Amorphous silicon-based thin film negative electrode with chemical state gradient and preparation method and application thereof

Abstract

This invention relates to the field of battery materials and electrochemical energy storage devices, providing an amorphous silicon-based thin-film anode with a chemical state gradient, its preparation method, and applications. The amorphous silicon-based thin-film anode comprises a substrate and an amorphous silicon-based active layer formed by continuous deposition on the substrate surface in a single step. The amorphous silicon-based active layer is a single continuous amorphous silicon thin film that is not multilayered. In the thickness direction, the chemical states of silicon exhibit a continuous and monotonically changing gradient distribution, manifested as a gradual and continuous transition from a predominantly low oxidation state to a predominantly high oxidation state, with Si being the dominant element in the low oxidation state. 0 Mainly contains Si 0 Si + Si 2+ At least one of the following; the highest oxidation state is Si. 4+ and Si 3+ At least one of the following. This invention achieves synergistic optimization of interface stability and bulk conductivity within a single thin film, improving battery cycle performance, and the process is precise and controllable.

Description

Technical Field

[0001] This invention relates to the field of battery materials and electrochemical energy storage devices, and provides an amorphous silicon-based thin film anode with a chemical state gradient, its preparation method and application, specifically a lithium-ion battery anode material and its manufacturing process, particularly a thin film anode with an intrinsic silicon chemical state gradient structure within the same continuous amorphous silicon thin film and its magnetron sputtering preparation method. Background Technology

[0002] Amorphous silicon (α-Si), as a negative electrode material for lithium-ion batteries, has advantages such as high theoretical specific capacity (approximately 3579 mAh / g) and a suitable charge-discharge platform, making it particularly suitable for thin-film batteries and micro-power devices where high area-capacity consistency is required. However, its huge volume expansion effect leads to repeated rupture and regeneration of the solid electrolyte interphase (SEI) film at the electrode / electrolyte interface, causing continuous interfacial side reactions, active lithium loss, and capacity decay, which severely restricts its practical application.

[0003] To improve the cycle stability of silicon-based anodes, existing technologies typically employ structural modification strategies. For example, patent CN104993115A discloses "a SiCO-Si gradient thin film electrode system for lithium batteries and its preparation method," which involves sequentially stacking a TiN barrier layer, an Al current collector layer, a SiAlCO transition layer, and Si and SiO layers via magnetron sputtering. 1 / 2 Multilayered thin films with different chemical compositions, such as SiO2, are used to attempt to buffer volume expansion through compositional gradients. However, such multilayered stacked structures inevitably introduce a large number of interlayer interfaces. These interfaces may lead to stress concentration within the film, insufficient bonding strength, and easy delamination during cycling; at the same time, the additional contact resistance at the interfaces also affects charge transport dynamics. In addition, the fabrication process requires multiple changes of target material and adjustment of deposition parameters, which is cumbersome and not conducive to large-scale uniform production and cost control.

[0004] Another common strategy is to oxidize the silicon material as a whole or coat its surface with an oxide layer (such as SiO2). While this can reduce interfacial reactivity, it often comes at the cost of sacrificing the overall electronic conductivity of the material, resulting in degraded rate performance and insufficient capacity utilization.

[0005] Therefore, there is an urgent need in this field for a new technical solution that can achieve intrinsic synergy between interface stability and bulk conductivity in a single continuous material system, while avoiding interface problems and complex processes caused by multilayer structures. Summary of the Invention

[0006] In view of the problems mentioned in the background art, the main objective of this invention is to provide an amorphous silicon-based thin film anode with intrinsic chemical state gradient and its preparation method.

[0007] In a first aspect, an amorphous silicon-based thin film anode with an intrinsic chemical state gradient is provided, comprising a substrate and an amorphous silicon-based active layer formed by continuous deposition on the surface of the substrate in a single step, wherein the amorphous silicon-based active layer is a single continuous amorphous silicon thin film that is not multilayered.

[0008] In some embodiments, the chemical states (oxidation states) of silicon exhibit a continuous and monotonically varying gradient distribution along the thickness direction of the amorphous silicon thin film, manifested as a gradual and continuous transition from a predominantly low oxidation state to a predominantly high oxidation state, wherein the low oxidation state is dominated by Si. 0 Mainly containing Si 0 Si + Si 2+ At least one of the following; the higher oxidation state is Si 4+ and Si 3+ At least one of them. This change is reflected in the oxygen content (O / Si atomic ratio) in the thin film increasing continuously and monotonically from the inside to the outside (e.g. Figure 3 (As shown).

[0009] In some implementations, the chemical state gradient is verified by XPS depth profiling, and its Si 2p peaks should show a continuous shift in binding energy, rather than discrete peak position jumps.

[0010] In some embodiments, the substrate is copper foil, stainless steel foil, titanium foil, nickel foil, or an insulating substrate with a conductive layer on its surface. Preferably, the insulating substrate is glass, nickel-plated glass, or a polymer substrate, and the conductive layer is ITO (indium tin oxide) or AZO (aluminum-doped zinc oxide).

[0011] In some embodiments, the thickness of the amorphous silicon thin film is 650~1250 nm.

[0012] In some embodiments, the amorphous silicon thin film contains elements including silicon and at least one selected from oxygen, carbon, and lithium.

[0013] The amorphous silicon-based thin-film anode prepared by this invention exhibits a chemical state gradient that is fundamentally different from the compositional gradient of thin-film anodes provided in existing technologies. The "chemical state gradient" of this invention refers to the continuous evolution of the relative proportions of atomic bonding states within the same chemical system, with the main material always being amorphous silicon. Specifically, this could be a continuous change in the relative proportions of Si-Si and Si-O bonds within a Si-O system. In contrast, the "compositional gradient" refers to the discrete stacking of materials with different chemical compositions, such as the discrete stacking of pure Si, SiO, and SiO2. The "chemical state gradient" of this invention is intrinsic, continuous, and monotonic; the continuous shift in the Si 2p binding energy can be observed through X-ray photoelectron spectroscopy (XPS) depth profiling.

[0014] Secondly, a method for preparing an amorphous silicon-based thin-film anode with an intrinsic chemical state gradient as described in this invention is provided, comprising:

[0015] Amorphous silicon-based thin films are formed on the substrate surface by one continuous deposition process using magnetron sputtering. During the magnetron sputtering process, elemental silicon is used as the target material. Under the premise of ensuring that the total gas flow rate and total gas pressure of the sputtering atmosphere are basically constant, the ratio of oxygen flow rate and argon flow rate entering the deposition chamber is dynamically adjusted to obtain amorphous silicon-based thin film anodes with intrinsic chemical state gradients.

[0016] In some implementations, the oxygen flow rate starts from zero and increases continuously and monotonically with increasing deposition time or film thickness, thereby changing the oxygen content in the amorphous silicon-based thin film in situ and continuously during the growth process, and ultimately constructing the desired chemical state gradient within the same thin film chemical system.

[0017] In some implementations, the proportion of oxygen flow rate remains zero or low for a period of time after the start of deposition, and then increases continuously and monotonically with time or film thickness.

[0018] In some implementations, the dynamic adjustment is achieved through a programmable interlocked proportional control valve at the gas inlet of the magnetron sputtering equipment. This valve can precisely and synchronously adjust the ratio of oxygen flow rate and argon flow rate according to a preset program while maintaining the total gas flow rate and total gas pressure basically constant, thereby ensuring the accuracy of gradient construction and process repeatability.

[0019] In some embodiments, the target material in the magnetron sputtering process further includes at least one selected from silicon dioxide targets, graphite targets, and lithium metal targets.

[0020] In some embodiments, the target material in the magnetron sputtering process is at least one of elemental silicon, a combination of elemental silicon and graphite, a combination of elemental silicon and lithium metal, or a combination of elemental silicon, graphite, and lithium metal. The introduction of graphite helps to further improve the electronic conductivity of the thin film and buffer volume expansion, while the introduction of lithium metal can achieve a certain degree of pre-intercalation, compensating for the initial irreversible capacity loss.

[0021] In some embodiments, the spacing between the substrate and the target is preferably 30-90 mm, specifically 80 mm.

[0022] In some embodiments, the temperature of the substrate / matrix is ​​10~300°C, preferably 25~300°C. In this invention, room temperature refers to 10-35°C.

[0023] In some embodiments, the total pressure is 0.1~2 Pa, preferably 0.1 Pa, 0.5 Pa, 0.6 Pa or 2 Pa.

[0024] In some embodiments, the total gas flow rate is 30-40 sccm.

[0025] In some implementations, the methods for dynamically adjusting the ratio of oxygen flow rate to argon flow rate entering the deposition chamber include:

[0026] Method 1: Initial sputtering phase: 0~20 minutes: Ar flow rate 40 sccm, O2 flow rate 0 sccm; Gradient sputtering phase: 20~100 minutes: O2 flow rate linearly increases from 0 sccm to 4 sccm, Ar flow rate linearly decreases from 40 sccm to 36 sccm; Final sputtering phase: 100~110 minutes: O2 flow rate 4 sccm, Ar flow rate 36 sccm;

[0027] Method 2: Initial sputtering phase: 0~15 minutes: Ar flow rate 30 sccm, O2 flow rate 0 sccm; Gradient sputtering phase: 15~75 minutes: O2 flow rate linearly increases from 0 sccm to 6 sccm, Ar flow rate linearly decreases from 30 sccm to 24 sccm; Final sputtering phase: 75~80 minutes: O2 flow rate 6 sccm, Ar flow rate 24 sccm;

[0028] Method 3: Initial sputtering phase: 0~20 minutes: Ar flow rate is 40 sccm, O2 flow rate is 0 sccm; Gradient sputtering phase: 20~110 minutes: O2 flow rate increases linearly from 0 sccm to 6 sccm, Ar flow rate decreases linearly from 40 sccm to 34 sccm; Final sputtering phase: 110~120 minutes: O2 flow rate is 6 sccm, Ar flow rate is 34 sccm.

[0029] In some embodiments, the sputtering power of the silicon target is 50~300 W, preferably 50 W, 100 W, 150 W, 200 W, 250 W, 300 W, or any two of the above values ​​forming a range.

[0030] In some embodiments, the sputtering power of the silicon dioxide target is 10~300 W, preferably 10 W, 30 W, 50 W, 100 W, 150 W, 200 W, 250 W, 300 W, or any two of the above values ​​forming a range.

[0031] In some embodiments, the sputtering power of the graphite target and the lithium metal target is 10~100 W, preferably any one of any two values ​​from 10 W, 30 W, 50 W, 100 W, or above.

[0032] In some embodiments, the sputtering time is 60 to 300 min, preferably 60 min, 80 min, 100 min, 110 min, 120 min, 150 min, 200 min, 250 min, 300 min, or any two of the above values ​​forming a range.

[0033] Thirdly, a method for preparing an amorphous silicon-based thin-film anode with an intrinsic chemical state gradient as described in this invention is provided, comprising:

[0034] Amorphous silicon-based thin films are formed on the substrate surface by continuous deposition in a single step using magnetron sputtering. During the magnetron sputtering process, elemental silicon and silicon dioxide targets are used as target materials. Under a specific sputtering gas atmosphere, while ensuring that the total gas flow rate and total gas pressure are basically constant, the sputtering power of the elemental silicon and silicon dioxide targets is dynamically adjusted. This allows the amount of silicon dioxide introduced to vary with the deposition time or deposition thickness, thereby achieving the fabrication of amorphous silicon-based thin film anodes with intrinsic chemical state gradients.

[0035] In some embodiments, the specific sputtering gas is selected from at least one of argon, oxygen, oxygen-enriched air with an oxygen content of 30% to 99%, and air.

[0036] In some embodiments, the target material in the magnetron sputtering process further includes at least one selected from graphite targets and lithium metal targets.

[0037] In some embodiments, the target material in the magnetron sputtering process is at least one of the following: a combination of elemental silicon and silicon dioxide targets; a combination of elemental silicon, silicon dioxide, and graphite targets; a combination of elemental silicon, silicon dioxide, and lithium metal targets; or a combination of elemental silicon, silicon dioxide, graphite, and lithium metal targets. The introduction of graphite helps to further improve the electronic conductivity of the thin film and buffer volume expansion, while the introduction of lithium metal can achieve a certain degree of pre-intercalation, compensating for the initial irreversible capacity loss.

[0038] In some embodiments, the spacing between the substrate and the target is preferably 30 to 90 mm, specifically 50 mm.

[0039] In some embodiments, the temperature of the substrate is 10~300 ℃, preferably 25~300 ℃.

[0040] In some embodiments, the total pressure is 0.1 to 2 Pa, preferably 0.1 Pa, 0.5 Pa, 0.6 Pa or 2 Pa.

[0041] In some embodiments, the total gas flow rate is 30-40 sccm.

[0042] In some embodiments, the sputtering power of the elemental silicon target is 50~300 W, preferably 50 W, 100 W, 150 W, 200 W, 250 W, 300 W, or any two of the above values ​​forming a range.

[0043] In some embodiments, the sputtering power of the silicon dioxide target is 10~300 W, preferably 10 W, 30 W, 50 W, 100 W, 150 W, 200 W, 250 W, 300 W, or any two of the above values ​​forming a range.

[0044] In some embodiments, the sputtering power of the graphite target and the lithium metal target is 10~100 W, preferably any one of any two values ​​from 10 W, 30 W, 50 W, 100 W, or above.

[0045] In some implementations, the sputtering power of the elemental silicon target and the silicon dioxide target is dynamically adjusted in the following ways:

[0046] Method 1: Sputtering power of elemental silicon target is 150 W for 10 minutes; turn on silicon dioxide target, start sputtering power at 10 W, and continuously and uniformly increase sputtering power from 10 W to 150 W within 10-110 minutes, with a power increase rate of 1.4 W / min; starting from the 110th minute, stop sputtering of elemental silicon target, and continue sputtering of silicon dioxide target at 150 W for 10 minutes.

[0047] Method 2: Sputtering power of elemental silicon target is 50 W; after sputtering for 20 minutes, turn on silicon dioxide target, start sputtering power of 10 W, and continuously increase sputtering power from 10 W to 50 W over 20-280 minutes; starting from the 280th minute, stop sputtering of elemental silicon target, and continue sputtering of silicon dioxide target at 50 W for another 20 minutes;

[0048] Method 3: Sputtering power of elemental silicon target is 300 W; after sputtering for 5 minutes, turn on silicon dioxide target, start sputtering power of 10 W, and continuously increase sputtering power from 10 W to 300 W within 5-55 minutes; starting from the 55th minute, stop sputtering of elemental silicon target, and continue sputtering of silicon dioxide target at 300 W for 5 minutes.

[0049] In some embodiments, the sputtering time is 60 to 300 minutes, preferably 60 minutes, 80 minutes, 100 minutes, 110 minutes, 120 minutes, 150 minutes, 200 minutes, 250 minutes, 300 minutes, or any two of the above values ​​forming a range.

[0050] Fourthly, the present invention provides an application of the amorphous silicon-based thin-film anode in lithium-ion batteries.

[0051] Beneficial effects:

[0052] (1) This invention provides two methods for preparing amorphous silicon-based thin-film anodes with intrinsic chemical state gradients. Method 1 involves adjusting the oxygen source flow rate, which is suitable for scenarios requiring precise control of the oxygen-silicon ratio gradient and offers greater process flexibility. Method 2 involves co-sputtering a single silicon target and a silicon dioxide target, which is suitable for scenarios where a high oxidation state surface layer is more critical, offering a simpler target combination that can be selected based on the specific application. The methods provided by this invention are simple and precise, requiring only programming control and continuous operation without interrupting deposition.

[0053] (2) This invention provides an amorphous silicon-based thin-film anode with innovative structure and superior performance: it achieves an intrinsic gradient of chemical states within a single continuous thin film, cleverly integrating a "high-stability interface" (oxygen-rich surface layer) and a "high-conductivity phase" (silicon-rich inner layer). The relatively oxygen-rich / high-oxidation-state silicon on the surface layer effectively suppresses electrolyte decomposition, forming a stable SEI; the low-oxidation-state silicon in the inner layer ensures rapid lithium-ion conduction. This structure fundamentally and synergistically solves the contradiction between interfacial side reactions and bulk conductivity.

[0054] (3) This invention provides an amorphous silicon-based thin film anode that effectively avoids interface problems: as it is a single continuous thin film, there is no interlayer interface in the multilayer stacked structure, which fundamentally avoids problems such as interface debonding and high interface resistance, and the structural integrity and mechanical integrity are better. The amorphous silicon-based active layer of the amorphous silicon-based thin film anode is a continuous amorphous silicon thin film that is not multilayer stacked; in its thickness direction, the chemical state of silicon element has a continuous and monotonically changing gradient distribution: in the region near the substrate / matrix side, the chemical state of silicon is mainly low oxidation state silicon; in the region near the electrolyte or electrolyte side, the chemical state of silicon is mainly high oxidation state silicon; there is a continuous transition region between the low oxidation state silicon and the high oxidation state silicon; in the amorphous silicon-based active layer, the ratio of oxygen atoms to silicon atoms (O / Si) increases continuously and monotonically from the substrate / matrix side to the electrolyte side along the thickness direction.

[0055] (4) This invention provides an amorphous silicon-based thin-film anode with significantly improved performance: compared to oxygen-free pure α-Si thin films, the amorphous silicon-based thin-film anode can significantly improve the initial coulombic efficiency and cycle life; compared to uniform silicon oxide thin films, it can maintain high capacity and excellent rate performance; compared to multilayer stacked gradient thin films, it has better interface stability and simpler process. Introducing graphite and lithium co-sputtering can further optimize electrochemical performance.

[0056] (5) The process of this invention is flexible and controllable: It adopts a programmable interlocking proportional control valve, which realizes precise, synchronous and continuous adjustment of gas flow through programmable commands. That is, in the coating process, the oxygen flow is slowly and continuously increased according to a preset ratio, and the argon flow is synchronously reduced according to the same ratio, while keeping the total gas pressure basically unchanged. It can achieve gradient using only a single silicon target with atmosphere adjustment, or it can use silicon / graphite / lithium multi-target co-sputtering to achieve more complex composition and gradient synergy. It does not require multiple target changes or complex manual parameter switching. The process window is wide, the repeatability is good, and it is suitable for large-scale production. Attached Figure Description

[0057] Figure 1 This is a schematic diagram illustrating the working principle of a programmable interlock proportional control valve. Figure 1 In the diagram, 1 is an argon cylinder, 2 is an oxygen cylinder, 3 and 8 are electrically controlled precision flow meters, 4 is a PLC, 5 is a magnetron sputtering device, 6 is a flow sensor, 7 is a mixing chamber, 9 is a gas pipeline, and 10 is a signal and electrical control circuit.

[0058] Figure 2 This is a schematic diagram of the structure of the amorphous silicon-based thin film anode with intrinsic chemical state gradient of the present invention.

[0059] Figure 3 This is an EDS depth profile of the oxygen content in the amorphous silicon-based thin-film anode sample obtained in Example 1 of this invention. The figure shows the continuous gradient change of oxygen content from the substrate / matrix side (low) to the electrolyte side (high).

[0060] Figure 4 The Si in the amorphous silicon-based thin film anode sample obtained in Example 1 of this invention 4+ Si 0 XPS depth profile of Si content. This figure shows the Si content. 4+ Si 0 The content changes in a continuous gradient from the substrate / matrix side to the electrolyte side; due to Si 2+ Si 3+ The content is low, so Si is omitted from the figure. 2+ Si 3+ The content curve of Si shows a continuous distribution in the middle region. 0 To Si 4+ The transition trend is consistent.

[0061] Terminology Explanation

[0062] Certain embodiments of the invention will now be described in detail, examples of which are illustrated by the accompanying structural and chemical formulas. The invention is intended to cover all alternatives, modifications, and equivalents, all of which are included within the scope of the invention as defined in the claims. Those skilled in the art will recognize that many similar or equivalent methods and materials can be used to practice the invention. The invention is by no means limited to the methods and materials described herein. In the event that one or more of the incorporated documents, patents, and similar materials differ from or contradict this application (including, but not limited to, defined terminology, application of terminology, described techniques, etc.), this application shall prevail.

[0063] It should be further appreciated that certain features of the invention, for clarity, have been described in multiple independent embodiments, but may also be provided in combination in a single embodiment. Conversely, various features of the invention, for brevity, have been described in a single embodiment, but may also be provided individually or in any suitable sub-combination.

[0064] Unless otherwise stated, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. All patents and publications related to this invention are incorporated herein by reference in their entirety.

[0065] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0066] In the following content, all numbers disclosed herein, whether or not they use words such as "approximately" or "about," are approximate values. The value of each number may vary by 1%, 2%, 5%, 7%, 8%, 10%, 15%, or 20%. Whenever a number with a value of N is disclosed, any numbers with values ​​of N+ / -1%, N+ / -2%, N+ / -3%, N+ / -5%, N+ / -7%, N+ / -8%, N+ / -10%, N+ / -15%, or N+ / -20% will be explicitly disclosed, where "+ / -" indicates addition or subtraction. Detailed Implementation

[0067] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention in any way. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure. Such structures and techniques have also been described in many publications.

[0068] All reagents used in this invention can be purchased commercially or prepared by the methods described in this invention.

[0069] like Figure 1 As shown in the dashed box, this is a schematic diagram of a programmable interlocking proportional control valve, which consists of two electrically controlled precision flow meters, one flow sensor, one mixing chamber, one PLC controller, and corresponding pipelines. Its operation is as follows: The total gas flow rate, initial sputtering time, gradient sputtering time, final sputtering time, initial and final argon flow rates, and initial and final oxygen flow rates are set on the PLC controller. After the program starts, the PLC outputs a control signal to automatically execute the entire process: ① Sputtering is performed in a pure argon atmosphere, with the sputtering time being the set initial sputtering time; ② During the gradient sputtering time, the oxygen flow rate increases uniformly and continuously from 0 to the final value, while the argon flow rate decreases uniformly and continuously from the initial value to the final value; ③ At the end of the gradient sputtering, the oxygen and argon flow rates are maintained for continued sputtering, with the sputtering time being the set final sputtering time.

[0070] Figure 1 In the diagram, 1 is an argon cylinder, 2 is an oxygen cylinder, 3 and 8 are electrically controlled precision flow meters, 4 is a PLC, 5 is a magnetron sputtering device, 6 is a flow sensor, 7 is a mixing chamber, 9 is a gas pipeline, and 10 is a signal and electrical control circuit.

[0071] In applications, for example, to adjust the ratio of argon to oxygen, the following parameters are input into the PLC: total gas flow rate 40 sccm, initial sputtering time 20 minutes, gradient sputtering time 80 minutes, final sputtering time 10 minutes, initial argon flow rate 40 sccm, final flow rate 36 sccm, initial oxygen flow rate 0, final flow rate 4 sccm. After setting and starting the PLC, the following can be achieved: sputtering a pure elemental silicon target for 20 minutes in an oxygen-free environment, followed by a uniform and continuous decrease in the argon flow rate from the initial value of 40 sccm to the final value of 36 sccm during the 80-minute gradient sputtering period, and a uniform and continuous increase in the oxygen flow rate from the initial value of 0 to the final value of 4 sccm, maintaining the argon flow rate at 36 sccm and the oxygen flow rate at 4 sccm for another 10 minutes.

[0072] This design achieves precise and repeatable control of process parameters, a continuous and smooth transition of chemical state gradients, avoids interface problems in multilayer stacking, and is suitable for large-scale industrial production.

[0073] Example 1 (continuous linear gradient, elemental silicon target only)

[0074] A method for preparing an amorphous silicon-based thin-film anode with an intrinsic chemical state gradient, comprising:

[0075] The cleaned copper foil substrate was placed in a DC magnetron sputtering apparatus, using a single-element silicon target as the sputtering source. The target-substrate distance was 80 mm, the single-element silicon target sputtering power was 150 W, and the substrate temperature was room temperature (~25℃). The chamber background vacuum was below 5.0 × 10⁻⁶ mm. -4 Pa. Input the following parameters into the PLC of the DC magnetron sputtering equipment: the programmable interlock proportional control valve regulates the gas flow rate, maintaining a total gas flow rate of 40 sccm; the total deposition time is 110 minutes, the initial sputtering time is 20 minutes, the gradient sputtering time is 80 minutes, the final sputtering time is 10 minutes, the argon flow rate starts at 40 sccm and ends at 36 sccm; the oxygen flow rate starts at 0 and ends at 4 sccm.

[0076] During deposition, the total gas pressure was kept constant at 0.6 Pa. The oxygen and argon flow rates were pre-programmed to control the deposition parameters as follows:

[0077] Initial sputtering phase: 0~20 minutes: Ar flow rate is 40 sccm, O2 flow rate is 0 sccm.

[0078] Gradient sputtering phase: 20~100 minutes: O2 flow rate increases linearly from 0 sccm to 4 sccm, and Ar flow rate decreases linearly from 40 sccm to 36 sccm.

[0079] Final sputtering stage: 100~110 minutes: O2 flow rate is 4 sccm, Ar flow rate is 36 sccm.

[0080] The resulting sample is denoted as S1 (the continuous gradient film of the present invention), and the thickness of the film is approximately 800 nm.

[0081] XPS Deep Profile of S1 (Ar) ⁺ (Sputter etching). Results are as follows: Figure 4 As shown, deep within the thin film (near the substrate), the Si 2p peak is located at ~99.3 eV (Si... 0 The dominant peak is 103.4 eV (Si) near the surface; as the surface approaches, the spectral peaks shift continuously towards higher binding energies, reaching ~103.4 eV near the surface. 4+ The main peak is Si, and the middle region exhibits Si. 2+ Si3+ The broadened peaks and the smooth, continuous peak shifts without steps demonstrate a continuous gradient distribution of chemical states.

[0082] from Figure 4 It can be confirmed that the continuous gradient silicon thin film as the active layer is a non-multilayer stacked continuous amorphous silicon thin film. The silicon chemical state in its thickness direction is distributed in a continuous monotonic gradient, transitioning continuously from low oxidation state silicon dominance on the substrate side to high oxidation state silicon dominance on the electrolyte side, and the oxygen-silicon atom ratio increases accordingly.

[0083] Example 2 (steep continuous gradient, elemental silicon target only)

[0084] The preparation process was the same as in Example 1, except that the sputtering power was 120 W, the total deposition time was 80 minutes, the total gas flow rate was 30 sccm, and the total gas pressure was constant at 0.5 Pa.

[0085] The oxygen and argon flow rates are pre-programmed to control the deposition parameters as follows:

[0086] Initial sputtering phase: 0~15 minutes: Ar flow rate is 30 sccm, O2 flow rate is 0 sccm.

[0087] Gradient sputtering phase: 15~75 minutes: O2 flow rate increases linearly from 0 sccm to 6 sccm, and Ar flow rate decreases linearly from 30 sccm to 24 sccm.

[0088] Final sputtering stage: 75~80 minutes: O2 flow rate 6 sccm, Ar flow rate 24 sccm.

[0089] The resulting sample is designated as S2, and the thickness of the resulting film is approximately 650 nm.

[0090] Example 3 (Continuous gradient, co-sputtering of silicon target + graphite target + lithium target)

[0091] A method for preparing an amorphous silicon-based thin-film anode with an intrinsic chemical state gradient, comprising:

[0092] The cleaned copper foil substrate was placed in a multi-target magnetron sputtering apparatus. A silicon target, graphite target, and lithium target were used as the sputtering sources, with a target-substrate distance of 80 mm. The sputtering power of the silicon target was 150 W, the graphite target was 50 W, and the lithium target was 30 W. The substrate temperature was 80 °C. The chamber background vacuum was below 5.0 × 10⁻⁶ mm. -4Pa. Input the following parameters into the PLC of the multi-target magnetron sputtering equipment: the programmable interlock proportional control valve regulates the gas flow rate, maintaining a total gas flow rate of 40 sccm; the total deposition time is 120 minutes, the initial sputtering time is 20 minutes, the gradient sputtering time is 90 minutes, the final sputtering time is 10 minutes, the argon flow rate starts at 40 sccm and ends at 34 sccm; the oxygen flow rate starts at 0 and ends at 6 sccm.

[0093] During deposition, the total gas pressure was kept constant at 0.6 Pa. The oxygen and argon flow rates were pre-programmed to control the deposition parameters as follows:

[0094] Initial sputtering phase: 0~20 minutes: Ar flow rate is 40 sccm, O2 flow rate is 0 sccm.

[0095] Gradient sputtering phase: 20~110 minutes: O2 flow rate increases linearly from 0 sccm to 6 sccm, and Ar flow rate decreases linearly from 40 sccm to 34 sccm.

[0096] Final sputtering stage: 110~120 minutes: O2 flow rate 6 sccm, Ar flow rate 34 sccm.

[0097] The resulting sample is designated as S3 (the co-sputtered gradient film of the present invention), and the thickness of the resulting film is approximately 850 nm.

[0098] Example 4 (Continuous gradient co-sputtering of elemental silicon target + silicon dioxide dual target)

[0099] A method for preparing an amorphous silicon-based thin-film anode with an intrinsic chemical state gradient, comprising:

[0100] The cleaned nickel foil substrate was placed in a multi-target magnetron sputtering apparatus, using a silicon target and a silicon dioxide target as the sputtering source, with a target-substrate distance of 80 mm. The total deposition time was 120 minutes. The program control settings were as follows: the sputtering power of the silicon target was 150 W for 10 minutes; the silicon dioxide target was then turned on, with an initial sputtering power of 10 W, which was continuously and uniformly increased to 150 W over the next 100 minutes at a power increase rate of 1.4 W / min; from the 110th minute, sputtering of the silicon target was stopped, while sputtering of the silicon dioxide target continued for 10 minutes at a power of 150 W. During the deposition process, an argon atmosphere was maintained with a total gas flow rate of 40 sccm and a constant total pressure of 0.6 Pa.

[0101] The resulting sample is designated as S4 (the dual-target gradient co-sputtering film of the present invention), and the thickness of the resulting film is approximately 1250 nm.

[0102] Example 5 (Continuous gradient co-sputtering of elemental silicon target + silicon dioxide dual target)

[0103] The preparation process was the same as in Example 4, except that a titanium foil substrate was used and the total deposition time was 300 minutes. The program control settings were as follows: sputtering power of the elemental silicon target was 50 W; after sputtering for 20 minutes, the silicon dioxide target was turned on with an initial sputtering power of 10 W, and the sputtering power was uniformly and continuously increased from 10 W to 50 W over the next 260 minutes; starting from the 280th minute, sputtering of the elemental silicon target was stopped, and sputtering of the silicon dioxide target continued for 20 minutes at a sputtering power of 50 W.

[0104] The resulting sample is designated as S5; the film thickness is approximately 1180 nm.

[0105] Example 6 (Continuous gradient co-sputtering of elemental silicon target + silicon dioxide dual target)

[0106] The preparation process was the same as in Example 4, except that a 316 stainless steel foil substrate was used, and the total deposition time was 60 minutes. The program control settings were as follows: sputtering power of the elemental silicon target was 300 W; after sputtering for 5 minutes, the silicon dioxide target was turned on, with an initial sputtering power of 10 W, and the sputtering power was uniformly and continuously increased from 10 W to 300 W over the next 50 minutes; starting from the 55th minute, sputtering of the elemental silicon target was stopped, and sputtering of the silicon dioxide target continued for 5 minutes at a sputtering power of 300 W.

[0107] The resulting sample is designated as S6; the film thickness is approximately 1150 nm.

[0108] Example 7 (Continuous linear gradient, elemental silicon target only)

[0109] The preparation process is the same as in Example 1, except that the magnetron sputtering deposition pressure is 0.1 Pa, the substrate temperature is 300 °C, the sputtering power of the elemental silicon target is 200 W, and the substrate is nickel-plated glass.

[0110] The resulting sample is designated as S7, and the thickness of the resulting film is approximately 800 nm.

[0111] Example 8 (Continuous gradient, co-sputtering of silicon target + graphite target + lithium target)

[0112] The preparation process was the same as in Example 3, except that the magnetron sputtering deposition pressure was 2.0 Pa, the sputtering power of the elemental silicon target was 150 W, the sputtering power of the graphite target was 10 W, the sputtering power of the lithium metal target was 100 W, the obtained sample was designated as S8, and the thickness of the obtained film was approximately 850 nm.

[0113] Comparative Example 1 (Pure Amorphous Silicon Thin Film)

[0114] The preparation process was the same as in Example 1, except that only 40 sccm of Ar was introduced throughout the process, without introducing oxygen. The resulting homogeneous and pure α-Si film was denoted as D1.

[0115] Comparative Example 2 (Uniform Silicon Oxide Thin Film)

[0116] The preparation process was the same as in Example 1, except that Ar was constantly introduced at 34 sccm and O2 at 6 sccm throughout the process. The resulting uniform SiO_x film was denoted as D2.

[0117] Comparative Example 3 (Multilayer Stacked Thin Film - Simulating Existing Technology)

[0118] In contrast, magnetron sputtering was used to sequentially deposit three thin films of different compositions to simulate the existing gradient structure:

[0119] First, on the same copper substrate, only 40 sccm of Ar is introduced throughout the process without introducing oxygen, and a pure Si layer with a thickness of ~267 nm is deposited.

[0120] Secondly, the target material was changed to a SiO target, and a SiO layer with a thickness of ~267 nm (O / Si≈1) was deposited.

[0121] Finally, the target material was changed to a SiO2 target, and an oxygen-rich silicon layer with a thickness of ~266 nm (O / Si≈2) was deposited.

[0122] The total thickness is approximately 800 nm, denoted as D3.

[0123] Comparative Example 4 (co-sputtering of elemental silicon and silicon dioxide targets, but the power of the silicon dioxide target remains unchanged)

[0124] The preparation process was the same as in Example 4, except that the sputtering power of both the elemental silicon target and the silicon dioxide target was 150 W, and co-sputtering was performed for a total deposition time of 120 minutes. During the deposition process, the total gas flow rate was 40 sccm and the total gas pressure was kept constant at 0.6 Pa. The total thickness was approximately 1250 nm, denoted as D4.

[0125] Application Example 1: Electrochemical Performance Testing

[0126] All samples prepared in Examples 1-8 and Comparative Examples 1-4 of this invention were used as negative electrodes, with lithium metal sheets as counter electrodes and 1M LiPF6 EC (ethylene carbonate) / DMC (dimethyl carbonate) (1:1 vol%) as electrolyte, to assemble several CR2032 coin cells. These cells were tested using a battery charge-discharge tester under the following conditions: 25°C, 0.1C charge-discharge, and a test power supply range of 0.01V~2V. The results are shown in Table 1.

[0127] Table 1 Comparison of electrochemical performance of each sample

[0128]

[0129] From the data in Table 1, it can be concluded that all gradient films of the present invention (each embodiment) are significantly superior to the comparative examples in terms of high first-efficiency, long-term cycle stability and low interfacial impedance.

[0130] In anode materials (especially silicon-based alloy materials), excessively high initial capacity is often accompanied by huge irreversible capacity loss. The capacity of the example (~2600-2855 mAh / g) is in a better balance range, which can provide high capacity while ensuring initial coulombic efficiency and stability.

[0131] All gradient films of this invention (various embodiments) exhibit high initial coulombic efficiency, meaning minimal irreversible capacity loss due to SEI film formation during the first charge-discharge cycle. The high efficiency of these embodiments demonstrates that the material design of this invention effectively reduces the consumption of active lithium, providing a basis for higher usable capacity and longer cycle life in the battery.

[0132] The excellent 100-cycle capacity retention of all gradient films of the present invention (various embodiments) demonstrates that their material structure exhibits extremely high stability during repeated charge-discharge cycles, with very slow capacity decay and long-term cycle stability. In contrast, the comparative examples, especially Comparative Example 1, show severe capacity decay, indicating that their structure may collapse or fail.

[0133] The post-cycle internal resistance of all gradient films (various embodiments) of this invention is crucial in reflecting the stability of the electrode interface and structural integrity. Increased internal resistance leads to decreased battery power, increased heat generation, and reduced energy efficiency. The extremely low internal resistance growth in the embodiments indicates stable electrode interfaces and well-maintained ion / electron conduction pathways. In contrast, the high internal resistance in the comparative embodiments signifies continuous interface deterioration or structural damage, corroborated by their poor capacity retention.

[0134] Compared to Comparative Example 1, which has high capacity but lacks sustainability, the embodiments of the present invention have excellent first coulombic efficiency, 100-cycle capacity retention, and 100-cycle battery internal resistance, resulting in superior overall performance.

[0135] Compared to the low initial capacity of Comparative Example 2, its energy density is not competitive.

[0136] Key findings: The gradient thin film of this invention outperforms the performance of both the multilayer stacked comparative example 3 and the gradient-free comparative example 4. This confirms that the intrinsic chemical state gradient within a continuous thin film has significant advantages over the compositional gradient of a multilayer discrete stack and the absence of a gradient in terms of interface stability (lower impedance growth) and cycle life. This verifies the inventiveness of the structural design of this invention and the effectiveness of the programmable interlocking proportional control valve in precisely controlling the gradient structure.

[0137] This invention (Examples 1-8) successfully solves key challenges commonly encountered in high-capacity anode materials, such as low initial efficiency, rapid cycle decay, and rapid increase in internal resistance, through a specific material preparation method. The examples achieve an optimal balance across four dimensions: high capacity, high initial efficiency, long cycle life, and low internal resistance. Examples 3 and 8, in particular, demonstrate excellent comprehensive electrochemical performance, validating the effectiveness and superiority of the technical solution of this invention. Conversely, the comparative examples demonstrate that without the key design features of this invention, it would be difficult to obtain a battery material with balanced performance and practicality. This invention achieves synergistic optimization of interface stability and bulk conductivity within a single thin film, improving battery cycle performance, and the process is precisely controllable.

[0138] The method of this invention has been described through preferred embodiments. Those skilled in the art will readily be able to modify or appropriately alter and combine the methods and applications described herein within the scope, spirit, and context of this invention to implement and apply the technology of this invention. Those skilled in the art can refer to the content herein to appropriately improve process parameters. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the scope of this invention.

Claims

1. An amorphous silicon-based thin-film anode with a continuous chemical state gradient, characterized in that, Includes a substrate and an amorphous silicon-based active layer disposed on the surface of the substrate; The substrate is copper foil, stainless steel foil, titanium foil, nickel foil, or an insulating substrate with a conductive layer on its surface; The amorphous silicon-based active layer is a continuous amorphous silicon thin film that is not multilayered; in its thickness direction, the chemical state of silicon exhibits a continuous and monotonically varying gradient distribution. In the region near the substrate, the silicon is predominantly in a low-oxidation state, with Si being the dominant form. 0 Mainly, including Si 0 Si + Si 2+ At least one of the following; in the region near the electrolyte or electrolyte solution, the chemical state of silicon is predominantly high-oxidation silicon, including Si. 4+ and Si 3+ At least one of them; The low-oxidation-state silicon and the high-oxidation-state silicon form a continuous transition region without abrupt changes; In the amorphous silicon-based active layer, the ratio of oxygen atoms to silicon atoms increases continuously and monotonically from the substrate side to the electrolyte side along the thickness direction; the chemical state gradient is verified by XPS depth profiling, and its Si 2p spectrum peak should show a continuous shift in binding energy, rather than discrete peak position jumps.

2. The amorphous silicon-based thin-film anode according to claim 1, characterized in that, The thickness of the amorphous silicon thin film is 650~1250 nm.

3. The amorphous silicon-based thin-film anode according to claim 1, characterized in that, The amorphous silicon-based active layer contains silicon, oxygen, and at least one of carbon and lithium.

4. A method for preparing an amorphous silicon-based thin-film anode as described in any one of claims 1 to 3, characterized in that, Includes the following steps: On the substrate surface, an amorphous silicon-based thin film is continuously deposited in one pass using a magnetron sputtering process. The magnetron sputtering target is a single-element silicon target, the sputtering power is 50-300 W, the deposition gas pressure is 0.1-2.0 Pa, and the substrate temperature is room temperature to 300℃. During the single continuous deposition process, oxygen and argon are continuously introduced into the deposition chamber. The amount of oxygen introduced is dynamically adjusted by a programmable interlock proportional control valve. The control method is as follows: the total gas flow rate and total gas pressure in the deposition chamber are kept constant. The oxygen flow rate is zero for a period of time after the start of deposition, and then increases continuously and monotonically with the increase of deposition time or film thickness. The argon flow rate decreases synchronously and continuously. By dynamically controlling the amount of oxygen introduced, a gradient structure with continuous and monotonically changing silicon chemical states can be formed within the same continuous amorphous silicon-based thin film as the deposition time or deposition thickness changes.

5. The preparation method according to claim 4, characterized in that, The total gas flow rate was 30-40 sccm, and the total gas pressure remained constant during the deposition process.

6. The preparation method according to claim 4, characterized in that, The magnetron sputtering target also includes a combination of graphite target and lithium metal target, or a combination of graphite target, lithium metal target and elemental silicon target; during co-sputtering, the sputtering power of graphite target and lithium metal target is 10-100 W respectively.

7. A method for preparing an amorphous silicon-based thin-film anode as described in any one of claims 1 to 3, characterized in that, The process includes the following steps: using a single silicon target and a silicon dioxide target as target materials, a magnetron sputtering process is employed under an argon atmosphere. First, the single silicon target is turned on for continuous sputtering at a power of 50-300W to deposit an amorphous silicon thin film on the substrate. After sputtering for 5-20 minutes, the silicon dioxide target is turned on for sputtering, and the power is slowly and continuously increased from 10W to 300W during the gradient sputtering time. During the deposition process, the power of the silicon dioxide target is continuously and dynamically adjusted to control the amount of silicon dioxide introduced, so that the amorphous silicon-based thin film changes with the deposition time or deposition thickness, thereby achieving a gradient structure in which the silicon chemical state changes continuously and monotonically within the same continuous amorphous silicon-based thin film.

8. The preparation method according to claim 7, characterized in that, The total gas flow rate and total gas pressure in the deposition chamber are kept constant, and the substrate temperature is between room temperature and 300°C.

9. The application of an amorphous silicon-based thin-film anode as described in any one of claims 1 to 3 or an amorphous silicon-based thin-film anode prepared by the preparation method described in any one of claims 4 or 7 in a lithium-ion battery.

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