Lithium metal negative electrode, preparation method and lithium battery

Abstract

The present invention discloses a lithium metal negative electrode, a preparation method and a lithium battery. The lithium metal negative electrode comprises Li, LiM alloy, Li c X, LiY and Li a XY b , wherein M is a metal element, X is an oxygen element or a nitrogen element, and Y is a halogen; when X is an oxygen element, a=3, b=1, and c=2; when X is a nitrogen element, a=5, b=2, and c=3. The present invention introduces MXY material as an additive into lithium metal, and utilizes the reaction between MXY material and lithium metal to generate Li, LiM alloy, LiX, LiY, Li a XY b Unlike traditional mixed SEI, the mixture formed by the present invention is a homogeneous mixed phase that includes lithium metal. During the charge and discharge process, it can not only provide lithium ions, but also accelerate the rapid transmission of lithium ions at the interface as SEI, reduce interfacial polarization, and guide the uniform deposition of lithium ions, thereby improving the anti-dendrite ability.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode materials, and in particular relates to a lithium metal negative electrode, a preparation method and a lithium battery. Background Art

[0002] Lithium metal anode has a high theoretical specific capacity (3860 mAh g -1 ), low electrochemical redox potential (3.04 V vs SHE) and low density (0.53 g cm -3 ), is considered to be the "holy grail" of the next generation of secondary lithium battery negative electrode materials.

[0003] At present, there are still many problems with lithium metal batteries: after repeated charge and discharge of the battery, an inert SEI film grows on the surface of the lithium metal negative electrode, which seriously hinders the + The low transport rate at the interface causes lithium to nucleate and grow into lithium dendrites that pierce the electrolyte layer, causing short circuits and battery safety issues. Furthermore, lithium metal possesses the strongest reducibility. When lithium metal comes into contact with solid electrolytes (sulfides, halides, polymer electrolytes), chemical reactions of varying degrees occur. Driven by electrochemistry, these reactions generate large amounts of highly electronically conductive LiM alloys and M metals, accompanied by the formation of polysulfide interphases with low ionic conductivity.

[0004] In order to reduce interfacial polarization and inhibit lithium dendrites, the commonly used methods are alloying and surface passivation. For example, LiAl and LiIn alloys are prepared. However, alloying cannot effectively solve the dendrite problem. Pretreatment of the lithium metal surface is, to a certain extent, the simplest and most direct strategy. It only requires artificial intervention to pre-generate a layer of artificial SEI on the surface of the lithium metal. However, this layer of SEI is usually composed of lithium alloys and lithium salts. The SEI film modified on the surface of lithium metal will increase the interface impedance, resulting in obstruction of lithium ions and reducing the lithium ion transmission capacity at the interface. During the battery charging and discharging process, lithium ions have difficulty passing through the SEI film quickly, and grow on the electrolyte side, causing the battery to short-circuit. Summary of the Invention

[0005] In view of the above deficiencies in the prior art, the object of the present invention is to provide a lithium metal negative electrode, a preparation method and a lithium battery to solve the problem that the existing methods cannot simultaneously solve the problem of lithium dendrites and lithium ion transport capacity.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] In the first aspect, the present invention provides a lithium metal negative electrode comprising Li, LiM alloy, Li c X, LiY and Li a XY b, where M is a metal element, X is an oxygen element or a nitrogen element, and Y is a halogen; when X is an oxygen element, a=3, b=1, and c=2; when X is a nitrogen element, a=5, b=2, and c=3.

[0008] Preferably, M is selected from one or more of La-based elements, In, Al, Bi, Zr, Hf, Sn, and Ge.

[0009] In another aspect, the present invention provides a method for preparing a lithium metal negative electrode, comprising the following steps:

[0010] The lithium metal is heated and melted to obtain molten lithium liquid;

[0011] Additives are added to the molten lithium solution, the solution is kept warm for reaction, and after cooling, a lithium metal negative electrode is obtained; the additive is MXY, wherein M is a metal element, X is an oxygen element or a nitrogen element, and Y is a halogen.

[0012] Preferably, the additive is at least one of LaOCl, InOCl, BiOCl, and AlOCl.

[0013] Preferably, the additive is at least one of ZrNCl, SnNCl, HfNCl, and GeNCl.

[0014] Preferably, the amount of the additive added is 2-20% of the mass of the lithium metal, more preferably 10%.

[0015] Preferably, the temperature of the thermal insulation reaction is 200-350°C.

[0016] Preferably, the reaction time of the insulation reaction is 5-60 min, more preferably 30 min.

[0017] In a third aspect, the present invention provides a lithium battery, which is a lithium metal battery and includes the lithium metal negative electrode as described in the first aspect.

[0018] Preferably, the electrolyte of the lithium battery is Li 7-x PS 6-x Cl x (0.5≤x≤2), Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 、Li7P2S8I、Li 10 GeP2S 12 One or more of the following, the positive electrode material of the lithium battery is LiNi m Co n Mn z O2 (m + n + z =1).

[0019] The beneficial effects of the present invention are:

[0020] The present invention introduces MXY material as an additive into lithium metal, and utilizes MXY material to react with lithium metal to generate Li, LiM alloy, Li c X, LiY, Li a XY b The mixture of X and Y elements (i.e., O or N) and halogens creates a Li3OY or Li5NY2 solid electrolyte with high ion conductivity. Unlike traditional methods of forming an SEI layer on a lithium metal sheet, the mixture formed in this invention is a homogeneous mixed phase that includes lithium metal. During the charge and discharge process, it not only provides lithium ions but also acts as an SEI, accelerating the rapid transport of lithium ions at the interface, reducing interfacial polarization, and guiding the uniform deposition of lithium ions, thereby improving anti-dendrite properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings of the embodiments.

[0022] Figure 1 Cross-sectional SEM images of the negative electrodes prepared in Example 1 and Comparative Example 5 of the present application;

[0023] Figure 2 Cross-sectional SEM images of the negative electrodes prepared in Example 3 and Comparative Example 6 of the present application;

[0024] Figure 3 The symmetrical battery assembled with the negative electrode prepared in Example 1 of the present application was -2 Cycling performance diagram at current density of ;

[0025] Figure 4 The symmetrical battery assembled with the negative electrode prepared in Example 2 of the present application was -2 Cycling performance diagram at current density of ;

[0026] Figure 5 The symmetrical battery assembled with the negative electrode prepared in Example 3 of the present application was -2 Cycling performance diagram at current density of ;

[0027] Figure 6 The symmetrical battery assembled with the negative electrode prepared in Example 4 of the present application was -2 Cycling performance diagram at current density of ;

[0028] Figure 7 The symmetrical battery assembled with the negative electrode prepared in Comparative Example 1 of this application was -2Cycling performance diagram at current density of ;

[0029] Figure 8 The symmetrical battery assembled with the negative electrode prepared in Comparative Example 2 of this application was -2 Cycling performance diagram at current density of ;

[0030] Figure 9 The symmetrical battery assembled with the negative electrode prepared in Comparative Example 3 of this application is -2 Cycling performance diagram at current density of ;

[0031] Figure 10 The symmetrical battery assembled with the negative electrode prepared in Comparative Example 4 of this application was -2 Cycling performance diagram at current density of ;

[0032] Figure 11 The symmetrical battery assembled with the negative electrode prepared in Comparative Example 5 of this application is -2 Cycling performance diagram at current density of ;

[0033] Figure 12 The symmetrical battery assembled with the negative electrode prepared in Comparative Example 6 of this application was -2 Cycling performance diagram at current density of ;

[0034] Figure 13 Cycling performance diagram of a solid-state battery assembled with the negative electrode prepared in Example 1 of the present application at a rate of 1C;

[0035] Figure 14 Cycling performance diagram of a solid-state battery assembled with the negative electrode prepared in Example 2 of the present application at a rate of 1C;

[0036] Figure 15 Cycling performance diagram of a solid-state battery assembled with the negative electrode prepared in Example 3 of the present application at a rate of 1C;

[0037] Figure 16 Cycling performance diagram of a solid-state battery assembled with the negative electrode prepared in Example 4 of the present application at a rate of 1C;

[0038] Figure 17 Cycling performance diagram of a solid-state battery assembled with the negative electrode prepared in Comparative Example 1 of the present application at a rate of 1C;

[0039] Figure 18 Cycling performance diagram of a solid-state battery assembled with the negative electrode prepared in Comparative Example 2 of this application at a rate of 1C;

[0040] Figure 19Cycling performance diagram of a solid-state battery assembled with the negative electrode prepared in Comparative Example 3 of this application at a rate of 1C;

[0041] Figure 20 Cycling performance diagram of a solid-state battery assembled with the negative electrode prepared in Comparative Example 4 of this application at a rate of 1C;

[0042] Figure 21 For this application Figure 20 The charge and discharge curve of the solid-state battery in the 10th cycle. DETAILED DESCRIPTION

[0043] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0044] The embodiment of the present invention provides a lithium metal negative electrode, comprising Li, LiM alloy, Li c X, LiY and Li a XY b , where M is a metal element, X is an oxygen element or a nitrogen element, and Y is a halogen; when X is an oxygen element, a=3, b=1, and c=2; when X is a nitrogen element, a=5, b=2, and c=3.

[0045] In some preferred embodiments, M is selected from one or more of La-based elements, In, Al, Bi, Zr, Hf, Sn, and Ge. Y can be one or more of F, Cl, Br, and I.

[0046] The preparation method of the above-mentioned lithium metal negative electrode comprises the following steps: heating and melting lithium metal to obtain a molten lithium liquid; adding an additive to the molten lithium liquid, keeping the temperature at 200-350°C for a reaction for 5-60 minutes, preferably 30 minutes, and cooling to obtain a lithium metal negative electrode, wherein the additive is MXY, M is a metal element, X is an oxygen element or a nitrogen element, and Y is a halogen.

[0047] In some preferred embodiments, the additive is MOY, such as LaOCl, InOCl, BiOCl, AlOCl, or LaOF, InOF, BiOF, AlOF, or LaOBr, InOBr, BiOBr, AlOBr, etc.

[0048] In some preferred embodiments, the additive is MNY, such as ZrNCl, SnNCl, HfNCl, GeNCl, or ZrNBr, SnNBr, HfNBr, GeNBr, etc.

[0049] In some preferred embodiments, the amount of the additive added is 2-20% of the mass of the lithium metal, more preferably 10%.

[0050] The present invention is further described in detail below through specific examples.

[0051] Example 1

[0052] A lithium metal negative electrode, the preparation method is as follows:

[0053] Lithium metal is heated to a molten state at 280°C. Then, LaOCl, a 10% additive by weight of the lithium metal, is added to the molten lithium metal and allowed to react at this temperature for 30 minutes. This process forms a mixed SEI containing Li, LiLa, Li2O, LiCl, and Li3OCl. After cooling, a composite lithium metal anode is obtained. The resulting composite lithium metal anode is then rolled into a lithium metal foil of uniform thickness using a roller press.

[0054] Example 2

[0055] A lithium metal negative electrode, the preparation method is as follows:

[0056] Lithium metal is heated to a molten state at 280°C. LaOCl, a 20% additive by weight, is then added to the molten lithium metal and allowed to react at this temperature for 40 minutes. This process forms a mixed SEI containing Li, LiLa, Li₂O, LiCl, and Li₃OCl. After cooling, a composite lithium metal anode is obtained. The resulting composite lithium metal anode is then rolled into a lithium metal foil of uniform thickness using a roller press.

[0057] Example 3

[0058] A lithium metal negative electrode, the preparation method is as follows:

[0059] Lithium metal is heated to a molten state at 280°C. Then, a 10% by weight additive, ZrNCl, is added to the molten lithium metal and allowed to react at this temperature for 30 minutes. This process forms a mixed SEI containing Li, LiZr, Li3N, LiCl, and Li5NCl2. After cooling, a composite lithium metal anode is obtained. The resulting composite lithium metal anode is then rolled into a lithium metal foil of uniform thickness using a roller press.

[0060] Example 4

[0061] A lithium metal negative electrode, the preparation method is as follows:

[0062] Lithium metal is heated to a molten state at 200°C. Then, GaOF, a 10% lithium metal additive, is added to the molten lithium metal and allowed to react at this temperature for 30 minutes. This process forms a mixed SEI containing Li, LiGa, Li2O, LiF, and Li3OF. This is then cooled to produce a composite lithium metal anode. The resulting composite lithium metal anode is then rolled into a lithium metal foil of uniform thickness using a roller press.

[0063] Comparative Example 1

[0064] Compared with Example 1, the additive used in Comparative Example 1 is LaCl3.

[0065] A lithium metal negative electrode, the preparation method is as follows:

[0066] Lithium metal is heated to a molten state at 280°C. Then, LaCl3, a 10% additive by weight of the lithium metal, is added to the molten lithium metal and allowed to react at this temperature for 30 minutes. This process forms a mixed SEI containing Li, LiLa, and LiCl. Cooling this process yields a composite lithium metal anode. The resulting composite lithium metal anode is then rolled into a lithium metal foil of uniform thickness using a roller press.

[0067] Comparative Example 2

[0068] Compared with Example 3, the additive used in Comparative Example 2 is ZrCl4.

[0069] A lithium metal negative electrode, the preparation method is as follows:

[0070] Lithium metal is heated to a molten state at 280°C. Then, a 10% by weight additive, ZrCl₄, is added to the molten lithium metal and allowed to react at this temperature for 30 minutes. This process forms a mixed SEI containing Li, LiZr, and LiCl. The mixture is then cooled to produce a composite lithium metal anode. The resulting composite lithium metal anode is then rolled into a lithium metal foil of uniform thickness using a roller press.

[0071] Comparative Example 3

[0072] Compared with Example 4, the additive used in Comparative Example 3 is GaF3.

[0073] A lithium metal negative electrode, the preparation method is as follows:

[0074] Lithium metal is heated to a molten state at 200°C. Then, a 10% by weight additive, GaF3, is added to the molten lithium metal and allowed to react at this temperature for 30 minutes. The resulting composite lithium metal anode is then cooled and rolled into a lithium metal foil of uniform thickness using a roller press.

[0075] Comparative Example 4

[0076] Without any treatment, pure lithium metal is rolled into lithium metal foil with uniform thickness through a roller press.

[0077] Comparative Example 5

[0078] (1) LaOCl powder was ultrasonically dispersed in water. Then, the LaOCl suspension was added dropwise onto Cu foil and dried in an oven to form a LaOCl layer on the Cu foil. The loading of the LaOCl powder on the Cu foil was 1 mg cm -2 .

[0079] (2) The LaOCl-Cu was mechanically rolled together with lithium foil; during this period, LaOCl was transferred to the lithium foil and spontaneously reacted with the lithium metal surface; to make the reaction more complete, it was further heated at 200 °C; and a lithium metal anode protected by a mixed artificial interface film of LiLa alloy and Li3OCl solid electrolyte was obtained.

[0080] Comparative Example 6

[0081] (1) ZrNCl powder was ultrasonically dispersed in water. Then, the ZrNCl suspension was added dropwise onto Cu foil and dried in an oven to form a ZrNCl layer on the Cu foil. The loading amount of the ZrNCl powder on the Cu foil was 1 mg cm -2 .

[0082] (2) The ZrNCl-Cu was mechanically rolled together with lithium foil; during this period, the ZrNCl was transferred to the lithium foil and spontaneously reacted with the lithium metal surface; to make the reaction more complete, it was further heated at 200 °C; and a lithium metal anode protected by a mixed artificial interface film of LiZr alloy and Li5NCl2 solid electrolyte was obtained.

[0083] 1. SEM characterization

[0084] Figure 1 The cross-sectional SEM images of the negative electrodes prepared in Example 1 and Comparative Example 5; Figure 2 The cross-sectional SEM images of the negative electrodes prepared in Example 3 and Comparative Example 6 are shown; Figure 1 a is comparative example 5, b is example 1, Figure 2 a is comparative example 6, b is example 3. From SEM, it can be seen that the lithium metal negative electrode prepared by the present invention is composed of Li, LiM alloy, LiX, LiY, Li a XY b The lithium metal negative electrode prepared in comparative examples 5-6 is a double-layer structure, which is based on a lithium metal sheet and loaded with an artificial interface membrane composed of an alloy and a solid electrolyte.

[0085] 2. Battery Preparation and Performance Testing

[0086] (1) Preparation of symmetrical battery:

[0087] Weigh a certain amount of sulfide electrolyte Li in the glove box 5.5 PS 4.5 Cl 1.5 The sulfide electrolyte layer was formed by cold pressing in a mold. The pressure during molding was controlled between 100 MPa and 400 MPa. The lithium metal foils prepared in the examples and comparative examples were then attached to both sides of the sulfide electrolyte layer and pressure was applied at 10-100 MPa to obtain 8 symmetrical batteries. -2 The charge and discharge test was carried out at a current density of . Figures 3 to 12 and as shown in Table 1.

[0088] Table 1

[0089]

[0090] From Table 1 and Figures 3 to 12 It can be seen that the symmetrical battery assembled by the lithium metal negative electrode prepared in the embodiment of the present application has a lower polarization voltage, which means that the internal resistance of the battery is small and the electrode reaction is easier to proceed, thereby improving the energy conversion efficiency and stability of the battery. Compared with Example 3, the polarization voltage of Comparative Example 2 is significantly increased, and short circuit is prone to occur, indicating that the mixed SEI containing Li3N and Li5NCl2 formed by the reaction of the nitrogen element in the additive with the lithium metal can improve the anti-dendrite ability, accelerate the transmission rate of lithium ions, reduce interfacial polarization, and improve the safety of the battery. The lithium metal negative electrode of Comparative Example 4 that has not been modified is prone to lithium dendrites piercing the electrolyte layer, causing a short circuit. The lithium metal negative electrode polarization voltage prepared by the methods of Comparative Examples 5 and 6 is higher, indicating that it has a larger internal resistance, which is not conducive to improving the energy conversion efficiency, and a slight short circuit occurs after the 18th cycle.

[0091] (2) Preparation of all-solid-state batteries

[0092] Preparation of composite cathode: sulfide electrolyte Li 5.5 PS 4.5 Cl 1.5 and conductive additive vapor-grown carbon fiber (VGCF) and cathode material LiNi 0.7 Co 0.1 Mn 0.2The materials were mixed with O2 using a mechanical mixing method at a rotation speed of 300 rpm and a ball milling time of 1.5 hours under the protection of high-purity argon (99.999%) to produce a composite positive electrode. The mass ratio of positive electrode material: sulfide electrolyte: conductive additive was 70:27:3.

[0093] Preparation of lithium metal battery: weigh a certain amount of sulfide electrolyte powder Li in the glove box 5.5 PS 4.5 Cl 1.5 Cold pressing is performed in a mold with the pressure controlled at 10 MPa to 100 MPa to obtain an electrolyte layer. Subsequently, a certain amount of the composite positive electrode prepared above is placed on one side of the electrolyte and pressed under a pressure of 10 MPa to 100 MPa. Finally, the lithium metal negative electrode prepared in the embodiment and the comparative example is attached to the other side of the electrolyte layer and cold pressing is performed in a mold with the pressure controlled at 10 MPa to 350 MPa to obtain 8 solid-state batteries respectively. Charge and discharge tests were performed at a rate of 1C respectively, and the ratio of the capacity after 50 cycles to the initial capacity is the capacity retention rate after the cycle. The test results are as follows Figures 13 to 21 shown.

[0094] from Figures 13 to 21 It can be seen that compared with Comparative Examples 1 to 4, the lithium metal negative electrode prepared in the present embodiment has good charge and discharge capacity and cycle stability, indicating that by introducing Li, LiM alloy, Li c X, LiY and Li a XY b , which can reduce the formation of lithium dendrites and improve the lithium ion transmission capacity; at the same time, it can enhance the cycle stability and avoid short circuit.

[0095] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For any details not described in individual embodiments, reference may be made to the description in other embodiments.

[0096] The above-described embodiments merely illustrate the implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A lithium metal negative electrode, characterized in that Contains Li, LiM alloy, Li c X, LiY and Li a XY b , wherein M is a metal element, X is an oxygen element or a nitrogen element, and Y is a halogen; when X is an oxygen element, a=3, b=1, and c=2; when X is a nitrogen element, a=5, b=2, and c=3; M is selected from one or more of La series elements, In, Al, Bi, Zr, Hf, Sn, and Ge.

2. The method for preparing a lithium metal negative electrode according to claim 1, wherein The following steps are involved: The lithium metal is heated and melted to obtain molten lithium liquid; Adding an additive to the molten lithium solution, carrying out heat preservation reaction, and cooling to obtain the lithium metal negative electrode; the additive is MXY, wherein M is a metal element, X is an oxygen element or a nitrogen element, and Y is a halogen.

3. The method for preparing a lithium metal negative electrode according to claim 2, wherein: The additive is at least one of LaOCl, InOCl, BiOCl, and AlOCl.

4. The method for preparing a lithium metal negative electrode according to claim 2, wherein: The additive is at least one of ZrNCl, SnNCl, HfNCl, and GeNCl.

5. The method for preparing a lithium metal negative electrode according to claim 2, wherein: The amount of the additive added is 2-20% of the mass of the lithium metal.

6. The method for preparing a lithium metal negative electrode according to claim 2, wherein: The temperature of the heat preservation reaction is 200-350°C.

7. The method for preparing a lithium metal negative electrode according to claim 2, wherein: The reaction time of the insulation reaction is 5-60 min.

8. A lithium battery, characterized in that: Comprising the lithium metal negative electrode as claimed in claim 1.

9. The lithium battery according to claim 8, wherein The electrolyte of the lithium battery is Li 7-x PS 6-x Cl x 、Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 、Li7P2S8I、Li 10 GeP2S 12 One or more of, 0.5≤x≤2; the positive electrode material of the lithium battery is LiNi m Co n Mn z O2, m + n + z = 1.

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