Lithium negative electrode with lithium tin alloy protective layer, battery and preparation method

Abstract

The invention discloses a lithium negative electrode with a lithium-tin alloy protective layer, a battery and a preparation method, the lithium negative electrode with the lithium-tin alloy protective layer comprises a lithium negative electrode wafer and the lithium-tin alloy protective layer located on the surface of the lithium negative electrode wafer, and the lithium-tin alloy protective layer is formed by tin salt on the surface of the lithium negative electrode wafer through self-alloying reaction. According to the lithium negative electrode with the lithium-tin alloy protection layer, the battery and the preparation method, the preparation is simple and convenient, the cost is low, the lithium-tin alloy protection layer is directly generated on the surface of the lithium negative electrode wafer in situ through a self-alloying chemical treatment method, and the lithium-tin alloy protection layer has excellent lithium ion transmission performance and good interface stability and can be applied to lithium ion batteries. And uniform deposition of lithium is facilitated, corrosion of electrolyte can be avoided, and finally long-time stable circulation of the battery is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and more specifically, to a lithium negative electrode with a lithium-tin alloy protective layer, a battery and a preparation method thereof. Background Art

[0002] With the rapid growth of global demand for renewable energy and electric vehicles, improving the energy density of energy storage systems has become an important direction of battery technology research. Among the many negative electrode materials, metallic lithium has a low redox potential (-3.04V) and a very high theoretical specific capacity (3860mAhg -1 ), is widely considered to be an ideal candidate material to replace traditional graphite anode. However, lithium metal batteries (LMBs) still face many challenges in practical applications, especially the growth of lithium dendrites. The formation of such dendrites not only leads to the waste of effective energy, but also may cause battery short circuit and even trigger serious safety hazards such as thermal runaway. In addition, the high activity of lithium makes the electrolyte easy to degrade and form an unstable solid electrolyte interface (SEI), which significantly affects the cycle stability and service life of the battery.

[0003] In order to solve these key problems in lithium metal batteries, researchers have proposed a variety of coping strategies. In recent years, lithium alloy materials (such as Li-Mg, Li-B and Li-Al, etc.) have gradually attracted attention, especially lithium-tin alloys, which have become a new research hotspot due to their excellent lithium affinity, rapid lithium ion diffusion ability and moderate potential difference. Lithium-tin alloys can not only effectively improve the transmission performance of lithium ions, but also show good performance in the uniform deposition of lithium and interface stability, providing new ideas for solving the performance bottleneck of lithium metal batteries. However, these technologies are not only highly complex, but also often accompanied by high costs, which limits their large-scale application.

[0004] Therefore, there is an urgent need to provide a lithium negative electrode, a battery and a preparation method having a lithium-tin alloy protective layer that is easy to prepare and has low cost. Summary of the invention

[0005] In view of this, the present invention provides a lithium negative electrode with a lithium-tin alloy protective layer, a battery and a preparation method, so as to achieve simple preparation and low cost.

[0006] On the one hand, the present invention provides a lithium negative electrode with a lithium-tin alloy protective layer, including a lithium negative electrode disc and a lithium-tin alloy protective layer located on the surface of the lithium negative electrode disc, wherein the lithium-tin alloy protective layer is formed by a tin salt on the surface of the lithium negative electrode disc through a self-alloying reaction.

[0007] Optionally, the thickness of the lithium-tin alloy protective layer is positively correlated with the concentration of the tin salt.

[0008] Optionally, the thickness of the lithium-tin alloy protective layer is 40 μm-100 μm.

[0009] Optionally, the tin salt is one of stannous chloride, stannous chloride, stannous fluoride or stannous tetrafluoride.

[0010] On the other hand, the present invention also provides a method for preparing a lithium negative electrode having a lithium-tin alloy protective layer, comprising:

[0011] Providing lithium negative electrode discs;

[0012] Preparing a tin salt solution, comprising: dissolving a tin salt in a first solvent, and stirring the solvent to uniformly prepare a tin salt solution of a certain concentration, wherein the first solvent does not react with lithium metal and is volatile;

[0013] The tin salt and lithium undergo a self-alloying reaction, comprising: applying the tin salt solution dropwise on the surface of the lithium negative electrode disc to undergo a self-alloying reaction at room temperature;

[0014] Obtaining the lithium-tin alloy protective layer comprises: standing the mixture until the first solvent is completely volatilized, thereby obtaining the lithium-tin alloy protective layer.

[0015] Optionally, the steps of preparing the tin salt solution, the step of self-alloying the tin salt with lithium, and the step of obtaining the lithium-tin alloy protective layer are all completed in a glove box, and the water and oxygen contents in the glove box are controlled within 0.1 ppm.

[0016] Optionally, the first solvent includes tetrahydrofuran, and the molar concentration of the tin salt in the tetrahydrofuran is 0.1 mol / L-0.5 mol / L.

[0017] Optionally, in the self-alloying reaction between the tin salt and lithium, 50 μL-60 μL of the tin salt solution is dripped onto the surface of the lithium negative electrode disc, and the diameter of the lithium negative electrode disc is 12 mm-16 mm.

[0018] Optionally, the self-alloying reaction time at room temperature is 5 min-10 min;

[0019] And / or, the standing time is 10 min-20 min.

[0020] On the other hand, the present invention provides a lithium battery, comprising a lithium negative electrode, an electrolyte, a separator and a lithium positive electrode, wherein the lithium negative electrode is prepared by the above-mentioned preparation method.

[0021] Compared with the prior art, the lithium negative electrode, battery and preparation method with a lithium-tin alloy protective layer provided by the present invention achieve at least the following beneficial effects:

[0022] The lithium negative electrode, battery and preparation method with a lithium-tin alloy protective layer provided by the present invention are simple to prepare and low in cost. The lithium-tin alloy protective layer is directly generated in situ on the surface of the lithium negative electrode disc by a self-alloying chemical treatment method. The lithium-tin alloy protective layer has excellent lithium ion transmission performance and good interface stability, which not only helps the uniform deposition of lithium but also avoids corrosion of the electrolyte, and finally realizes a long-term stable cycle of the battery. In addition, this preparation method is not only applicable to lithium metal negative electrodes, but also provides a new idea for the protection of other metal negative electrodes such as sodium and potassium, and has a wide range of application potential and significant cost-effectiveness.

[0023] Of course, any product implementing the present invention does not necessarily need to achieve all of the technical effects described above at the same time.

[0024] Further features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments of the present invention with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0026] Figure 1 It is a flow chart of a method for preparing a lithium negative electrode with a lithium-tin alloy protective layer provided by the present invention;

[0027] Figure 2 It is a cross-sectional scanning electron microscope image of the lithium-tin alloy protective layer generated by the reaction of stannous chloride solutions with different concentrations (Figures ac are 0.1M, 0.2M and 0.3M respectively);

[0028] Figure 3 It is the electrochemical impedance spectrum of the symmetrical battery without lithium-tin alloy protective layer and the symmetrical battery with lithium-tin alloy protective layer after standing for 12 hours (where a is a partial enlarged view of b);

[0029] Figure 4 This is the long cycle diagram of a symmetrical battery without a lithium-tin alloy protective layer and with a lithium-tin alloy protective layer. DETAILED DESCRIPTION

[0030] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

[0031] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0032] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

[0033] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0034] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0035] The present invention provides a lithium negative electrode with a lithium-tin alloy protective layer, comprising a lithium negative electrode disc and a lithium-tin alloy protective layer located on the surface of the lithium negative electrode disc, wherein the lithium-tin alloy protective layer is formed by a tin salt on the surface of the lithium negative electrode disc through a self-alloying reaction.

[0036] Lithium anode is an important component of lithium-ion battery. It has high energy density and low electrode potential, and is the key to achieving high energy output in lithium-ion battery. As the physical form of lithium anode, lithium anode disc plays the role of storing and releasing lithium ions in lithium-ion battery.

[0037] In the present invention, the lithium-tin alloy protective layer is an alloy layer located on the surface of the lithium negative electrode disc, which is formed by a tin salt on the surface of the lithium negative electrode disc through a self-alloying reaction. The formation of the lithium-tin alloy protective layer is based on the principle of self-alloying reaction. Under normal temperature conditions, the tin salt reacts with the lithium on the surface of the lithium negative electrode disc to generate a lithium-tin alloy, which is deposited on the surface of the lithium negative electrode disc to form a protective layer. The preparation method is simple and low in cost. The lithium-tin alloy protective layer can improve the interfacial stability between the lithium negative electrode and the electrolyte, reduce the interfacial reaction of the lithium negative electrode during the charge and discharge process, and thus improve the cycle life of the battery. It is understandable that lithium dendrites are one of the main causes of short circuits and safety hazards in lithium-ion batteries. The lithium-tin alloy protective layer can inhibit the growth of lithium dendrites on the surface of the lithium negative electrode, which is of great significance for improving the safety and stability of lithium-ion batteries. Of course, the lithium-tin alloy protective layer can significantly improve the key indicators of the lithium-ion battery, such as the cycle performance, rate performance and energy density, thanks to the protective effect of the protective layer on the lithium negative electrode, which reduces the loss and damage of the lithium negative electrode during the charge and discharge process.

[0038] Optionally, the thickness of the lithium-tin alloy protective layer is positively correlated with the concentration of the tin salt solution.

[0039] The higher the concentration of the tin salt solution, the more tin ions there are per unit volume, and the more opportunities there are for self-alloying reactions with lithium atoms on the surface of the lithium negative electrode disc. The increase in reaction rate accelerates the deposition of lithium-tin alloy on the surface of the lithium negative electrode disc, thereby increasing the thickness of the lithium-tin alloy protective layer to a certain extent. In addition, within a certain concentration range, the higher the concentration of the tin salt solution, the more lithium-tin alloy is deposited on the surface of the lithium negative electrode disc through self-alloying reactions, and the increase in the deposition amount is directly reflected in the increase in the thickness of the protective layer.

[0040] Optionally, the thickness of the lithium-tin alloy protective layer is 40 μm-100 μm.

[0041] It should be noted that a thicker lithium-tin alloy protective layer can more effectively inhibit the growth of lithium dendrites, thereby increasing the cycle life of the battery. However, the thickness of the lithium-tin alloy protective layer cannot be too thick. An overly thick protective layer will also increase the internal resistance of the battery and affect the diffusion rate of lithium ions, thereby reducing the rate performance of the battery to a certain extent. In the present invention, the thickness of the lithium-tin alloy protective layer is 40μm-100μm, for example, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, and of course, it can also be any value between 40μm-100μm, which can effectively inhibit the growth of lithium dendrites and will not increase the internal resistance of the battery, which is beneficial to improving the cycle performance and rate performance of lithium-ion batteries.

[0042] Optionally, the tin salt is one of stannous chloride, stannous chloride, stannous fluoride or stannous tetrafluoride.

[0043] Stannous chloride, tin tetrachloride, stannous fluoride and tin tetrafluoride can all be used as sources of tin salts for forming a lithium-tin alloy protective layer. These tin salts can form a protective lithium-tin alloy layer by undergoing a self-alloying reaction with lithium on the surface of the lithium negative electrode.

[0044] The following Examples 1 to 3 are schematically illustrated by taking stannous chloride as an example of tin salt. Tin tetrachloride, stannous fluoride and tin tetrafluoride also undergo self-alloying reaction with lithium metal to generate lithium-tin alloy, which is the same as the principle of stannous chloride and will not be described in detail in the present invention.

[0045] Stannous chloride (SnCl 2 ) can form a lithium-tin alloy by self-alloying with lithium (Li). This reaction involves lithium being embedded in the stannous chloride lattice and reacting with it, first forming metallic tin and lithium chloride, and then the metallic tin further reacts with lithium to form a lithium-tin alloy. The chemical reaction formula is:

[0046] 1. Lithium is embedded in stannous chloride and reacts with it to produce metallic tin and lithium chloride:

[0047] SnCl 2 +2Li→Sn+2LiCl

[0048] 2. The generated metallic tin further reacts with lithium to form a lithium-tin alloy (with Li 4 Sn as an example):

[0049]

[0050] It should be noted that these reactions are simplified representations and the actual reactions may be more complicated.

[0051] On the other hand, the present invention also provides a method for preparing a lithium negative electrode having a lithium-tin alloy protective layer, referring to Figure 1 , Figure 1 A flow chart of a method for preparing a lithium negative electrode having a lithium-tin alloy protective layer provided by the present invention comprises:

[0052] S1, providing lithium negative electrode disc;

[0053] S2, preparing a tin salt solution, comprising: dissolving the tin salt in a first solvent, and stirring to uniformly prepare a tin salt solution of a certain concentration, wherein the first solvent does not react with lithium metal and is volatile;

[0054] S3, the tin salt and lithium undergo a self-alloying reaction, including: applying a tin salt solution dropwise to the surface of the lithium negative electrode disc, and undergoing a self-alloying reaction at room temperature;

[0055] S4, obtaining a lithium-tin alloy protective layer, including: standing still until the first solvent is completely volatilized, thereby obtaining the lithium-tin alloy protective layer.

[0056] In the present invention, a self-alloying reaction is carried out between tin salt and lithium, and an alloying reaction can occur spontaneously, and a lithium-tin alloy protective layer can be generated at room temperature without harsh conditions, and the method is simple and low in cost.

[0057] Optionally, the steps of preparing the tin salt solution, the step of self-alloying the tin salt with lithium, and the step of obtaining the lithium-tin alloy protective layer are all completed in a glove box, and the water and oxygen contents in the glove box are controlled within 0.1 ppm.

[0058] It should be noted that metallic lithium is very active and can react with air at room temperature, so the water and oxygen content needs to be strictly controlled to ensure that metallic lithium does not react with air, but instead undergoes a self-alloying reaction with tin salts. Therefore, the above steps all need to be completed in a glove box, and the water and oxygen content must be strictly controlled to ensure that metallic lithium does not react with air.

[0059] Optionally, the first solvent includes tetrahydrofuran, and the molar concentration of the tin salt in tetrahydrofuran is 0.1 mol / L-0.5 mol / L.

[0060] Of course, the first solvent is not limited to tetrahydrofuran, as long as it does not react with lithium metal and is volatile, it is not specifically limited here. For the solubility of the tin salt solution, optionally, the molar concentration of the tin salt in tetrahydrofuran can be 0.1mol / L, 0.2mol / L, 0.5mol / L, and self-alloying reaction occurs with lithium, and the reaction rate is moderate, the product performance is excellent, the operation is simple and the safety is good. The concentration of the tin salt is between 0.1mol / L-0.5mol / L, and the reaction rate of the tin salt with lithium is relatively moderate, neither too fast to cause the reaction to be difficult to control, nor too slowly to affect the production efficiency, and the moderate reaction rate is conducive to the uniform reaction and the uniform distribution of the product. The concentration of the tin salt is between 0.1mol / L-0.5mol / L, which helps to form a lithium-tin alloy with excellent performance, and the lithium-tin alloy has a high theoretical specific capacity. The excellent tin salt concentration can regulate the composition and structure of the lithium-tin alloy, thereby optimizing its cycle stability and rate performance. These electrochemical properties. Of course, the concentration of tin salt is between 0.1mol / L-0.5mol / L, and the tin salt solution may have better fluidity and stability, which is convenient for experimental operation and processing. In addition, the appropriate concentration can also help reduce waste and pollution and improve the utilization rate of raw materials.

[0061] Optionally, during the self-alloying reaction between tin salt and lithium, 50 μL-60 μL of tin salt solution is dripped onto the surface of a lithium negative electrode disc, and the diameter of the lithium negative electrode disc is 12 mm-16 mm.

[0062] The volume of tin salt is corresponding to the diameter of the lithium negative electrode disc. The larger the diameter of the lithium negative electrode disc, the larger the volume of the absorbed tin salt solution. The smaller the diameter of the lithium negative electrode disc, the smaller the volume of the absorbed tin salt solution. This ensures that a lithium-tin alloy protective layer with a thickness of 40μm-100μm is formed on the surface of the lithium negative electrode disc. As mentioned above, it can effectively inhibit the growth of lithium dendrites without increasing the internal resistance of the battery, which is beneficial to improving the cycle performance and rate performance of lithium-ion batteries.

[0063] In addition, the tin salt solution is dripped onto the surface of the lithium negative electrode disc. During the dripping process, the solution should be evenly distributed to avoid local concentrations that are too high or too low.

[0064] Optionally, the self-alloying reaction time at room temperature is 5 min-10 min;

[0065] And / or, the standing time is 10 min-20 min.

[0066] The time for the self-alloying reaction at room temperature can be 5min, 6min, 7min, 8min, 9min, 10min. The length of the self-alloying reaction time will affect the formation and performance of the alloy. Too short a time will lead to incomplete reaction, while too long a time may lead to overreaction or unnecessary by-products. The time for the self-alloying reaction at room temperature is 5min-10min, which can ensure complete reaction without generating unnecessary by-products.

[0067] The standing time can be 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, or any value between 10 min and 20 min. The purpose of standing is to volatilize the solvent tetrahydrofuran, and the standing time can stabilize the reaction product on the surface of the lithium negative electrode disc. The standing time helps to form a more uniform and stable lithium-tin alloy protective layer and reduce possible internal stress or defects.

[0068] On the other hand, the present invention provides a lithium battery, comprising a lithium negative electrode, an electrolyte, a separator and a lithium positive electrode, wherein the lithium negative electrode is prepared by the above preparation method.

[0069] Embodiment 1:

[0070] First, a lithium negative electrode disc is provided, and the diameter of the lithium negative electrode disc is 16 mm;

[0071] Secondly, prepare the lithium-tin alloy protective layer:

[0072] A 0.1M stannous chloride solution was prepared using tetrahydrofuran as solvent and stannous chloride as solute. Then, 50 μL of stannous chloride solution was dropped onto the surface of a 16 mm lithium sheet using a pipette in a glove box. At this time, the stannous chloride solution and metallic lithium rapidly self-alloyed. Then, the solution was allowed to stand for 20 minutes until the tetrahydrofuran was completely volatilized, and the desired lithium-tin alloy protective layer was finally formed.

[0073] Then, a button cell was prepared using a lithium negative electrode coated with a lithium-tin alloy protective layer.

[0074] Secondly, symmetrical battery assembly: assemble the battery in the glove box in the order of positive electrode shell, lithium positive electrode, electrolyte, diaphragm, electrolyte, lithium negative electrode, gasket, spring sheet, and negative electrode shell.

[0075] Finally, the symmetrical battery performance test: the electrochemical impedance spectroscopy test was performed using an electrochemical workstation (Shanghai Chenhua, CHI660E), with the frequency range set to 0.1Hz-105 Hz and the voltage perturbation set to 5mV. The CT2001A model equipment and test system of Wuhan Landian Company were used to perform constant current charge and discharge tests on the battery, and the 1mA cm -2 The charge and discharge current, 1mAh cm-2 The charge and discharge cut-off capacity.

[0076] Example 2

[0077] First, a lithium negative electrode disc is provided, and the diameter of the lithium negative electrode disc is 16 mm;

[0078] Secondly, prepare the lithium-tin alloy protective layer:

[0079] A 0.2M stannous chloride solution was prepared using tetrahydrofuran as solvent and stannous chloride as solute. Then, 50 μL of stannous chloride solution was dropped onto the surface of a 12 mm lithium sheet using a pipette in a glove box. At this time, the stannous chloride solution and metallic lithium rapidly self-alloyed. Then, the solution was allowed to stand for 10 minutes until the tetrahydrofuran was completely volatilized, and the desired lithium-tin alloy protective layer was finally formed.

[0080] Then, a button cell was prepared using a lithium negative electrode coated with a lithium-tin alloy protective layer.

[0081] Symmetrical battery assembly: Assemble the battery in the glove box in the order of positive electrode shell, lithium positive electrode, electrolyte, diaphragm, electrolyte, lithium negative electrode, gasket, spring sheet, and negative electrode shell.

[0082] Finally, the symmetrical battery performance test: the electrochemical impedance spectroscopy test was performed using an electrochemical workstation (Shanghai Chenhua, CHI660E), with the frequency range set to 0.1Hz-105 Hz and the voltage perturbation set to 5mV. The CT2001A model equipment and test system of Wuhan Landian Company were used to perform constant current charge and discharge tests on the battery, and the 1mA cm -2 The charge and discharge current, 1mAh cm -2 The charge and discharge cut-off capacity.

[0083] Example 3

[0084] First, a lithium negative electrode disc is provided, and the diameter of the lithium negative electrode disc is 16 mm;

[0085] Secondly, prepare the lithium-tin alloy protective layer:

[0086] A 0.5M stannous chloride solution was prepared using tetrahydrofuran as solvent and stannous chloride as solute. Then, 50 μL of stannous chloride solution was dropped onto the surface of a 13 mm lithium sheet using a pipette in a glove box. At this time, the stannous chloride solution and metallic lithium rapidly self-alloyed. Then, the solution was allowed to stand for 15 minutes until the tetrahydrofuran was completely volatilized, and the desired lithium-tin alloy protective layer was finally formed.

[0087] Then, a button cell was prepared using a lithium negative electrode coated with a lithium-tin alloy protective layer.

[0088] Symmetrical battery assembly: Assemble the battery in the glove box in the order of positive electrode shell, lithium positive electrode, electrolyte, diaphragm, electrolyte, lithium negative electrode, gasket, spring sheet, and negative electrode shell.

[0089] Finally, the symmetrical battery performance test: the electrochemical impedance spectroscopy test was performed using an electrochemical workstation (Shanghai Chenhua, CHI660E), with the frequency range set to 0.1Hz-105 Hz and the voltage perturbation set to 5mV. The CT2001A model equipment and test system of Wuhan Landian Company were used to perform constant current charge and discharge tests on the battery, and the 1mA cm -2 The charge and discharge current, 1mAh cm -2 The charge and discharge cut-off capacity.

[0090] Comparative Example 1:

[0091] The button cell was prepared using a bare lithium sheet without a lithium-tin alloy protective layer, and the diameter of the bare lithium sheet was 16 mm.

[0092] Symmetrical battery assembly: Assemble the battery in the glove box in the order of positive electrode shell, lithium sheet, electrolyte, diaphragm, electrolyte, lithium sheet, gasket, spring sheet, and negative electrode shell.

[0093] Symmetrical battery performance test: Electrochemical impedance spectroscopy was performed using an electrochemical workstation (Shanghai Chenhua, CHI660E). The frequency range was set to 0.1 Hz-105 Hz and the voltage disturbance was 5 mV. The CT2001A equipment and test system of Wuhan Blue Electric Company were used to perform constant current charge and discharge tests on the battery, and the 1 mA cm -2 The charge and discharge current, 1mAh cm -2 The charge and discharge cut-off capacity.

[0094] Experimental results:

[0095] The cross-sectional scanning electron microscope images of the lithium-tin alloy protective layers obtained in Examples 1 to 3 are shown in FIG. Figure 2 The electrochemical impedance spectra of the batteries prepared in Examples 1 to 3 above after standing for 12 hours are shown in Figure 3 The test results of the battery cycle performance obtained above are shown in Figure 4 . Figure 3 and Figure 4 In the figures, bare Li represents a comparative example, Li—Sn-0.1 represents Example 1, Li—Sn-0.2 represents Example 2, and Li—Sn-0.5 represents Example 3.

[0096] like Figure 2As shown, the cross-sectional scanning electron microscope images of the material indicate that the thicknesses of the lithium-tin alloy protective layers prepared from 0.1M, 0.2M, and 0.5M stannous chloride solutions are 40μm, 60μm, and 100μm, respectively, indicating that the higher the concentration of the tin salt solution, the thicker the prepared lithium-tin alloy protective layer.

[0097] like Figure 3 As shown, from the electrochemical impedance spectra of Examples 1-3 and Comparative Example 1, it can be seen that the interface resistance of the bare lithium sheet is as high as 173.4Ω after standing overnight. This is due to the active chemical properties of lithium, which causes it to continuously react with the electrolyte and form an SEI film (solid electrolyte interface film), and the continuous growth of the SEI film is not conducive to the rapid transmission of lithium ions at the interface. In contrast, the interface resistance of the lithium sheet coated with the lithium-tin alloy protective layer is much smaller than that of the bare lithium sheet. The interface resistance of the lithium-tin alloy protective layer is 15.8Ω, 8.1Ω and 7.1Ω respectively, which shows that the lithium-tin alloy protective layer not only prevents the lithium surface from directly contacting the electrolyte, but also provides an excellent lithium ion transmission channel.

[0098] like Figure 3 As shown, from the cycle performance diagrams of Examples 1-3 and Comparative Example 1, it can be seen that during the cycle, the active lithium not coated with the lithium-tin alloy protective layer causes the rapid growth of dendrites and the accumulation of dead lithium due to the continuous occurrence of side reactions and the continuous rupture and repair of the SEI film, and finally the battery fails in about 200 hours. The performance of the batteries coated with the lithium-tin alloy protective layer is improved, and they can cycle for 300 hours, 800 hours and 350 hours respectively. This shows that the lithium-tin alloy protective layer has an excellent lithium ion diffusion coefficient, which promotes the uniform deposition of lithium during the cycle; in addition, the lithium-tin alloy protective layer can also avoid the rupture of the SEI film due to volume expansion and stabilize the electrode / electrolyte interface. It is worth noting that the inventors found that the alloy protective layer of moderate thickness has the best protection effect on the lithium negative electrode. When the thickness of the alloy protective layer is too thin or too thick, its cycle life is far less than the optimal thickness. This is mainly due to the fact that the thin alloy protective layer is not very stable and easy to rupture, while the thick alloy protective layer affects the interface resistance and hinders the transmission of lithium ions.

[0099] In summary, by comparing the performance of the example battery with that of the comparative example battery, it can be learned that the prepared lithium-tin alloy protective layer has excellent lithium ion transmission performance and good interface stability, which not only helps to uniformly deposit lithium but also avoids corrosion of the electrolyte to achieve long-term stable cycle of the battery. Applying it to lithium metal secondary batteries can significantly improve the service life and safety of the battery.

[0100] It can be seen from the above embodiments that the lithium negative electrode, battery and preparation method with a lithium-tin alloy protective layer provided by the present invention achieve at least the following beneficial effects:

[0101] The lithium negative electrode, battery and preparation method with a lithium-tin alloy protective layer provided by the present invention are simple to prepare and low in cost. The lithium-tin alloy protective layer is directly generated in situ on the surface of the lithium negative electrode disc by a self-alloying chemical treatment method. The lithium-tin alloy protective layer has excellent lithium ion transmission performance and good interface stability, which not only helps the uniform deposition of lithium but also avoids corrosion of the electrolyte, and finally realizes a long-term stable cycle of the battery. In addition, this preparation method is not only applicable to lithium metal negative electrodes, but also provides a new idea for the protection of other metal negative electrodes such as sodium and potassium, and has a wide range of application potential and significant cost-effectiveness.

[0102] Although some specific embodiments of the present invention have been described in detail by way of example, it will be appreciated by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present invention. It will be appreciated by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A lithium negative electrode having a lithium-tin alloy protective layer, characterized in that: It comprises a lithium negative electrode disc and a lithium-tin alloy protective layer located on the surface of the lithium negative electrode disc. The lithium-tin alloy protective layer is formed by tin salt on the surface of the lithium negative electrode disc through self-alloying reaction.

2. The lithium negative electrode with a lithium-tin alloy protective layer according to claim 1, characterized in that: The thickness of the lithium-tin alloy protective layer is positively correlated with the concentration of the tin salt.

3. The lithium negative electrode with a lithium-tin alloy protective layer according to claim 2, characterized in that: The thickness of the lithium-tin alloy protective layer is 40 μm-100 μm.

4. The lithium negative electrode with a lithium-tin alloy protective layer according to claim 1, characterized in that: The tin salt is one of stannous chloride, stannous tetrachloride, stannous fluoride or stannous tetrafluoride.

5. A method for preparing a lithium negative electrode having a lithium-tin alloy protective layer, characterized in that: include: Providing lithium negative electrode discs; Preparing a tin salt solution, comprising: dissolving a tin salt in a first solvent, and stirring the solvent to uniformly prepare a tin salt solution of a certain concentration, wherein the first solvent does not react with lithium metal and is volatile; The tin salt and lithium undergo a self-alloying reaction, comprising: applying the tin salt solution dropwise on the surface of the lithium negative electrode disc to undergo a self-alloying reaction at room temperature; Obtaining the lithium-tin alloy protective layer comprises: standing the mixture until the first solvent is completely volatilized, thereby obtaining the lithium-tin alloy protective layer.

6. The preparation method according to claim 5, characterized in that: The steps of preparing the tin salt solution, the step of self-alloying the tin salt with lithium, and the step of obtaining the lithium-tin alloy protective layer are all completed in a glove box, and the water and oxygen contents in the glove box are controlled within 0.1 ppm.

7. The preparation method according to claim 5, characterized in that: The first solvent includes tetrahydrofuran, and the molar concentration of the tin salt in the tetrahydrofuran is 0.1 mol / L-0.5 mol / L.

8. The preparation method according to claim 5, characterized in that: During the self-alloying reaction between the tin salt and lithium, 50 μL-60 μL of the tin salt solution is dripped onto the surface of the lithium negative electrode disc, and the diameter of the lithium negative electrode disc is 12 mm-16 mm.

9. The preparation method according to claim 5, characterized in that: The time for the self-alloying reaction at room temperature is 5 min to 10 min; And / or, the standing time is 10 min-20 min.

10. A lithium battery, characterized in that: The invention comprises a lithium negative electrode, an electrolyte, a separator and a lithium positive electrode, wherein the lithium negative electrode is prepared by the preparation method according to any one of claims 5 to 9.

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