MSe / Si / C composite material, silicon negative electrode and its preparation and application

Abstract

The present invention belongs to the field of silicon negative electrode battery materials and specifically discloses a method for preparing a MSe / Si / C composite material. The method comprises mixing M-MOF and a selenium source and performing a calcination reaction to obtain an MSe / C product. The MSe / C is then subjected to a vapor deposition treatment in a silicon source atmosphere to obtain an MSe / Si / C composite material. The M is a transition metal element; and the M-MOF is a metal framework material of a transition metal element. The present invention also provides a material obtained by the preparation method and its application in a battery. The process of the present invention can induce uniform and efficient deposition of silicon, facilitates the in-situ construction of an electronic and ion conduction network of M and Li2Se during the charge and discharge phase, and helps improve the low-temperature fast charging performance of the material.

Description

Technical Field

[0001] The present invention relates to battery negative electrodes, and in particular to the field of silicon negative electrode materials. Background Art

[0002] Lithium-ion batteries are widely used in modern electronic devices and play an important role in promoting the development of sustainable energy. First, lithium-ion batteries have a high energy density, which means they can store more electrical energy in a smaller volume and weight, making them very suitable for portable electronic products. Second, they have a long cycle life and a low self-discharge rate, which makes them an ideal energy solution for electric vehicles and energy storage systems. In addition, with the global focus on reducing greenhouse gas emissions, lithium-ion batteries, as a key component of clean energy technology, can help increase the utilization of renewable energy sources such as solar and wind power. Therefore, research on lithium-ion batteries can not only promote technological progress, but also promote environmental protection and energy transformation.

[0003] The low energy density of lithium-ion batteries is mainly due to their working principles and material limitations. First, the energy density of lithium-ion batteries is limited by the lithium ion storage capacity of the positive and negative electrode materials. The theoretical specific capacity of the widely used graphite negative electrode material is 372mAh / g, and the theoretical specific capacity of positive electrode materials such as lithium cobalt oxide and lithium manganese oxide is also relatively limited. Secondly, the performance of the electrolyte and diaphragm materials also affects the energy density of the battery. They need to provide good ion conductivity while ensuring safety. In addition, battery design and manufacturing processes also have an impact on energy density, such as the space utilization inside the battery, the thickness and density of the electrodes, etc. Finally, during the charging and discharging process of lithium-ion batteries, the volume expansion and contraction of the electrode materials will lead to a decrease in battery life, which also indirectly limits the improvement of its energy density.

[0004] Compared with traditional graphite negative electrodes, silicon negative electrodes have a higher theoretical specific capacity, which is about ten times that of graphite. This means that in batteries of the same volume or weight, silicon negative electrodes can store more electrical energy. In addition, the potential of the silicon negative electrode is close to that of lithium, which helps to increase the voltage platform of the battery and thus increase the energy density of the battery. The silicon negative electrode also has good conductivity and a low lithium ion diffusion barrier, which helps to improve the charge and discharge efficiency of the battery. However, the silicon negative electrode has a large volume expansion problem during the cycle, which may lead to damage to the electrode structure and shorten the cycle life. Therefore, researchers are working hard to overcome these challenges through methods such as nanotechnology and composite material design to realize the application of silicon negative electrodes in commercial lithium-ion batteries.

[0005] The current problems with silicon negative electrodes mainly include volume expansion, poor cycle stability and low electrical conductivity. First, silicon undergoes significant volume changes during the insertion and extraction of lithium ions, which can lead to mechanical damage to the electrode material and shorten the battery life. Secondly, due to the volume expansion of silicon, the interfacial stability between the electrode and the electrolyte deteriorates during the cycle, which further affects the cycle life of the battery. Finally, the ionic conductivity and electronic conductivity of pure silicon are both low, which limits its electrochemical performance as an electrode material, especially affecting its performance in low-temperature fast charging. Summary of the Invention

[0006] In order to solve the problem that silicon materials are difficult to balance excellent electron-ion dual conduction capabilities and difficult to exert excellent low-temperature fast charging performance, the first purpose of the present invention is to provide a preparation method of MSe / Si / C composite materials, aiming to prepare an excellent electron-ion conduction network that can be constructed in situ, and significantly improve the low-temperature fast charging performance of silicon negative electrode materials.

[0007] The second object of the present invention is to provide an MSe / Si / C composite material prepared by the preparation method and its application in the preparation of lithium-ion batteries and silicon negative electrodes thereof.

[0008] The third object of the present invention is to provide a silicon negative electrode comprising the MSe / Si / C composite material and its preparation.

[0009] A fourth object of the present invention is to provide a lithium-ion battery comprising the MSe / Si / C composite material and an electrochemical formation method thereof.

[0010] The preparation method of the MSe / Si / C composite material comprises the following steps: mixing M-MOF and a selenium source and performing a calcination reaction to obtain an MSe / C product; and then subjecting the MSe / C to a vapor deposition treatment in a silicon source atmosphere to obtain the MSe / Si / C composite material.

[0011] The M is a transition metal element; the M-MOF is a metal framework material of a transition metal element.

[0012] The present invention innovatively selenides M-MOF to obtain a selenide product that retains the physicochemical structure of the M-MOF material, which is then used as a substrate for silicon deposition. This is beneficial to the physicochemical structure of the selenide product, inducing uniform and effective deposition of silicon. It is further used as a negative electrode material, which can in situ construct an electronic and ion conduction network of M and Li2Se during the charge and discharge stages, and can reduce the volume expansion problem of silicon. This can effectively improve the electrochemical properties of the material, especially its low-temperature fast charging performance.

[0013] In the present invention, the special framework structure of M-MOF is utilized for selenization, and an in-situ selenization product of the physicochemical structure can be constructed, which is beneficial to the subsequent deposition of silicon, and further beneficial to the in-situ construction of an ion-electron dual network in the assembled battery during the first cycle of charge and discharge, thereby improving the electrochemical properties of the obtained silicon-based material.

[0014] In the present invention, the M is at least one of Ni, Co, Fe, Zn and Mn.

[0015] Preferably, the M-MOF is at least one of ZIF-67, ZIF-8, and MOF-74.

[0016] Preferably, the M-MOF comprises ZIF-67 and MOF-74; more preferably, the weight ratio of ZIF-67 to MOF-74 is 1:0.1 to 0.3. Studies have shown that the M-MOF described herein, combined with the preparation process described herein, helps further optimize the physical and chemical structure of the prepared product and further enhances its low-temperature fast-charging performance.

[0017] In the present invention, the selenium source is selenium powder.

[0018] Preferably, the weight ratio of the M-MOF to the selenium source is 1:0.1-1.5; more preferably 1:0.4-0.6.

[0019] In the present invention, the atmosphere in the calcination stage is a protective atmosphere.

[0020] Preferably, the calcination temperature is 600-1000°C, preferably 650-850°C; more preferably 650-750°C. Studies have shown that under the process described in the present invention, further combined with the joint control of the time, the physical and chemical structure of the material can be optimized, making it adaptable to low temperature requirements, and achieving better low-temperature fast charging performance.

[0021] Preferably, the holding time at the roasting temperature is 1 to 5 hours, preferably 2 to 4 hours.

[0022] In the present invention, the silicon source atmosphere comprises at least one silicon-containing functional gas selected from silane, dichlorosilane, and trichlorosilane. The silicon source includes silane and also includes at least one auxiliary silicon source gas selected from dichlorosilane and trichlorosilane. Preferably, in the silicon source, the volume ratio of silane to auxiliary silicon source gas can be 1:0.1~0.2. Studies have shown that under the preferred process and conditions, it helps to induce and improve the deposition of silicon, and helps to further improve the performance of the prepared material under low-temperature fast charging requirements.

[0023] Preferably, the content of the silicon-containing functional gas in the silicon source atmosphere is 20-80v%, and further can be 25-45v%.

[0024] Preferably, the temperature of the vapor deposition is 450-700°C, more preferably 500-600°C.

[0025] Preferably, the vapor deposition time is 1 to 5 hours, preferably 2 to 4 hours.

[0026] The present invention also provides a MSe / Si / C composite material prepared by the preparation method.

[0027] The preparation method described in the present invention can give the prepared material special physical and chemical characteristics, and the material prepared by the preparation method can construct a special electron-ion conduction network in situ during the first charge and discharge stage, which can improve the expansion problem of silicon and effectively improve its electrochemical properties, especially its low-temperature fast charging performance.

[0028] The present invention also provides a silicon negative electrode, comprising a current collector and a negative electrode material composited on its surface, wherein the negative electrode material comprises a negative electrode active material, and the negative electrode active material comprises the MSe / Si / C composite material of the present invention.

[0029] In the present invention, in addition to the MSe / Si / C composite material of the present application, the other components and contents of the silicon negative electrode can be well-known or reasonably controlled based on well-known principles and means.

[0030] For example, the content of the MSe / Si / C composite material in the negative electrode material is 70-95 wt.%.

[0031] For example, the negative electrode material further includes a binder and a conductive agent.

[0032] The present invention also provides a pre-lithiation-delithiation silicon negative electrode, which is a silicon negative electrode obtained by inserting lithium and then delithiating the silicon negative electrode according to the present invention; wherein the lithium insertion cutoff potential is 0.005~0.01V; the lithium desorption cutoff potential is 1~1.2V.

[0033] Research in the present invention shows that performing the lithium insertion and delithiation treatments on the silicon negative electrode, and further coordinating the delithiation potential, is conducive to the in-situ construction of the ion-electron conduction network on silicon, which is beneficial to improving the electrochemical properties of the silicon material, especially effectively improving its low-temperature fast charging performance.

[0034] The present invention also provides a lithium-ion battery, comprising a battery cell composed of a positive electrode, a barrier layer and a negative electrode, wherein the negative electrode is the silicon negative electrode described in the present invention or the pre-lithium embedded and delithium silicon negative electrode described.

[0035] In the lithium-ion battery of the present invention, when the negative electrode is a silicon negative electrode, the assembled lithium-ion battery is pre-electrochemically treated, wherein the electrochemical lithium insertion potential of the negative electrode side is 0.005-0.01V; and the lithium desorption potential is 1-1.2V.

[0036] The lithium-ion battery of the present invention, except for the silicon negative electrode of the present invention, may have other components and component structures that are well known.

[0037] Beneficial effects

[0038] The present invention innovatively selenides M-MOF and deposits silicon, which is beneficial to the physicochemical structure of the selenized product and induces uniform and effective deposition of silicon. It is further used as a negative electrode material, which can in situ construct the electronic and ion conduction network of M and Li2Se during the charge and discharge stages, and can reduce the volume expansion problem of silicon. This can effectively improve the electrochemical properties of the material, especially its low-temperature fast charging performance. DETAILED DESCRIPTION

[0039] The present invention will be described in detail below with reference to the embodiments, but the present invention is not limited thereto.

[0040] Example 1

[0041] Step 1:

[0042] ZIF-67 (M-MOF) and selenium powder with a weight ratio of 1:0.5 were reacted at 700℃ under Ar for 3h to obtain porous CoSe-C material.

[0043] Step 2:

[0044] The porous CoSe-C material was reacted in a 30V% silane (silicon source, specifically SiH4) and Ar mixed gas at 550°C for 3h to obtain a MSe / Si / C composite material with nano-silicon embedded in the porous substrate.

[0045] Step 3: Testing:

[0046] The composite material described above was used as the negative electrode material to form a pole piece. The composite material prepared in Example 1 was used as the electrode material (negative electrode active material) to prepare an electrode slurry and pole piece. The slurry ratio was 75:15:10 for electrode material: binder (CMC): conductive agent (SP). The slurry was stirred evenly, coated onto copper foil, and then dried under vacuum. The dried electrode piece served as the working electrode of a button cell, and a lithium sheet served as the counter electrode. The battery was assembled using an electrolyte consisting of 1 M LiPF₂ dissolved in ethylene carbonate (EC): ethyl methyl carbonate (EMC): methyl propionate (MP) (20:60:20 v / v%). The battery was charged and discharged once, with the negative electrode side controlled to: 1.0 V ≤ delithiation potential ≤ 1.2 V, and the lithium insertion potential to 0.005–0.01 V. This resulted in the in-situ conversion of CoSe to Co+Li₂Se, thus constructing a dual-conductive substrate that conducts both electrons and ions. The battery was then subjected to electrochemical performance testing.

[0047] Example 2

[0048] Compared with Example 1, the only difference is that the M-MOF is changed. The experimental groups are:

[0049] Group A: M-MOF is MOF-74;

[0050] Group B: M-MOF is ZIF-67 and MOF-74 with a weight ratio of 1:0.2;

[0051] The amount of M-MOF used and other operations and parameters were the same as in Example 1.

[0052] Example 3

[0053] Compared with Example 1, the only difference is that the temperature of step 1 is 800° C., and other operations and parameters are the same as Example 1.

[0054] Example 4

[0055] Compared with Example 1, the only difference is that the silicon source atmosphere in step 2 is changed. The experimental groups are:

[0056] Group A: The silicon source atmosphere is dichlorosilane;

[0057] Group B: The silicon source atmosphere is a mixture of silane and dichlorosilane with a volume ratio of 1:0.2;

[0058] Other operations and parameters are the same as in Example 1.

[0059] Example 5

[0060] Compared with Example 1, the only difference is that in step 1, the weight ratio of M-MOF and selenium powder is 1:0.4; the holding time is 2 hours; in step 2, the silane atmosphere content is 40v%, the deposition temperature is 600°C, and the deposition time is 2 hours; other operations and parameters are the same as in Example 1.

[0061] Example 6

[0062] Compared with Example 1, the only difference is that in the test of step 3, the delithiation potential of the first charge and discharge is 2.1 V, and the other operations and parameters are the same as those in Example 1.

[0063] Comparative Example 1

[0064] Compared with Example 1, the only difference is that in step 1, no selenium powder is added, and other operations and parameters are the same as in Example 1.

[0065] Comparative Example 2

[0066] Compared with Example 1, the only difference is that the M-MOF is carbonized in advance and then mixed with selenium powder for selenization. The temperature of carbonization and selenization are both 700°C, and the time is 1.5 hours respectively, to obtain a porous CoSe-C material. Other operations and parameters are the same as in Example 1.

[0067] Comparative Example 3

[0068] Compared with Example 1, the only difference is that the M-MOF is replaced by an equal amount of a mixed raw material containing an M source (cobalt carbonate) and a carbon source (2-methylimidazole) in a molar ratio of 1:2. Other operations and parameters are the same as those in Example 1.

[0069] The first delithiation capacity and first coulombic efficiency of the above materials were tested at a current density of 0.2C. The capacity was then tested at a current density of 0.2C. The ratio of the capacity at 2C to 0.2C was used as an indicator of its rapid charge and discharge performance. The larger the value, the stronger the rapid charge and discharge capability of the material. The constant current charge and discharge voltage range was 0.01-1.5V. The results are shown in Table 1:

[0070]

[0071] The present invention innovatively selenides M-MOF and further uses it as a substrate for silicon deposition, which can facilitate the physicochemical structure of the selenized product and induce uniform and effective deposition of silicon. It can further be used as a negative electrode material, which can construct an electronic and ion conduction network of M and Li2Se in situ during the charge and discharge stage, and can reduce the volume expansion problem of silicon, so as to effectively improve the electrochemical properties of the material, especially its low-temperature fast charging performance. In addition, it can be seen from Examples 1 and 2 of Table 1 that the use of the composite M-based MOF in conjunction with the process of the present invention is conducive to further optimizing the physicochemical structure suitable for low-temperature fast charging, which helps to further improve its low-temperature fast charging performance. In addition, it can be seen from Examples 1 and 4 that adding a certain halogen-containing silicon source atmosphere to the silicon source atmosphere can further optimize the low-temperature fast charging performance of the prepared material.

Claims

1. A method for preparing a MSe / Si / C composite material, characterized in that: The M-MOF and selenium source are mixed and calcined to obtain a MSe / C product; the MSe / C is then vapor-deposited in a silicon source atmosphere to obtain a MSe / Si / C composite material; The M is at least one of Zn and Mn; the M-MOF is a metal framework material of a transition metal element, wherein the M-MOF is at least one of ZIF-67, ZIF-8, and MOF-74; the weight ratio of the M-MOF to the selenium source is 1:0.1-1.5; and the calcination temperature is 600-1000°C; The silicon source atmosphere comprises at least one silicon-containing functional gas selected from silane, dichlorosilane and trichlorosilane; The temperature of the vapor deposition is 450-700°C.

2. The method for preparing the MSe / Si / C composite material according to claim 1, wherein: The M-MOF includes ZIF-67 and MOF-74.

3. The method for preparing the MSe / Si / C composite material according to claim 1, wherein: The selenium source is selenium powder.

4. The method for preparing the MSe / Si / C composite material according to claim 1, wherein: The atmosphere during the calcination stage is a protective atmosphere.

5. The method for preparing the MSe / Si / C composite material according to claim 1, wherein: The calcination temperature is 650~850℃.

6. The method for preparing the MSe / Si / C composite material according to claim 1, wherein: The holding time at the roasting temperature is 1~5h.

7. The method for preparing the MSe / Si / C composite material according to claim 1, wherein: The silicon source includes silane and at least one auxiliary silicon source gas selected from dichlorosilane and trichlorosilane, and the volume ratio of silane to the auxiliary silicon source gas in the silicon source is 1:0.1-0.

2.

8. The method for preparing the MSe / Si / C composite material according to claim 1, wherein: The content of silicon-containing functional gas in the silicon source atmosphere is 20-80v%.

9. The method for preparing the MSe / Si / C composite material according to claim 1, wherein: The vapor deposition time is 1~5h.

10. A MSe / Si / C composite material obtained by the preparation method according to any one of claims 1 to 9.

11. A silicon negative electrode, comprising a current collector and a negative electrode material composited on its surface, wherein the negative electrode material contains a negative electrode active material, characterized in that: The negative electrode active material comprises the MSe / Si / C composite material according to claim 10.

12. The silicon negative electrode according to claim 11, wherein The content of the MSe / Si / C composite material in the negative electrode material is 70-95 wt.%.

13. The silicon negative electrode according to claim 11 or 12, characterized in that: The negative electrode material also contains a binder and a conductive agent.

14. A pre-lithiation and de-lithiation silicon negative electrode, characterized in that: A silicon negative electrode according to any one of claims 11 to 13 which is subjected to lithium insertion and then lithium removal treatment; Among them, the cutoff potential of lithium insertion is 0.005~0.01V; the cutoff potential of lithium desorption is 1~1.2V.

15. A lithium-ion battery comprising a battery cell composed of a positive electrode, a barrier layer and a negative electrode, characterized in that: The negative electrode is the silicon negative electrode according to any one of claims 11 to 13 or the pre-lithium-embedded / delithium-de-lithium silicon negative electrode according to claim 14.

16. The lithium-ion battery according to claim 15, wherein When the negative electrode is a silicon negative electrode, the assembled lithium-ion battery is pre-electrochemically treated, wherein the electrochemical lithium insertion potential of the negative electrode side is 0.005-0.01V; and the lithium desorption potential is 1-1.2V.

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