 The images show the XRD patterns of the ternary cathode materials of Examples 1-2 and Comparative Examples 1-3.

[0043] Figure 2 This is a SEM image of the ternary cathode material of Example 1.

[0044] Figure 3 The figures show the high-temperature cycling performance test results of the ternary cathode materials in Examples 1-2 and Comparative Examples 1-2. Detailed Implementation

[0045] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0046] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. It should be noted that, unless otherwise stated, the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items, "above," "below," includes the stated number, and "one or more" with "multiple" means two or more.

[0048] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0049] During their research, the inventors discovered that in secondary batteries containing ternary cathode materials such as nickel, cobalt, and manganese, the internal stress of active ions (such as lithium ions) during deep charge-discharge cycles leads to the collapse of the internal structure of the ternary cathode material and surface structure reconstruction caused by the migration of oxygen atoms. To address these technical problems, a traditional method is to dry-dope the ternary material with elements, such as by doping with a single nano-oxide or co-doping with multiple elements. This can improve the structural stability of the ternary material to some extent, thereby enhancing its cycle performance.

[0050] However, further research by the inventors revealed that when multiple elements are co-doped, the ternary materials obtained using traditional dry doping methods exhibit disordered distribution of various dopant elements, making it difficult to fully leverage the synergistic effect of different dopant elements on improving the material's electrochemical performance. Therefore, when used as cathode materials in secondary batteries, ternary materials obtained through traditional dry doping doping do not significantly improve structural stability or battery cycle performance. The inventors also found that this is mainly due to the fact that traditional doping methods are typically solid-state methods. During high-temperature processing, most dopant elements cannot diffuse into the material's crystal lattice but are instead randomly distributed on the shallow surface and outer layers of the ternary material. Consequently, the doping of these elements does not significantly improve the crystal structure of the ternary material, and therefore, its effect on improving structural stability and secondary battery cycle performance is also minimal. To address the aforementioned technical problems, the inventors proposed the following technical solution.

[0051] A first aspect of this application provides a ternary cathode material, comprising: a ternary cathode material matrix containing doped regions, wherein the doped regions include aluminum-rich doped regions distributed within the bulk phase of the ternary cathode material matrix and titanium-rich doped regions distributed on the surface layer of the ternary cathode material matrix.

[0052] The ternary cathode material provided in this application includes a doped region composed of an aluminum-rich doped region formed in the bulk phase and a titanium-rich doped region formed on the surface. In other words, after doping, the aluminum concentration in the bulk phase of the ternary cathode material is high, while the titanium concentration in the shallow surface layer is high. The Al element provided by the aluminum-rich doped region in the bulk phase of the ternary cathode material can form strong Al-O bonds in the bulk phase, effectively stabilizing the lattice structure of the material during deep charge-discharge cycles of the secondary battery, suppressing structural collapse during cycling, improving the stability of the material's crystal structure, and thus effectively improving the structural stability of the secondary battery and enhancing its cycle performance.

[0053] Furthermore, the Ti element provided by the titanium-rich doped region on the surface of the ternary cathode material can form Ti 4+ / Ti 3+ The addition of charge carriers increases the carrier concentration, effectively improving the electronic / ionic conductivity of the micro-regions on the material surface, thereby enhancing the rate performance of the material and the secondary battery. Furthermore, the Ti elements provided by the titanium-rich doped regions on the surface of the ternary cathode material can form Ti-O bonds, reducing the activity of surface oxygen atoms, suppressing surface structure reconstruction caused by oxygen atom migration, inhibiting lattice distortion, further improving the stability of the material's crystal structure, and enhancing the structural stability and cycle performance of the secondary battery.

[0054] In some embodiments, the mass percentage of aluminum in the aluminum-rich doped region is 0.01% to 10%.

[0055] In this embodiment, the mass percentage of aluminum in the aluminum-rich doped region is controlled within a suitable range, which is conducive to the formation of strong Al-O bonds in the bulk phase, effectively stabilizing the crystal structure of the ternary cathode material during deep charge-discharge cycles in the secondary battery, suppressing structural collapse during the cycle, and improving the stability of the material's crystal structure.

[0056] In some embodiments, the mass percentage of titanium in the titanium-rich doped region is 0.01% to 10% based on the total mass of the ternary cathode material. For example, the mass percentage of titanium can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or within any of the above values.

[0057] In some implementations, the mass percentage of aluminum in the aluminum-rich doped region is 0.01% to 10% based on the total mass of the ternary cathode material. For example, the mass percentage of aluminum can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or any of the above values.

[0058] In this embodiment, the mass percentage of titanium in the titanium-rich doped region is controlled within a suitable range, which is beneficial for the formation of Ti-O bonds on the surface of the material, thereby reducing the activity of oxygen atoms on the surface, inhibiting the surface structure reconstruction caused by the migration of oxygen atoms, suppressing the lattice distortion of the surface, and further improving the stability of the material's crystal structure.

[0059] Furthermore, controlling the mass percentage of aluminum in the aluminum-rich doped region and titanium in the titanium-rich doped region within appropriate ranges can further promote the synergistic effect of Al and Ti elements on improving the crystal structure of the material, thereby enhancing the structural stability and cycle performance of the secondary battery.

[0060] In some embodiments, the average particle size of the ternary cathode material is 4 μm to 20 μm, for example, it can be 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 18 μm, or within any range of the above values. Controlling the average particle size of the ternary cathode material within the above range is beneficial to improving the structural stability and cycle performance of the secondary battery.

[0061] The average particle size of ternary cathode materials has a well-known meaning in the art and can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0062] A second aspect of this application provides a method for preparing a ternary cathode material, comprising the following steps:

[0063] S10 provides a ternary cathode precursor and a sol containing MAX-type compound dopants;

[0064] S20. The ternary cathode precursor, the sol containing the MAX-type compound dopant, and the lithium salt are mixed to prepare a pre-doped material.

[0065] S30. The pre-doped material is subjected to segmented sintering treatment to form doped regions in the ternary cathode material matrix. The doped regions include aluminum-rich doped regions distributed in the bulk phase of the ternary cathode material matrix and titanium-rich doped regions distributed on the surface of the ternary cathode material matrix.

[0066] In the preparation method of the ternary cathode material provided in this application, the ternary cathode precursor is liquid-phase mixed doping (wet doping) using a sol of MAX-type compound dopant. Since the MAX compound has a layered structure, in which the M and X elements form a layered structure, and A exists as an intercalating agent in the layered structure formed by MX, the activity of A is relatively high. Its characteristics are similar to those of ternary materials. The MAX compound has good electronic conductivity and mechanical strength, so it has a good effect as a dopant (because M and A are generally metal elements, and X is generally carbon element. The different activities of M and A can achieve gradient doping). The gradient doping of M and A can improve the structural stability of the ternary material (similar to forming a super-stable structural region) and suppress grain cracks and structural degradation. Meanwhile, liquid-phase mixed doping can increase the coating contact area of ​​the dopant on the ternary cathode precursor, making it easier for the dopant elements to enter the lattice of the ternary material during the subsequent sintering process, and achieve an ordered doping distribution inside the material lattice. Strong bond energy dopant-oxygen atom bonds are formed in the lattice, thereby effectively suppressing the structural collapse caused by lithium ion deintercalation during cycling, and improving the stability of the ternary cathode material crystal structure and the structural stability of the secondary battery.

[0067] In addition, the segmented sintering treatment can achieve gradient doping of elements, enabling the MAX-type compound dopant to decompose into different doping elements in different sintering segments, and helping different doping elements to have sufficient time to occupy the metal vacancies in the lattice of the ternary material, realizing doping in the bulk and surface layers of the ternary cathode material, so as to obtain a gradient doping distribution pattern that transitions from an aluminum-rich doping region in the bulk of the material to a titanium-rich doping region on the surface. Such a doping region can effectively stabilize the lattice structure of the ternary cathode material during cycling, and fully exert the synergistic effect of different doping elements on improving the electrochemical performance of the ternary cathode material. In this application, it is mainly reflected in the formation of a transition region between the aluminum-rich doping region and the titanium-rich doping region, and a eutectic structure formed by Li-Ti-Al-O is formed in the transition region. The eutectic formed by Al and Ti can simultaneously exert the stabilizing effect of Al and Ti elements on the material structure, forming a "super-stable transition region", which can well absorb the stress during the cycling of the material, provide a basis for a stable structure, and inhibit the distortion of the lattice, thereby effectively improving the cycling performance of the secondary battery.

[0068] In some embodiments, providing the sol containing the MAX-type compound dopant in step S10 includes the following steps:

[0069] S100: Making the particles containing the MAX-type compound dopant contact and mix with the dispersant in pure aqueous solution to obtain a mixed solution;

[0070] S110: Performing ball milling on the mixed solution to make the average particle size of the particles containing the MAX-type compound dopant be 20 nm to 200 nm, obtaining the sol containing the MAX-type compound dopant.

[0071] In some embodiments, the molecular formula of the MAX-type compound dopant is Ti m AlC n , where 0 < m < 5 and 0 < n < 5. Preferably, the MAX-type compound dopant is Ti3AlC2.

[0072] In some embodiments, the type of the dispersant is not specifically limited and can be selected according to actual needs. For example, the dispersant can include one or several of cetyltrimethylammonium chloride, dodecyltrimethylammonium chloride, cetylpyridinium chloride, sodium benzenesulfonate, lauroyl glutamate, and diethanolamide.

[0073] In some embodiments, the mass ratio of the particles containing the MAX-type compound dopant to the dispersant is 1:(0.01 - 1.5). For example, the mass ratio of the two can be 1:0.05, 1:0.10, 1:0.30, 1:0.50, 1:0.80, 1:1.10, 1:1.30 or within the range composed of any of the above values.

[0074] In some embodiments, the solid content of the sol containing MAX-type compound dopants is 5% to 50%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or any range thereof. Controlling the solid content within a suitable range is beneficial for improving the utilization rate of MAX-type compound dopants, while avoiding excessive agglomeration and precipitation.

[0075] Specifically, if the solid content of the mixture of particles containing MAX-type compound dopants, water, and dispersant is exactly in the range of 5% to 50%, then evaporation of water is not necessary; if the resulting mixture is too thin, or if a sol with the target solid content is to be obtained, the mixture can be placed in a rotary evaporator and the solvent can be evaporated at a temperature not exceeding 50°C to obtain a sol with the target solid content.

[0076] In some embodiments, the ternary cathode precursor in step S10 can be obtained by the following steps:

[0077] Cobalt sulfate, manganese sulfate, and nickel sulfate were added to a 2 mol / L ammonia solution to prepare a base solution. Sodium hydroxide was introduced into the base solution via a peristaltic pump to carry out a precipitation reaction. The pH of the solution was controlled by introducing ammonia solution, and the reaction temperature was monitored by a thermometer. After the reaction was completed, the solution was washed, dried, and sieved to remove iron to obtain the final ternary cathode precursor.

[0078] In some embodiments, the mixing process of the ternary cathode precursor, the sol containing the MAX-type compound dopant, and the lithium salt in step S20 includes the following steps:

[0079] S200: The ternary cathode precursor is brought into contact with and mixed evenly with a sol containing a MAX-type compound dopant to obtain a mixture;

[0080] S210. After drying the mixture, it is uniformly mixed with lithium salt to prepare a pre-doped material.

[0081] In some embodiments, the molecular formula of the ternary cathode precursor is Ni x Co y Mn 1-x-y (OH)₂, of which 0.33 <x<0.95,0.05<y<0.77。

[0082] In some embodiments, the average particle size of the ternary cathode precursor is 4 μm to 20 μm. For example, the average particle size can be 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 18 μm, or any value within the range above. An average particle size within this range is beneficial for subsequent doping and sintering processes, thereby facilitating the acquisition of ternary cathode materials with good structural stability and cycle performance.

[0083] The average particle size of the ternary cathode precursor has a well-known meaning in the art and can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, according to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0084] In some embodiments, the mass ratio of the ternary cathode precursor to the MAX-type compound dopant is 1:(0.0005 to 0.05). For example, the mass ratio can be 1:0.001, 1:0.005, 1:0.01, 1:0.05, or any range thereof. Controlling the mass ratio of the ternary cathode precursor to the MAX-type compound dopant within a suitable range is beneficial for achieving ordered doping of subsequent elements.

[0085] In some embodiments, the molar ratio of lithium element in the lithium salt to alloy element in the ternary cathode precursor is 1:(1.0 to 1.1).

[0086] In some embodiments, the type of lithium salt is not specifically limited and can be selected according to actual needs. For example, lithium salt may include one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, and lithium chloride.

[0087] In some embodiments, the drying method in step S210 is not specifically limited and can be selected according to actual needs. For example, it can be oven drying, natural drying, spray drying, etc. Preferably, the drying method is spray drying.

[0088] In some embodiments, the segmented sintering process of the pre-doped material in step S30 includes the following steps:

[0089] S300, at 400℃~500℃, preferably 450℃~500℃, the pre-doped material is subjected to a first sintering treatment for 3h~5h, preferably 3.5h~4.5h, to obtain the first sintered material;

[0090] S310. The first sintering material is subjected to a second sintering treatment at 700℃~1000℃, preferably 750℃~950℃, for 10h~20h, preferably 12h~18h, to obtain a ternary cathode material.

[0091] It should be noted that in order to form gradient doping of elements in ternary cathode materials, the pre-doped material needs to undergo segmented sintering in steps S300 and S310, and the heating rate during the segmented sintering process needs to be controlled.

[0092] In some embodiments, step S300 first performs a first sintering treatment, that is, a low-temperature sintering treatment. The temperature of the first sintering treatment needs to be controlled between 400℃ and 500℃, for example, 450℃; the time needs to be controlled between 3h and 5h, for example, 3.5h, 4h, 4.5h or within any range of the above values; the heating rate is ≤3℃ / min.

[0093] During low-temperature sintering, by controlling the temperature, time, and heating rate within a suitable range, the highly active Al element in the MAX-type compound dopant can migrate to the surface to form Al2O3. As the temperature increases, the Al element gradually diffuses and migrates into the bulk phase of the ternary material, achieving aluminum doping within the bulk phase of the ternary material and forming an aluminum-rich doped region within the bulk phase.

[0094] In some embodiments, step S310 involves a second sintering process, namely, a high-temperature sintering process. The temperature of the second sintering process needs to be controlled between 700°C and 1000°C, for example, 750°C, 800°C, 850°C, 900°C, 950°C, or any value above; the time needs to be controlled between 10h and 20h, for example, 12h, 14h, 16h, 18h, or any value above; the heating rate needs to be ≤5°C / min.

[0095] During high-temperature sintering, by controlling the temperature, time, and heating rate within a suitable range, that is, by coordinating the temperature, time, and heating rate, the MAX-type compound dopant can be completely decomposed to form TiO2, and Ti elements can be doped in the shallow surface layer of the material.

[0096] In some embodiments, the sintering atmosphere for the first and second sintering processes is not particularly limited and can be selected according to actual needs. For example, the sintering atmosphere can be air, oxygen, or a mixture of air and oxygen.

[0097] Therefore, by performing segmented sintering, gradient doping of elements can be achieved, allowing MAX-type compound dopants to decompose into different doping elements in different sintering stages. This also helps specific doping elements to occupy transition metal vacancies in the ternary material lattice for a sufficient time, achieving doping in both the bulk and surface layers of the ternary cathode material. Specifically, in the low-temperature stage, highly active Al elements first enter the material lattice and occupy metal vacancies, achieving bulk doping and ensuring an Al-rich internal structure. In the high-temperature stage, Ti elements enter the bulk phase. Since most Al elements have preferentially occupied metal vacancies, some Ti elements decomposed in the high-temperature stage can also occupy metal vacancies. Most Ti elements preferentially dope in the shallow surface layer (5nm~500nm). Thanks to the characteristics of MAX compounds, gradient doping of Al and Ti is achieved, resulting in an ordered distribution of gradient doping from the aluminum-rich doped region in the bulk phase to the titanium-rich doped region on the surface. This doping region can effectively stabilize the lattice structure of the ternary cathode material during cycling and fully leverage the synergistic effect of different doping elements on improving the electrochemical performance of the ternary cathode material, thereby effectively improving the cycle performance of the secondary battery.

[0098] A third aspect of the embodiments of this application provides a positive electrode sheet, including the ternary positive electrode material provided in the first aspect of this application or the ternary positive electrode material prepared by the preparation method provided in the second aspect of this application.

[0099] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the ternary positive electrode material of the second aspect of this application.

[0100] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0101] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0102] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0103] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0104] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as ternary positive electrode material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0105] A fourth aspect of the embodiments of this application provides a secondary battery, including the positive electrode provided in the third aspect of this application.

[0106] In some implementations, the type of secondary battery is not specifically limited and may include any battery in which an electrochemical reaction occurs to convert chemical energy into electrical energy, such as a lithium-ion battery or a sodium-ion battery.

[0107] In some embodiments, the secondary battery also includes a negative electrode, an electrolyte, and a separator. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0108] A fifth aspect of this application provides an electronic device including the secondary battery provided in the fourth aspect of this application. The secondary battery can be used as a power source in the electronic device.

[0109] In some embodiments, the type of electronic device is not particularly limited, and it can be any electronic device known in the prior art. For example, electronic devices may include, but are not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0110] Example

[0111] The following are specific embodiments, which describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations within the scope of the disclosure of this application will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0112] Example 1

[0113] (1) 200g of 10μm Ti3AlC2, 20g of hexadecyltrimethylammonium chloride and 1000g of deionized water were added to a ball mill jar, 200g of zirconium balls were added, and the mixture was ground at 2000rpm / min for 10h and ultrasonicated for 1h to obtain a sol containing Ti3AlC2 dopant with an average particle size of 20nm and a solid content of 20%.

[0114] (2) 25 kg of Ni with an average particle size of 4.0 μm 0.6 Co 0.1 Mn 0.3 The (OH)2 precursor was added to the sol obtained in step (1) and stirred for 1 hour. Then, it was spray-dried and granulated to obtain the precursor. The precursor and lithium hydroxide were mixed evenly in a molar ratio of Li element / (Ni+Co+Mn) element of 1.1:1 to obtain the pre-doped material.

[0115] (3) The pre-doped material was sintered in a box furnace under an oxygen atmosphere in stages. The temperature of the low-temperature section was 450℃, the sintering time was 3h, and the heating rate was 3℃ / min; the sintering temperature of the high-temperature section was 930℃, the sintering time was 11h, and the heating rate was 5℃ / min. After being crushed by a jaw crusher, roller crusher, and airflow pulverizer, a ternary cathode material LiNi with Al and Ti elements gradient doping was obtained. 0.6 Co 0. 1Mn 0.23 Al 0.05 Ti 0.02 O2.

[0116] Example 2

[0117] (1) 200g of 20μm Ti3AlC2, 15g of hexadecyltrimethylammonium chloride and 500g of deionized water were added to a ball mill jar, 200g of zirconium balls were added, and the mixture was ground at 2000rpm / min for 3h and ultrasonicated for 1h to obtain a sol containing Ti3AlC2 dopant with an average particle size of 200nm and a solid content of 40%.

[0118] (2) 25 kg of Ni with an average particle size of 4.0 μm 0.6 Co 0.1 Mn 0.3 The (OH)2 precursor was added to the sol obtained in step (1) and stirred for 1 hour. Then, it was spray-dried and granulated to obtain the precursor. The precursor and lithium hydroxide were mixed evenly in a molar ratio of Li element / (Ni+Co+Mn) element of 1.03:1 to obtain the pre-doped material.

[0119] (3) The pre-doped material was sintered in a box furnace under an oxygen atmosphere in stages. The temperature of the low-temperature section was 450℃, the sintering time was 3h, and the heating rate was 3℃ / min; the sintering temperature of the high-temperature section was 930℃, the sintering time was 11h, and the heating rate was 5℃ / min. After being crushed by a jaw crusher, roller crusher, and airflow pulverizer, a ternary cathode material LiNi with Al and Ti elements gradient doping was obtained. 0.6 Co 0. 1Mn 0.23 Al 0.05 Ti 0.02 O2.

[0120] Example 3

[0121] (1) 200g of 20μm Ti3AlC2, 15g of hexadecyltrimethylammonium chloride and 400g of deionized water were added to a ball mill jar, 200g of zirconium balls were added, and the mixture was ground at 2000rpm / min for 3h and ultrasonicated for 1h to obtain a sol containing Ti3AlC2 dopant with an average particle size of 200nm and a solid content of 50%.

[0122] (2) 25 kg of Ni with an average particle size of 4.0 μm 0.6 Co 0.1 Mn 0.3 The (OH)2 precursor was added to the sol obtained in step (1) and stirred for 1 hour. Then, it was spray-dried and granulated to obtain the precursor. The precursor and lithium hydroxide were mixed evenly in a molar ratio of Li element / (Ni+Co+Mn) element of 1.03:1 to obtain the pre-doped material.

[0123] (3) The pre-doped material was sintered in a box furnace under an oxygen atmosphere in stages. The temperature of the low-temperature section was 450℃, the sintering time was 3h, and the heating rate was 3℃ / min; the sintering temperature of the high-temperature section was 930℃, the sintering time was 11h, and the heating rate was 5℃ / min. After being crushed by a jaw crusher, roller crusher, and airflow pulverizer, a ternary cathode material LiNi with Al and Ti elements gradient doping was obtained. 0.6 Co 0. 1Mn 0.22 Al 0.06 Ti 0.02 O2.

[0124] Comparative Example 1

[0125] The preparation method of Comparative Example 1 is similar to that of Example 1, except that the ternary cathode material is not doped, i.e., 25 kg of Ni with an average particle size of 4.0 μm is used. 0.6 Co 0.1 Mn 0.3 The (OH)₂ precursor and lithium hydroxide were mixed uniformly at a molar ratio of Li / (Ni+Co+Mn) of 1.1:1, and then sintered in a box furnace under an oxygen atmosphere at a heating rate of 10℃ / min, a sintering temperature of 930℃, and a sintering time of 11h. After sintering, the mixture was crushed by a jaw crusher, roller crusher, and air jet mill to obtain undoped ternary cathode material LiNi. 0.6 Co 0.1 Mn 0.3 O2.

[0126] Comparative Example 2

[0127] The preparation method of Comparative Example 2 is similar to that of Example 1, except that the ternary cathode material is doped with Al and Ti elements using a conventional dry doping method, specifically using 25 kg of Ni with an average particle size of 4.0 μm. 0.6 Co 0.1 Mn 0.3The (OH)2 precursor, 11.90 kg of lithium hydroxide (Li element / (Ni+Co+Mn) element molar ratio of 1.1:1), 120 g of nano-alumina and 100 g of nano-titanium oxide were mixed evenly and then sintered in a box furnace under an oxygen atmosphere. The heating rate was 10℃ / min, the sintering temperature was 930℃, and the sintering time was 11 h. After sintering, the material was crushed by a jaw crusher, roller crusher, and air jet mill to obtain the Al and Ti doped ternary cathode material LiNi. 0.6 Co 0.1 Mn 0.23 Al 0.05 Ti 0.02 O2.

[0128] Comparative Example 3

[0129] The preparation method of Comparative Example 3 is similar to that of Example 1, except that the ternary cathode material is doped with Al using a traditional dry doping method, specifically 25 kg of Ni with an average particle size of 4.0 μm. 0.6 Co 0.1 Mn 0.3 The (OH)2 precursor, 1190 kg of lithium hydroxide (with a molar ratio of Li to (Ni+Co+Mn) of 1.1:1), and 120 g of nano-alumina were mixed evenly and then sintered in a box furnace under an oxygen atmosphere. The heating rate was 10 °C / min, the sintering temperature was 930 °C, and the sintering time was 11 h. After sintering, the material was crushed by a jaw crusher, roller crusher, and air jet mill to obtain the Al-doped ternary cathode material LiNi. 0.6 Co 0.1 Mn 0.25 Al 0.05 O2.

[0130] Comparative Example 4

[0131] The preparation method of Comparative Example 4 is similar to that of Example 1, except that the predoped material is sintered only once in step (3), that is, the predoped material is sintered at 930°C for 11 hours in an oxygen atmosphere in a box furnace, with a heating rate of 10°C / min.

[0132] The ternary cathode materials or lithium-ion batteries prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to relevant performance tests. The test results are shown in Tables 1 and 2 below.

[0133] The test conditions or standards for each performance test item are as follows:

[0134] (1) XRD testing of ternary cathode materials

[0135] The ternary cathode material powder was placed in the sample stage of an XRD instrument (model Bruker D8), and a scanning rate of 2° / min was used with a scanning angle range of 10° to 90° to obtain the results shown in the attached figure. Figure 1 The XRD diffraction pattern shown.

[0136] (2) SEM testing of ternary cathode materials

[0137] The ternary cathode material was tested using a ZEISS Sigma 300 scanning electron microscope. The morphology of the samples was observed according to standard JY / T010-1996, and the results are shown in the attached figure. Figure 2 The topographic diagram shown.

[0138] (3) Distribution test of doped elements in ternary cathode materials

[0139] The XRD patterns of the ternary cathode materials prepared in Examples 1-2 and Comparative Examples 1-3 after 50 cycles at 2.8-4.4V and 0.5C / 1C rate were analyzed and compared, as shown in the attached figures. Figure 1 As shown in the figure. The samples of Example 1 and Comparative Examples 1 to 3 were subjected to XRD refinement, and the refined data are shown in Table 1 below; XRD refinement refers to the refinement of XRD data using the Rietveld method.

[0140] (4) Rate performance test of lithium-ion batteries

[0141] The prepared ternary cathode material was assembled into a coin cell, wherein the electrode material was conductive carbon black in a ratio of 90:10 wt%, the solvent was NMP, and the electrode surface density was 1.2 mg / cm³. 2 At a voltage of 2.8-4.4V and a temperature of 25℃, the device was charged and discharged once at a rate of 0.1C / 0.1C, then charged and discharged at rates of 0.1C / 1C, 0.2C / 1C, 0.5C / 2C, and 1C / 1C, and finally tested for 50 cycles at a rate of 1C / 1C.

[0142] (4) High-temperature cycle performance test of lithium-ion batteries

[0143] The lithium-ion battery was charged at 55°C with a constant current of 1C to 4.4V, then charged with a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then discharged with a constant current of 1C to 2.5V. This constituted one charge-discharge cycle, and the discharge capacity at this point was recorded as D01. The lithium-ion battery was subjected to the same charge-discharge process for 50 cycles, and the discharge capacity on the 50th cycle was recorded as D1. A comparative graph of this charge-discharge cycle process was plotted, as shown in the attached figure. Figure 3 The graph shown is a curve of lithium-ion battery capacity retention versus cycle number.

[0144] Table 1

[0145]

[0146] Table 2

[0147]

[0148] From the appendix Figure 1 As can be seen, no impurity peaks appeared after 50 cycles of the samples prepared according to the methods of Examples 1-2 and Comparative Examples 1-3, indicating that the doping of Al and Ti did not change the crystal structure of the material, and the material structure has good stability and no structural changes occurred.

[0149] Table 1 shows the XRD refinement results of Sample 1 and Comparative Examples 1-3. The table shows that after 50 cycles at 2.8-4.4V and a 0.5C / 1C rate, the I003 / 104 value of Sample 1 is greater than that of Comparative Examples 2-4. The cell parameters c, a, c / a, and cell volume all increase, which is beneficial for Li. + Diffusion in the bulk phase can reduce the cyclic DCR. This is based on the substitution of transition metal vacancies by Al and Ti, and the fact that their bond energies are higher than those of Ni / Co / Mn and O, which helps to enhance the stability of the layered structure and suppress the formation of rock salt phases. On the other hand, coating can stabilize the electrode / electrolyte interface and suppress Ni diffusion. 4+ The reaction with the electrolyte alleviates the corrosion of the positive electrode material by HF in the electrolyte and inhibits the formation of oxygen vacancies.

[0150] As can be seen from the comparison of Examples 1, 2, and 3 with Comparative Example 2 in Table 1 above, the ternary cathode material with Al and Ti element gradient doping prepared by the method provided in this application has higher charge-discharge capacity, first efficiency, and cycle performance than the ternary cathode material obtained by conventional dry doping in Comparative Example 2. This shows that element gradient doping can indeed improve the stability of the material's crystal structure and effectively improve the structural stability of the secondary battery, thereby enhancing its cycle performance.

[0151] By comparing Examples 1 and 2 with Comparative Example 4, it can be seen that the ternary cathode material obtained by segmented sintering in this application has higher charge-discharge capacity, first efficiency and cycle performance than the ternary cathode material prepared by one sintering in Comparative Example 4. This shows that segmented sintering is indeed beneficial to forming doped regions in ternary cathode materials, improving the stability of the material's crystal structure, and thus effectively improving the structural stability of the secondary battery and its cycle performance.

[0152] In Table 2 above, compared with Comparative Examples 1 to 4, the ternary cathode materials in Examples 1 to 3 have higher charging capacities at 0.5C, 1C, and 2C than those in Comparative Examples 1 to 4, indicating that the preparation method provided in this application can effectively improve the rate performance of ternary cathode materials.

[0153] From the appendix Figure 1 As can be seen, no impurity peaks appeared in the samples of Examples 1-2 and Comparative Examples 1-3, indicating that the gradient doping of elements does not change the crystal structure of the ternary cathode material. Moreover, the intensity ratio of the 003 / 104 peaks of the samples all exceeded 1.2, indicating that the ternary cathode material has a low Li / Ni mixing value.

[0154] From the appendix Figure 3 It can be seen that the high-temperature cycling performance of the ternary cathode material prepared by the preparation method provided in this application is significantly higher than that of Comparative Examples 1 and 2, indicating that the preparation method provided in this application can improve the cycling performance of lithium-ion batteries, and that this preparation method is significantly better than the traditional dry doping method.

[0155] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0156] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A ternary cathode material, characterized in that, include: A ternary cathode material matrix containing doped regions, wherein the doped regions include aluminum-rich doped regions distributed within the bulk phase of the ternary cathode material matrix and titanium-rich doped regions distributed on the surface of the ternary cathode material matrix. The preparation method of the ternary cathode material includes: Provides ternary cathode precursors and sols containing MAX-type compound dopants; The ternary cathode precursor, the sol containing the MAX-type compound dopant, and the lithium salt are mixed to prepare a pre-doped material; The pre-doped material is subjected to segmented sintering to form doped regions in the ternary cathode material matrix. The segmented sintering process includes a first sintering process and a second sintering process. The first sintering process is carried out at 400℃~500℃, and the second sintering process is carried out at 700℃~1000℃. The doped regions include aluminum-rich doped regions distributed in the bulk phase of the ternary cathode material matrix and titanium-rich doped regions distributed on the surface of the ternary cathode material matrix.

2. The ternary cathode material according to claim 1, characterized in that, The ternary cathode material matrix further includes a transition region located between the aluminum-rich doped region and the titanium-rich doped region, and a eutectic structure formed by Li-Ti-Al-O is distributed in the transition region.

3. The ternary cathode material according to claim 1, characterized in that, The ternary cathode material satisfies at least one of the following conditions (1) to (3): (1) The average particle size of the ternary cathode material is 4 μm to 20 μm; (2) Based on the total mass of the ternary cathode material, the mass percentage of aluminum in the aluminum-rich doped region is 0.01%~10%; (3) Based on the total mass of the ternary cathode material, the mass percentage of titanium in the titanium-rich doped region is 0.01%~10%.

4. The ternary cathode material according to any one of claims 1-3, characterized in that, The molecular formula of the ternary cathode material matrix is ​​LiNi. x Co y Mn 1-x-y O2, where 0.33 ≤ x < 0.95, 0.05 <y≤0.77。 5. A method for preparing a ternary cathode material, characterized in that, include: Provides ternary cathode precursors and sols containing MAX-type compound dopants; The ternary cathode precursor, the sol containing the MAX-type compound dopant, and the lithium salt are mixed to prepare a pre-doped material; The pre-doped material is subjected to segmented sintering to form doped regions in the ternary cathode material matrix. The segmented sintering process includes a first sintering process and a second sintering process. The first sintering process is carried out at 400℃~500℃, and the second sintering process is carried out at 700℃~1000℃. The doped regions include aluminum-rich doped regions distributed in the bulk phase of the ternary cathode material matrix and titanium-rich doped regions distributed on the surface of the ternary cathode material matrix.

6. The preparation method according to claim 5, characterized in that, The segmented sintering process of the pre-doped material includes: The pre-doped material is subjected to the first sintering treatment at 450℃~500℃ for 3h~5h to obtain the first sintered material; The first sintering material is subjected to a second sintering treatment at 750℃~950℃ for 10h~20h to obtain the ternary cathode material.

7. The preparation method according to claim 6, characterized in that, One or more of the following conditions must be met: (1) The pre-doped material is subjected to the first sintering treatment for 3.5h to 4.5h; (2) The first sintering material is subjected to the second sintering treatment for 12h to 18h.

8. The preparation method according to claim 5, characterized in that, The mixing process of the ternary cathode precursor, the sol containing the MAX-type compound dopant, and the lithium salt includes: The ternary cathode precursor is brought into contact with and mixed with the sol containing the MAX-type compound dopant to obtain a mixture; The mixture is dried and then mixed with the lithium salt.

9. The preparation method according to any one of claims 5-8, characterized in that, The ternary cathode precursor satisfies at least one of the following conditions (1) to (2): (1) The molecular formula of the ternary cathode precursor is Ni x Co y Mn 1-x-y (OH)₂, of which 0.33 <x<0.95,0.05<y<0.77; (2) The average particle size of the ternary cathode precursor is 4μm~20μm.

10. The preparation method according to any one of claims 5-8, characterized in that, The preparation method satisfies at least one of the following conditions (1) to (3): (1) The lithium salt includes one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate and lithium chloride; (2) The mass ratio of the ternary cathode precursor to the MAX-type compound dopant is 1:(0.0005~0.05); (3) The molar ratio of lithium element in the lithium salt to the sum of all metal elements in the ternary cathode precursor is 1:(1.0~1.1).

11. The preparation method according to any one of claims 5-8, characterized in that, The sol containing MAX-type compound dopants includes: The particles containing the MAX-type compound dopant are brought into contact with and mixed with a dispersant in a pure aqueous solution to obtain a mixture; The mixture is ball-milled to reduce the average particle size of the particles containing the MAX-type compound dopant to 20 nm to 200 nm.

12. The preparation method according to claim 11, characterized in that, The preparation method satisfies at least one of the following conditions (1) to (4): (1) The mass ratio of the particles containing the MAX-type compound dopant to the dispersant is 1:(0.01~1.5); (2) The solid content of the sol containing the MAX-type compound dopant is 5%~50%; (3) The molecular formula of the MAX-type compound dopant is Ti m AlC n , of which 0 <m<5,0<n<5; (4) The dispersant includes one or more of hexadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, hexadecylpyridine chloride, sodium benzenesulfonate, lauroylglutamic acid and diethanolamide.

13. A positive electrode plate, characterized in that, This includes the ternary cathode material according to any one of claims 1-4 or the ternary cathode material prepared by the preparation method according to any one of claims 5-12.

14. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 13.

15. An electronic device, characterized in that, Includes the secondary battery as described in claim 14.

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