WO2023216013A1

WO2023216013A1 - Negative electrode pole piece, preparation method for negative electrode pole piece, secondary battery, battery module, battery pack and electrical device

Info

Publication number: WO2023216013A1
Application number: PCT/CN2022/091367
Authority: WO
Inventors: 廖赏举; 刘成勇; 胡波兵; 蔡晓岚; 王瀚森; 谢张荻
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-05-07
Filing date: 2022-05-07
Publication date: 2023-11-16
Also published as: CN117716542A

Abstract

The present application provides a negative electrode pole piece, a preparation method for the negative electrode pole piece, a secondary battery, a battery module, a battery pack and an electrical device. The negative electrode pole piece comprises: a lithium metal layer, and a composite protective film located on at least one surface of the lithium metal layer, the composite protective film comprising a precipitated salt film layer and an oxide film layer, and at least a part of the oxide film layer being distributed in the precipitated salt film layer. The composite protective film in the negative electrode pole piece provided by the present application can achieve the purpose of protecting lithium metal during charge and discharge cycles while inducing the uniform deposition of the lithium metal during the charge and discharge cycles and reducing the growth of lithium dendrites and the generation of dead lithium, thus helping to improve the capacity, cycle performance and safety performance of the secondary battery.

Description

Negative electrode plate, preparation method of negative electrode plate, secondary battery, battery module, battery pack and electrical device

Technical field

This application belongs to the technical field of electrochemistry, and specifically relates to a negative electrode plate, a preparation method of the negative electrode plate, a secondary battery, a battery module, a battery pack and an electrical device.

Background technique

Secondary batteries, represented by lithium-ion batteries, are widely used in all aspects of today's life due to their advantages such as no memory effect, long cycle life, and environmental protection. In recent years, secondary batteries have developed rapidly in the fields of new energy vehicles and large-scale energy storage. Among the existing anode materials for secondary batteries, lithium metal anode has become the best choice for the next generation of high-specific-energy secondary battery anode materials due to its high theoretical specific capacity (3860mAh/g). However, due to the high activity of the lithium metal anode, it is easy to react with environmental media in secondary batteries, resulting in poor cycle performance of the secondary battery, which greatly limits its large-scale application in secondary batteries.

Contents of the invention

The purpose of this application is to provide a negative electrode plate, a negative electrode plate used in a secondary battery, a secondary battery and a power consumption device, aiming to improve the cycle performance and safety performance of the secondary battery.

In order to achieve the above-mentioned object of the invention, the first aspect of the present application provides a negative electrode sheet, including: a lithium metal layer, and a composite protective film located on at least one surface of the lithium metal layer, wherein the composite protective film includes a precipitated salt film layer and an oxide film layer, at least a part of the oxide film layer is distributed in the precipitated salt film layer.

The composite protective film formed by the precipitated salt film layer and the oxide film layer in this application is very dense. In the secondary battery, it can isolate the organic solvent in the electrolyte and the contact between the lithium salt anion and the lithium metal, reducing the irreversible loss of the electrolyte. This can achieve the purpose of protecting lithium metal during the charge and discharge cycle.

In any embodiment of the present application, the precipitated salt film layer includes (M ₁ ) _x1 (PO ₄ ) _y1 , (M ₁ ) _x2 (CO ₃ ) _y2 , or a combination thereof, where M ₁ is Li, Mn, Mg , Ba, Ca and Sr, x ₁ , y ₁ and x ₂ , y ₂ make the net charge of the compound zero.

The precipitated salt film layer is mainly composed of inorganic phosphates and carbonates. It has good lithium ion conductivity and can isolate electrons, so it can provide a migration channel for lithium ions to induce uniform lithium ion dispersion. deposition, thereby reducing the generation of lithium dendrites and improving the safety performance of secondary batteries.

In any embodiment of the present application, the oxide film layer includes (M ₁ ) _m _On , where M ₁ is Li, Mn, Mg, Ba, Ca, Sr or a combination thereof, and m and n are such that the metal The net charge of oxides is zero.

The oxide film layer and the precipitated salt film layer in this application are compounded/mixed together to form a composite protective film of the lithium metal layer. The composite protective film is a solid electrolyte layer, has high mechanical strength, and can act on the lithium metal layer. It has a strong isolation and protection effect, and can also induce uniform deposition of lithium metal during charge and discharge cycles, inhibit the growth of lithium dendrites, and improve the cycle performance and safety performance of secondary batteries.

In any embodiment of the present application, the oxide film layer is located on a side of the composite protective film close to the lithium metal layer, and the precipitated salt film layer is located on a side of the composite protective film away from the lithium metal layer. side.

In any embodiment of the present application, the thickness of the composite protective film is 1 μm to 25 μm, optionally 3 μm to 20 μm.

In any embodiment of the present application, the thickness of the oxide film layer ranges from 50 nm to 200 nm, optionally from 70 nm to 160 nm.

The thickness of the oxide film layer and the composite protective film is within an appropriate range, which can not only provide a good migration channel for lithium ions, but also enable lithium ions to have better conductivity in the composite protective film, thereby reducing the interface impedance and inducing lithium metal. Uniform deposition can reduce or avoid the growth of lithium dendrites; it can also effectively isolate the contact between organic solvents and lithium salt anions in the electrolyte and lithium metal, reducing the irreversible loss of the electrolyte, thereby protecting lithium metal during charge and discharge cycles. the goal of.

In any embodiment of the present application, the passivation interval of the composite protective film is 110 mV to 420 mV.

The passivation interval of the composite protective film is within the above range, indicating that the composite protective film in this application has good high voltage resistance and will not be easily decomposed even under high voltage, because it can play a long-lasting role in protecting the lithium metal layer. The protective effect is beneficial to improving the cycle performance of secondary batteries.

A second aspect of the present application provides a method for preparing a negative electrode sheet, including: a film forming step, including reacting a lithium metal layer with a film-forming liquid to form a composite protective film to obtain a negative electrode sheet, wherein the composite protective film It includes a precipitated salt film layer and an oxide film layer, at least part of the oxide film layer is distributed in the precipitated salt film layer; the film-forming liquid includes precipitated salt cations, precipitated salt anions dissolved in an inert solvent, Oxidizing oxygen acid salts, complexing agents and catalysts.

By using an aqueous solvent that easily reacts with lithium metal, and configuring the film-forming liquid according to the reaction mechanism of the deposited film, and then reacting with the lithium metal layer through the reaction of the film-forming liquid and the lithium metal layer, a controllable, high-temperature film-forming liquid can be formed on the surface of the lithium metal layer. Voltage inorganic salt composite protective film. This composite protective film can effectively isolate the organic solvent in the electrolyte and the contact between lithium salt anions and lithium metal, reduce the irreversible loss of the electrolyte, thereby achieving the purpose of protecting the lithium metal layer during the charge and discharge cycle. .

In any embodiment of the present application, the preparation method further includes a step of providing a film-forming liquid. The step of providing a film-forming liquid includes: combining the first film-forming salt containing the precipitation salt cation, the complexing agent and the The catalyst is dissolved in a first inert solvent to obtain a first solution; the second film-forming salt containing the precipitation salt anion and the oxidizing oxygen acid salt are dissolved in a second inert solvent to obtain a second solution; The first solution and the second solution are mixed evenly to obtain the film-forming liquid.

In any embodiment of the present application, the first film-forming salt includes MnCl ₂ , Mn(NO ₃ ) ₂ , MnSO ₄ ·H ₂ O, MgSO ₄ , Ca(NO ₃ ) ₂ , Ba(NO ₃ ) ₂ , Sr(NO ₃ ) ₂ or combinations thereof.

In any embodiment of the present application, the second film-forming salt includes carbonate, phosphate or a combination thereof, optionally (M ₂ ) ₂ CO ₃ , (M ₂ ) _x3 H _y3 (PO4) _z3 , ( M ₂ ) _x4 H _y4 (P ₂ O ₇ ) _z4 or a combination thereof, where M ₂ is Li, Na, K or a combination thereof, x ₃ , y ₃ , z ₃ and x ₄ , y ₄ , z ₄ make all The net charge of the second film-forming salt is zero.

In any embodiment of the present application, the complexing agent includes ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, ethanolamine or a combination thereof.

In any embodiment of the present application, the oxidizing oxygen-containing acid salt includes nitrate, inorganic salt (M ₂ ) _x5 (M ₃ ) _y5 O _z5 or a combination thereof, optionally NaNO ₃ , KNO ₃ , Ca(NO ₃ ) ₂ , KMnO ₄ , Na ₂ FeO ₄ , K ₂ Cr ₂ O ₇ , NaCoO ₂ , NaVO ₂ or combinations thereof, where M ₂ is Li, Na, K or combinations thereof, M ₃ is V, Cr, Mn , Fe, Co, Ni or combinations thereof, z ₅ is 1 to 7, x ₅ , y ₅ , z ₅ make the net charge of the oxidizing oxo acid salt be zero.

In any embodiment of the present application, the catalyst includes an ammonium salt, which may be NH ₄ NO ₃ , (NH ₄ ) ₂ SO ₄ , NH ₄ Cl or a combination thereof.

In any embodiment of the present application, in the film-forming liquid, the concentration of the first film-forming salt, the second film-forming salt, the complexing agent and the oxidizing oxygen acid salt is 10 g /L to 50g/L, and the concentration of the catalyst is 10g/L to 30g/L.

By adjusting the components of the film-forming liquid and controlling the concentration of the corresponding components within an appropriate range, a dense solid electrolyte composite protective film that can conduct lithium ions but not electrons can be converted in situ on the surface of lithium metal. The composite protective film has low interface impedance, strong interface bonding force, and high mechanical strength. It can isolate the reaction between the electrolyte and lithium metal, weaken or avoid the irreversible loss of the electrolyte, and can induce uniform deposition of lithium metal during the cycle, inhibiting The growth of lithium dendrites improves the cycle performance and safety performance of secondary batteries.

In any embodiment of the present application, the pH value of the film-forming liquid is 5 to 7. By adjusting the pH value of the film-forming liquid, the acidity of the film-forming liquid can be reduced and its alkalinity can be increased, thereby increasing the number of basic acid radicals in the solution, which is beneficial to promoting the formation of the precipitated salt film layer.

A third aspect of this application provides a secondary battery, including the negative electrode sheet described in the first aspect of this application or the negative electrode sheet produced by the preparation method described in the second aspect of this application.

A fourth aspect of this application provides a battery module, including the secondary battery described in the third aspect of this application.

A fifth aspect of this application provides a battery pack, including the battery module described in the fourth aspect of this application.

A sixth aspect of this application provides an electrical device, including at least one of the secondary battery described in the third aspect of this application, the battery module described in the fourth aspect, or the battery pack described in the fifth aspect of this application.

The battery modules, battery packs and electrical devices of the present application include the secondary battery provided by the present application, and thus have at least the same advantages as the secondary battery.

Description of the drawings

Figure 1 is a surface morphology diagram of an embodiment of the composite protective film in the negative electrode sheet of the present application.

FIG. 2 is a schematic diagram of an embodiment of the secondary battery of the present application.

FIG. 3 is an exploded schematic diagram of an embodiment of the secondary battery of the present application.

FIG. 4 is a schematic diagram of an embodiment of the battery module of the present application.

Figure 5 is a schematic diagram of an embodiment of the battery pack of the present application.

FIG. 6 is an exploded view of FIG. 5 .

FIG. 7 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, not all implementations. example. The related embodiments described herein are illustrative in nature and are intended to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limitations of the present application.

For the sake of simplicity, only certain numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with other lower limits to form an unexpressed range, and likewise any upper limit can be combined with any other upper limit to form an unexpressed range. Furthermore, each individually disclosed point or single value may itself serve as a lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.

In the description herein, “above” and “below” include the numbers unless otherwise stated.

Unless otherwise stated, terms used in this application have their commonly understood meanings as generally understood by those skilled in the art. Unless otherwise stated, the values of each parameter mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if the items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

The theoretical specific capacity of lithium metal anode (3860mAh/g) is extremely high, making it the best choice for the next generation of high-specific-energy secondary battery anode materials. However, during the research process, the inventor found that lithium metal has extremely high activity. On the one hand, it easily undergoes oxidation-reduction reactions with environmental media during storage and transportation and becomes ineffective. It is also more likely to react violently with aqueous solutions, thus limiting the secondary battery preparation process. Many inorganic salt film-forming liquids are used; on the other hand, during the charging and discharging process of secondary batteries, it is easy to react with the electrolyte to form an SEI film. As the cycle time increases, the SEI film will gradually thicken, resulting in an interface The impedance increases and leads to the generation of dead lithium, which in turn causes capacity loss and affects the cycle performance of the secondary battery. At the same time, during the charging and discharging process of the secondary battery, uneven lithium deposition can lead to the generation of lithium dendrites. The growth of lithium dendrites may puncture the separator and cause the battery to short-circuit or even explode.

At present, in order to solve the storage and transportation problem, the existing technology mostly adopts the method of coating a layer of polymer on the surface of lithium metal. However, this method has complex process and high cost, and the main link between the polymer and lithium metal is organic. -It is combined by inorganic bonds, and the binding force is poor; in addition, the polymer protective film has many defects and has poor protection ability for lithium metal anodes. Moreover, the polymer film layer is not resistant to high voltage and is easy to decompose under high voltage, so Limited ability to protect lithium metal.

In order to solve the above problems, the inventor proposed a negative electrode sheet through extensive research. By using an aqueous solvent that easily reacts with lithium metal, the film-forming liquid is configured according to the reaction mechanism of the deposited film, and the lithium metal and lithium metal are controlled by spraying. The reaction speed of the film-forming liquid deposits a composite protective film with controllable thickness and high voltage resistance on the surface of lithium metal. This composite protective film can achieve the purpose of protecting lithium metal during the charge and discharge cycle of the secondary battery, and can Promote the uniform deposition of lithium metal, which is beneficial to improving the cycle performance and safety performance of secondary batteries.

Negative pole piece

A first aspect of the embodiment of the present application provides a negative electrode sheet, including: a lithium metal layer, and a composite protective film located on at least one surface of the lithium metal layer, wherein the composite protective film includes a precipitated salt film layer and an oxide film layer, at least a portion of the oxide film layer being distributed in the precipitated salt film layer.

Without intending to be limited to any theory, the inventor found that the composite protective film formed by the precipitated salt film layer and the oxide film layer in the present application is very dense and can isolate the organic solvent in the electrolyte and the lithium salt anion from the secondary battery. The contact of lithium metal reduces the irreversible loss of the electrolyte, thereby achieving the purpose of protecting lithium metal during the charge and discharge cycle; at the same time, the composite protective film can induce the uniform deposition of lithium metal during the charge and discharge cycle and reduce the growth of lithium dendrites. and the generation of dead lithium, which is beneficial to improving the capacity, cycle performance and safety performance of secondary batteries.

In some embodiments, referring to Figure 1, the precipitated salt film layer and the oxide film layer in the composite protective film are mixed and distributed, wherein the precipitated salt film layer is located on the side of the composite protective film away from the lithium metal layer, and the oxide film layer is located on the side of the composite protective film away from the lithium metal layer. The film layer is located on the side of the composite protective film close to the lithium metal layer. The composite protective film is mainly combined with the lithium metal layer through chemical bonds. The bonding effect is strong and the mechanical strength is high, and it can play a greater role in protecting the lithium metal layer. The strong protective effect enables it to effectively isolate the electrolyte during long-term charge and discharge cycles and reduce the SEI film generated by its reaction with the electrolyte, thus reducing the interface impedance and improving the ion conduction capacity and cycle performance of the secondary battery.

In some embodiments, the precipitated salt film layer includes (M ₁ ) _x1 (PO ₄ ) _y1 , (M ₁ ) _x2 (CO ₃ ) _y2 , or a combination thereof, where M ₁ is Li, Mn, Mg, Ba At least one of , Ca and Sr, x ₁ , y ₁ and x ₂ , y ₂ make the net charge of the compound zero. For example, the precipitated salt film layer can be Li ₃ PO ₄ , LiCO ₃ , Mn ₃ (PO ₄ ) ₂ , MnCO ₃ , Mg ₃ (PO ₄ ) ₂ , MgCO ₃ , Ba ₃ (PO ₄ ) ₂ , BaCO ₃ , Ca ₃ (PO ₄ ) ₂ , CaCO ₃ , Sr ₃ (PO ₄ ) ₂ , SrCO ₃ or combinations thereof.

In some embodiments, the oxide film layer includes (M ₁ ) _m _On , where M ₁ is Li, Mn, Mg, Ba, Ca, Sr or a combination thereof, and m and n are such that the metal oxide The net charge is zero. For example, the oxide film layer may be Li ₂ O, MnO, MgO, BaO, CaO, SrO or a combination thereof.

In some embodiments, the composite protective film has a thickness of 1 μm to 25 μm. For example, the thickness of the composite protective film is 3 μm, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm, 21 μm, 23 μm or within the range of any of the above values. Optionally, the thickness of the composite protective film is 3 μm to 20 μm.

In some embodiments, the thickness of the oxide film layer is 50 nm to 200 nm. For example, the thickness of the oxide film layer is 70nm, 90nm, 110nm, 130nm, 150nm, 170nm, 190nm or within the range of any of the above values. Optionally, the thickness of the oxide film layer is 70 nm to 160 nm.

In this application, the thickness of the oxide film layer and the composite protective film have well-known meanings in the art, and can be measured using methods known in the art, such as using a multimeter (for example, Mitutoyo 293-100 type, with an accuracy of 0.1 μm).

In this application, the thickness of the oxide film layer and the composite protective film is within an appropriate range, which can not only provide a good migration channel for lithium ions, but also enable the lithium ions to have better conductivity in the composite protective film, thereby reducing the interface impedance and It induces the uniform deposition of lithium metal and reduces or avoids the growth of lithium dendrites; it can also effectively isolate the contact between organic solvents and lithium salt anions in the electrolyte and lithium metal, reducing the irreversible loss of the electrolyte, thereby achieving the best performance during the charge and discharge cycle. The purpose of protecting lithium metal.

In some embodiments, the passivation interval of the composite protective film is 110 mV to 420 mV. For example, the passivation interval of the composite protective film can be 130mV to 400mV, 150mV to 380mV, 170mV to 360mV, 190mV to 340mV, 210mV to 320mV, 230mV to 300mV or 250mV to 280mV.

The passivation interval of the composite protective film in this application has a well-known meaning in the art, and can be tested using methods known in the art. For example, a three-electrode system can be used to measure the electrochemical polarization curve, and the composite protective film can be obtained through the electrochemical polarization curve. Passivation interval of protective film. The passivation interval of the composite protective film is within the above range, indicating that the composite protective film in this application has good high voltage resistance and will not be easily decomposed even under high voltage, because it can play a long-lasting role in protecting the lithium metal layer. The protective effect is beneficial to improving the cycle performance of secondary batteries.

A second aspect of the embodiment of the present application provides a method for preparing a negative electrode sheet, including:

The film forming treatment step includes reacting the lithium metal layer with the film forming liquid to form a composite protective film to obtain the negative electrode piece, wherein the composite protective film includes a precipitated salt film layer and an oxide film layer, and the oxide film layer At least a portion of is distributed in the precipitated salt film layer.

This application adopts an aqueous solvent that easily reacts with lithium metal, and configures a film-forming liquid according to the reaction mechanism of the deposited film. Then through the reaction of the film-forming liquid and the lithium metal layer, a controllable, thickness-controllable, and scalable film-forming liquid can be formed on the surface of the lithium metal layer. A high-voltage resistant inorganic salt composite protective film. This composite protective film can effectively isolate the organic solvent in the electrolyte and the contact between lithium salt anions and lithium metal, reduce the irreversible loss of the electrolyte, thereby protecting the lithium metal layer during the charge and discharge cycle. the goal of.

In some embodiments, the film-forming fluid includes precipitating salt cations, precipitating salt anions, oxidizing oxyacid salts, complexing agents, and catalysts dissolved in an inert solvent.

In some embodiments, the preparation method further includes a step of providing a film-forming liquid, and the step of providing a film-forming liquid includes:

S10. Dissolve the first film-forming salt containing the precipitation salt cation, the complexing agent and the catalyst in the first inert solvent to obtain a first solution;

S20. Dissolve the second film-forming salt containing the precipitation salt anion and the oxidizing oxygen acid salt in a second inert solvent to obtain a second solution;

S30. Mix the first solution and the second solution to obtain the film-forming liquid.

In some embodiments, in the film-forming liquid, the concentration of the first film-forming salt, the second film-forming salt, the complexing agent and the oxidizing oxygen acid salt is 10 g/L to 50g/L, for example, it can be 10g/L, 15g/L, 20g/L, 25g/L, 30g/L, 35g/L, 40g/L, 45g/L, 50g/L or any of the above values. within the composition range. The concentration of the catalyst is 10g/L to 30g/L, for example, it can be 10g/L, 15g/L, 20g/L, 25g/L, 30g/L or within the range of any of the above values.

By adjusting the components of the film-forming liquid and controlling the concentration of the corresponding components within an appropriate range, this application can convert in situ on the lithium metal surface to generate a dense solid-state electrolyte composite protection that can conduct lithium ions but not electrons. The composite protective film has low interfacial resistance, strong interfacial bonding force, and high mechanical strength. It can isolate the reaction between the electrolyte and lithium metal, weaken or avoid the irreversible loss of the electrolyte, and can induce uniform deposition of lithium metal during the cycle. , inhibiting the growth of lithium dendrites and improving the cycle performance and safety performance of secondary batteries.

In some embodiments, the film-forming liquid can react with the lithium metal layer by spraying to form the composite protective film. Among them, the thickness of the composite protective film formed on the lithium metal layer can be controlled by controlling the spraying rate. Specifically, the film-forming liquid can be sprayed on the lithium metal layer through an atomizer, and the thickness of the formed composite protective film can be controlled within the appropriate range described above in this application by controlling the spray volume of the atomizer.

In some embodiments, the first film-forming salt includes MnCl ₂ , Mn(NO ₃ ) ₂ , MnSO ₄ ·H ₂ O, MgSO ₄ , Ca(NO ₃ ) ₂ , Ba(NO ₃ ) ₂ , Sr( NO ₃ ) ₂ or combinations thereof.

In some embodiments, the second film-forming salt includes carbonate, phosphate or a combination thereof, optionally (M ₂ ) ₂ CO ₃ , (M ₂ ) _x3 H _y3 (PO4) _z3 , (M ₂ ) _x4 H _y4 (P ₂ O ₇ ) _z4 or a combination thereof, where M ₂ is Li, Na, K or a combination thereof, x ₃ , y ₃ , z ₃ and x ₄ , y ₄ , z ₄ make the The net charge of the two film-forming salts is zero. For example, the second film-forming salt can be Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , Li ₂ HPO ₄ , LiH ₂ PO ₄ , Na ₂ HPO ₄ , NaH ₂ PO ₄ , K ₂ HPO ₄ , KH ₂ PO ₄ , Li ₃ HP ₂ O ₇ , Li ₂ H ₂ P ₂ O ₇ , LiH ₃ P ₂ O ₇ , Na ₃ HP ₂ O 7 , Na ₂ H ₂ P ₂ _{O 7} _, NaH ₃ P ₂ O ₇ , K ₃ HP ₂ O ₇ , K ₂ H ₂ P ₂ O ₇ , KH ₃ P ₂ O ₇ or combinations thereof.

In some embodiments, the complexing agent includes ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, ethanolamine, or combinations thereof.

In some embodiments, the oxidizing oxygen acid salt includes nitrate, inorganic salt (M ₂ ) _x5 (M ₃ ) _y5 O _z5 or a combination thereof, optionally NaNO ₃ , KNO ₃ , Ca(NO ₃ ) _2. KMnO ₄ , Na ₂ FeO ₄ , K ₂ Cr ₂ O ₇ , NaCoO ₂ , NaVO ₂ or combinations thereof, where M ₂ is Li, Na, K or combinations thereof, M ₃ is V, Cr, Mn, Fe , Co, Ni or a combination thereof, z ₅ is 1 to 7, x ₅ , y ₅ , z ₅ make the net charge of the oxidizing oxygen acid salt be zero.

In some embodiments, the catalyst includes an ammonium salt, optionally NH ₄ NO ₃ , (NH ₄ ) ₂ SO ₄ , NH ₄ Cl, or a combination thereof.

Each component of the film-forming liquid provided in this application exists stably in the solution. When it comes into contact with lithium metal and reacts, the interface pH increases. At this time, the insoluble inorganic salts in the solution reach critical supersaturation and induce deposition. , it is converted into a dense (inorganic salt) solid electrolyte composite protective film on the surface of lithium metal. This composite protective film is combined with lithium metal through chemical bonds. The binding effect is strong and can play a lasting role in protecting the lithium metal layer under high voltage. Protective effects.

As a specific example, the reaction process between the film-forming liquid and lithium metal in this application can be as follows:

Li-e→Li ⁺ (1)

2Li+VO ₃ ^- →VO ₂ +Li ₂ O (2)

2H ⁺ +e→H ₂ (3)

H ₂ PO ₄ ^- →HPO ₄ ^2- +H ⁺ (4)

HPO ₄ ^2- →PO ₄ ^3- +H ⁺ (5)

H ₂ O→H ⁺ +OH ^- (6)

Li ⁺ +OH ^- →LiOH (7)

3Li ⁺ +PO ₄ ^3- →Li ₃ PO ₄ (8)

Mn ²⁺ +HPO ₄ ^2- →MnHPO ₄ (9)

Among them, lithium metal reacts with soluble hydrogen phosphate to consume hydrogen ions and form an insoluble phosphate precipitation film with strong protective effect. The conversion and precipitation efficiency can be controlled by adjusting the solution composition and the amount of spray liquid can be controlled. Reaction rate and precipitation thickness of composite protective film.

As shown in the following formulas (9) to (11), a part of Mn ²⁺ can be complexed by introducing a complexing agent (represented by A) into the film-forming liquid to maintain the concentration of free Mn ²⁺ in the solution, so that during the reaction During the process, the Mn ²⁺ consumed at the interface can be replenished in time, while reducing the concentration of free Mn ²⁺ in the solution, promoting the ionization of H ₂ PO ^4- , increasing the concentration of PO ₄ ^3- in the solution, and making the H in the solution react with the interface The concentration difference of ₂ PO ^4- is reduced, which reduces the dependence on the ionization and diffusion processes to supplement the H ₂ PO ^4- consumed during the film formation process, and improves the stability of the solution; in addition, after the complexing agent is introduced, the complexation in the solution The mixture can complex a part of Mn ²⁺ and release H ⁺ at the same time, promoting the dissolution of Li and increasing the precipitation rate. The reaction formula is as follows (B represents the intermediate product):

A+Mn ²⁺ →Mn(B) ²⁺ +H ⁺ (10)

The precipitation reaction occurs at the interface as follows:

Mn(B) ²⁺ +HPO ₄ ^2- →MnHPO ₄ +B (11)

B+H ⁺ →A (12)

As shown in the following formulas (12) to (14), by introducing a catalyst into the film-forming liquid, the activation energy required for the reaction can be reduced to promote the reaction, increase the chemical reaction rate, and the catalyst itself does not change before and after the reaction. The reaction equation is as follows:

6NH ₄ ⁺ +Mn ²⁺ →Mn(NH ₃ ) ₆ ²⁺ +H ⁺ (13)

Mn(NH ₃ ) ₆ ²⁺ +HPO ₄ ^2- →MnHPO ₄ +6NH ₃ (14)

NH ₃ +H ⁺ →NH ₄ ⁺ (15)

It can be seen from the above formulas (12) to (14) that NH ⁴⁺ in the catalyst in the solution can be hydrolyzed to generate NH ₃ ·H ₂ O and release H ⁺ , and Mn ²⁺ can be combined to reduce free Mn ²⁺ concentration to maintain solution stability; when Mn ²⁺ is consumed by the interface reaction, it can be released and replenished in time. The ligand NH ₃ combines with H ⁺ to generate NH ⁴⁺ . NH ⁴⁺ combines with H ⁺ at the interface to promote the ionization of H ₂ PO ^4- and accelerate the precipitation rate, thus playing a catalytic role.

During the reaction process between the above-mentioned film-forming liquid and lithium metal, a Mn ²⁺ buffer pair can be established by introducing a complexing agent to avoid the reduction of the effective components of the film-forming solution; an appropriate amount of catalyst can increase the nucleation density of MnHPO ₄ and improve MnHPO The precipitation rate is ₄ , which improves the corrosion resistance of the formed composite protective film; an appropriate amount of oxidizing oxygen acid salt can promote the formation of a dense passivating Li ₂ O film layer from lithium, thereby increasing the precipitation rate.

In some embodiments, the pH value of the film-forming liquid is 5 to 7. By adjusting the pH value of the film-forming liquid, the acidity of the film-forming liquid can be reduced and its alkalinity can be increased, thereby increasing the number of basic acid radicals in the solution. , which is conducive to promoting the formation of precipitated salt film layer.

In some embodiments, the negative electrode sheet further includes a negative electrode current collector, wherein the lithium metal layer is laminated on at least one side of the negative electrode current collector using a calendering process.

In some embodiments, the negative electrode current collector has two surfaces opposite in its thickness direction, and the lithium metal layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

A metal foil or porous metal plate can be used as the negative electrode current collector. For example, a foil or porous plate made of metals such as copper, nickel, titanium, iron, or alloys thereof. As an example, the negative electrode current collector is copper foil.

The negative electrode sheet can be prepared according to conventional methods in the art. For example, a lithium metal sheet is bonded to the surface of a copper foil to obtain a negative electrode sheet. The lamination can be achieved by, but is not limited to, roller pressing.

secondary battery

A third aspect of the embodiment of the present application provides a secondary battery, including any device in which an electrochemical reaction occurs to convert chemical energy and electrical energy into each other, and specific examples thereof include all kinds of lithium primary batteries or lithium secondary batteries. In particular, the lithium secondary battery includes a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

In some embodiments, the secondary battery of the present application includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.

[Negative pole piece]

The negative electrode sheet used in the secondary battery of the present application is the negative electrode sheet of the first aspect of the embodiment of the present application or the negative electrode sheet prepared by the preparation method of the second aspect of the embodiment of the present application.

[Positive pole piece]

The material, composition and manufacturing method of the positive electrode sheet used in the secondary battery of the present application may include any technology known in the prior art.

The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material. As an example, the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In some embodiments, the positive active material layer includes a positive active material. The specific type of the positive active material is not specifically limited and can be selected according to requirements. For example, the cathode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. In the secondary battery of the present application, the modified compound of each positive electrode active material mentioned above may be doping modification, surface coating modification, or doping and surface coating modification of the positive electrode active material.

As examples, lithium transition metal oxides may include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, One or more of lithium nickel cobalt aluminum oxide and its modified compounds. As examples, the lithium-containing phosphate with an olivine structure may include lithium iron phosphate, a composite of lithium iron phosphate and carbon, a lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, a lithium manganese iron phosphate, a lithium manganese iron phosphate and carbon One or more of the composite materials and their modified compounds. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination.

In some embodiments, the positive active material layer optionally further includes 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.

In some embodiments, the positive active material layer optionally further includes a binder. As examples, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil can be used as the positive electrode current collector. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may be selected from one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may be selected from polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.

The positive electrode piece in this application can be prepared according to conventional methods in this field. For example, the positive electrode active material layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying, and cold pressing. The cathode slurry is usually formed by dispersing the cathode active material, optional conductive agent, optional binder and any other components in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

The positive electrode sheet of the present application does not exclude other additional functional layers in addition to the positive active material layer. For example, in some embodiments, the positive electrode sheet of the present application also includes a conductive undercoat layer (for example, composed of a conductive agent and a binder) sandwiched between the positive electrode current collector and the positive electrode active material layer and disposed on the surface of the positive electrode current collector. ). In other embodiments, the positive electrode sheet of the present application further includes a protective layer covering the surface of the positive electrode active material layer.

[Electrolyte]

The electrolyte plays a role in conducting active ions between the positive electrode piece and the negative electrode piece. The electrolyte solution that can be used in the secondary battery of the present application can be an electrolyte solution known in the art.

In some embodiments, the electrolyte solution includes an organic solvent, a lithium salt and optional additives. The types of the organic solvent, lithium salt and additives are not specifically limited and can be selected according to needs.

In some embodiments, as examples, the lithium salts include, but are not limited to, LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate), LiClO ₄ (lithium perchlorate), LiFSI (lithium bisfluorosulfonimide) ), LiTFSI (lithium bistrifluoromethanesulfonimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluoromethanesulfonate), LiBOB (lithium difluoromethanesulfonate), LiPO ₂ F ₂ (difluorophosphoric acid Lithium), LiDFOP (lithium difluorodioxalate phosphate) and LiTFOP (lithium tetrafluorooxalate phosphate). One type of the above-mentioned lithium salt may be used alone, or two or more types may be used simultaneously.

In some embodiments, as examples, the organic solvent includes, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), carbonic acid Dimethyl ester (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate Ester (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), Methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE) ) at least one of the following. One type of the above-mentioned organic solvent may be used alone, or two or more types may be used simultaneously. Optionally, two or more of the above organic solvents are used simultaneously.

In some embodiments, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance. wait.

As examples, the additives include, but are not limited to, fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite Ester (ES), 1,3-propene sultone (PS), 1,3-propene sultone (PST), sulfonate cyclic quaternary ammonium salt, succinic anhydride, succinonitrile (SN) , at least one of adiponitrile (AND), tris(trimethylsilane)phosphate (TMSP), and tris(trimethylsilane)borate (TMSB).

The electrolyte solution can be prepared according to conventional methods in the art. For example, the organic solvent, lithium salt, and optional additives can be mixed evenly to obtain an electrolyte. There is no particular restriction on the order in which the materials are added. For example, add lithium salt and optional additives to the organic solvent and mix evenly to obtain an electrolyte; or add lithium salt to the organic solvent first, and then add the optional additives. The additives are added to the organic solvent and mixed evenly to obtain an electrolyte.

[Isolation film]

The isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows active ions to pass through. There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolation membrane can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited to these. The isolation film can be a single-layer film or a multi-layer composite film. When the isolation film is a multi-layer composite film, the materials of each layer may be the same or different. In some embodiments, a ceramic coating or a metal oxide coating can also be provided on the isolation film.

In some embodiments, the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer packaging. The outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag. The material of the soft bag can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

This application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. FIG. 2 shows an example of a square-structured secondary battery 5 .

In some embodiments, referring to FIG. 3 , the outer package may include a housing 51 and a cover 53 . The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 is used to cover the opening to close the accommodation cavity. The positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into the electrode assembly 52 . The number of electrode assemblies 52 contained in the secondary battery 5 can be one or several, and can be adjusted according to needs.

In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be multiple. The specific number can be adjusted according to the application and capacity of the battery module.

Figure 4 is a battery module 4 as an example. Referring to FIG. 4 , in the battery module 4 , a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 . Of course, it can also be arranged in any other way. Furthermore, the plurality of secondary batteries 5 can be fixed by fasteners.

Optionally, the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

Figures 5 and 6 show the battery pack 1 as an example. Referring to FIGS. 5 and 6 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box 2 and a lower box 3 . The upper box 2 is used to cover the lower box 3 and form a closed space for accommodating the battery module 4 . Multiple battery modules 4 can be arranged in the battery box in any manner.

electrical device

A fifth aspect of the embodiments of the present application provides an electrical device, which device includes at least one of a secondary battery, a battery module, or a battery pack of the present application. The secondary battery, battery module or battery pack may be used as a power source for the device or as an energy storage unit for the device. The device may be, but is not limited to, mobile equipment, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. For example, a notebook computer, a pen input type computer, a mobile computer, an e-book player, a portable telephone, a portable fax machine, a portable copy machine, a portable printer, a stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, electric Tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

The device can select secondary batteries, battery modules or battery packs according to its usage requirements.

Figure 7 is an example device. The device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and energy density, battery packs or battery modules can be used.

Example

The present disclosure is more particularly described in the following examples, which are intended to be illustrative only, as it will be apparent to those skilled in the art that various modifications and changes can be made within the scope of the present disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods, and can be directly were used without further processing and the equipment used in the examples is commercially available.

Example 1

Preparation of negative electrode plates

1) Pretreatment: In a drying room with a temperature of 25°C and a humidity of less than 2%, place a lithium foil with a thickness of 25μm in absolute ethanol. Preprocess for 10 seconds to react with hydrogen to remove the surface impurity layer. Soak and clean in DOL/DME, wash away the reaction product with ethanol, blow dry, and place in a drying dish for later use;

2) Film-forming liquid configuration: 35g/L manganese sulfate monohydrate, 24g/L EDTA ₄ Na and 1g/L ammonium sulfate are prepared together, 35g/L sodium dihydrogen phosphate, 10g/L NaNO ₃ and 10mL 0.001mol/L Prepare NaOH together, dissolve them separately, mix and adjust the volume to obtain a film-forming liquid;

3) Preparation of composite protective film: Spray on the lithium foil treated in step 1) through an atomizer, control the thickness of the film layer by controlling the amount of spray liquid, maintain the temperature at 10°C, spray rate 5mL/min, atomize The distance between the device and the lithium foil is 10cm, and the lithium foil belt speed is 1m/s. The lithium belt is sprayed three times during the transportation process, and then the prepared sample is washed and dried with absolute ethanol. The thickness of the composite protective film can be controlled by controlling the transmission speed of the lithium foil and the spray volume, recorded as H. After chemical conversion treatment, a glassy, uniform and dense crystalline film on the surface is formed, and a lithium foil with a composite protective film is obtained, which is washed with ethanol, DOL/DME, and dried;

4) Preparation of the negative electrode sheet: The lithium foil with the composite protective film is bonded to the surface of the copper foil by rolling to obtain the negative electrode sheet.

Preparation of positive electrode plates

Mix the cathode active material LiCoO ₂ , conductive carbon black, and binder PVDF according to the mass ratio of 96.7:1.7:1.6, add an appropriate amount of solvent NMP, and use it in a vacuum mixer to obtain a cathode slurry; apply the cathode slurry evenly on the cathode on both surfaces of the current collector aluminum foil; then vacuum dried at 70°C for 12 hours, and then cut into strips to obtain the positive electrode piece.

Preparation of electrolyte

Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) at a volume ratio of 1:1:1 to obtain an organic solvent; dissolve LiPF ₆ in the above organic solvent, and then Add fluoroethylene carbonate (FEC) and mix evenly to obtain an electrolyte; the concentration of LiPF ₆ is 1 mol/L.

Preparation of isolation film

PE porous film is used as the isolation membrane.

Preparation of lithium metal secondary batteries

Stack the positive electrode piece, isolation film, and negative electrode piece in order, so that the isolation film is between the positive and negative electrodes for isolation, and wind it to obtain the electrode assembly; place the electrode assembly in the outer packaging, and inject the prepared electrolyte After liquidization and packaging, the lithium metal secondary battery is obtained through processes such as formation, degassing, and trimming.

Examples 2 to 14 and Comparative Examples 1 to 3

The preparation method of the lithium metal secondary battery is similar to Example 1. The difference is that the negative electrode plate and related parameters in the preparation process are adjusted. The specific parameters are shown in Table 1. Comparative Example 1 does not contain a composite protective film. , Comparative Example 2 uses an ordinary polymer protective film instead of the composite protective film in Comparative Example 1. The thickness of the composite protective film in Comparative Example 3 is not within the protection scope of this application, and "/" means that it does not contain corresponding substances.

Table 1

test part

(1) Thickness test of composite protective film

Use Saicheng CHY-CA desktop thickness gauge to measure five evenly distributed points on the surface of the sample to observe whether the composite protective film is evenly prepared and record the average thickness.

(2) Testing of passivation interval of composite protective film

A three-electrode system was used to measure the electrochemical polarization curve of a square sample (surface area: 1cm ² ), scanning separately from OCP toward both sides, with a scanning rate of 0.333mV/s, a cathodic polarization curve cutoff potential of -300mV, and an anode polarization curve cutoff potential of 1.6 V, the cut-off current is 10mA, and the passivation interval of the composite protective film is analyzed after fitting.

(3) Lithium metal secondary battery cycle performance test

The cycle test temperature is 25°C. Charge the battery to 4.3V at a constant current of 0.33C and charge to 0.025C at a constant voltage. After standing for 5 minutes, discharge it to 2.8V at 0.33C. The capacity obtained in this step is the initial capacity. 0.33C charging/0.33C discharging cycle test until the secondary battery cycle capacity retention rate is 80%, and the corresponding cycle life is recorded.

(4) Safety performance test of lithium metal secondary batteries

Place the battery core in a graduated measuring cup for circulation, place the battery in a thermally conductive silicone oil bath at 60°C, and submerge the battery core. Charge the battery to 4.3V at a constant current of 0.33C, charge to 0.025C at a constant voltage, let it sit for 5 minutes and then discharge it to 2.8V at a rate of 0.33C; use the capacity obtained in this step as the initial capacity, and perform 0.33C charge/0.33C discharge. The cycle test is carried out until the secondary battery cycle capacity retention rate is 10%. After the cycle is completed, the readings are taken to determine the volume of gas produced by the cell and the corresponding cell status is recorded. A gas production volume of less than 10% is mild gas production, a volume of 10%-50% is moderate gas production, and a volume of more than 50% is severe gas production.

Table 2 gives the performance test results of Examples 1 to 14 and Comparative Examples 1 to 3.

Table 2

	复合保护膜钝化区间(mV)Composite protective film passivation interval (mV)	容量保持率80％的循环圈数Number of cycles for 80% capacity retention	高温循环性能安全测试High temperature cycle performance safety test
实施例1Example 1	240240	330330	无异常No abnormality
实施例2Example 2	160160	200200	无异常No abnormality
实施例3Example 3	320320	460460	无异常No abnormality
实施例4Example 4	210210	240240	无异常No abnormality
实施例5Example 5	280280	360360	无异常No abnormality
实施例6Example 6	220220	300300	无异常No abnormality
实施例7Example 7	290290	485485	无异常No abnormality
实施例8Example 8	110110	135135	中度产气Moderate gas production
实施例9Example 9	120120	140140	中度产气Moderate gas production
实施例10Example 10	135135	150150	轻度产气Mild gas production
实施例11Example 11	260260	310310	无异常No abnormality
实施例12Example 12	270270	336336	无异常No abnormality
实施例13Example 13	280280	360360	无异常No abnormality
实施例14Example 14	420420	极化太大无法循环Too polarized to cycle	极化太大无法循环Too polarized to cycle
对比例1Comparative example 1	00	8080	冒烟起火Smoke and fire
对比例2Comparative example 2	9090	110110	严重产气Severe gas production
对比例3Comparative example 3	100100	120120	严重产气Severe gas production

Comparing Examples 1 to 14 and Comparative Examples 1 to 2, it can be seen that the passivation interval of the composite protective film in the negative electrode sheet of the present application is significantly higher than that of Comparative Examples 1 and 2, indicating that the composite protective film can play a role in protecting the lithium metal layer. Very good protective effect; in addition, the number of cycles at which the capacity retention rate of the secondary batteries in Comparative Examples 1 and 2 is 80% is significantly lower than that in Examples 1 to 14, and the lithium metal secondary batteries in Comparative Examples 1 and 2 have The high temperature cycle performance is also poor, which shows that the composite protective film can effectively improve the cycle performance and safety performance of the secondary battery. Comparing Examples 1 to 14 and Comparative Example 3, it can be seen that when the thickness of the composite protective film is not as specified in this application, Within the selected range, the passivation interval of the composite protective film and the cycle performance of the secondary battery are significantly reduced, indicating that the thickness of the composite protective film needs to be controlled within the range selected in this application.

The above are only specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person familiar with the technical field can easily think of various equivalent methods within the technical scope disclosed in the present application. Modification or replacement, these modifications or replacements shall be covered by the protection scope of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claims.

Claims

A negative pole piece, including:

A lithium metal layer, and a composite protective film located on at least one surface of the lithium metal layer, wherein the composite protective film includes a precipitated salt film layer and an oxide film layer, at least a part of the oxide film layer is distributed on in the precipitated salt film layer.
The negative electrode sheet according to claim 1, wherein the precipitated salt film layer includes (M 1 ) x1 (PO 4 ) y1 , (M 1 ) x2 (CO 3 ) y2 or a combination thereof, wherein M 1 is At least one of Li, Mn, Mg, Ba, Ca and Sr, x 1 , y 1 and x 2 , y 2 such that the net charge of the compound is zero.
The negative electrode plate according to claim 1 or 2, wherein the oxide film layer includes (M 1 ) m On , wherein M 1 is Li, Mn, Mg, Ba, Ca, Sr or a combination thereof, m, n are such that the net charge of the metal oxide is zero.
The negative electrode plate according to any one of claims 1 to 3, wherein the oxide film layer is located on a side of the composite protective film close to the lithium metal layer, and the precipitated salt film layer is located on the side of the composite protective film close to the lithium metal layer. The side of the composite protective film away from the lithium metal layer.
The negative electrode piece according to any one of claims 1-4, satisfying at least one of the following conditions:

The thickness of the composite protective film is 1 μm to 25 μm, optionally 3 μm to 20 μm;

The thickness of the oxide film layer is 50nm to 200nm, optionally 70nm to 160nm;

The passivation range of the composite protective film is 110mV to 420mV.
A method for preparing a negative electrode piece, including:

The film forming treatment step includes reacting the lithium metal layer with the film forming liquid to form a composite protective film to obtain the negative electrode piece, wherein the composite protective film includes a precipitated salt film layer and an oxide film layer, and the oxide film layer At least a portion of is distributed in the precipitated salt film layer;

The film-forming liquid includes precipitation salt cations, precipitation salt anions, oxidizing oxygen acid salts, complexing agents and catalysts dissolved in an inert solvent.
The method according to claim 6, further comprising a step of providing a film-forming liquid, the step of providing a film-forming liquid comprising:

Dissolve the first film-forming salt including the precipitation salt cation, the complexing agent and the catalyst in a first inert solvent to obtain a first solution;

Dissolving the second film-forming salt including the precipitating salt anion and the oxidizing oxygen acid salt in a second inert solvent to obtain a second solution;

The first solution and the second solution are mixed evenly to obtain the film-forming liquid.
The preparation method according to claim 7, meeting at least one of the following conditions:

The first film-forming salt includes MnCl 2 , Mn(NO 3 ) 2 , MnSO 4 ·H 2 O, MgSO 4 , Ca(NO 3 ) 2 , Ba(NO 3 ) 2 , Sr(NO 3 ) 2 or its combination;

The second film-forming salt includes carbonate, phosphate or a combination thereof, optionally (M 2 ) 2 CO 3 , (M 2 ) x3 H y3 (PO4) z3 , (M 2 ) x4 H y4 (P 2 O 7 ) z4 or its combination,

Wherein, M 2 is Li, Na, K or a combination thereof, x 3 , y 3 , z 3 and x 4 , y 4 , z 4 make the net charge of the second film-forming salt zero;

The complexing agent includes ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, ethanolamine or combinations thereof;

The oxidizing oxygen acid salts include nitrates, inorganic salts (M 2 ) x5 (M 3 ) y5 O z5 or combinations thereof, which can be selected from NaNO 3 , KNO 3 , Ca(NO 3 ) 2 , KMnO 4 , Na 2 FeO 4 , K 2 Cr 2 O 7 , NaCoO 2 , NaVO 2 or combinations thereof,

Wherein, M 2 is Li, Na, K or a combination thereof, M 3 is V, Cr, Mn, Fe, Co, Ni or a combination thereof, z 5 is 1 to 7, x 5 , y 5 , z 5 makes the above The net charge of an oxidizing oxo acid salt is zero;

The catalyst includes an ammonium salt, which may be NH 4 NO 3 , (NH 4 ) 2 SO 4 , NH 4 Cl or a combination thereof.
The method according to claim 8, wherein in the film-forming liquid, the first film-forming salt, the second film-forming salt, the complexing agent and the oxidizing oxygen acid salt are The concentration is 10g/L to 50g/L, and the concentration of the catalyst is 10g/L to 30g/L.
The method according to any one of claims 6-9, further comprising a pH value of the film-forming liquid of 5 to 7.
A secondary battery, including the negative electrode sheet according to any one of claims 1 to 5 or the negative electrode sheet produced by the method according to any one of claims 6 to 10.
A battery module including the secondary battery according to claim 11.
A battery pack including the battery module according to claim 12.
An electrical device including at least one selected from the group consisting of the secondary battery of claim 11, the battery module of claim 12, or the battery pack of claim 13.