CN116083927B - Uniform pre-magnesia method for silicon oxide anode material and application of uniform pre-magnesia method in lithium ion battery - Google Patents
Uniform pre-magnesia method for silicon oxide anode material and application of uniform pre-magnesia method in lithium ion battery Download PDFInfo
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Abstract
The application provides a method for uniformly pre-magnesia treatment of a silicon oxide negative electrode material and application of a uniform magnesia product in a lithium ion battery. The product is prepared by using commercial silicon oxide as a cathode and a graphite crucible as an anode through an expandable fused salt electrolysis method and is based on oxygen ions in MgCl 2 And CaCl 2 Significantly different solubilities in molten salts, in MgCl 2 ‑CaCl 2 In the ternary fused salt system of NaCl, the silicon oxide is electrochemically converted into Si and SiO x And uniformly distributed magnesium silicate, namely, uniform pre-magnesia of SiO particles is realized by adopting an electrochemical method. In addition, electrochemically uniform pre-magneilized SiO has a typical micro/nano hierarchical structure rich in voids. Uniformly distributed inactive SiO x 、Mg 2 SiO 4 Phase, small amount of MgSiO 3 The micro/nano hierarchical structure rich in the phase and the gap is beneficial to relieving the volume change in the lithium removal/intercalation process, and the common superposition of the two factors can greatly improve the first coulomb efficiency of uniformly pre-magneilized SiO serving as the negative electrode material of the lithium ion battery and effectively improve the cycle performance of the SiO.
Description
Technical Field
The application relates to the technical field of lithium ion battery cathode materials, in particular to a method for uniformly pre-magnesia treatment of a silicon oxide cathode material, a uniform magnesia product and application thereof in a lithium ion battery.
Background
The silicon-based material is used as the anode material with the most prospect of the next generation of high-energy density lithium ion battery, and has extremely high theoretical specific capacity (3579 mAh g -1 ,Li 15 Si 4 ) Low lithium-removing/inserting potential<0.5V vs.Li/Li + ) And the advantage of abundant resources has led to extensive research. However, pure Si undergoes a drastic volume change (300%) during delithiation, such that mechanical cracking of active particles, loss of effective electrical contact, and continued unstable SEI film growth, resulting in low coulombic efficiency and poor cycling stability. In contrast, silicon oxide (SiO) exhibits proper volume expansion (120%) and satisfactory specific capacity as its internal microstructure with unique silicon nano domains embedded in amorphous silicon dioxide substrate can alleviate certain volume changes>2000mAh g -1 ) And excellent cycle stability. Unfortunately, during the first lithiation, the amorphous SiO within the SiO 2 The substrate may be transformed into irreversible products such as: li (Li) 4 SiO 4 ，Li 2 O, which results in extremely low first coulombic efficiency (ICE, 50%). Nevertheless, these first lithium intercalation resulted in irreversible products (Li 4 SiO 4 ,Li 2 O) can be used as a buffer layer to inhibit the volume expansion of the active silicon nano domains, thus remarkably improving the cycle performance of SiO as a negative electrode of a lithium ion battery.
Thus, prelithiation is used as a method of reacting a lithium source with SiO prior to assembly into a battery, to react the irreversibly active amorphous SiO in SiO 2 Conversion to inactive buffer phase (Li) 4 SiO 4 ,Li 2 O) to increase the ICE of SiO without affecting its cyclic performance. However, both simple chemical prelithiation processes and precisely controlled electrochemical prelithiation processes involve extremely active metallic lithium or lithium compounds, which have to be carried out under extreme conditions in trace amounts of water, oxygen, which seriously hampers the commercialization of SiO. In addition, although in the process of miningSiO using stable lithium metal powder and special encapsulation process x The requirement for effectively reducing the water oxygen value in the case of materials is still not met by current electrode processing techniques (e.g., aqueous binders, etc.).
In recent years, as the reaction conditions of pre-magnesium are milder, it has gained more attention as a more practical alternative to pre-lithiation. The existing pre-magnesia process is mainly carried out by two methods, namely, the rear end is respectively supplemented with magnesium, namely, metal magnesium or magnesium compound and SiO are heated for magnesia reaction; and front-end magnesium supplement, i.e. SiO 2 And carrying out physical vapor deposition on Si and Mg together to obtain Mg-doped SiO. However, these methods have the following disadvantages: (1) When the rear-end magnesium supplement is adopted, a core-shell structure can be formed due to the existence of a reaction interface, so that the magnesium can not be uniformly added, and the cycle performance is not ideal; (2) When the front-end magnesium supplement is adopted, the working environment with high temperature and low pressure is needed>1300℃,<10 Pa), increasing production cost and environmental pollution; (3) The addition of magnesium in any way reduces the silicon content of the active material, resulting in a reduction in the specific mass capacity.
Therefore, there is a need to develop a low cost and mild operating condition for a uniform pre-magnesia process that increases the first coulombic efficiency and maintains its excellent cycle stability performance without decreasing the specific SiO capacity.
Disclosure of Invention
Based on the above reasons, in view of the problems or defects existing in the prior art, the present application aims to provide a method for uniformly pre-magnesia treating a silicon oxide negative electrode material, a uniform magnesia product and application in a lithium ion battery, so as to solve the problems of severe conditions, uneven magnesia, reduced specific capacity and the like encountered in the prior art of pre-lithiation and front-end and back-end magnesium supplementing technologies of the silicon oxide material; meanwhile, the method can ensure smooth progress of uniform pre-magnesia by only mild lower temperature and shorter operation process.
In order to achieve the first object of the present application, the present application adopts the following technical scheme:
for negative silicon oxideThe method for uniformly pre-magnesizing the polar material adopts molten salt electrochemical method to pre-magnesize SiO, and after the pre-magnesizing is completed, the SiO is converted into Si and electrochemical inactive magnesium silicate (Mg 2 SiO 4 A small amount of MgSiO 3 ) And a small amount of residual SiO x 。
Further, according to the technical scheme, the Mg phase Mg 2 SiO 4 A small amount of MgSiO 3 Uniformly distributed in the SiO, the uniformly pre-magneilized SiO product produced has a typical micro/nano hierarchical structure containing voids.
Further, the pre-magnesia process specifically includes the following steps:
(1) Weighing a certain amount of molten salt electrolyte, fully grinding and drying for later use;
(2) Weighing a certain amount of commercial SiO, wrapping the weighed SiO by using foam nickel, fixing the foam nickel on a molybdenum wire by using a molybdenum wire to serve as a self-made silicon oxide contact electrode, taking the self-made silicon oxide contact electrode as a cathode, taking a graphite crucible as an anode, and carrying out molten salt electrochemical uniform pre-magnesia under the conditions that the melting point of the molten salt electrolyte in the step (1) is higher than the electrolysis temperature and the proper electrolysis voltage;
(3) After the electrolysis is completed, a self-made contact electrode is put out from molten salt and cooled to room temperature under the protection of inert gas, residual molten salt and etching byproduct MgO are removed by cleaning after foam nickel and molybdenum wires are removed, cleaning and suction filtration collection are carried out again, and vacuum drying is carried out, so that the final product is the SiO (HEM-SiO) subjected to uniform electrochemical pre-magnesium.
Further, according to the technical scheme, in the step (1), the molten salt electrolyte is MgCl 2 Or contains MgCl 2 For example MgCl 2 、MgCl 2 -CaCl 2 、MgCl 2 -NaCl, or MgCl 2 -CaCl 2 -any of NaCl, etc.
Preferably, in the above technical solution, when the molten salt electrolyte is MgCl 2 -CaCl 2 -when NaCl, the MgCl 2 ，CaCl 2 And NaCl in a molar ratio of 2:1:1 to 0.5:1:1, more preferably 1:1:1, with a total of 100g.
Further, according to the technical scheme, the temperature adopted in the drying in the step (1) is 200 ℃, and the drying time is 12 hours.
Further, according to the technical scheme, the total amount of SiO in the step (2) is 1g.
Further, in the above technical solution, the size of the nickel foam in the step (2) is 4cm long, 4cm wide, and 1.7mm thick, and the PPI 110 is described.
Further, according to the technical scheme, in the step (2), the diameter of the Mo wire used for fixing is 0.1mm, and the diameter of the Mo wire used for conducting is 1mm.
Specifically, according to the technical scheme, the specific process of electrochemical uniform premagnesization of molten salt in the step (2) is as follows:
filling the molten salt electrolyte dried in the step (1) into a graphite crucible, transferring the graphite crucible into a quartz tube with one end closed, and heating the quartz tube under a protective atmosphere; the electrolysis adopts a two-electrode system, a graphite crucible is used as an anode, a self-made silicon oxide contact electrode is used as a cathode, molten salt in a molten state is used as electrolyte, and constant voltage electrolysis is adopted.
Preferably, according to the technical scheme, the quartz tube is 500mm long, 94mm in inner diameter and 3mm in wall thickness.
Preferably, in the above technical solution, the constant voltage used in the electrolysis is 2.0-2.8V, preferably 2.5V.
Preferably, according to the technical scheme, the electrolysis time is 0.5-2 h, preferably 1h.
Preferably, in the above technical solution, the inert gas is Ar gas.
Preferably, in the above technical solution, the temperature of the molten salt electrolysis process is 600-950 ℃, preferably 850 ℃.
Further, according to the technical scheme, deionized water and dilute hydrochloric acid are adopted for cleaning and removing residual molten salt in the step (3), wherein: the dilute hydrochloric acid concentration was 0.1M.
A second object of the present application is to provide a uniform electrochemical pre-magnesian SiO prepared by the above method.
The third object of the application is to provide the application of the uniform electrochemical pre-magnesium SiO prepared by the method in the cathode of the lithium ion battery.
The application relates to a lithium ion battery cathode which comprises a silicon-containing active substance, a conductive agent and a binder, wherein the silicon-containing active substance is uniform electrochemical pre-magnesium SiO prepared by the method.
Compared with the prior art, the preparation method of the uniform electrochemical magnesium SiO with the micro/nano hierarchical structure characteristic and the application of the uniform electrochemical magnesium SiO in the lithium ion battery cathode have the following advantages and beneficial effects:
(1) Compared with other pre-lithiation and pre-magnesia reaction methods adopting metallic lithium, magnesium and lithiate, the environment of pre-magnesia adopting molten salt electrochemistry does not need a harsh environment, and only needs molten salt electrochemistry reaction for 1h at 850 ℃ under argon environment.
(2) Compared with other premagnesized silicon oxide materials, the silicon oxide which is premagnesized by molten salt electrochemistry has the characteristics of multiple pores and can uniformly convert irreversible amorphous SiO in SiO 2 Conversion of the substrate to reversibly active Si and inactive Mg 2 SiO 4 Phase and MgSiO 3 The first coulomb efficiency of SiO is effectively improved, and the first mass specific capacity of SiO is not affected.
(3) The uniform electrochemical magnesium SiO has not only inactive Mg 2 SiO 4 And MgSiO 3 As a buffer substance, and also has a typical micro/nano hierarchical structure containing pores, the co-superposition of the two factors can effectively relieve the volume change in the lithium intercalation and deintercalation process, thereby improving the cycle stability of the lithium ion battery cathode material. The performance is far superior to commercial silica.
Drawings
The technical scheme of the embodiment of the application is further described in detail through the drawings and the embodiments.
FIG. 1 is an X-ray diffraction pattern of the material of example 1 of the present application, A-raw silica, B-sample of example 1 after 1h electrolysis at 2.5V voltage with deionized water, C-sample of example 1 after 1h electrolysis at 2.5V voltage with 0.1M dilute hydrochloric acid, i.e. uniform electrochemical magnesium SiO;
FIG. 2 is a Raman spectrum of the material of example 1 of the present application, A-raw silica, B-Raman spectrum of uniform electrochemical magnesium SiO prepared in example 1 of the present application;
FIG. 3 is a transmission electron microscope image of the original silica in example 1 of the present application;
FIG. 4 is a transmission electron microscope image of uniform electrochemical magnesium SiO prepared in example 1 of the present application;
FIG. 5 is a focused ion beam microscope image and the corresponding energy spectrum of uniform electrochemical magnesium SiO prepared in example 1 of the present application;
FIG. 6 is an X-ray diffraction pattern of 2.5V-1.5h of the magnesium SiO prepared in example 2 of the present application.
FIG. 7X-ray diffraction patterns of the magnesium products of comparative example 1, inventive example 1 and comparative example 2, wherein A-magnesium product of comparative example 1, B-magnesium product of inventive example 1, and C-magnesium product of comparative example 2.
FIG. 8 is a first charge-discharge curve of an active material// metal lithium battery, wherein A-commercial silicon oxide is used as the active material, B-example 1 produces 2.5V-1h of magnesium SiO as the active material, and C-example 2 produces 2.5V-1.5h of magnesium SiO as the active material;
FIG. 9 is the cycling stability of an active material// lithium metal battery with A-commercial silicon oxide as the active material, B-example 1 to produce 2.5V-1h of magnesium SiO as the active material, and C-example 2 to produce 2.5V-1.5h of magnesium SiO as the active material;
Detailed Description
Embodiments of the present application will be described in detail below with reference to the accompanying drawings. The present embodiment is implemented on the premise of the technical scheme of the present application, and a detailed implementation and a specific operation process are provided, but the protection scope of the present application is not limited to the following embodiments.
Various modifications to the precise description of the application will be readily apparent to those skilled in the art from the information contained herein without departing from the spirit or scope of the appended claims. It is to be understood that the scope of the application is not limited to the defined processes, properties or components, as these embodiments, as well as other descriptions, are merely illustrative of specific aspects of the application. Indeed, various modifications of the embodiments of the application which are obvious to those skilled in the art or related fields are intended to be within the scope of the following claims.
For a better understanding of the present application, and not to limit its scope, all numbers expressing quantities, percentages, and other values used in the present application are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated otherwise, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. Each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
The application uses commercial silica with a size particle size of about 5 microns as a precursor, preferably MgCl 2 -CaCl 2 -NaCl as electrolyte, using a double electrode system, wherein a graphite crucible as anode, silica as cathode, prepared by scalable fused salt electrolysis, based on oxygen ions in MgCl 2 And CaCl 2 Significantly different solubilities in molten salts, in MgCl 2 -CaCl 2 In the ternary fused salt system of NaCl, the silicon oxide is electrochemically converted into Si and SiO x Uniformly distributed Mg 2 SiO 4 The uniform pre-magnesia of SiO particles is realized by adopting an electrochemical method, and the uniform electrochemical magnesia SiO with typical micro/nano hierarchical structure characteristics is prepared. The structure can effectively improve the first coulombic efficiency of the silicon oxide, and a large number of pores in the micro/nano hierarchical structure can relieve the volume change in the lithium removal/intercalation process, thereby improving the cycle performance of the silicon oxide serving as a cathode material of a lithium ion battery. The cathode material is subjected to electrochemical test at 0.1Ag -1 The first coulombic efficiency (ICE) under the current density can reach 81.1 percent, and the first discharge specific capacity is 2340.8mAh g -1 Even at 0.5A g -1 After 200 circles of current density circulation, the specific capacity still can reach 1010.6mAh g -1 Capacity retentionThe rate was 68.86%.
The starting materials used in the examples described below, unless otherwise specified, were all considered to be commercially available.
The particle size of the commercially available silica (CAS No. 10097-28-6) in the following examples of the present application was about 5 μm. The parameters of the silica provided are merely illustrative of the operability of the embodiment for uniformly pre-magnesia of SiO based molten salt electrolysis systems. The preparation of uniform electrochemical magnesium SiO by using silicon oxides with different specifications as starting materials falls into the scope of the authority protection of the application.
Example 1
The method for uniformly pre-magnesia treating the silicon oxide anode material in the embodiment comprises the following steps:
(1) Weighing MgCl with the total weight of 100g and the molar ratio of 1:1:1 2 、CaCl 2 And NaCl as an electrolyte, were poured into a mortar for thorough mixing and grinding, and after grinding, were transferred into a graphite crucible having a height of 80mm, an inner diameter of 65mm and a wall thickness of 5mm, and dried in a blast drying oven at 200℃for 12 hours to remove moisture.
(2) 1g of commercial silica was weighed out and used with a total area of 16mm 2 The foamed nickel (the foamed nickel has a size of 4cm long, 4cm wide, 1.7mm thick, PPI 110) was wrapped around the silicon oxide, and then was fixed on a Mo wire having a diameter of 1mm by using a Mo wire having a diameter of 0.1mm as a working electrode.
(3) Will be filled with MgCl 2 -CaCl 2 Placing graphite crucible of NaCl electrolyte into a quartz tube with a length of 500mm and a section of closed, vertically placing the quartz tube in a pit furnace, heating to 850 ℃, and preserving heat at 850 ℃ for 10min until MgCl is obtained 2 -CaCl 2 Inserting a working electrode into an electrolyte after NaCl is completely melted, carrying out 2.5V constant voltage electrolysis for 1h, recording a current-time curve in the electrolysis process by a computer, extracting the working electrode from the electrolyte after the electrolysis is completed, naturally cooling the working electrode to room temperature in Ar, carefully removing foam nickel and molybdenum wires, soaking the working electrode with deionized water and 0.1M dilute hydrochloric acid to remove residual salt and electrolysis byproducts MgO, washing and filtering a sample, and vacuum drying the sample at 60 ℃ for 12h to obtain the nano-zinc-manganese dioxide electrolyte2.5V-1h of magnesium SiO, namely uniform electrochemical magnesium SiO with micro/nano hierarchical structure characteristics.
The curve a in fig. 1 shows an X-ray diffraction pattern of the original silica, and it is understood that the silica has a typical amorphous X-ray diffraction peak. The curve B in FIG. 1 shows the X-ray diffraction pattern of the material obtained by cleaning with deionized water after SiO electrolysis in example 1 of the present application. The curve C in FIG. 1 shows the material obtained by removing MgO as a by-product after SiO electrolysis in example 1 of the present application by soaking in dilute hydrochloric acid for 30min after washing with deionized water, i.e. uniform electrochemical magnesium SiO. From the figure, it can be seen that amorphous silicon oxide is converted into crystalline Si, mgO, and Mg after electrolysis 2 SiO 4 Phase and small amount of MgSiO 3 And (3) removing MgO as a byproduct by the dilute hydrochloric acid to obtain a final product. FIG. 2 is a comparison of Raman spectra of SiO and uniform electrochemical magnesium SiO, showing that the uniform electrochemical magnesium SiO also has the characteristics of partial amorphous Si, indicating that more than Si and Mg are present in the uniform electrochemical magnesium SiO body 2 SiO 4 Phase, also SiO x The phases are present. Fig. 3 and 4 are respectively a transmission electron microscope image of original SiO and uniform electrochemical magnesium SiO, and it can be seen from the image that the primary particle size of SiO is about 5 μm, and after electrochemical magnesium, the microstructure is converted into a typical micro/nano hierarchical structure, specifically, micro secondary particles formed by fusing nano particles, and the nano particles and the like contain a large number of pores, which can effectively relieve the volume change in the lithium removal/intercalation process. Fig. 5 is a focused ion beam microscope (FIB-SEM) image and an energy spectrum of the enantiomer of uniform electrochemical magnesium SiO, and typical uniform electrochemical magnesium SiO particles were cut with focused Ga ions to analyze their microstructure and internal element distribution, which demonstrated that the internal silicon, magnesium, and oxygen elements were all uniformly distributed. By combining the above, the SiO after molten salt electrolysis has evenly distributed Si, siO x ，Mg 2 SiO 4 The phase and the typical micro-nano hierarchical structure containing gaps can effectively relieve the volume change in the lithium intercalation and deintercalation process, and are favorable for being used as a lithium ion battery anode material.
Example 2
The method for uniformly pre-magnesia treating the silicon oxide anode material in the embodiment comprises the following steps:
(1) 100g of MgCl in a molar ratio of 1:1:1 are weighed out 2 、CaCl 2 And NaCl as an electrolyte, were poured into a mortar for thorough mixing and grinding, and after grinding, were transferred into a graphite crucible having a height of 80mm, an inner diameter of 65mm and a wall thickness of 5mm, and dried in a blast drying oven at 200℃for 12 hours to remove moisture.
(2) 1g of commercial silica was weighed out and used with a total area of 16mm 2 The foamed nickel (the foamed nickel has a size of 4cm long, 4cm wide, 1.7mm thick, PPI 110) was wrapped around the silicon oxide, and then was fixed on a Mo wire having a diameter of 1mm by using a Mo wire having a diameter of 0.1mm as a working electrode.
(3) Will be filled with MgCl 2 -CaCl 2 Placing graphite crucible of NaCl electrolyte into a quartz tube with a length of 500mm and a section of closed, vertically placing the quartz tube in a pit furnace, heating to 850 ℃, and preserving heat at 850 ℃ for 10min until MgCl is obtained 2 -CaCl 2 After the NaCl is completely melted, a working electrode is inserted into an electrolyte, 2.5V constant voltage electrolysis is carried out on the electrolyte for 1.5 hours, a current-time curve in the electrolysis process is recorded by a computer, after the electrolysis is completed, the working electrode is lifted out of the electrolyte and naturally cooled to room temperature in Ar, then foam nickel and molybdenum wires are carefully removed, deionized water is used for soaking 0.1M dilute hydrochloric acid to remove residual salt and electrolysis byproducts MgO, and then a sample is washed, filtered and dried in vacuum at 60 ℃ for 12 hours, so that 2.5V-1.5 hours of magnesium SiO is obtained.
FIG. 6 is an X-ray diffraction pattern of example 2, showing that Mg in the composition thereof 2 SiO 4 Weaker than 2.5V electrolysis for 1h due to the prolonged electrolysis time leading to SiO in the SiO body 2 Gradually decreasing to be incapable of reacting with MgO generated in situ in the electrolytic process to generate Mg 2 SiO 4 And (3) phase (C).
Comparative example 1
A method for uniformly pre-magnesia treating a silicon oxide anode material of the comparative example, comprising the steps of:
(1) Weighing MgCl with the total weight of 100g and the molar ratio of 1:1:1 2 、CaCl 2 And NaCl as electrolyte, willIt was poured into a mortar for thorough mixing and grinding, after grinding it was transferred to a graphite crucible having a height of 80mm, an inner diameter of 65mm and a wall thickness of 5mm, and dried in a forced air drying oven at 200℃for 12 hours to remove moisture.
(2) 1g of commercial silica was weighed out and used with a total area of 16mm 2 The foamed nickel (the foamed nickel has a size of 4cm long, 4cm wide, 1.7mm thick, PPI 110) was wrapped around the silicon oxide, and then was fixed on a Mo wire having a diameter of 1mm by using a Mo wire having a diameter of 0.1mm as a working electrode.
(3) Will be filled with MgCl 2 -CaCl 2 The graphite crucible of NaCl electrolyte is placed in a quartz tube which is 500mm long and is closed, the quartz tube is vertically placed in a pit furnace and heated to 850 ℃, and the temperature is kept at 850 ℃ for 10min until MgCl is obtained 2 -CaCl 2 After the NaCl is completely melted, the working electrode is stretched into the electrolyte, 2.2V constant voltage electrolysis is carried out for 1h, a current-time curve in the electrolysis process is recorded by a computer, after the electrolysis is completed, the working electrode is lifted out of the electrolyte, the working electrode is naturally cooled to room temperature in Ar, then foam nickel and molybdenum wires are carefully removed, the residual salt is removed by soaking in deionized water, then the sample is washed and filtered, and vacuum drying is carried out for 12h at 60 ℃ to obtain 2.2V-1h magnesium SiO.
Comparative example 2
A method for uniformly pre-magnesia treating a silicon oxide anode material of the comparative example, comprising the steps of:
(1) Weighing MgCl with the total weight of 100g and the molar ratio of 1:1:1 2 、CaCl 2 And NaCl as an electrolyte, were poured into a mortar for thorough mixing and grinding, and after grinding, were transferred into a graphite crucible having a height of 80mm, an inner diameter of 65mm and a wall thickness of 5mm, and dried in a blast drying oven at 200℃for 12 hours to remove moisture.
(2) 1g of commercial silica was weighed out and used with a total area of 16mm 2 The foamed nickel (the foamed nickel has a size of 4cm long, 4cm wide, 1.7mm thick, PPI 110) was wrapped around the silicon oxide, and then was fixed on a Mo wire having a diameter of 1mm by using a Mo wire having a diameter of 0.1mm as a working electrode.
(3) Will be filled with MgCl 2 -CaCl 2 The graphite crucible of NaCl electrolyte is placed in a quartz tube which is 500mm long and is closed, the quartz tube is vertically placed in a pit furnace and heated to 850 ℃, and the temperature is kept at 850 ℃ for 10min until MgCl is obtained 2 -CaCl 2 After the NaCl is completely melted, the working electrode is stretched into the electrolyte, 2.8V constant voltage electrolysis is carried out on the working electrode for 1h, a current-time curve in the electrolysis process is recorded by a computer, after the electrolysis is completed, the working electrode is lifted out of the electrolyte, the working electrode is naturally cooled to room temperature in Ar, then foam nickel and molybdenum wires are carefully removed, the residual salt is removed by soaking in deionized water, and then the sample is washed, filtered and dried in vacuum for 12h at 60 ℃ to obtain 2.8V-1h magnesium SiO.
The graph A, B, C in FIG. 7 shows the X-ray diffraction patterns of the magnesium-based products of comparative example 1, inventive example 1 and comparative example 2, respectively. From the figure, the composition of the magnesium product under different electrolysis conditions is significantly different, and the MgO phase is significantly reduced at a low electrolysis voltage of 2.2V, which means that the electrolysis efficiency is reduced, the net rate of O ion generation is reduced, and the yield of MgO generated by Mg ions in the molten salt is reduced. While at a high electrolysis voltage of 2.8V Mg is generated 2 Si phase, since the electrolysis voltage of 2.8V has exceeded MgCl 2 The decomposition voltage of the molten salt at 850 ℃.
Application example 1
(1) The uniform electrochemical magnesium SiO (as active substance), conductive agent (SP) and binder (sodium alginate) prepared in example 1 are mixed according to the mass ratio of 8:1:1, uniformly mixing and grinding, coating on a copper foil, and drying at 60 ℃ for 12 hours. A polypropylene film (Celgard 2400) was used as a separator, a metal lithium foil was used as a counter electrode, and 1M lithium hexafluorophosphate (LiPF) 6 ) Ethylene Carbonate (EC) dimethyl carbonate (DMC) and diethyl carbonate (DEC) (1:1:1, v:v:v) 10% fluoroethylene carbonate (FEC) is added into the mixed solution as electrolyte, the complete CR2032 button battery is assembled. The electrode was tested for electrochemical performance using the constant current charge-discharge technique (GCD). The voltage window is 0.01-1.5V, and the test current density is 0.1A g -1 And 0.5Ag -1 。
Application example 2
(1) 2.5V-1.5 obtained in example 2The mass ratio of the h magnesium SiO (serving as an active substance) to the conductive agent (SP) to the binder (sodium alginate) is 8:1:1, uniformly mixing and grinding, coating on a copper foil, and drying at 60 ℃ for 12 hours. A polypropylene film (Celgard 2400) was used as a separator, a metal lithium foil was used as a counter electrode, and 1M lithium hexafluorophosphate (LiPF) 6 ) Ethylene Carbonate (EC) dimethyl carbonate (DMC) and diethyl carbonate (DEC) (1:1:1, v:v:v) 10% fluoroethylene carbonate (FEC) is added into the mixed solution as electrolyte, the complete CR2032 button battery is assembled. The electrode was tested for electrochemical performance using the constant current charge-discharge technique (GCD). The voltage window is 0.01-1.5V, and the test current density is 0.1Ag -1 And 0.5Ag -1 。
Comparative example 1 was used
(1) The mass ratio of the commercial silicon oxide (as an active substance) to the conductive agent (SP) to the binder (sodium alginate) is 8:1:1, uniformly mixing and grinding, coating on a copper foil, and drying at 60 ℃ for 12 hours. The membrane is made of polypropylene film (Celgard 2400), the counter electrode is made of metal lithium sheet, and the 1M lithium hexafluorophosphate (LiPF) 6 ) Ethylene Carbonate (EC) dimethyl carbonate (DMC) and diethyl carbonate (DEC) (1:1:1, v:v:v) 10% fluoroethylene carbonate (FEC) is added into the mixed solution as electrolyte, the complete CR2032 button battery is assembled. The electrode was tested for cycling performance using constant current charge-discharge (GCD). The voltage window is 0.01-1.5V, and the test current density is 0.1Ag -1 And 0.5Ag -1 。
FIG. 8 shows commercial silica, siO 2.5V-1h from example 1, i.e., uniform electrochemical SiO 2.5V-1.5h from example 2 as negative electrode active material in 0.1Ag -1 As can be seen from the graph, the initial coulombic efficiencies of the silicon oxide, the uniform electrochemical magnesium SiO and the 2.5V-1.5h magnesium SiO are 59.7%,81.1%,82.9% and the initial specific discharge capacities are 2222.5mAh g respectively -1 ,2340.8mAh g -1 ,2564.0mAh g -1 . The initial coulombic efficiencies of uniform electrochemical magnesium SiO and 2.5V-1.5h magnesium SiO as high as 81.1% and 82.9% can be attributed to the irreversible active amorphous SiO in the SiO body 2 The substrate being electrochemically converted into reversibilitySi and inactive Mg of (2) 2 SiO 4 And (3) phase (C). And the first effect and the first discharge specific capacity can be continuously improved along with the extension of the electrolysis time. FIG. 9 shows commercial silica, siO 2.5V-1h from example 1, i.e., uniform electrochemical SiO 2.5V-1.5h from example 2 as negative electrode active material in 0.1Ag -1 Activated at a low current density for 3 cycles at 0.5Ag -1 Cycling stability of 200 cycles under current density, after 200 cycles, specific discharge capacities of silica, uniform electrochemical magnesium SiO and 2.5V-1.5h magnesium SiO are 570.1mAh g respectively -1 ,1010.6mAh g -1 ,804.5mAh g -1 . As is clear from the graph, the cycle performance of SiO after the magnesium treatment is also greatly improved, but the longer the electrolysis time is, the cycle performance is rather deteriorated, because excessive magnesium treatment can cause the SiO remaining in the magnesium treated SiO body x And Mg (magnesium) 2 SiO 4 And less, thereby lacking buffering of inactive substances.
In summary, siO which is electrolyzed for 1h under the electrolysis voltage of 2.5V and is uniformly electrochemically magnesium-plated has excellent electrochemical performance and has better application prospect.
Claims (8)
1. A method for uniformly pre-magnesian anode material, which is characterized in that: pre-magnesian treatment is carried out on SiO by adopting a molten salt electrochemical method, and after the pre-magnesian treatment is finished, the SiO is converted into Si, electrochemical inactive magnesium silicate and a small amount of residual SiO x The method comprises the steps of carrying out a first treatment on the surface of the Wherein: the molten salt electrolyte adopted by the molten salt electrochemical method is MgCl 2 Or contains MgCl 2 Is a combination of molten salts; the voltage adopted by the molten salt electrochemical method is 2.0-2.8V.
2. The method according to claim 1, characterized in that: the method specifically comprises the following steps:
(1) Weighing a certain amount of molten salt electrolyte, fully grinding and drying for later use; the molten salt electrolyte is MgCl 2 Or contains MgCl 2 Is a combination of molten salts;
(2) Weighing a certain amount of commercial SiO, wrapping the weighed SiO by using foam nickel, fixing the foam nickel on a molybdenum wire by using a molybdenum wire to serve as a self-made silicon oxide contact electrode, taking the self-made silicon oxide contact electrode as a cathode, taking a graphite crucible as an anode, and carrying out molten salt electrochemical uniform pre-magnesia under the conditions that the melting point of the molten salt electrolyte in the step (1) is higher than the electrolysis temperature and the proper electrolysis voltage; the voltage adopted by the electrolysis is 2.0-2.8V;
(3) After the electrolysis is completed, a self-made contact electrode is put out from molten salt and cooled to room temperature under the protection of inert gas, residual molten salt and etching byproduct MgO are removed by cleaning after foam nickel and molybdenum wires are removed, cleaning and suction filtration collection are carried out again, and vacuum drying is carried out, so that the final product is the SiO subjected to uniform electrochemical pre-magnesium.
3. The method according to claim 2, characterized in that: when the molten salt electrolyte is MgCl 2 -CaCl 2 -when NaCl, the MgCl 2 ，CaCl 2 And NaCl in a molar ratio of 2:1:1 to 0.5:1:1.
4. The method according to claim 2, characterized in that: the electrolysis time in the step (2) is 0.5-2 h, and the electrolysis temperature is 600-950 ℃.
5. A homogeneously electrochemically pre-magneilized SiO prepared by the method of any one of claims 1-4.
6. The homogeneous electrochemical pre-magnesium SiO according to claim 5, wherein: the magnesium product is Mg 2 SiO 4 A small amount of MgSiO 3 And is uniformly distributed in SiO; the homogeneously premagnesized SiO prepared had a typical micro/nano hierarchical structure with voids.
7. Use of the homogeneously electrochemically pre-magneilized SiO prepared by the method of any one of claims 1-4 in a negative electrode of a lithium ion battery.
8. The utility model provides a lithium ion battery negative pole which characterized in that: comprising a silicon-containing active substance, a conductive agent, and a binder, wherein the silicon-containing active substance is a uniform electrochemically pre-magneilized SiO produced by the method of any one of claims 1-4.
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