Secondary battery, preparation method therefor and electrical device

Abstract

A secondary battery, a preparation method therefor and an electrical device. The secondary battery comprises a composite negative electrode sheet; the composite negative electrode sheet comprises a negative electrode sheet and a modification layer, at least one side of the negative electrode sheet being provided with the modification layer; the modification layer contains a nitrogen-containing inorganic compound. The nitrogen-containing inorganic compound contains a nitride and a nitrate compound; the nitride contains at least one of a metal element and a non-metal element; the metal element comprises one or more of Al, Zr, Mg, Cr, Nb, Ta and Ti; the non-metal element comprises one or more of Si, B and C; the nitrate compound comprises MxNyOz, wherein M comprises one or more of M' and M", M' comprises one or more of Li and Na, M" comprises one or more of Al, Zr, Mg, Cr, Nb, Ta and Ti, 0<x≤1, 0<y≤5 and 0<z≤15.

Description

Secondary batteries and their preparation methods, and electrical equipment Technical Field

[0001] This application relates to the field of batteries, specifically to secondary batteries and their preparation methods and electrical devices. Background Technology

[0002] Batteries are not only used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. Cycle life is a crucial indicator for rechargeable batteries; a longer cycle life translates to a lower levelized cost of electricity (LCOE) over the entire lifecycle. Currently, the cycle life of rechargeable batteries needs further improvement.

[0003] Application content

[0004] The first aspect of this application proposes a secondary battery, including a composite negative electrode sheet, the composite negative electrode sheet including a negative electrode sheet and a modification layer, the modification layer being disposed on at least one side of the negative electrode sheet, the modification layer comprising: nitrogen-containing inorganic compounds; the nitrogen-containing inorganic compounds including nitrides and nitrate compounds;

[0005] Nitrides contain at least one of a metallic element and a non-metallic element; the metallic element includes one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti, and the non-metallic element includes one or more of Si, B, and C;

[0006] Nitrate compounds include M x N y O z Wherein, M includes one or more of M' and M”; M' includes one or more of Li and Na; M” includes one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti; 0 <x≤1,0<y≤5,0<z≤15。

[0007] This application forms a modification layer on the surface of the negative electrode. The nitrides in the modification layer can serve as ceramic materials, exhibiting high high-temperature and chemical stability. Under long-term cycling and high-temperature conditions, they provide excellent isolation and protection for the negative electrode, improving the interfacial stability between the negative electrode and the electrolyte, and thus enhancing the battery's cycle life. The nitrate compounds in the modification layer contribute to the uniform distribution of lithium ions, providing suitable lithium-ion conduction channels and guiding the uniform insertion and extraction of lithium ions between the electrode and the electrolyte. This ensures uniform growth of the SEI film on the electrode surface, rather than localized overgrowth, thereby improving the uniformity of the SEI film, enhancing its formation quality, and ultimately increasing the battery's cycle life.

[0008] In some embodiments of the present application, the nitride includes one or more of aluminum nitride, zirconium nitride, magnesium nitride, chromium nitride, niobium nitride, tantalum oxide, titanium nitride, silicon nitride, boron nitride, carbon nitride, titanium carbon nitride, chromium aluminum nitride, and their respective non-stoichiometric nitrides. These nitrides containing at least one of metal and non-metal in the embodiments of the present application have good high-temperature resistance characteristics, which are beneficial to improving the thermal stability performance of the battery and also beneficial to improving the high-temperature cycle life of the battery.

[0009] In some embodiments of the present application, the nitride includes one or more of aluminum nitride, zirconium nitride, magnesium nitride, chromium nitride, niobium nitride, tantalum oxide, titanium nitride, titanium carbon nitride, chromium aluminum nitride, and their respective non-stoichiometric nitrides. These nitrides containing at least one of metal and non-metal in the embodiments of the present application have good high-temperature resistance characteristics, which are beneficial to further improving the thermal stability performance of the battery and also beneficial to improving the high-temperature cycle life of the battery; in addition, they can provide a metal source for the formation of nitrate compounds.

[0010] In some embodiments of the present application, the nitrate compound includes M' 1-a N b O c , Zr(NO2)4, Zr(NO3)4, Al(NO3)3, Mg(NO3)2, Cr(NO3)3, Nb(NO3)5, (Nb(NO3)3, Nb(NO3)4, Ta(NO3)5, Ta(NO3)4, Ti(NO3)4, Ti(NO3)3, where 0 < a < 1, 0 < b < 5, 0 < c < 15. These nitrate compounds are beneficial to further improving the conductivity of the secondary battery and enhancing the uniformity of the SEI film, thereby better improving the cycle life of the battery.

[0011] In some embodiments of the present application, the nitrate compound includes M' 1-a N b O c , and also includes one or more of Zr(NO2)4, Zr(NO3)4, Ti(NO3)4, Ti(NO3)3, where 0 ≤ a < 1, 0 < b ≤ 5, 0 < c ≤ 15. It is beneficial to better improve the film-forming quality of the SEI film, including the uniformity and mechanical properties of the SEI, and further enhance the cycle life of the battery.

[0012] In some embodiments of the present application, based on the test results of the modified layer by X-ray photoelectron spectroscopy analysis, it satisfies any one of the following (i) to (ii):

[0013] (i) The mass content of the nitride is 2% - 8%;

[0014] (ii) The mass content of nitrate compounds is 1.5% to 6%.

[0015] When the nitride content meets the above conditions, it can not only provide physical isolation and improve interface stability, but also achieve lower battery internal resistance, which is beneficial to improving battery cycle performance.

[0016] The content of nitrate compounds meets the above conditions, which helps to improve the uniformity of SEI and increase the cycle life of the battery; at the same time, it helps to obtain a lower battery internal resistance.

[0017] In some embodiments of this application, the test results of the modified layer based on X-ray photoelectron spectroscopy analysis satisfy any one of the following (i) to (ii):

[0018] (i) The mass content of nitrides is 2.5% to 7.5%;

[0019] (ii) The mass content of nitrate compounds is 2% to 5.5%.

[0020] When the nitride content meets the above conditions, it can provide good physical isolation and improve interface stability, while also achieving lower battery internal resistance, which is beneficial for further improving the battery's cycle performance.

[0021] Meeting the above conditions regarding the content of nitrate compounds is beneficial for further improving the uniformity of SEI and increasing the cycle life of the battery; at the same time, it is also beneficial for obtaining lower battery internal resistance.

[0022] In some embodiments of this application, the electrochemically active specific surface area of ​​the composite negative electrode is 7 cm². 2 / g~8.7cm 2 / g. The electrochemically active specific surface area of ​​the composite negative electrode meets the above conditions, which helps to reduce the side reaction activity between the negative electrode and the electrolyte, and can reduce the consumption of active lithium during cycling, thereby improving the cycle life of the battery.

[0023] In some embodiments of this application, the electrochemically active specific surface area of ​​the composite negative electrode is 7.2 cm². 2 / g~8.6cm 2 / g. The electrochemically active specific surface area of ​​the composite negative electrode meets the above conditions, which is beneficial to further reduce the side reaction activity between the negative electrode and the electrolyte, and can reduce the consumption of active lithium during cycling, thereby improving the cycle life of the battery.

[0024] In some embodiments of this application, the thickness of the modification layer is 5 nm to 50 nm. This is beneficial for obtaining better battery kinetic performance, thereby improving the battery's cycle life.

[0025] In some embodiments of this application, the thickness of the modification layer is 10 nm to 30 nm. This is beneficial for obtaining better battery dynamic performance, thereby improving the cycle life of the battery.

[0026] The second aspect of this application discloses a method for preparing a secondary battery, including preparing a composite negative electrode sheet, wherein preparing the composite negative electrode sheet includes:

[0027] A composite negative electrode is obtained by forming a modification layer on at least one side of the negative electrode; the modification layer comprises: a nitrogen-containing inorganic compound; the nitrogen-containing inorganic compound includes nitrides and nitrate compounds; the nitride comprises at least one of a metallic element and a non-metallic element; the metallic element includes one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti, and the non-metallic element includes one or more of Si, B, and C; the nitrate compound includes M x N y O z Wherein, M includes one or more of M' and M”; M' includes one or more of Li and Na; M” includes one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti; 0 <x≤1,0<y≤5,0<z≤15。

[0028] The embodiments of this application modify the surface of the negative electrode by forming a modification layer, which can be matched with existing battery manufacturing processes. The modification at the powder level helps to simplify the process.

[0029] In some embodiments of this application, a modification layer is formed on at least one side of the negative electrode using thin film deposition technology. The thin film deposition technology includes one or more of physical vapor deposition (PVD) and chemical vapor deposition (CVD). PVD includes one or more of magnetron sputtering, arc ion plating, and electron beam evaporation. Forming a modification layer on the surface of the negative electrode using thin film deposition technology requires minimal changes to the process; it eliminates the need for additional binders or other auxiliary materials, thus improving the cycle life of the battery.

[0030] In some embodiments of this application, a modification layer is formed on at least one side of the negative electrode using magnetron sputtering, including the steps of:

[0031] Perform vacuuming;

[0032] A working gas is introduced, and under the action of an electric field and a magnetic field, a sputtering target is deposited on the negative electrode to form a modification layer, thus obtaining a composite electrode. The working parameters for controlling sputtering include one or more of the following: vacuum degree, working gas flow rate, discharge power, and sputtering time.

[0033] By using magnetron sputtering to deposit a modification layer on the surface of the negative electrode, the material type of the functional layer can be controlled by selecting the target material and the type of working gas; the performance of the modification layer can be controlled by adjusting the working parameters, such as working gas flow rate, discharge power, sputtering time, etc.

[0034] In some embodiments of this application, the target material includes at least one of a metallic element and a non-metallic element; the working gas includes a carrier gas and a reactant gas, and the reactant gas includes a nitrogen source.

[0035] In some embodiments of this application, the secondary battery satisfies at least one of the following:

[0036] Metallic elements include one or more of the following: aluminum, magnesium, zirconium, chromium, niobium, tantalum, and titanium.

[0037] Non-metallic elements include one or more of silicon, boron, and carbon.

[0038] In some embodiments of this application, the nitrogen source includes one or more of N2 and NH3.

[0039] In some embodiments of this application, the magnetron sputtering conditions satisfy one or more of the following (a) to (d):

[0040] (a) The vacuum degree is 1×10 -2 Pa ~ 10 × 10 -1 Pa;

[0041] (b) The discharge power is 1000W to 5000W;

[0042] (c) Sputtering time is 100s to 2500s;

[0043] (d) The working gas flow rate is 1 sccm to 50 sccm.

[0044] Meeting the above vacuum conditions facilitates the acquisition of high-purity nitrides, fully leveraging the role of nitrides in this application, and better improving the cycle life of the battery.

[0045] When the discharge power meets the above conditions, it is beneficial to control the formation of a modified layer with a smaller thickness, relatively lower electrochemically active specific surface area, and better density.

[0046] Meeting the above conditions during sputtering facilitates the acquisition of a thinner modification layer, which in turn improves the battery's kinetic performance, increases battery capacity, and enhances its cycle life.

[0047] Meeting the above conditions with the working gas flow rate facilitates the control of forming a modification layer with a relatively small thickness and a relatively low electrochemically active specific surface area.

[0048] In some embodiments of this application, the magnetron sputtering conditions satisfy one or more of the following (a) to (d):

[0049] (a) Vacuum degree is 5×10 -2 Pa ~ 5 × 10 -1 Pa;

[0050] (b) The discharge power is 2000W to 4000W;

[0051] (c) Sputtering time is 300s to 800s;

[0052] (d) The working gas flow rate is 1 sccm to 20 sccm.

[0053] By adjusting one or more parameters such as vacuum level, discharge power, sputtering time, and working gas flow rate, the performance of the modified layer can be further improved, such as thickness, electrochemical specific surface area, and content of modified layer components, so as to better enhance the cycle performance of the battery.

[0054] The third aspect of this application discloses an electrical device comprising the secondary battery described in the first aspect above, or a secondary battery prepared by the method described in the second aspect above.

[0055] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0056] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0057] Figure 1 is the N1s XPS diagram of the negative electrode prepared in Example 18 and Comparative Example 1 of this application; Figure 1(a) shows the N1s XPS diagram of the negative electrode prepared in Example 18, and Figure 1(b) shows the N1s XPS diagram of the negative electrode prepared in Comparative Example 1.

[0058] Figure 2 is the N1s XPS diagram of the negative electrode sheets prepared in Example 13 and Comparative Example 1 of this application. In Figure 2(a), the N1s XPS diagram of the negative electrode sheet prepared in Example 13 is shown, and in Figure 2(b), the N1s XPS diagram of the negative electrode sheet prepared in Comparative Example 1 is shown.

[0059] Figure 3 is a cycle performance test diagram of the batteries prepared in Example 13 and Comparative Example 1 of this application.

[0060] Figure 4 is a schematic diagram of a battery according to one embodiment of this application.

[0061] Figure 5 is an exploded view of the battery according to one embodiment of this application, as shown in Figure 4.

[0062] Figure 6 is a schematic diagram of a battery module according to one embodiment of this application.

[0063] Figure 7 is a schematic diagram of a battery pack according to one embodiment of this application.

[0064] Figure 8 is an exploded view of a battery pack according to an embodiment of this application, as shown in Figure 7.

[0065] Figure 9 is a schematic diagram of an electrical device in which a battery is used as a power source according to an embodiment of this application.

[0066] Explanation of reference numerals in the attached drawings: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0067] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0068] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0069] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0070] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0071] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0072] Currently, judging from market trends, battery applications are becoming increasingly widespread. Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of battery applications, market demand is also constantly increasing.

[0073] Taking energy storage as an example, the huge market demand for energy storage calls for more targeted battery products for energy storage applications. Unlike power battery products, which focused more on improving energy density in the past few years, the current performance focus of energy storage lithium-ion batteries is "cycle life," which is also a key indicator for lithium battery companies to compete on. Longer cycle life in energy storage batteries means lower levelized cost of electricity (LCOE) over their entire lifecycle. In existing technologies, coating treatments such as carbon coating and polymer coating can be applied to the surface of powder-level materials to improve the high-temperature cycling stability of the powder materials, which helps reduce the irreversible capacity of lithium-ion batteries and improve battery cycle life. However, modification at the powder level often involves changes to the slurry formulation and adjustments to process parameters, increasing the difficulty of mass production.

[0074] Therefore, the first aspect of this application proposes a secondary battery, including a composite negative electrode sheet. The composite negative electrode sheet includes a negative electrode sheet and a modification layer. The modification layer is disposed on at least one side of the negative electrode sheet. The modification layer comprises: a nitrogen-containing inorganic compound; the nitrogen-containing inorganic compound includes nitrides and nitrate compounds; the nitrides include at least one of a metal element and a non-metal element; the metal element includes one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti; the non-metal element includes one or more of Si, B, and C; the nitrate compound includes M x N y O z Wherein, M includes one or more of M' and M”; M' includes one or more of Li and Na; M” includes one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti; 0 <x≤1,0<y≤5,0<z≤15。

[0075] Nitrogen-containing inorganic substances have a well-known meaning in the art and can be detected by methods well-known in the art. As examples, they can be detected by methods such as X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP).

[0076] X-ray photoelectron spectroscopy (XPS) can detect the elemental composition and chemical state within 10 nm of a sample surface. Therefore, in this embodiment, XPS can be used to probe the surface of the composite negative electrode (i.e., the surface of the composite negative electrode with the modified layer). Combining full-spectrum analysis and partial-spectrum analysis, the elemental types and chemical states of the modified layer can be determined, thereby identifying nitrogen-containing inorganic and organic compounds within the detectable range of the modified layer. Specific testing methods include using an Axis Supra / Supra+ X-ray photoelectron spectrometer, referencing standard GB / T 33502-2017.

[0077] Inductively coupled plasma (ICP) is a technique used for elemental analysis. It primarily uses inductively coupled plasma as an excitation source to atomize and excite elements in a sample, enabling qualitative and quantitative analysis. ICP can be divided into two types: ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) and ICP-MS (Inductively Coupled Plasma Mass Spectrometry). As an example, the specific testing method was as follows: Measurements were performed using a Thermo Fisher Scientific ICAP-7000 inductively coupled plasma optical emission spectrometer (ICP-OES) according to EPA 6010D-2018, "Inductively Coupled Plasma Emission Spectrometry".

[0078] The secondary battery provided in this application improves the cycle life of the battery by forming a modification layer on the surface of the negative electrode.

[0079] In the embodiments of this application, the nitride contains at least one of a metallic element and a non-metallic element; the metallic element includes one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti, and the non-metallic element includes one or more of Si, B, and C.

[0080] The nitride used in the modification layer can be a nitride containing one or more metal elements, a nitride containing one or more non-metal elements, or a nitride containing both metal and non-metal elements.

[0081] As an example, the metal element can be one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti. Nitrides containing these metal elements can be used as ceramic materials, which have high high-temperature stability and chemical stability. Under long-term cycling and high-temperature cycling conditions, they play a good role in isolating and protecting the negative electrode, improving the interfacial stability between the negative electrode and the electrolyte, and thus improving the cycle life of the battery.

[0082] As an example, non-metallic elements can be one or more of Si, B, and C. Nitrides containing these non-metallic elements can be used as ceramic materials, which have high high-temperature stability and chemical stability. Under long-term cycling and high-temperature cycling conditions, they can provide good protection for the negative electrode, improve the interfacial stability between the negative electrode and the electrolyte, and better improve the cycle life of the battery.

[0083] In the embodiments of this application, M in the nitrate compound includes one or more of M' and M”. As an example, M' may be the same as the charge carrier in the secondary battery, such as M' including one or more of Li and Na; M” may be the same as the metal element in the nitride, such as M” including one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti.

[0084] Nitrate compounds in the modification layer help to achieve uniform distribution of lithium ions. They can provide suitable lithium ion conduction channels, guiding lithium ions to be uniformly inserted and extracted between the electrode and the electrolyte. This allows the SEI film to grow uniformly on the electrode surface, rather than growing excessively in certain areas. Therefore, it is beneficial to improve the uniformity of the SEI film, improve the film formation quality of the SEI, and increase the cycle life of the battery.

[0085] This is because, on the one hand, nitrate compounds possess good chemical and electrochemical stability, which helps prevent the continuous decomposition of the electrolyte, making the SEI film formation process more stable and uniform. On the other hand, nitrate compounds contribute to the uniform distribution of lithium ions. They can provide suitable lithium ion conduction channels, guiding lithium ions to uniformly insert and extract between the electrode and the electrolyte. This allows the SEI film to grow uniformly on the electrode surface rather than undergoing localized overgrowth, thus improving the uniformity of the SEI film, enhancing the film quality, and increasing the battery's cycle life. This is because nitrate compounds have a relatively open crystal structure (similar to a layered structure), which contains certain gaps and channels; nitrate compounds also contain a certain number of vacancies and defects. These vacancies and defects can act as "relay stations" for the migration of charge carriers (such as lithium ions), allowing lithium ions to jump from one vacancy to an adjacent vacancy.

[0086] Furthermore, in the embodiments of this application, the material of the modification layer can be directly made of nitrogen-containing inorganic materials, without binders, dispersants and other auxiliary materials, which is conducive to better improving the cycle performance of the battery.

[0087] In some embodiments of this application, the nitrides include one or more of aluminum nitride, zirconium nitride, magnesium nitride, chromium nitride, niobium nitride, tantalum oxide, titanium nitride, silicon nitride, boron nitride, carbon nitride, titanium carbon nitride, chromium aluminum nitride, and their respective non-stoichiometric nitrides.

[0088] In the embodiments of this application, the nitrides include one or more of aluminum nitride (AlN), zirconium nitride (ZrN, Zr3N4), magnesium nitride (Mg3N2), chromium nitride (CrN, Cr2N), niobium nitride (NbN), tantalum oxide (TaN), and titanium nitride (TiN), or one or more non-stoichiometric nitrides of these nitrides. Among them, "non-stoichiometric nitrides" include: ① anion-deficient type, in which the number of nitrogen atoms is less than the theoretical value, leading to the formation of oxygen vacancies; ② cation-excess type, in which the number of metal atoms is more than the theoretical value, leading to the formation of interstitial defects.

[0089] In the embodiments of this application, the nitrides include one or more of silicon nitride (Si3N4), boron nitride (BN), and carbon nitride (C3N4), or one or more of these nitrides in a non-stoichiometric form. "Non-stoichiometric nitrides" include: ① anion-deficient type, in which the number of nitrogen atoms is less than the theoretical value, leading to the formation of nitrogen vacancies; ② cation-excess type, in which the number of non-metallic atoms is more than the theoretical value, leading to the formation of non-metallic interstitial defects.

[0090] In the embodiments of this application, the nitride includes one or more of (TiCN) and chromium aluminum nitride (CrAlN), or one or more of the non-stoichiometric nitrides of these nitrides.

[0091] Furthermore, the nitrides include one or more of aluminum nitride (AlN), zirconium nitride (at least one of ZrN and Zr3N4), magnesium nitride (Mg3N2), chromium nitride (at least one of CrN and Cr2N), niobium nitride (NbN), tantalum oxide (TaN), and titanium nitride (TiN).

[0092] Furthermore, nitrides also include one or more of silicon nitride (Si3N4), boron nitride (BN), and carbon nitride (C3N4).

[0093] Furthermore, one or more of these metal-containing nitrides, non-metal-containing nitrides, and metal- and non-metal-containing nitrides in the embodiments of this application have good high-temperature resistance characteristics, can isolate the continuous reaction of the electrolyte and the negative electrode, generate less heat, which is beneficial to improving the thermal stability of the battery and also beneficial to improving the high-temperature cycle life of the battery.

[0094] In some embodiments of this application, the nitrides include one or more of aluminum nitride, zirconium nitride, magnesium nitride, chromium nitride, niobium nitride, tantalum oxide, titanium nitride, titanium carbon nitride, chromium aluminum nitride, and their respective non-stoichiometric nitrides.

[0095] In this embodiment, the nitrides include, but are not limited to, the aforementioned metal nitrides. They possess high high-temperature stability and chemical stability, and under conditions of long-term cycling and high-temperature cycling, they effectively protect the negative electrode in the modification layer, improving the interfacial stability between the negative electrode and the electrolyte, and thus enhancing the battery's cycle life. Furthermore, these metal nitrides can provide a metal source for the formation of nitrate compounds, promoting their formation and improving the uniformity of the SEI film, thereby enhancing the battery's cycle life.

[0096] Furthermore, nitrides include one or more of zirconium nitride, titanium nitride, and their respective non-stoichiometric nitrides.

[0097] In this embodiment, the use of one or more of the above-mentioned metal nitrides in the modification layer can effectively improve the interfacial stability between the negative electrode and the electrolyte, and also facilitate the formation of an SEI film with good uniformity, thereby improving the cycle life of the battery.

[0098] In some embodiments of this application, the nitrate compound includes M' 1-a N b O c One or more of Zr(NO2)4, Zr(NO3)4, Al(NO3)3, Mg(NO3)2, Cr(NO3)3, Nb(NO3)5, Nb(NO3)3, Nb(NO3)4, Ta(NO3)5, Ta(NO3)4, Ti(NO3)4, and Ti(NO3)3, wherein 0 <a<1,0<b<5,0<c<15。

[0099] In the embodiments of this application, nitrate compounds include two types, one of which is M' 1-a N b O cAs an example, the metal ions in these nitrate compounds can originate from charge carriers in secondary batteries, such as lithium ions in lithium-ion batteries and sodium ions in sodium-ion batteries, which helps improve the conductivity of the secondary battery and enhance the uniformity of the SEI film. Another type includes one or more of Zr(NO2)4, Zr(NO3)4, Al(NO3)3, Mg(NO3)2, Cr(NO3)3, Nb(NO3)5, Nb(NO3)3, Nb(NO3)4, Ta(NO3)5, Ta(NO3)4, Ti(NO3)4, and Ti(NO3)3. The metal ions in these nitrate compounds can originate from the metal elements of nitrides, which helps improve the conductivity of the secondary battery and enhance the uniformity of the SEI film. Furthermore, it helps to give the SEI film better strength (mechanical properties) and improve its stability.

[0100] In some embodiments of this application, the nitrate compound includes M' 1-a N b O c It also includes one or more of Zr(NO2)4, Zr(NO3)4, Ti(NO3)4, and Ti(NO3)3, where 0 ≤ a < 1, 0 <b≤5,0<c≤15。

[0101] In the embodiments of this application, the nitrate compound in the modified layer may contain M' 1-a N b O c As an example, M' can be derived from charge carriers in a secondary battery, such as lithium ions or sodium ions; the nitrate compounds in the modification layer also include one or more of Zr(NO2)4, Zr(NO3)4, Ti(NO3)4, and Ti(NO3)3, and the metal ions in these nitrate compounds can be derived from the metal elements in the nitrides.

[0102] The presence of these nitrate compounds in the modification layer helps to improve the film quality of the SEI film, including the uniformity and mechanical properties of the SEI, thereby further improving the long-term cycle performance of the secondary battery during charge and discharge.

[0103] In some embodiments of this application, the test results of the modified layer based on X-ray photoelectron spectroscopy analysis satisfy any one of the following (i) to (ii):

[0104] (i) The mass content of nitrides is 2% to 8%;

[0105] (ii) The mass content of nitrate compounds is 1.5% to 6%.

[0106] X-ray photoelectron spectroscopy (XPS) can detect the elemental composition and chemical state within 10 nm of a sample surface. Therefore, in this embodiment, XPS can be used to probe the surface of the composite negative electrode (i.e., the surface of the composite negative electrode with the modified layer). By combining full-spectrum analysis and partial-spectrum analysis, the elemental types and chemical states of the modified layer can be determined, thereby identifying the nitrogen-containing inorganic substances within the detectable range of the modified layer. The mass content of nitrides and nitrates can then be calculated using peak area. Specific testing methods include using an Axis Supra / Supra+ X-ray photoelectron spectrometer, referencing standard GB / T 33502-2017.

[0107] As an example, the mass content of nitrides is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, etc.

[0108] As an example, the mass content of nitrate compounds is 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, etc.

[0109] The mass content of nitrides is related to the thickness of the modification layer. If the mass content of nitrides increases, the thickness of the modification layer will tend to increase, and the internal resistance of the battery will also tend to increase. In the embodiments of this application, based on the test results of the modification layer by X-ray photoelectron spectroscopy analysis, the nitride content meets the above conditions. While playing a role in physical isolation and improving interface stability, it can also achieve a lower battery internal resistance, which is beneficial to improving the cycle performance of the battery.

[0110] The mass content of nitrate compounds is related to the thickness of the modification layer. If the mass content of nitrate compounds increases, the thickness of the modification layer will tend to increase, and the internal resistance of the battery will also tend to increase. In the embodiments of this application, based on the test results of the modification layer using X-ray photoelectron spectroscopy analysis, the content of nitrate compounds meets the above conditions, which is beneficial for improving the uniformity of the SEI and increasing the cycle life of the battery; at the same time, it is beneficial for obtaining a lower internal resistance and a secondary battery with good overall performance.

[0111] In some embodiments of this application, the test results of the modified layer based on X-ray photoelectron spectroscopy analysis satisfy any one of the following (i) to (ii):

[0112] (i) The mass content of nitrides is 2.5% to 7.5%;

[0113] (ii) The mass content of nitrate compounds is 2% to 5.5%.

[0114] In this embodiment, based on the test results of X-ray photoelectron spectroscopy analysis of the modified layer, the mass content of nitride meets the above conditions, which is beneficial to obtaining a lower battery internal resistance and also beneficial to improving the interface stability between the negative electrode and the electrolyte, effectively increasing the cycle life of the battery.

[0115] In this embodiment, based on the test results of X-ray photoelectron spectroscopy analysis of the modified layer, the mass content of nitrate compounds meets the above conditions, which is beneficial to obtaining a lower battery internal resistance, and also beneficial to improving the uniformity of the SEI film, effectively increasing the cycle life of the battery.

[0116] In some embodiments of this application, the modification layer further comprises a nitrogen-containing organic compound; the nitrogen-containing organic compound includes one or more of amino, carboxyl, hydroxyl, aldehyde, carbonyl, ester, and alkyl groups.

[0117] Nitrogen-containing organic compounds have a well-known meaning in the art and can be detected by methods known in the art. For example, they can be detected by methods such as X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP). For example, X-ray photoelectron spectroscopy (XPS) can detect the elemental composition and chemical state within 10 nm of the sample surface. Therefore, in the embodiments of this application, XPS can be used to probe the surface of the composite negative electrode (i.e., the surface of the composite negative electrode with the modified layer), and the elemental types and chemical states of the modified layer can be determined by combining full-spectrum analysis and partial-spectrum analysis, thereby identifying nitrogen-containing inorganic and organic compounds within the detectable range of the modified layer. Specific testing methods include using an Axis Supra / Supra+ X-ray photoelectron spectrometer, referring to standard GB / T 33502-2017.

[0118] The modification layer formed by nitrogen-containing organic compounds can provide a certain degree of physical isolation, reducing the contact between the active sites on the negative electrode surface and the electrolyte, mitigating side reactions, reducing lithium consumption, improving interface stability, and enhancing battery cycle life. Furthermore, the nitrogen-containing organic compound modification layer possesses high molecular chain toughness, which can increase the flexibility and tensile strength of the SEI film, allowing it to remain intact even under pressure changes or expansion and contraction of electrode materials within the battery, thus further improving the battery's long-term cycle life.

[0119] Nitrogen-containing organic compounds can be formed through reactions between nitrides and substances in the electrolyte (such as alkyl solvents); or directly through the decomposition of substances in the electrolyte, such as nitrogen-containing additives. Furthermore, nitrogen in nitrides can connect with some active functional groups on the surface of the negative electrode (for example, carboxyl (-COOH), hydroxyl (-OH), aldehyde (-CHO), carbonyl (=O), ester (-COO-), alkyl, amino, etc.) to form nitrogen-containing organic compounds. This consumes some of the active functional groups on the surface of the negative electrode, passivating excessive active sites and reducing the number of active sites on the negative electrode surface. This mitigates side reactions between the negative electrode and the electrolyte, reduces the formation of by-products, and improves battery kinetic performance and cycle life. It also helps maintain the structural stability of the negative electrode active material, improves the cycle stability of the SEI film, reduces lithium consumption, and increases battery cycle life. (Sources of nitrogen-containing organic compounds...)

[0120] In some embodiments of this application, the nitrogen-containing organic compound includes one or more of lithium carbamate, lithium methylamino, lithium amino, 2-aminobenzoic acid, ethanolamine, aminoacetaldehyde, methyl carbamate, ethylamine, amino acids, and polypyrrole.

[0121] The nitrogen atoms in the nitrogen-containing organic compounds provided in this application possess lone pairs of electrons, which can combine with active sites on the electrode surface through chemical bonds or coordination interactions, forming a uniform and stable SEI film on the electrode surface. The nitrogen-containing organic compounds polymerize on the electrode surface to form a continuous protective film, effectively preventing direct contact between the electrode material and the electrolyte, reducing the dissolution of the electrode material and the decomposition of the electrolyte, thereby improving the stability of the battery during cycling. Furthermore, the nitrogen-containing organic compound modification layer has high molecular chain toughness, which can increase the flexibility and tensile strength of the SEI film, allowing it to remain intact even when subjected to pressure changes inside the battery or when the electrode material expands or contracts.

[0122] As an example:

[0123] Polypyrrole: It can polymerize on the electrode surface to form a continuous and stable protective film, which can effectively prevent direct contact between the electrode material and the electrolyte, reduce the dissolution of the electrode material and the decomposition of the electrolyte, and thus help improve the cycle stability of the battery.

[0124] Amino alcohol derivatives, such as ethanolamine: The amino group can react with other substances, and the hydroxyl group can participate in hydrogen bond formation or react with other groups containing active hydrogen, which helps to create an environment conducive to lithium-ion transport in the SEI film, reduce lithium-ion transport resistance, and thus improve the cycle performance of the battery.

[0125] Amino acid derivatives, such as 2-aminobenzoic acid and methyl carbamate, have highly reactive amino and carboxyl groups in their molecules. They can combine with other substances through condensation, esterification, and other reactions, participate in the construction of the SEI film, enhance the stability and integrity of the SEI film, and improve the cycle stability of the battery.

[0126] In some embodiments of this application, based on the test results of X-ray photoelectron spectroscopy analysis of the modified layer, the mass content of nitrogen-containing organic compounds is 0.6% to 3%.

[0127] X-ray photoelectron spectroscopy (XPS) can detect the elemental composition and chemical state within 10 nm of a sample surface. Therefore, in this embodiment, XPS can be used to probe the surface of the composite negative electrode (i.e., the surface of the composite negative electrode with the modified layer). By combining full-spectrum analysis and partial-spectrum analysis, the elemental types and chemical states of the modified layer can be determined, thereby identifying nitrogen-containing organic compounds within the detectable range of the modified layer. The mass content of these nitrogen-containing organic compounds can then be calculated using the peak area. Specific testing methods include using an Axis Supra / Supra+ X-ray photoelectron spectrometer, referencing standard GB / T 33502-2017.

[0128] As an example, based on the test results of X-ray photoelectron spectroscopy analysis of the modified layer, the mass content of nitrogen-containing organic compounds is 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, etc.

[0129] In the embodiments of this application, the mass content of nitrogen-containing organic matter meets the above conditions, which is beneficial to provide good protection for the negative electrode, improve the interfacial stability between the negative electrode and the electrolyte, maintain the amount of active sites on the surface of the negative electrode in the required state, obtain good battery capacity, and better improve the cycle performance of the battery.

[0130] In some embodiments of this application, based on the test results of X-ray photoelectron spectroscopy analysis of the modified layer, the content of nitrogen-containing organic compounds is 0.8% to 2.5%.

[0131] In this embodiment, based on the mass of the composite negative electrode sheet, the content of nitrogen-containing organic matter meets the above conditions, which is beneficial to improve the interfacial stability between the negative electrode sheet and the electrolyte, and can also help reduce excessive active sites on the surface of the negative electrode sheet, thereby further improving the cycle life of the battery.

[0132] In some embodiments of this application, the electrochemically active specific surface area of ​​the composite negative electrode is 7 cm². 2 / g~8.7cm 2 / g.

[0133] The "electrochemical active specific surface area" of the composite negative electrode sheet, i.e., the active specific surface area of ​​the composite negative electrode sheet that actually participates in the reaction, characterizes the number of active sites during charging and discharging. A larger electrochemical active specific surface area indicates more active sites in the composite negative electrode sheet, and a faster rate of charge exchange between active ions and electrons. The active specific surface area of ​​the negative electrode sheet can be measured using methods known in the art. As an example, the specific test method used in this application embodiment is as follows: In a glove box, the negative electrode sheet, separator, lithium sheet, etc., are assembled into a coin cell in a certain order. The assembled coin cell is connected to an electrochemical workstation, with a potential range possibly between 0.01 and 3V (vs. Li / Li). Cyclic voltammetry is performed at a scan rate of 5mV / s, usually multiple scans are performed to allow the electrode to reach a stable state, and the current-potential curve is recorded. Based on the cyclic voltammetry curve, a suitable potential range is selected in the non-Faraday region, and the double-layer capacitance C is calculated using the slope of the current-potential curve. dl Then, according to the known formula ECSA = C dl / C s Calculate the electrochemically active specific surface area, where C s The specific capacitance per unit area varies depending on the negative electrode material. s Value. Currently, there are some industry standards and literature references that can be used as the basis for testing, such as the standard "Graphite Anode Materials for Lithium-ion Batteries" (GB / T 30835-2014), which provides some guidance for the electrochemical performance testing of anode materials.

[0134] As an example, the electrochemically active specific surface area of ​​the composite negative electrode is 7 cm². 2 / g, 7.1cm 2 / g, 7.2cm 2 / g, 7.3cm 2 / g, 7.4cm 2 / g, 7.5cm 2 / g, 7.6cm 2 / g, 7.7cm 2 / g, 7.8cm 2 / g, 7.9cm 2 / g、8cm 2 / g, 8.1cm 2 / g, 8.2cm 2 / g, 8.3cm 2 / g, 8.4cm 2 / g, 8.5cm 2 / g, 8.6cm 2 / g, 8.7cm 2 / g etc., or a range consisting of any two of the above values, or a value within the range.

[0135] In this embodiment, by forming a modification layer on the surface of the negative electrode, the modification layer can physically isolate some of the active sites on the surface of the negative electrode, reducing the chance of these active sites coming into contact with the electrolyte. In addition, the nitrides in the modification layer may also form nitrogen-containing organic compounds with the active sites on the surface of the negative electrode through chemical bonds or van der Waals forces, which helps to reduce the active sites on the surface of the negative electrode and helps to maintain the electrochemical active specific surface area of ​​the composite negative electrode within a reasonable range. In particular, meeting the above conditions can effectively reduce the side reaction activity between the negative electrode and the electrolyte, reduce the consumption of active lithium during cycling, and thus improve the cycle life of the battery.

[0136] In some embodiments of this application, the electrochemically active specific surface area of ​​the composite negative electrode is 7.2 cm². 2 / g~8.6cm 2 / g.

[0137] In this embodiment, the electrochemically active specific surface area of ​​the composite negative electrode meets the above conditions, which can effectively reduce the side reaction activity between the negative electrode and the electrolyte, reduce the consumption of active lithium during cycling, and thus improve the cycle life of the battery.

[0138] In some embodiments of this application, the thickness of the modification layer is 5 nm to 50 nm.

[0139] The "thickness" of the modification layer has a well-known definition in the art and can be measured using well-known testing methods, such as transmission electron microscopy (TEM) and scanning electron microscopy (SEM). As an example, using TEM, specifically FIB-TEM refers to a technique combining focused ion beam (FIB) technology with transmission electron microscopy (TEM). The procedure is as follows: First, the target area of ​​the negative electrode is finely milled using FIB to obtain a sufficiently thin slice for subsequent TEM testing. The sample holder with the slice is then loaded into the transmission electron microscope. The thickness of the functional layer is directly measured on the image using TEM software tools. To improve accuracy, measurements can be repeated at multiple locations, and the average value can be calculated as the thickness of the functional layer. FIB: Thermo Scientific-Scios 2HiVac; TEM: Thermo Scientific-Talos F200S G2.

[0140] As an example, the thickness of the modification layer is 5nm, 7nm, 9nm, 11nm, 13nm, 15nm, 17nm, 19nm, 21nm, 23nm, 25nm, 27nm, 29nm, 31nm, 33nm, 35nm, 37nm, 39nm, 41nm, 43nm, 45nm, 47nm, 49nm, 50nm, etc., or a range of any two of the above values, or a value within the range.

[0141] Increasing the thickness of the surface modification layer on the negative electrode increases the length of the lithium-ion transport path, potentially increasing the battery's internal resistance. In this embodiment, the modification layer is relatively thin, at the nanometer level (below 50 nm). Therefore, the lithium-ion transport path is relatively short, minimizing the impact on lithium-ion transport efficiency and facilitating better battery kinetic performance, thereby improving the battery's cycle life.

[0142] In some embodiments of this application, the thickness of the modification layer is 10 nm to 30 nm.

[0143] In this embodiment, the thickness of the modification layer meets the above conditions, which is beneficial to obtaining better battery dynamic performance and thus better improving the cycle life of the battery.

[0144] Therefore, a second aspect of the present application proposes a method for preparing a secondary battery, including preparing a composite negative electrode sheet, wherein preparing the composite negative electrode sheet includes:

[0145] A composite negative electrode is obtained by forming a modification layer on at least one side of the negative electrode; the modification layer comprises: a nitrogen-containing inorganic compound; the nitrogen-containing inorganic compound includes nitrides and nitrate compounds; the nitride comprises at least one of a metallic element and a non-metallic element; the metallic element includes one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti, and the non-metallic element includes one or more of Si, B, and C; the nitrate compound includes M x N y O z Wherein, M includes one or more of M' and M”; M' includes one or more of Li and Na; M” includes one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti; 0 <x≤1,0<y≤5,0<z≤15。

[0146] In this embodiment, the nitride containing at least one of a metallic or non-metallic element can serve as a ceramic material, exhibiting high high-temperature and chemical stability. Under long-cycle and high-temperature conditions, it effectively isolates and protects the negative electrode, improving the interfacial stability between the negative electrode and the electrolyte, thus enhancing the battery's cycle life. As a nitrate compound in the modification layer, it contributes to the uniform distribution of lithium ions, providing suitable lithium-ion conduction channels and guiding the uniform insertion and extraction of lithium ions between the electrode and the electrolyte. This ensures uniform growth of the SEI film on the electrode surface, rather than localized overgrowth, thereby improving the uniformity of the SEI film, enhancing its formation quality, and ultimately increasing the battery's cycle life.

[0147] Furthermore, existing technologies that use negative electrode material (powder) coating to improve battery cycle life involve coating the surface of powder-level materials. Modifying the powder layer often involves altering the slurry formulation and adjusting process parameters, increasing the difficulty of mass production. In contrast, the embodiments of this application modify the negative electrode sheet by forming a modification layer on its surface, which is compatible with existing battery manufacturing processes and simplifies the process compared to powder-level modification.

[0148] In some embodiments of this application, a modification layer is formed on at least one side of the negative electrode using thin film deposition technology; the thin film deposition technology includes one or more of physical vapor deposition and chemical vapor deposition; the physical vapor deposition method includes one or more of magnetron sputtering, arc ion plating, and electron beam evaporation.

[0149] In this embodiment, a modification layer can be formed on the surface of the negative electrode using thin film deposition technology, which requires minimal changes to the process; no additional binders or other auxiliary materials are needed, which helps to improve the cycle life of the battery.

[0150] In this embodiment, a modification layer is deposited on the surface of the negative electrode using thin-film deposition technology. During the thin-film deposition process, nitrides are gradually deposited on the surface of the negative electrode. During battery formation, the nitrides on the surface of the negative electrode come into contact with the electrolyte. Some of the nitrides can undergo redox reactions to form nitrate compounds. In addition, charge carriers in the electrolyte, such as lithium ions, may also participate in the reaction, forming lithium-containing nitrate compounds. The nitrides and nitrate compounds in the modification layer can provide physical isolation between the negative electrode and the electrolyte, improving interface stability.

[0151] Furthermore, during battery formation, the nitrides in the modification layer undergo redox reactions to form nitrate compounds. As an example, the nitrides on the surface of the modification layer can react with solvents and lithium salts in the electrolyte during capacity formation to form LiN. x O yThe compound, the electrolyte provides the oxygen source, and the active functional groups in the negative electrode can also provide a small amount of oxygen to participate in the reaction, producing LiN. x O y Compounds can improve the uniformity of the SEI, thereby improving the cycle performance of the battery. This is because: on the one hand, LiN x O y It possesses good chemical and electrochemical stability, which can prevent the continuous decomposition of the electrolyte, making the SEI film formation process more stable and uniform; on the other hand, LiN x O y It contributes to the uniform distribution of lithium ions. It provides suitable lithium ion conduction channels, guiding the uniform insertion and extraction of lithium ions between the electrode and the electrolyte. This ensures that the SEI film grows uniformly on the electrode surface rather than undergoing localized overgrowth, thus improving the uniformity of the SEI film, enhancing its formation quality, and extending the battery's cycle life. This is because LiN... x O y It possesses a relatively open crystal structure (similar to a layered structure), within which certain voids and channels exist; LiN x O y The material contains a certain number of vacancies and defects. These vacancies and defects can act as "relay stations" for lithium-ion migration, allowing lithium ions to jump from one vacancy to an adjacent vacancy.

[0152] In some embodiments of this application, a modification layer is formed on at least one side of the negative electrode using magnetron sputtering, including the steps of:

[0153] Perform vacuuming;

[0154] A working gas is introduced, and under the action of an electric field and a magnetic field, a sputtering target is deposited on the negative electrode to form a modification layer, thus obtaining a composite electrode. The working parameters include one or more of the following: working gas flow rate, discharge power, and sputtering time.

[0155] In this embodiment, magnetron sputtering is used to deposit a modification layer on the surface of the negative electrode. The material type of the functional layer can be controlled by selecting the target material and the type of working gas. The performance of the modification layer can be controlled by adjusting the working parameters, such as the working gas flow rate, discharge power, and sputtering time.

[0156] Furthermore, in this embodiment, by depositing a nanometer-thick nitride on the surface of the negative electrode by magnetron sputtering, a layer of nitrate with a near-average structure can be formed on the surface of the nitride film during the battery formation process, thereby promoting the uniform growth of the SEI film, improving the uniformity of the SEI film, and thus helping to improve the cycle life of the battery.

[0157] In some embodiments of this application, the target material includes at least one of a metallic element and a non-metallic element; the working gas includes a carrier gas and a reactant gas, and the reactant gas includes a nitrogen source.

[0158] In the sputtering chamber, the target material serves as the cathode, and the negative electrode serves as the anode. A high voltage is applied between them to create an electric field. Simultaneously, a magnetic field is placed near the target material. Under the combined influence of the electric and magnetic fields, electrons in the working gas dissociate to form ions and new electrons. These high-energy ions and electrons bombard the target surface, giving the target atoms or molecules sufficient energy to be sputtered. The sputtered atoms or molecules, or other active particles, combine with the ions dissociated from the reactive gas and deposit on the surface of the negative electrode to form a new substance, creating a modification layer. Specifically, nitrogen ions react with active particles of metal or non-metal to form nitrogen-containing inorganic substances, while some of these active nitrogen ions react with active groups on the surface of the negative electrode to form nitrogen-containing organic substances.

[0159] In some embodiments of this application, the secondary battery satisfies at least one of the following:

[0160] Metallic elements include one or more of the following: aluminum, magnesium, zirconium, chromium, niobium, tantalum, and titanium.

[0161] Non-metallic elements include one or more of silicon, boron, and carbon.

[0162] In this embodiment, a target material containing the aforementioned metallic or non-metallic elements can be selected, which can deposit ceramic materials containing nitrides of these elements. These materials have high high-temperature stability and chemical stability, improve the interfacial stability between the negative electrode and the electrolyte, provide good heat insulation, and improve the cycle life of the battery.

[0163] In some embodiments of this application, the nitrogen source includes one or more of N2 and NH3. Nitrogen sources include, but are not limited to, one or more of N2 and NH3.

[0164] In some embodiments of this application, magnetron sputtering satisfies one or more of the following (a) to (d):

[0165] (a) The vacuum degree is 1×10 -2 Pa ~ 10 × 10 -1 Pa;

[0166] (b) The discharge power is 1000W to 5000W;

[0167] (c) Sputtering time is 100s to 2500s;

[0168] (d) The working gas flow rate is 1 sccm to 50 sccm.

[0169] In this embodiment, the vacuum level affects the purity and other properties of the modified layer material. Meeting the above-mentioned vacuum level facilitates the acquisition of high-purity nitrides, fully leveraging the role of the nitrides in this application, and better improving the cycle life of the battery.

[0170] As an example, the vacuum level is 1×10⁻⁶. -2 Pa, 2×10 -2 Pa, 3×10 -2 Pa, 4×10 -2 Pa, 5×10 -2 Pa, 6×10 -2 Pa, 7×10 -2 Pa, 8×10 -2 Pa, 9×10 -2 Pa, 1×10 -1 Pa, 2×10 -1 Pa, 3×10 -1 Pa, 4×10 -1 Pa, 5×10 -1 Pa, 6×10 -1 Pa, 7×10 -1 Pa, 8×10 -1 Pa, 9×10 -1 Pa, 10×10 -1 Pa, etc., is either a range consisting of any two of the above values ​​or a value within the range.

[0171] In this embodiment, the discharge power affects the thickness, electrochemically active specific surface area, and density of the modified layer. A discharge power that meets the above conditions facilitates the formation of a modified layer with a smaller thickness, relatively lower electrochemically active specific surface area, and better density.

[0172] As an example, the discharge power is 1000W, 1200W, 1400W, 1600W, 1800W, 2000W, 2200W, 2400W, 2600W, 2800W, 3000W, 3200W, 3400W, 3600W, 3800W, 4000W, 4200W, 4400W, 4600W, 4800W, 5000W, etc., or a range of any two of the above values, or a value within a range.

[0173] In this embodiment, sputtering time affects the thickness and composition content of the modified layer. A sputtering time that meets these conditions is beneficial for obtaining a thinner modified layer, which in turn improves the battery's kinetic performance, increases battery capacity, and ultimately enhances its cycle life.

[0174] As an example, the sputtering time is 100s, 200s, 300s, 400s, 500s, 600s, 700s, 800s, 900s, 1000s, 1100s, 1300s, 1500s, 1700s, 1900s, 2100s, 2300s, 2500s, etc., or a range of any two of the above values, or a value within a range.

[0175] In this embodiment, the working gas flow rate affects the thickness of the modified layer, the electrochemically active specific surface area, and other characteristics. When the working gas flow rate meets the above conditions, it is beneficial to control the formation of a modified layer with a smaller thickness and a relatively lower electrochemically active specific surface area.

[0176] As an example, the working gas flow rate is 1 sccm, 5 sccm, 10 sccm, 15 sccm, 20 sccm, 25 sccm, 30 sccm, 35 sccm, 40 sccm, 45 sccm, 50 sccm, etc., or a range of any two of the above values, or a value within the range.

[0177] In addition, in some embodiments of this application, the operating parameters also include heating temperature.

[0178] In this embodiment, the heating temperature refers to the heating temperature of the negative electrode sheet. In a specific example, the negative electrode sheet may be heated to improve the reaction efficiency, or it may not be heated, i.e., it can be heated at room temperature or normal ambient temperature.

[0179] Furthermore, the heating temperature is 0℃ to -200℃.

[0180] For example, heating temperatures include 0℃, 5℃, 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, and 200℃.

[0181] In some embodiments of this application, magnetron sputtering satisfies one or more of the following (a) to (d):

[0182] (a) Vacuum degree is 5×10 -2 Pa ~ 5 × 10 -1 Pa;

[0183] (b) The discharge power is 2000W to 4000W;

[0184] (c) Sputtering time is 300s to 800s;

[0185] (d) The working gas flow rate is 1 sccm to 20 sccm.

[0186] In this embodiment, the vacuum degree meets the above conditions, which is conducive to obtaining nitrides with high purity, giving full play to the role of nitrides in this application, and better improving the cycle life of the battery.

[0187] In this embodiment, the discharge power meets the above conditions, which is beneficial for controlling the formation of a modified layer with a smaller thickness, relatively lower electrochemically active specific surface area, and better density.

[0188] In this embodiment, the sputtering time meets the above conditions, which is beneficial to obtaining a thinner modification layer, improving the dynamic performance of the battery, increasing the battery capacity, and better improving the cycle life of the battery.

[0189] In this embodiment, the working gas flow rate meets the above conditions, which is beneficial for controlling the formation of a modified layer with a relatively small thickness and a relatively low electrochemically active specific surface area. Further, the working gas flow rate is 15 sccm to 20 sccm.

[0190] In some embodiments of this application, the modification layer further comprises a nitrogen-containing organic compound; the nitrogen-containing organic compound includes one or more of amino, carboxyl, hydroxyl, aldehyde, carbonyl, ester, and alkyl groups.

[0191] The preparation method provided in this application uses thin-film deposition technology to deposit nitrides on the surface of the negative electrode. The nitrogen in the nitrides can connect with some of the active functional groups on the surface of the negative electrode to form nitrogen-containing organic matter, consuming some of the active functional groups on the surface of the negative electrode. This passivates excessive active sites on the surface of the negative electrode, reducing the number of active sites and thus mitigating the occurrence of side reactions between the negative electrode and the electrolyte, reducing the formation of by-products, and improving battery kinetic performance and cycle life. It also helps maintain the structural stability of the negative electrode active material, improves the cycle stability of the SEI film, reduces lithium consumption, and increases the battery's cycle life. Furthermore, the modification layer formed by the nitrogen-containing organic matter and nitrogen-containing inorganic matter can also play a certain physical isolation role, reducing the contact between the active sites on the surface of the negative electrode and the electrolyte, mitigating the occurrence of side reactions, reducing lithium consumption, improving interface stability, and improving the battery's cycle life.

[0192] The battery with a composite negative electrode proposed in this application can be used in electrical devices that use the battery as a power source or in various energy storage systems that use the battery as an energy storage element. Electrical devices can include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0193] In one embodiment of this application, a battery is provided.

[0194] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor for ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0195] [Positive electrode tablets]

[0196] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including the positive active material of the first aspect of this application.

[0197] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0198] 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.).

[0199] In some embodiments, when the battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 )), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0200] In some implementations, such as when the battery is a sodium-ion battery, the positive electrode active material may, as an example, include, but is not limited to, at least one of layered transition metal oxides, polyanionic compounds, and Prussian blue analogues.

[0201] Examples of the aforementioned layered transition metal oxides include:

[0202] Na 1-x Cu h Fe k Mn l M 1 m O 2-y M 1 It is one or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, and Ba, 0 <x≤0.33,0<h≤0.24,0≤k≤0.32,0<l≤0.68,0≤m<0.1,h+k+l+m=1,0≤y<0.2;

[0203] Na 0.67 Mn 0.7 Ni z M 2 0.3-z O2, where M 2is one or more of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn, and Ba, where 0 < z ≤ 0.1;

[0204] Na a Li b Ni c Mn d Fe[[ID=十二]] e O2, where 0.67 < a ≤ 1, 0 < b < 0.2, 0 < c < 0, 0.67 < d + e < 0.8, and b + c + d + e = 1.

[0205] As examples of the above polyanion compounds, for example, the following can be listed:

[0206] A 1 f M 3 g (PO4) i O j X 1 3-j , where A 1 is one or more of H, Li, Na, K, and NH4, M 3 is one or more of Ti, Cr, Mn, Fe, Co, Ni, V, Cu, and Zn, X 1 is one or more of F, Cl, and Br, 0 < f ≤ 4, 0 < g ≤ 2, 1 ≤ i ≤ 3, 0 ≤ j ≤ 2;

[0207] Na n M 4 PO4X 2 , where M 4 is one or more of Mn, Fe, Co, Ni, Cu, and Zn, X 2 is one or more of F, Cl, and Br, 0 < n ≤ 2;

[0208] Na<000C0159>M 5 q (SO4)3, where M 5 is one or more of Mn, Fe, Co, Ni, Cu, and Zn, 0 < p ≤ 2, 0 < q ≤ 2;

[0209] Na s Mn t Fe 3-t (PO4)2(P2O7), where 0 < s ≤ 4, O ≤ t ≤ 3, for example, t is 0, 1, 1.5, 2, or 3.

[0210] As examples of the above Prussian blue analogs, for example, the following can be listed: ]

[0211] Au M 6 v [M 7 (CN)6] w ·xH2O, where A is H + 、NH4 + 、one or more of alkali metal cations and alkaline earth metal cations, M 6 and M 7 are each independently one or more of transition metal cations, 0 < u ≤ 2, 0 < v ≤ 1, 0 < w ≤ 1, 0 < x < 6. For example, A is H + 、Li + 、Na + 、K + 、NH4 + 、Rb + 、Cs + 、Fr + 、Be 2+ 、Mg 2+ 、Ca 2+ 、Sr 2+ 、Ba 2+ and Ra 2+ one or more of, M 6 and M 7 are each independently cations of one or more transition metal elements selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, and W.

[0212] The modified compounds of the above materials can be doping modification and / or surface coating modification of the materials.

[0213] In some embodiments, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0214] In some embodiments, the positive electrode active material layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0215] In some embodiments, the positive electrode sheet can be prepared by the following method: dispersing the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet can be obtained.

[0216] [Negative electrode plate]

[0217] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0218] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0219] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0220] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and titanates. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. When the battery is a lithium-ion battery, lithium titanate is used; when the battery is a sodium-ion battery, sodium titanate is used. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0221] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0222] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0223] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0224] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0225] [Electrolytes]

[0226] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specify any particular type of electrolyte; it can be selected according to requirements.

[0227] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0228] In some embodiments, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0229] In some embodiments of this application, when the battery is a sodium-ion battery, the electrolyte sodium salt may include at least one of sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium dioxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, or sodium bis(trifluoromethanesulfonyl)imide.

[0230] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0231] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0232] [Isolation membrane]

[0233] In some embodiments, the battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0234] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0235] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0236] In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0237] In some implementations, the battery's outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The battery's outer packaging can also be a soft pack, such as a pouch. The soft pack can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0238] This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 4 shows a square battery 5 as an example.

[0239] In some embodiments, referring to FIG5, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0240] In some implementations, the batteries can be assembled into battery modules, and the number of batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0241] Figure 6 shows a battery module 4 as an example. Referring to Figure 6, in the battery module 4, multiple batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other arbitrary way. Furthermore, the multiple batteries 5 can be fixed in place using fasteners.

[0242] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of batteries 5 are received.

[0243] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0244] Figures 7 and 8 show a battery pack 1 as an example. Referring to Figures 7 and 8, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0245] In addition, this application also provides an electrical device, which includes at least one of the battery, battery module, or battery pack provided in this application. The battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0246] As electrical equipment, batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0247] Figure 9 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this device, a battery pack or battery module can be used.

[0248] Another example device could be a mobile phone, tablet, laptop, etc. These devices typically require a slim and lightweight design and can use a battery as their power source.

[0249] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0250] [Preparation of Lithium-ion Batteries]

[0251] Example 1

[0252] (1) Preparation of the positive electrode:

[0253] Lithium iron phosphate, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 97.2:0.7:2.1 to form a homogeneous positive electrode slurry with a solid content of 45%. The positive electrode slurry was coated onto the surface of the positive electrode current collector aluminum foil, and then dried, cold-pressed, slit, and cut to obtain the positive electrode sheet. The compacted density of the positive electrode sheet was 2.45 g / cm³. 3 Its surface density is 21.68 mg / cm³. 2 .

[0254] (2) Preparation of composite negative electrode:

[0255] 1) The negative electrode active material artificial graphite, conductive agent carbon black (Super P), thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96.82:0.53:0.7:1.95. Deionized water was added as a solvent, and the mixture was stirred under vacuum to obtain a homogeneous negative electrode slurry with a solid content of 50%. This slurry was uniformly coated onto both surfaces of a 6 μm thick copper foil negative electrode current collector and dried at 110℃ for 20 min. After drying, the electrode was cold-pressed to obtain a coating weight of 10.71 mg / cm². 2 The compacted density is 1.4 g / cm³. 3 The negative electrode has a thickness of 159μm.

[0256] 2) Fix the cut electrode in the experimental area; set the target material to elemental zirconium, and evacuate to achieve a vacuum level of 5*10. -2 Pa; turn on the intermediate frequency power supply, introduce the working gas, specifically the carrier gas argon and the reactant gas nitrogen, adjust the working gas flow rate to 20 sccm, the discharge power to 3000W and the sputtering time to 500s, and obtain the composite negative electrode sheet.

[0257] (3) Preparation of the diaphragm:

[0258] A 12μm thick polyethylene film was selected as the separator.

[0259] (4) Preparation of electrolyte:

[0260] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Fully dried lithium salt LiPF6 was dissolved in the organic solvent at a concentration of 1 mol / L. The mixture was then thoroughly mixed to obtain an electrolyte.

[0261] (5) Battery assembly:

[0262] The positive electrode, composite negative electrode, and separator are stacked in a specific pattern to form a battery chip. Then, the battery chip is packaged in a suitable container, electrolyte is added, and a sealed cap is installed to fix the cell assembly, giving it a certain finished cell shape.

[0263] Example 2-Example 21

[0264] The battery preparation methods provided in Examples 2-21 are as shown in Example 1, and the specific differences in various parameters are shown in Table 1.

[0265] Comparative Example 1

[0266] (1) Preparation of the positive electrode:

[0267] Lithium iron phosphate, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 97.2:0.7:2.1 to form a homogeneous positive electrode slurry with a solid content of 45%. The positive electrode slurry was coated onto the surface of the positive electrode current collector aluminum foil, and then dried, cold-pressed, slit, and cut to obtain the positive electrode sheet. The compacted density of the positive electrode sheet was 2.45 g / cm³. 3 Its surface density is 21.68 mg / cm³. 2 .

[0268] (2) Preparation of negative electrode:

[0269] Artificial graphite (anode active material), carbon black (Super P) (conductive agent), sodium carboxymethyl cellulose (CMC) (thickener), and styrene-butadiene rubber (SBR) (binder) were mixed in a mass ratio of 96.82:0.53:0.7:1.95. Deionized water was added as a solvent, and the mixture was stirred under vacuum to obtain a homogeneous anode slurry with a solid content of 50%. This slurry was uniformly coated onto both surfaces of a 6 μm thick copper foil anode current collector and dried at 110 °C for 20 min. After drying, the electrode was cold-pressed to obtain a coating weight of 10.71 mg / cm². 2 The compacted density is 1.4 g / cm³. 3 The negative electrode has a thickness of 159μm.

[0270] (3) Preparation of the diaphragm:

[0271] A 12μm thick polyethylene film was selected as the separator.

[0272] (4) Preparation of electrolyte:

[0273] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Fully dried lithium salt LiPF6 was dissolved in the organic solvent at a concentration of 1 mol / L. The mixture was then thoroughly mixed to obtain an electrolyte.

[0274] (5) Battery assembly:

[0275] The positive electrode, negative electrode, and separator are stacked in a specific pattern to form a battery chip. Then, the battery chip is packaged in a suitable container, electrolyte is added, and a sealed cap is installed to fix the cell assembly, giving it a certain finished cell shape.

[0276] The preparation parameters for the examples and comparative examples are shown in Table 1.

[0277] Table 1 Summary of preparation parameters in the examples and comparative examples

[0278] In Table 1:

[0279] Examples 1-16: M x N y O z The compounds are LiNO3 and Zr(NO3)4.

[0280] Example 17: M x N y O z It is LiNO3.

[0281] Example 18: M x N y O z The components are LiNO3 and Ti(NO3)4.

[0282] Example 19: M x N y O z The components are LiNO3 and Ti(NO3)4.

[0283] Example 20: M x N y O z The compounds are LiNO3, Cr(NO3)3, and Al(NO3)3.

[0284] Example 21: M x N y O zIt is LiNO3.

[0285] [Performance Testing]

[0286] 1. Testing Method

[0287] (1) ICP test:

[0288] Reference standard EPA 6010D-2018.

[0289] (2) XPS test:

[0290] Testing instrument: Axis Supra / Supra+ X-ray photoelectron spectrometer; reference standard GB / T 33502-2017. It can perform XPS detection on the surface of the negative electrode of the formed battery, and perform peak separation of nitrogen (N) for nitrides, nitrates, and organic nitrogen, calculating the corresponding content based on the peak area of ​​each substance.

[0291] (3) Electrochemically active specific surface area test:

[0292] Testing instrument: Electrochemical workstation.

[0293] Specific testing method: In a glove box, assemble the negative electrode, separator, lithium sheet, etc., into a coin cell in a specific order. Connect the assembled coin cell to an electrochemical workstation; the potential range may be between 0.01 and 3V (vs. Li / Li). Perform cyclic voltammetry scans at a scan rate of 5mV / s, typically multiple scans, to allow the electrodes to reach a stable state, and record the current-potential curves. Based on the cyclic voltammetry curves, select an appropriate potential range outside the Faraday region, and calculate the double-layer capacitance C using the slope of the current-potential curves. dl Then, according to the known formula ECSA = C dl / C s Calculate the electrochemically active specific surface area, where C s The specific capacitance per unit area varies depending on the negative electrode material. s Value. Currently, there are some industry standards and literature references that can be used as the basis for testing, such as the standard "Graphite Anode Materials for Lithium-ion Batteries" (GB / T30835-2014), which provides some guidance for the electrochemical performance testing of anode materials.

[0294] (4) Thickness Measurement: FIB-TEM refers to a technique that combines focused ion beam (FIB) technology with transmission electron microscopy (TEM). The operation steps are as follows: First, a thin slice is obtained by fine milling the target area of ​​the negative electrode using FIB, which is used for subsequent TEM testing. The sample holder with the thin slice is loaded into the transmission electron microscope. The thickness of the functional layer is directly measured on the image using TEM software tools. To improve accuracy, the measurement can be repeated at multiple locations (e.g., 9 sampling points), and the average value can be calculated as the thickness of the functional layer. FIB: Thermo Scientific-Scios 2HiVac, TEM: Thermo Scientific-Talos F200S G2.

[0295] (5) Cyclic performance test:

[0296] Step 1: Charge at 0.33C to 3.65V at 25℃, then charge at 3.65V constant voltage to 0.05C0; let stand for 5 minutes; discharge at 0.33C to 2V, and record the capacity at this point as C0 (this step is the actual initial capacity for testing).

[0297] Step 2: Charge the battery cell to 3.45V with 0.5C0 and to 3.65V with 0.33C0; let it stand for 10 minutes; discharge it to 2V with 1C0 and to 2V with 0.33C until the capacity loss is ≤80%, and record the number of cycles.

[0298] 2. Test Results

[0299] 1. As shown in Figure 1, the N1S spectrum of the negative electrode obtained from the battery after capacity formation in Example 18 was obtained by XPS testing. In Figure 1, (a) is the peak fitting diagram of N1S for titanium nitride, and (b) is the peak fitting diagram of N1S for Comparative Example 1 (without modification layer). The peaks at 395-397 eV represent metal nitrides, ~400 eV represent organic nitrogen (C-NH2), and >405 eV represent nitrates. From Figures (a) and (b) in Figure 1, it can be seen that Figure (a) can fit three N element peaks, representing titanium nitride, organic nitrogen, and nitrate (lithium nitrate Li). x N y O z and titanium nitrate Ti x N y O z Figure (a) shows that the nitrogen element in the surface layer of the modified layer exists in titanium nitride, organic nitrogen, and nitrate; while Figure (b) shows that the nitrogen element in the surface layer of the electrode modified layer in Comparative Example 1 exists only in organic nitrogen.

[0300] 2. As shown in Figure 2, the N1S spectrum of the negative electrode obtained from the disassembly of the battery after capacity formation in Example 13 was obtained by XPS testing. From Figures (a) and (b) in Figure 2, it can be seen that Figure (a) can fit three N element peaks, which represent zirconium nitride, organic nitrogen, and nitrate (lithium nitrate Li). x N y O z and titanium nitrate Zr x N y O z Figure (a) shows that the nitrogen element in the surface layer of the modified layer exists in zirconium nitride, organic nitrogen, and nitrate; while Figure (b) shows that the nitrogen element in the surface layer of the electrode modified layer in Comparative Example 1 exists only in organic nitrogen.

[0301] 3. As shown in Figure 3, the provided battery underwent a cycle performance test, and the test results are shown in Figure 3. Figure 3 shows that, compared to the comparative example, the cell with the zirconium nitride modification layer exhibits excellent cycle life. Using the preparation method of Example 13, by controlling the parameters of the intermediate frequency magnetron sputtering, a nitride modification layer can be formed on the surface of the negative electrode. The zirconium nitride in the modification layer can promote the formation of Zr(NO3)4 compounds in the SEI film, improve the uniformity of the SEI, and enhance the cycle performance of the cell.

[0302] 4. As shown in Table 2, in the battery provided in Example 13, the nitride in the modification layer of the negative electrode is zirconium nitride (ZrN). The ICP test results are shown in Table 2. It can be seen from Table 2 that the metal element Zr in the relevant modification layer can be clearly detected in the negative electrode of the product.

[0303] Table 2 shows the ICP test results of the negative electrode sheets obtained in Comparative Example 1 and Example 13.

[0304] Note: In Table 2, “Base” represents the negative electrode of Comparative Example 1; “ZrN” represents the negative electrode of Example 1.

[0305] 5. As shown in Table 3, performance tests were conducted on the lithium-ion batteries provided in the examples and comparative examples, and the test results are shown in Table 3. Table 3 shows that, compared to the comparative examples, the battery cell with the nitride modification layer has excellent cycle life. As in the experimental method of the examples, by controlling the parameters of the intermediate frequency magnetron sputtering, a nitride modification layer can be formed on the surface of the negative electrode. The zirconium nitride in the modification layer can promote the formation of nitrate compounds M in the SEI film of the product. x N y O z The formation of the modified layer improves the uniformity of the SEI and provides a suitable transport channel for lithium ions, thus improving the cycle performance of the cell. However, Comparative Example 1, which did not undergo the modified layer treatment, had a relatively poor cycle life.

[0306] Table 3

[0307] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. Secondary battery, of which, The invention includes a composite negative electrode sheet, which comprises a negative electrode sheet and a modification layer. The modification layer is disposed on at least one side of the negative electrode sheet. The modification layer comprises a nitrogen-containing inorganic compound, which includes nitrides and nitrates. The nitride contains at least one of a metallic element and a non-metallic element; the metallic element includes one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti, and the non-metallic element includes one or more of Si, B, and C; The nitrate compounds include M x N y O z Wherein, M includes one or more of M' and M”; M' includes one or more of Li and Na; M” includes one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti; 0 <x≤1,0<y≤5,0<z≤15。 2. The secondary battery according to claim 1, wherein, The nitrides include one or more of aluminum nitride, zirconium nitride, magnesium nitride, chromium nitride, niobium nitride, tantalum oxide, titanium nitride, silicon nitride, boron nitride, carbon nitride, titanium carbon nitride, chromium aluminum nitride, and their respective non-stoichiometric nitrides.

3. The secondary battery according to claim 1 or 2, wherein, The nitrides include one or more of aluminum nitride, zirconium nitride, magnesium nitride, chromium nitride, niobium nitride, tantalum oxide, titanium nitride, titanium nitride carbon, chromium aluminum nitride, and their respective non-stoichiometric nitrides.

4. The secondary battery according to any one of claims 1 to 3, wherein, The nitrate compounds include M' 1-a N b O c One or more of Zr(NO2)4, Zr(NO3)4, Al(NO3)3, Mg(NO3)2, Cr(NO3)3, Nb(NO3)5, Nb(NO3)3, Nb(NO3)4, Ta(NO3)5, Ta(NO3)4, Ti(NO3)4, and Ti(NO3)3, wherein 0 <a<1,0<b<5,0<c<15。 5. The secondary battery according to any one of claims 1 to 4, wherein, The nitrate compounds include M' 1-a N b O c It also includes one or more of Zr(NO2)4, Zr(NO3)4, Ti(NO3)4, and Ti(NO3)3, where 0 ≤ a < 1, 0 <b≤5,0<c≤15。 6. The secondary battery according to any one of claims 1 to 5, wherein, The test results of the modified layer based on X-ray photoelectron spectroscopy analysis satisfy any one of the following (i) to (ii): (i) The mass content of the nitride is 2% to 8%; (ii) The mass content of the nitrate compound is 1.5% to 6%.

7. The secondary battery according to any one of claims 1 to 6, wherein, Based on the test results of X-ray photoelectron spectroscopy analysis of the modified layer, any one of the following (i) to (ii) is satisfied: (i) The mass content of the nitride is 2.5% to 7.5%; (ii) The mass content of the nitrate compound is 2% to 5.5%.

8. The secondary battery according to any one of claims 1 to 7, wherein, The composite negative electrode has an electrochemically active specific surface area of ​​7 cm². 2 / g~8.7cm 2 / g.

9. The secondary battery according to any one of claims 1 to 8, wherein, The composite negative electrode has an electrochemically active specific surface area of ​​7.2 cm². 2 / g~8.6cm 2 / g.

10. The secondary battery according to any one of claims 1 to 9, wherein, The thickness of the modified layer is 5 nm to 50 nm.

11. The secondary battery according to any one of claims 1 to 10, wherein, The thickness of the modified layer is 10 nm to 30 nm.

12. A method for preparing a secondary battery, wherein, This includes preparing a composite negative electrode, wherein preparing the composite negative electrode includes: A composite negative electrode is obtained by forming a modification layer on at least one side of the negative electrode; the modification layer comprises: a nitrogen-containing inorganic compound; the nitrogen-containing inorganic compound includes nitrides and nitrate compounds; the nitride comprises at least one of a metallic element and a non-metallic element; the metallic element includes one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti, and the non-metallic element includes one or more of Si, B, and C; the nitrate compound includes M x N y O z Wherein, M includes one or more of M' and M”; M' includes one or more of Li and Na; M” includes one or more of Al, Zr, Mg, Cr, Nb, Ta, and Ti; 0 <x≤1,0<y≤5,0<z≤15。 13. The method according to claim 12, wherein, The modification layer is formed on at least one side of the negative electrode using thin film deposition technology; the thin film deposition technology includes one or more of physical vapor deposition and chemical vapor deposition; the physical vapor deposition method includes one or more of magnetron sputtering, arc ion plating, and electron beam evaporation.

14. The method according to claim 13, wherein, The modification layer is formed on at least one side of the negative electrode by magnetron sputtering, comprising the steps of: Perform vacuuming; A working gas is introduced, and under the action of an electric field and a magnetic field, a sputtering target is deposited on the negative electrode to form the modification layer, thereby obtaining the composite electrode. The operating parameters of the controlled sputtering include one or more of the following: vacuum degree, working gas flow rate, discharge power, and sputtering time.

15. The method according to claim 14, wherein, The target material includes at least one of a metallic element and a non-metallic element; the working gas includes a carrier gas and a reaction gas, and the reaction gas includes a nitrogen source.

16. The method according to claim 15, wherein, Meet at least one of the following: The metallic element includes one or more of the following: aluminum, magnesium, zirconium, chromium, niobium, tantalum, and titanium. The non-metallic elements include one or more of silicon, boron, and carbon.

17. The method according to claim 15 or 16, wherein, The nitrogen source includes one or more of N2 and NH3.

18. The method according to any one of claims 14 to 17, wherein, The magnetron sputtering conditions satisfy one or more of the following (a) to (d): (a) The vacuum level is 1×10 -2 Pa ~ 10 × 10 -1 Pa; (b) The discharge power is 1000W to 5000W; (c) The sputtering time is 100s to 2500s; (d) The working gas flow rate is 1 sccm to 50 sccm.

19. The method according to any one of claims 14 to 18, wherein, The magnetron sputtering conditions satisfy one or more of the following (a) to (d): (a) The vacuum level is 5 × 10⁻⁶ -2 Pa ~ 5 × 10 -1 Pa; (b) The discharge power is 2000W to 4000W; (c) The sputtering time is 300s to 800s; (d) The working gas flow rate is 1 sccm to 20 sccm.

20. An electrical appliance, wherein, The secondary battery includes any one of claims 1 to 11, or the secondary battery prepared by any one of claims 12 to 19.

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