Gradient lithium concentration pre-lithiation negative electrode based on directional temperature control and dynamic atmosphere regulation and control

Abstract

The invention discloses a gradient lithium concentration pre-lithiation negative electrode based on directional temperature control and dynamic atmosphere regulation and control, which can efficiently and continuously prepare a surface in-situ generated lithium-rich compound layer through a three-step process of physical pre-lithiation, directional temperature gradient treatment and dynamic atmosphere regulation and control. And lithium ions are in gradient distribution (from low surface to high inside) along the depth direction of the electrode. The prepared negative electrode material sequentially comprises the lithium-rich compound layer and the gradient lithium slow-release layer from outside to inside, the structure can control the lithium deintercalation sequence in an electrode in a gradient manner, and the problems of traditional pre-lithiation thermal runaway risk and lithium precipitation on the surface of the electrode are synchronously reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery anode materials, and relates to a gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation, and particularly relates to a gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation for a lithium ion battery anode and a preparation method thereof. Background Art

[0002] Lithium ion batteries have become the core energy storage devices in fields such as electric vehicles and consumer electronics due to their high energy density and long cycle life. However, the theoretical specific capacity of traditional graphite anodes (372 mAh / g) has approached its physical limit, making it difficult to meet the high energy density requirements. Silicon-based anodes (such as pure silicon, silicon-carbon composites) are regarded as the next-generation anode materials with a theoretical capacity of up to 3579 mAh / g, but their industrialization still faces two major challenges: low initial Coulombic efficiency (usually <80%) and electrode pulverization caused by volume expansion (>300%) during the cycling process.

[0003] To break through the above bottlenecks, prelithiation technology has been widely studied to compensate for the first lithium loss. Existing prelithiation methods mainly include: 1. Lithium vapor deposition (such as CN119240688A), which forms a lithium layer on the anode surface through high-temperature chemical vapor deposition. However, the process temperature (>300°C) is likely to cause phase change failure of silicon-based materials, and the local lithium concentration is too high, resulting in a decrease in the interfacial bonding strength; 2. Composite electrolyte prelithiation (such as CN109888392A), which compensates for lithium during the first charge and discharge by adding sacrificial agents such as LiNO3. However, the side reaction products (such as Li2O / LiOH) cause the interfacial impedance to increase by ≥300% after cycling; 3. Chemical prelithiation (such as CN110212152A), which releases lithium by reacting compounds such as Li3N with silicon. However, the residual unreacted lithium salts exacerbate the decomposition of the electrolyte. In addition, the above technologies have common defects: 1. Thermal runaway risk: The exothermic lithiation reaction (enthalpy change ΔH≈-200 kJ / mol) causes a local temperature rise >80°C, increasing the probability of ignition; 2. Gradient control failure: The uniform lithium distribution triggers the "edge priority effect", and the surface lithium deposition overpotential is reduced to <50 mV, resulting in low utilization rate of internal active substances.

[0004] CN115642229A discloses a method for preparing a prelithiated anode, a prelithiated anode, and a secondary battery. The method for preparing the prelithiated anode includes: obtaining a lithium-supplemented anode by pressure-compounding the anode and an ultra-thin lithium foil or a lithium alloy foil, transferring the lithium-supplemented anode to a vacuum oven for vacuum storage, and baking the lithium-supplemented anode in the vacuum oven (at 50-100 °C for 4-48 hours) to obtain the prelithiated anode. This prelithiation method can improve the initial efficiency of the secondary battery, and the process is simple and easy to operate, and can be mass-produced and applied. However, the vacuum baking in this method causes a temperature difference between the surface and the interior of the electrode sheet, resulting in poor lithium distribution uniformity, lithium aggregation on the surface of the electrode sheet, a low surface lithium deposition overpotential, and a low utilization rate of the internal active substances, which affects the subsequent cycle performance; at the same time, the vacuum baking temperature (50-100 °C) is superimposed on the prelithiation heat release (ΔH≈-200 kJ / mol), resulting in a significant increase in the local temperature and a significant increase in the probability of thermal runaway. Summary of the Invention

[0005] The object of the present invention is to provide a gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation, aiming to provide a new reference for the prelithiation technology of the negative electrode of lithium-ion batteries. The "gradient lithium concentration prelithiated anode with directional temperature control and dynamic atmosphere regulation" technology proposed by the present invention breaks through the above bottleneck through the following innovative mechanisms: 1. Improvement of two-way temperature control safety: Applying a cold source (10-15 °C) on the surface forms a dynamic thermal balance with the prelithiation heat release process, suppressing local temperature rise and reducing the risk of thermal runaway; 2. Dendrite inhibition: The axial temperature gradient (ΔT = 30-40 °C) drives lithium ions to migrate towards the high-temperature current collector side, forming a slow-release gradient structure with a low lithium concentration on the surface and a high lithium concentration inside. During cycling, the internal lithium source can dynamically supplement the surface loss, and at the same time reduce the phenomenon of lithium precipitation with a high lithium concentration on the electrode surface; 3. Optimization of composition: Dynamic atmosphere regulation induces the formation of a lithium-rich compound layer. A low-cost, high-uniformity, and dynamically adjustable lithium distribution prelithiation technology is developed, and the performance breakthrough of the negative electrode is achieved through the collaborative design of structure and process.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] <First aspect>

[0008] The present invention relates to a gradient lithium concentration prelithiated anode, and the anode sequentially includes a lithium-rich compound layer and a gradient lithium slow-release layer from the surface to the inside; the lithium concentration in the gradient lithium slow-release layer gradually increases from the surface to the inside and shows a gradient distribution along the depth direction of the electrode. Through directional temperature control and dynamic atmosphere regulation, the present invention effectively regulates the lithium-rich compound components on the prelithiated surface and at the same time forms a structure in which lithium ions are distributed in a gradient, which is sequentially a lithium-rich compound layer and a gradient lithium slow-release layer from the surface to the inside ( Figure 1) The gradient lithium slow-release layer of the gradient lithium concentration prelithiated anode has a gradually increasing lithium concentration in the direction from the surface to the interior, with the lowest lithium concentration at the surface and gradually increasing in the inner layer of the prelithium layer, forming a gradient distribution of lithium concentration ( Figure 2 ), which can not only avoid excessive lithium deposition and local overreaction, reduce the battery performance degradation due to local over-discharge or uneven lithium deposition, and thus improve the cycling stability of the anode material.

[0009] As an embodiment, the lithium-rich compound layer includes at least one of the following compounds: Li2O, Li2CO3, LiC6, LiC 12 , LiC 24 , Li7Si3, Li 13 Si4, Li 22 Si5. A multi-stage mass transfer channel is constructed, significantly enhancing the thermodynamic stability of the electrode.

[0010] As an embodiment, the anode includes at least one of the following active materials: graphite, silicon-carbon material, silicon-oxygen material, hard carbon material, soft carbon material, tin oxide, porous carbon material, sulfur-based material, phosphorus-based material, carbon nanotube / graphene composite, etc.

[0011] As an embodiment, the gradient lithium concentration prelithiated anode is prepared by a gradient prelithiation composite anode preparation method based on two-way temperature control and dynamic atmosphere regulation.

[0012] <Second aspect>

[0013] The present invention provides a method for preparing the aforementioned gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation, and the method includes the following steps:

[0014] S1. Physical prelithiation: In a dry environment protected by an inert atmosphere (such as argon or nitrogen), stack and assemble an ultra-thin lithium film and a negative electrode matrix material, and apply uniform pressure through a mechanical rolling or hot pressing composite process to cause plastic deformation on the surface of the lithium film and the matrix and form a metallurgical bonding interface, constructing a preliminary prelithiated composite structure;

[0015] S2. Directional temperature gradient treatment: Apply a cold source on the surface of the electrode plate and a heat source on the current collector side to form an axial temperature gradient, driving lithium ions to migrate to the high-temperature region (current collector side);

[0016] S3. Dynamic atmosphere regulation: During the temperature control process, introduce a CO2 / N2 mixed gas, and regulate the components of the surface lithium-rich compound layer (Li2CO3 / Li2O composite layer) by regulating the gas ratio, reaction temperature and time, inhibiting side reactions and enhancing interface stability.

[0017] As an embodiment, in step S1, the ultra-thin lithium film includes at least one of thin films with lithium components such as lithium metal film, lithium alloy film, lithium oxide thin film, and lithium ion conductor thin film.

[0018] As an embodiment, in step S1, the negative electrode matrix material includes at least one of the following active substances: graphite, silicon-carbon material, silicon-oxygen material, hard carbon material, soft carbon material, tin oxide, porous carbon material, sulfur-based material, phosphorus-based material, carbon nanotube / graphene composite material, etc.

[0019] As an embodiment, in step S1, the ultra-thin lithium film has a thickness of 2-20 μm, a surface roughness Ra ≤ 0.1 μm, a lithium content ≥ 90 wt%, and an ionic conductivity ≥ 10 -6 S / cm.

[0020] As an embodiment, in step S1, the mechanical roll pressing method has a pressure range of 2-5 MPa and a roll pressing speed of 10-50 mm / s.

[0021] As an embodiment, in step S2, the cold source for the directional temperature gradient treatment is realized by the medium heat exchange method, and the temperature range is 10-15 °C.

[0022] As an embodiment, in step S2, the current collector heat source is realized by heat conduction and electric heating methods, the temperature range is 40-45 °C, the counter-roll pressure range is 5-20 MPa, and the pressure holding time is 15-30 minutes.

[0023] As an embodiment, the axial temperature gradient ΔT = 30-40 °C. The cold pressing absorbs the reaction heat in real time to inhibit local temperature rise; an axial temperature gradient (ΔT = 30-40 °C) is formed by surface cold pressing and current collector side hot pressing to drive the directional migration of lithium ions and construct a slow-release gradient structure with a low surface and a high interior.

[0024] As an embodiment, in step S3, the gas is a CO2 / N2 mixed atmosphere, and the CO2 / N2 ratio range is 1:1-1:3.

[0025] As an embodiment, in step S3, the gas flow rate range is 50-100 mL / min, and the pressure range is 0.1-0.5 MPa.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1) The method for preparing a gradient lithium concentration prelithiated negative electrode based on directional temperature control and dynamic atmosphere regulation provided by the present invention realizes the regulation of the dynamic distribution of lithium ions, avoids a single technical route, and solves the problem of lithium deposition on the electrode surface;

[0028] 2) The method for preparing a gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation provided by the present invention realizes the regulation of the composition of the lithium-rich compound layer on the electrode surface;

[0029] 3) The method for preparing a gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation provided by the present invention is adapted to the dry electrode process to solve the risk of thermal runaway. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Other features, objects, and advantages of the present invention will become more apparent by reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0031] Figure 1 FIG. is a SEM image and a schematic diagram of the cross-sectional structure of a gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation;

[0032] Figure 2 FIG. is the oxygen element distribution map of the cross-section of a gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation;

[0033] Figure 3 FIG. is the XRD spectrum of a gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation;

[0034] Figure 4 FIG. is the XRD pattern of a gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation with different directional temperature gradient treatment times;

[0035] Figure 5 FIG. is the XPS pattern of a gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation with different directional temperature gradient treatment times;

[0036] Figure 6 FIG. is the transmission electron microscope image of a gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The present invention will be described in detail below with reference to the embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those of ordinary skill in the art can make several adjustments and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0038] Embodiment 1

[0039] This embodiment relates to a method for preparing a gradient lithium concentration pre-lithiated anode based on directional temperature control and dynamic atmosphere regulation. The method of "physical pre-lithiation - directional temperature gradient treatment - dynamic atmosphere regulation" is adopted to form a structure with a gradient distribution of lithium ions while effectively regulating the components of the lithium-rich compound layer on the pre-lithiated surface. From the surface to the inside, it is successively a lithium-rich compound layer and a gradient lithium slow-release layer ( Figure 1 ). It avoids excessive lithium deposition and local overreaction, reduces the battery performance decay due to local over-discharge or uneven lithium deposition, and thus improves the cycle stability of the anode material.

[0040] The specific preparation is as follows:

[0041] S1. Physical pre-lithiation: In a dry environment protected by an inert atmosphere (such as argon or nitrogen), a 5-micron ultra-thin lithium film and a graphite anode are stacked and assembled. The graphite anode is made of anode material (graphite, accounting for 94.5%), conductive agent (Ketjen black, accounting for 1.0%), binder (SBR, accounting for 2.25%), and thickener (CMC, accounting for 2.25%), with a thickness of 65.1 μm. Uniform pressure is applied through a mechanical rolling process, the rolling pressure is 5 MPa, and the rolling speed is 10 mm / s, so that the lithium film and the substrate surface undergo plastic deformation and form a metallurgical bonding interface, constructing a preliminary pre-lithiated composite structure;

[0042] S2. Directional temperature gradient treatment: A cold source is applied to the surface of the electrode plate by the medium heat exchange method, the temperature is set at 10°C (temperature control accuracy ±1°C), and a heat source is applied to the current collector side of the graphite anode by the heat conduction method, the temperature is set at 45°C (temperature control accuracy ±2°C), the pressure is set at 10 MPa, and the pressure holding time is 15 minutes to form an axial temperature gradient, driving lithium ions to migrate to the high-temperature area (current collector side);

[0043] S3. Dynamic atmosphere regulation: During the temperature control process, a CO2 / N2 mixed gas is introduced, the CO2 / N2 introduction ratio is 1:1, the gas flow rate is 50 mL / min, the pressure is set at 0.3 MPa, and the components of the lithium-rich compound layer on the surface (Li2CO3 / Li2O composite layer) are regulated to inhibit side reactions and enhance interface stability.

[0044] The gradient lithium concentration pre-lithiated anode provided by this embodiment effectively regulates the components of the lithium-rich compound layer on the pre-lithiated surface while forming a structure with a gradient distribution of lithium ions. From the surface to the inside, it is successively a lithium-rich compound layer and a gradient lithium slow-release layer ( Figure 1 ). The lithium concentration in the gradient lithium slow-release layer gradually increases along the direction from the surface to the inside, and the lithium concentration is the lowest at the surface and gradually increases in the inner layer of the pre-lithiated layer, forming a gradient distribution of lithium concentration ( Figure 2 ).

[0045] The gradient lithium concentration prelithiated graphite anode provided in this embodiment forms lithium-rich compounds such as LiC6 and LiC 12 , LiC 24 compounds ( Figure 3 ). Lithium ions enter the graphite sheet layer structure through an intercalation reaction to form a uniform lithium-carbon compound, promoting the uniform embedding of lithium, avoiding uneven local lithium distribution, and forming a gradient lithium slow-release layer. A lithium-rich compound layer containing Li2O and Li2CO3 ( Figure 5 Example 1, Figure 6 ) is formed on the surface of the gradient lithium concentration prelithiated graphite anode provided in the embodiment. The lithium ion diffusion barriers of Li2CO3 (0.227 - 0.491 eV) and Li2O (0.152 eV) are relatively low, close to that of bulk graphite, and are more likely to form a continuous and smooth structure in the electrode, which can effectively inhibit parasitic reactions.

[0046] Example 2

[0047] Adopt the method of "physical prelithiation - directional temperature gradient treatment - dynamic atmosphere regulation" to effectively regulate the components of the lithium-rich compound on the prelithiated surface while forming a structure with a gradient distribution of lithium ions. The specific process is as follows:

[0048] S1. Physical prelithiation: In a dry environment protected by an inert atmosphere (such as argon or nitrogen), stack and assemble a 5-micron ultra-thin lithium film with a graphite anode. The graphite anode is made of a negative electrode material (graphite, accounting for 94.5%), a conductive agent (Ketjenblack EC, accounting for 1.0%), a binder (SBR, accounting for 2.25%), and a thickener (CMC, accounting for 2.25%), with a thickness of 64.8 μm. Apply a uniform pressure through a mechanical rolling process, with a rolling pressure of 5 MPa and a rolling speed of 10 mm / s, so that the lithium film and the substrate surface undergo plastic deformation and form a metallurgical bonding interface to construct a preliminary prelithiated composite structure;

[0049] S2. Directional temperature gradient treatment: Apply a cold source on the surface of the electrode plate through the medium heat exchange method, with the temperature set at 10 °C (temperature control accuracy ±1 °C), and apply a heat source on the current collector side through the heat conduction method, with the temperature set at 45 °C (temperature control accuracy ±2 °C). The pressure is set to 10 MPa, and the pressure holding time is 20 minutes to form an axial temperature gradient and drive lithium ions to migrate to the high-temperature region (current collector side);

[0050] S3. Dynamic atmosphere regulation: During the temperature control process, introduce a CO2 / N2 mixed gas, with a CO2 / N2 introduction ratio of 1:1, a gas flow rate of 50 mL / min, and a pressure set at 0.3 MPa to regulate the components of the lithium-rich compound layer on the surface (Li2CO3 / Li2O composite layer), inhibit side reactions, and enhance interface stability.

[0051] The gradient lithium concentration prelithiated graphite anode based on directional temperature control and dynamic atmosphere regulation provided by this embodiment can effectively regulate the components of the lithium-rich compound layer on the prelithiated surface while forming a structure with a gradient distribution of lithium ions. From the surface to the inside, there are a lithium-rich compound layer and a gradient lithium slow-release layer in sequence. The lithium concentration in the gradient lithium slow-release layer gradually increases along the direction from the surface to the inside, and the lithium concentration is the lowest at the surface and gradually increases in the inner layer of the prelithium layer, forming a gradient distribution of lithium concentration.

[0052] The lithium-rich compounds formed on the gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation provided by this embodiment form LiC 12 , LiC 24 compounds ( Figure 4 In Example 2, the pressure holding time in this embodiment becomes longer, and lithium ions have more sufficient time to diffuse. Therefore, the highly lithiated phase LiC6 transforms into LiC with a lower degree of lithiation 12 , LiC 24 ), and lithium ions enter the graphite sheet layer structure through an intercalation reaction to form a uniform lithium-carbon compound, promoting the uniform embedding of lithium and avoiding uneven local lithium distribution, thereby forming a gradient lithium slow-release layer. On the surface of the gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation provided by the embodiment, a stable lithium-rich compound layer containing Li2O and Li2CO3 is formed ( Figure 5 Example 2). The lithium ion diffusion barriers of Li2CO3 (0.227 - 0.491 eV) and Li2O (0.152 eV) are relatively low, close to that of bulk graphite, and are more likely to form a continuous and smooth structure in the electrode, which can effectively inhibit parasitic reactions.

[0053] Example 3

[0054] Adopt the method of "physical prelithiation - directional temperature gradient treatment - dynamic atmosphere regulation" to effectively regulate the components of the lithium-rich compound layer on the prelithiated surface while forming a structure with a gradient distribution of lithium ions. The specific process is as follows:

[0055] S1. Physical prelithiation: In a dry environment protected by an inert atmosphere (such as argon or nitrogen), stack and assemble a 5-micron ultra-thin lithium film with a graphite anode. The graphite anode is made of a negative electrode material (graphite, accounting for 94.5%), a conductive agent (Ketjenblack EC, accounting for 1.0%), a binder (SBR, accounting for 2.25%), and a thickener (CMC, accounting for 2.25%), with a thickness of 66.0 μm. Apply uniform pressure through a mechanical rolling process, with a rolling pressure of 5 MPa and a rolling speed of 10 mm / s, so that the lithium film and the substrate surface undergo plastic deformation and form a metallurgical bonding interface, constructing a preliminary prelithiated composite structure;

[0056] S2. Directional temperature gradient treatment: Apply a cold source on the surface of the electrode sheet through the medium heat exchange method, set the temperature to 10 °C (temperature control accuracy ±1 °C), apply a heat source on the current collector side through the heat conduction method, set the temperature to 45 °C (temperature control accuracy ±2 °C), set the pressure to 10 MPa, and keep the pressure for 25 minutes to form an axial temperature gradient, driving lithium ions to migrate to the high-temperature area (current collector side);

[0057] S3. Dynamic atmosphere regulation: Introduce a CO2 / N2 mixed gas during the temperature control process, with a CO2 / N2 introduction ratio of 1:1, a gas flow rate of 50 mL / min, and a pressure setting of 0.3 MPa to regulate the components of the surface lithium-rich compound layer (Li2CO3 / Li2O composite layer), inhibit side reactions, and enhance interface stability.

[0058] The gradient lithium concentration pre-lithiated graphite negative electrode based on directional temperature control and dynamic atmosphere regulation provided by this embodiment can effectively regulate the components of the pre-lithiated surface lithium-rich compound layer while forming a structure with a gradient distribution of lithium ions. From the surface to the inside, it is successively a lithium-rich compound layer and a gradient lithium slow-release layer. The lithium concentration in the gradient lithium slow-release layer gradually increases along the direction from the surface to the inside, and the lithium concentration is the lowest at the surface and gradually increases in the inner layer of the pre-lithium layer, forming a gradient distribution of lithium concentration.

[0059] The stable lithium-rich compound formed by the gradient lithium concentration pre-lithiated negative electrode provided by this embodiment forms LiC 24 compound. Lithium ions enter the graphite sheet layer structure through an intercalation reaction to form a uniform lithium-carbon compound, promoting the uniform embedding of lithium, avoiding uneven local lithium distribution, and forming a gradient lithium slow-release layer. The surface of the gradient lithium concentration pre-lithiated negative electrode provided by the embodiment forms a stable lithium-rich compound layer containing Li2O and Li2CO3( Figure 5 Example 3). The lithium ion diffusion barriers of Li2CO3 (0.227 - 0.491 eV) and Li2O (0.152 eV) are relatively low, close to that of bulk graphite, and are more likely to form a continuous and smooth structure in the electrode, which can effectively inhibit parasitic reactions.

[0060] Example 4

[0061] Adopt the method of "physical pre-lithiation - directional temperature gradient treatment - dynamic atmosphere regulation" to effectively regulate the components of the pre-lithiated surface lithium-rich compound layer while forming a structure with a gradient distribution of lithium ions. The specific process is as follows:

[0062] S1. Physical prelithiation: In a dry environment protected by an inert atmosphere (such as argon or nitrogen), a 5-micron ultra-thin lithium film is laminated with a graphite negative electrode. The graphite negative electrode is made of a negative electrode material (graphite, accounting for 94.5%), a conductive agent (Ketjenblack EC, accounting for 1.0%), a binder (SBR, accounting for 2.25%), and a thickener (CMC, accounting for 2.25%). The thickness is 65.0 μm. Uniform pressure is applied through a mechanical rolling process. The rolling pressure is 5 MPa, and the rolling speed is 10 mm / s, causing plastic deformation on the surface of the lithium film and the matrix and forming a metallurgical bonding interface to construct a preliminary prelithiated composite structure;

[0063] S2. Directional temperature gradient treatment: A cold source is applied to the surface of the electrode plate by the medium heat exchange method, with the temperature set at 10 °C (temperature control accuracy ±1 °C). A heat source is applied to the current collector side by the heat conduction method, with the temperature set at 45 °C (temperature control accuracy ±2 °C). The pressure is set at 10 MPa, and the pressure holding time is 30 minutes to form an axial temperature gradient and drive lithium ions to migrate to the high-temperature region (current collector side);

[0064] S3. Dynamic atmosphere regulation: During the temperature control process, a CO2 / N2 mixed gas is introduced. The CO2 / N2 introduction ratio is 1:1, the gas flow rate is 50 mL / min, and the pressure is set at 0.3 MPa to regulate the components of the surface lithium-rich compound layer (Li2CO3 / Li2O composite layer), inhibit side reactions, and enhance interface stability.

[0065] The gradient lithium concentration prelithiated graphite negative electrode provided by this embodiment effectively regulates the components of the prelithiated surface lithium-rich compound layer while forming a structure with a gradient distribution of lithium ions. From the surface to the inside, there are a lithium-rich compound layer and a gradient lithium slow-release layer in sequence. The lithium concentration in the gradient lithium slow-release layer gradually increases along the direction from the surface to the inside, and the lithium concentration is the lowest at the surface and gradually increases in the inner layer of the prelithium layer, forming a gradient distribution of lithium concentration.

[0066] The stable lithium-rich compound formed by the gradient lithium concentration prelithiated negative electrode provided by this embodiment forms LiC 24 compounds. Lithium ions enter the graphite lamellar structure through an intercalation reaction to form a uniform lithium-carbon compound, promoting the uniform embedding of lithium, avoiding uneven local lithium distribution, and forming a gradient lithium slow-release layer. A stable lithium-rich compound layer containing Li2O and Li2CO3 is formed on the surface of the gradient lithium concentration prelithiated negative electrode provided by the embodiment. The lithium ion diffusion barriers of Li2CO3 (0.227 - 0.491 eV) and Li2O (0.152 eV) are relatively low, close to that of bulk graphite, and are more inclined to form a continuous and smooth structure in the electrode, which can effectively inhibit parasitic reactions.

[0067] Example 5

[0068] Adopt the method of "physical prelithiation - directional temperature gradient treatment - dynamic atmosphere regulation" to effectively regulate the components of the lithium-rich compound layer on the prelithiated surface and form a structure with a gradient distribution of lithium ions at the same time. The specific process is as follows:

[0069] S1. Physical prelithiation: In a dry environment protected by an inert atmosphere (such as argon or nitrogen), stack and assemble a 5-micron ultra-thin lithium film with a silicon-carbon negative electrode. The silicon-carbon negative electrode is made of silicon-carbon negative electrode active material (accounting for 92%), conductive agent (Ketjenblack EC, accounting for 2.0%), carbon nanotubes (accounting for 2.0%), binder (SBR, accounting for 2.5%) and thickener (CMC, accounting for 1.5%), with a thickness of 31.0 μm. Apply uniform pressure through a mechanical rolling process, with a rolling pressure of 5 MPa and a rolling speed of 10 mm / s, so that the lithium film and the substrate surface undergo plastic deformation and form a metallurgical bonding interface, constructing a preliminary prelithiated composite structure;

[0070] S2. Directional temperature gradient treatment: Apply a cold source on the surface of the electrode plate by the medium heat exchange method, with the temperature set at 10°C (temperature control accuracy ±1°C), and apply a heat source on the current collector side by the heat conduction method, with the temperature set at 45°C (temperature control accuracy ±2°C), the pressure is set at 10 MPa, and the pressure holding time is 30 minutes to form an axial temperature gradient and drive lithium ions to migrate to the high-temperature area (current collector side);

[0071] S3. Dynamic atmosphere regulation: During the temperature control process, introduce a CO2 / N2 mixed gas, with the CO2 / N2 introduction ratio of 1:2, the gas flow rate of 50 mL / min, and the pressure set at 0.3 MPa to regulate the components of the lithium-rich compound layer on the surface (Li2CO3 / Li2O composite layer), inhibit side reactions and enhance interface stability.

[0072] The gradient lithium concentration prelithiated silicon-carbon negative electrode based on directional temperature control and dynamic atmosphere regulation provided by this embodiment effectively regulates the components of the lithium-rich compound layer on the prelithiated surface and forms a structure with a gradient distribution of lithium ions at the same time. From the surface to the inside, it is successively a lithium-rich compound layer and a gradient lithium slow-release layer. The lithium concentration in the gradient lithium slow-release layer gradually increases along the direction from the surface to the inside, and the lithium concentration is the lowest at the surface and gradually increases in the inner layer of the prelithiated layer, forming a gradient distribution of lithium concentration.

[0073] The stable lithium-rich compound formed by the gradient lithium concentration prelithiated silicon-carbon negative electrode based on directional temperature control and dynamic atmosphere regulation provided by this embodiment forms Li 22 Si5, Li 13In the Si4 compound, lithium ions enter the silicon-carbon structure through an alloying reaction to form a uniform lithium-silicon compound, which promotes the uniform embedding of lithium, avoids uneven local lithium distribution, and forms a gradient lithium slow-release layer. On the surface of the gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation provided by the embodiment, a lithium-rich compound layer containing Li2O, Li2CO3, and Li3N is formed, which is more inclined to form a continuous and smooth structure in the electrode and can effectively inhibit parasitic reactions.

[0074] Example 6

[0075] Adopt the method of "physical prelithiation - directional temperature gradient treatment - dynamic atmosphere regulation" to effectively regulate the components of the lithium-rich compound layer on the prelithiated surface while forming a structure with a gradient distribution of lithium ions. The specific process is as follows:

[0076] S1. Physical prelithiation: In a dry environment protected by an inert atmosphere (such as argon or nitrogen), stack and assemble a 5-micron ultra-thin lithium film with a silicon-carbon negative electrode. The silicon-carbon negative electrode is made of silicon-carbon negative electrode active material (accounting for 92%), conductive agent (Ketjenblack superconducting carbon black, accounting for 2.0%), carbon nanotubes (accounting for 2.0%), binder (SBR, accounting for 2.5%), and thickener (CMC, accounting for 1.5%), with a thickness of 31.2 μm. Apply uniform pressure through a mechanical rolling process, with a rolling pressure of 5 MPa and a rolling speed of 10 mm / s, so that the lithium film and the substrate surface undergo plastic deformation and form a metallurgical bonding interface to construct a preliminary prelithiated composite structure;

[0077] S2. Directional temperature gradient treatment: Apply a cold source on the surface of the electrode by the medium heat exchange method, with the temperature set at 10 °C (temperature control accuracy ±1 °C), and apply a heat source on the current collector side by the heat conduction method, with the temperature set at 45 °C (temperature control accuracy ±2 °C). The pressure is set at 10 MPa, and the pressure holding time is 30 minutes to form an axial temperature gradient and drive lithium ions to migrate to the high-temperature region (current collector side);

[0078] S3. Dynamic atmosphere regulation: During the temperature control process, introduce a CO2 / N2 mixed gas, with the CO2 / N2 introduction ratio of 1:3, a gas flow rate of 50 mL / min, and a pressure set at 0.3 MPa to regulate the components of the lithium-rich compound layer on the surface (Li2CO3 / Li2O composite layer), inhibit side reactions, and enhance interface stability.

[0079] The gradient lithium concentration prelithiated silicon-carbon negative electrode provided by this embodiment effectively regulates the components of the lithium-rich compound layer on the prelithiated surface while forming a structure with a gradient distribution of lithium ions. From the surface to the inside, it is successively a lithium-rich compound layer and a gradient lithium slow-release layer. The lithium concentration in the gradient lithium slow-release layer gradually increases along the direction from the surface to the inside, and the lithium concentration is the lowest at the surface and gradually increases in the inner layer of the prelithiated layer, forming a gradient distribution of lithium concentration.

[0080] The stable lithium-rich compounds formed in the gradient lithium concentration prelithiated silicon-carbon anode based on directional temperature control and dynamic atmosphere regulation provided in this embodiment are Li7Si3 and Li 13 Si4 compounds. Lithium ions enter the silicon-carbon structure through an alloying reaction to form a uniform lithium-silicon compound, promoting the uniform embedding of lithium, avoiding uneven local lithium distribution, and forming a gradient lithium slow-release layer. For the gradient lithium concentration prelithiated anode based on directional temperature control and dynamic atmosphere regulation provided in the embodiment, a stable lithium-rich compound layer containing Li2O and Li2CO3 is formed on the surface. The lithium ion diffusion barriers of Li2CO3 (0.227 - 0.491 eV) and Li2O (0.152 eV) are relatively low, close to that of bulk graphite, and are more inclined to form a continuous and smooth structure in the electrode, which can effectively inhibit parasitic reactions.

[0081] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A gradient lithium concentration prelithiated negative electrode, characterized in that, The negative electrode sequentially includes a lithium-rich compound layer and a gradient lithium slow-release layer from the surface to the interior; the lithium concentration in the gradient lithium slow-release layer gradually increases from the surface to the interior and is distributed in a gradient along the electrode depth direction.

2. The gradient lithium concentration prelithiated negative electrode according to claim 1, wherein The lithium-rich compound layer includes at least one of the following compounds: Li2O, Li2CO3, LiC6, LiC 12 , LiC 24 , Li7Si3, Li 13 Si4, Li 22 Si5.

3. The gradient lithium concentration prelithiated negative electrode according to claim 1, wherein The negative electrode includes at least one of the following active materials: graphite, silicon-carbon material, silicon-oxygen material, hard carbon material, soft carbon material, tin oxide, porous carbon material, sulfur-based material, phosphorus-based material, carbon nanotube / graphene composite material.

4. A method for preparing a gradient lithium concentration prelithiated negative electrode as described in any one of claims 1-3 based on directional temperature control and dynamic atmosphere control, characterized in that, The method includes the following steps: S1. Physical prelithiation: In a dry environment protected by an inert atmosphere, an ultra-thin lithium film and a negative electrode matrix material are laminated and assembled, and a uniform pressure is applied through a mechanical rolling or hot pressing composite process, so that the lithium film and the matrix surface undergo plastic deformation and form a metallurgical bonding interface, and a preliminary prelithiated composite structure is constructed. S2. Directional temperature gradient treatment: A cold source is applied to the surface of the electrode, and a heat source is applied to the current collector side to form an axial temperature gradient to drive the migration of lithium ions to the high-temperature area. S3. Dynamic atmosphere regulation: A CO2 / N2 mixed gas is introduced during the temperature control process in S2, and the components of the surface lithium-rich compound layer are regulated by regulating the gas ratio, reaction temperature and time.

5. The method for preparing a gradient lithium concentration prelithiated negative electrode according to claim 4, characterized in that, In step S1, the ultra-thin lithium film includes at least one of a lithium metal film, a lithium alloy film, a lithium oxide thin film, and a lithium ion conductor thin film.

6. The method for preparing a gradient lithium concentration prelithiated negative electrode according to claim 4, wherein In step S1, the thickness of the ultra-thin lithium film is 2 - 20 μm, the surface roughness Ra ≤ 0.1 μm, the lithium content ≥ 90 wt%, and the ionic conductivity ≥ 10 -6 S / cm.

7. The method for preparing a gradient lithium concentration prelithiated negative electrode according to claim 4, characterized in that, In step S1, the pressure range of mechanical rolling is 2-5 MPa, and the rolling speed is 10-50 mm / s.

8. The method for preparing a gradient lithium concentration prelithiated negative electrode according to claim 4, characterized in that, In step S2, the cold source is realized by a medium heat exchange method, and the temperature range is 10-15 °C. The current collector heat source is realized by a heat conduction and electric heating method, and the temperature range is 40-45 °C. The counter-roll pressure range is 5-20 MPa, and the pressure holding time is 15-30 minutes.

9. The method for preparing a gradient lithium concentration prelithiated negative electrode according to claim 4 or 8, characterized in that, The axial temperature gradient ΔT = 30-40 °C.

10. The method for preparing a gradient lithium concentration pre-lithiated negative electrode according to claim 4, wherein In step S3, the CO2 / N2 ratio range is 1:1-1:3, the gas flow rate range is 50-100 mL / min, and the pressure range is 0.1-0.5 MPa.

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