Lithium metal material, method for controlling orientation of crystal faces of lithium metal, electrode sheet and battery

Abstract

Disclosed in the present invention are a lithium metal material, a method for controlling the orientation of crystal faces of a lithium metal, an electrode sheet and a battery. The surface of the lithium metal material has a crystal face (110), a crystal face (211) and a crystal face (200); and the ratio of the intensity of the characteristic peak of the crystal face (110) to the intensity of the characteristic peak of the crystal face (211) is greater than or equal to 3, and the ratio of the intensity of the characteristic peak of the crystal face (110) to the intensity of the characteristic peak of the crystal face (200) is greater than or equal to 3. The intensity of the crystal face (110) on the surface of the lithium metal material is high, and the lithium metal material has the high-exposure crystal face (110) and can be used in a lithium metal battery. Due to a low surface diffusion energy barrier of lithium ions on the lithium crystal face (110), the material tends to form a high-dimensional structure rather than one-dimensional dendrites; therefore, when used in a lithium metal battery, the lithium metal material can effectively reduce the risk of internal short circuits under high-current and long-term cycling conditions.

Description

Lithium metal materials, methods for controlling the orientation of lithium metal crystal planes, and electrodes and batteries Technical Field

[0001] This invention relates to the field of battery electrode materials technology, and in particular to a lithium metal material, a method for controlling the orientation of lithium metal crystal planes, and electrodes and batteries. Background Technology

[0002] With the rapid development of technology and the widespread adoption of electronic devices and electric vehicles, the demand for high-efficiency, high-energy-density batteries is increasing daily. Traditional battery technologies can no longer meet this growing demand, thus necessitating the development of new battery technologies to satisfy the urgent market needs.

[0003] Among these new types of batteries, lithium metal batteries have attracted much attention due to their higher energy density. Lithium metal boasts a specific capacity of up to 3860 mAh / g (11 times higher than graphite), and its redox potential is as low as -3.04V compared to a standard hydrogen electrode (meaning a higher discharge voltage plateau). Calculations show that replacing the graphite anode with lithium metal could increase the volumetric energy gain by up to 62% and the gravimetric energy gain by up to 45%. This means that with the same volume and weight, batteries can store more energy, resulting in longer driving ranges for electric vehicles, mobile phones, and other devices.

[0004] However, lithium metal batteries face many challenges in practical applications, such as impractical rate performance, unsafe cycling conditions, and limited cycle life. To address these issues, the scientific community has focused on developing novel lithium metal matrices, starting with lithium metal materials.

[0005] Studies have shown that lithium ions have a lower surface diffusion barrier on the lithium (110) crystal plane, tending to form high-dimensional structures rather than one-dimensional dendrites. However, existing commercial lithium foils typically exhibit three types of crystal planes on their surface: (110), (200), and (211). Among them, the (110) crystal plane has low strength and a large surface diffusion barrier, making it prone to forming one-dimensional dendrites under high current conditions. After long cycling, the disordered growth of dendrites can easily puncture the separator, causing a short circuit between the positive and negative electrodes, posing a safety risk.

[0006] Summary of the Invention

[0007] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a lithium metal material, a method for controlling the orientation of lithium metal crystal planes, as well as electrodes and batteries.

[0008] In a first aspect, the present invention provides a lithium metal material having a (110) crystal plane, a (211) crystal plane, and a (200) crystal plane on its surface; wherein the ratio of the characteristic peak intensity of the (110) crystal plane to the characteristic peak intensity of the (211) crystal plane is greater than or equal to 3, and the ratio of the characteristic peak intensity of the (110) crystal plane to the characteristic peak intensity of the (200) crystal plane is greater than or equal to 3.

[0009] The lithium metal material according to the embodiments of the present invention has at least the following beneficial effects: the surface (110) crystal plane of the lithium metal material has high strength and high exposure (110) crystal plane, which can be applied to lithium metal batteries. Since the diffusion barrier of lithium ions on the surface of lithium (110) crystal plane is low, it tends to generate high-dimensional structures rather than one-dimensional dendrites. Therefore, the lithium metal material applied to lithium metal batteries can effectively reduce the risk of internal short circuit under high current long cycle conditions.

[0010] In some embodiments of the present invention, the thickness of the lithium metal material is 8μm-350μm; further, the thickness of the lithium metal material can be 10μm-300μm, 50μm-250μm, 100μm-200μm, 60μm-220μm, 50μm-150μm, 20μm-80μm, 50μm-100μm, 150μm-300μm, etc.

[0011] In some embodiments of the present invention, the density of the lithium metal material is 0.534 g / cm³. 3 -0.545g / cm 3 .

[0012] Traditional methods for exposing the (110) crystal plane typically involve accumulating the number of roll-bonding cycles (more than 8 times). Specifically, multiple roll-bonding cycles are used to expose the (110) crystal plane. This method has practical drawbacks: as the size of lithium crystal grains decreases with the increase of the number of roll-bonding cycles, smaller grains lead to a reduction in the space for atomic dislocations. Therefore, the lithium metal foil gradually hardens during the roll-bonding process, and the hardening of the roll-bonding material further seriously affects the service life of the roll. In addition, in industrial applications, lithium metal cannot directly contact the roll, as lithium metal and the roll material will alloy. Therefore, in general lithium roll-bonding processes, PET is required as a film to isolate the lithium metal from the roll material, which makes it difficult to industrialize roll-bonding.

[0013] In a second aspect, the present invention provides a method for controlling the orientation of lithium metal crystal planes, comprising: stretching a lithium metal foil under conditions where the dew point is below -40°C.

[0014] The method for controlling the orientation of lithium metal crystal planes according to embodiments of the present invention has at least the following beneficial effects: This method, by stretching lithium metal foil, can promote the exposure of the (110) crystal plane orientation of the lithium metal foil. Specifically, lithium metal foil is a polycrystalline material composed of many domains. Commercial lithium foil typically exhibits three characteristic peaks under XRD detection, belonging to the (110), (200), and (211) lithium crystal planes, respectively. When the lithium metal foil is subjected to a specific tensile force, the material itself will undergo grain rotation, grain boundary sliding, and lattice dislocation to adapt to the direction of the external stress, i.e., crystal plane deformation. Crystal plane deformation tends to occur along crystal planes with tightly packed atoms, thereby causing these planes to align in a specific direction, which in turn promotes the exposure of more (110) crystal planes. The above method, through stretching, facilitates the realization of lithium metal (110) crystal plane orientation. Compared with the method of exposing lithium metal (110) crystal planes several times through rolling and bonding, it is simple to operate, conducive to industrialization, and avoids the problem of material hardening caused by multiple rolling processes.

[0015] Dew point, or dew point temperature, refers to the temperature at which air reaches relative humidity saturation, or the temperature at which water vapor and water reach equilibrium. The lower the dew point temperature, the drier the air. Because lithium metal foil is highly reactive, the presence of moisture during the stretching process can affect product performance and quality. Specifically, lithium metal undergoes an irreversible chemical reaction at excessively high dew point temperatures (e.g., above -40°C), with the reaction equation: 2Li + 2H₂O = 2LiOH + H₂. This reaction is violent and releases a large amount of heat, and hydrogen, being a flammable gas, can easily trigger an uncontrollable combustion reaction. Furthermore, lithium in LiOH is non-reactive and, after assembling the battery cell, constitutes "dead lithium," affecting not only the insertion and extraction of lithium ions during deposition but also occupying volume and weight, reducing the energy density of the battery cell—an undesirable component. Therefore, lithium metal should not be exposed to air under high dew point conditions. Consequently, during the lithium metal crystal orientation process (including stretching), it is necessary to monitor and strictly control the dew point to be below -40°C.

[0016] In some embodiments of the present invention, the stretching process includes at least two stretches, each stretching along the same direction as the lithium metal foil. The number of stretches during the stretching process can specifically be 3, 5, 6, 8, 10, 11, etc. As mentioned above, by applying a stretching force to the lithium metal foil, the material tends to deform along the closely packed crystal planes to adapt to the direction of external stress, thereby causing these planes to align in a specific direction and exposing the lithium metal (110) crystal planes. As the number of stretches in the same direction increases, the alignment degree continuously increases, which is conducive to forming highly exposed (110) crystal planes, and even tends to form lithium metal materials containing a single (110) crystal plane.

[0017] In some embodiments of the present invention, during the stretching process, after each stretching is completed, the stretched lithium foil is folded in half before the next stretching is performed. Specifically, the folding can be done symmetrically along the center line of the wide surface of the stretched lithium foil. Stretching is a key process for exposing the (110) crystal plane. By stretching the lithium foil multiple times, the peak intensity of the lithium (110) crystal plane can be significantly enhanced. However, since the thickness of the lithium foil will become thinner as the stretching process proceeds, a folding process can be added between two adjacent stretching processes to control the product thickness to a certain extent, ensure the strength of the stretched material, prevent material breakage due to stretching, and improve the stability and reliability of the stretching process.

[0018] In some embodiments of the present invention, during the stretching process, after the first stretching is completed, the folding and stretching are repeated 5-10 times. That is, during the stretching process, the number of stretching times can be controlled to be 6-11 times. Increasing the number of stretching times can increase the crystal plane alignment, which is beneficial to forming a single (110) crystal plane lithium metal material.

[0019] In some embodiments of the present invention, during the stretching process, the tensile force applied for each stretch is 2 N / cm. 2 -20 N / cm 2 ; and / or, the elongation at each stretch is controlled between 50% and 80%.

[0020] The tensile force in the stretching process determines the stretching speed. Polycrystalline materials require strain time to undergo crystal plane transformation under external force. Excessive stretching speed prevents the formation of ordered lithium metal texture evolution, while insufficient stretching force will not cause lithium metal to stretch. By controlling the tensile force applied during the stretching process to 2 N / cm... 2 -20 N / cm 2 This allows for effective control of the stretching speed, causing lithium metal to undergo a crystal plane transformation and form an ordered texture evolution. Furthermore, the tensile force applied during the stretching process can be 5 N / cm. 2 -20 N / cm 2 5N / cm 2 -15 N / cm 2 6N / cm 2 -18 N / cm 2 8N / cm 2 -16 N / cm 2 10N / cm 2 -15 N / cm 2 6N / cm 2 -12 N / cm 2 Alternatively, the tensile force applied during the stretching process can be 3 N / cm. 2 5N / cm 27N / cm 2 9N / cm 2 10N / cm 2 12N / cm 2 14 N / cm 2 15N / cm 2 17 N / cm 2 19N / cm 2 20N / cm 2 wait.

[0021] The elongation rate of the stretching treatment mainly affects the evolution of the (110) crystal plane. Excessive elongation may cause lithium metal band breakage, while insufficient elongation will not reach the shortest distance for the (110) crystal plane evolution. Therefore, by controlling the elongation rate of the stretching treatment within the range of 50%-80%, the effective evolution of the (110) crystal plane in lithium metal can be ensured. Furthermore, the elongation rate of the stretching treatment can be controlled at 55%-75%, 55%-65%, 60%-80%, 60%-70%, 65%-75%, or 50%, 52%, 58%, 60%, 63%, 65%, 68%, 70%, 72%, 75%, 77%, 80%, etc.

[0022] In addition, the stretching process can be performed by fixing the opposite ends of the lithium foil, specifically stretching along the length or width of the lithium foil. When the stretching process involves multiple stretches, it is necessary to ensure that each stretch is performed in the same direction as the lithium foil.

[0023] In some embodiments of the present invention, the density change of the lithium foil before and after the stretching treatment is 0-2%. The stretching treatment essentially applies an external stress to the lithium foil, which causes a reduction in grain size. Smaller grains result in less space for atomic dislocations, leading to increased material hardness and density from a physicochemical perspective. Smaller grains result in a denser lithium layer during initial deposition, increasing the volumetric edgeometric expansion (ED).

[0024] In some embodiments of the present invention, the thickness of the lithium metal foil is 20μm-500μm. Further, the thickness of the lithium metal foil can be 50μm-500μm, 50μm-450μm, 80μm-400μm, 100μm-450μm, 150μm-400μm, 150μm-350μm, 200μm-500μm, 250μm-450μm, 250μm-350μm, 300μm-500μm, 300μm-400μm, etc.

[0025] In some embodiments of the present invention, after the stretching process is completed, the method further includes: coating the stretched lithium foil with a polymer film and then performing a roll forming process. Since the stretching process of the lithium foil before the roll forming process can expose the (110) crystal orientation of the lithium foil, only one roll forming process is required after the stretching process is completed to shape it. Compared with the conventional method of exposing the lithium (110) crystal plane, which requires several roll forming and bonding processes and requires the use of a polymer film to isolate the pressure roller before each roll forming, this method is simple to operate, can greatly reduce the input of materials and manpower, is more conducive to industrialization, and can avoid the problem that the traditional method of multiple roll forming processes can easily cause the roll forming material to harden and affect the service life of the pressure roller.

[0026] In some embodiments of the present invention, the thickness change of the lithium metal foil before and after the roll forming process is controlled within 30%-50%; and / or, after the stretching process is completed, the stretched lithium metal foil is first folded in half, and then a polymer film is used to cover the folded lithium metal foil before the roll forming process is performed.

[0027] Since the rolling process generates stress on the lithium metal strip, resulting in smaller crystal size and crystal plane transformation, the thickness change during rolling should be minimized in the product forming process to maintain as many (110) crystal planes as possible. However, too small a thickness change cannot form a smooth lithium metal surface. Therefore, by controlling the thickness change of the lithium metal foil before and after rolling within 30%-50%, a smooth lithium metal material can be formed, while maintaining as many (110) crystal planes as possible. The thickness change rate of the lithium metal foil before and after rolling can be further controlled at 32%-48%, 35%-45%, 38%-42%, 35%-40%, 40%-45%, 40%-50%, or 30%, 33%, 35%, 37%, 40%, 43%, 45%, 47%, 48%, 50%, etc.

[0028] After the stretching process is completed, the stretched lithium foil can be folded in half to control the material to a certain thickness. Then, a polymer film is used to cover the folded lithium foil, followed by roll forming.

[0029] Before the rolling process, the folded lithium foil is first coated with a polymer film to isolate the lithium foil from contact with the pressure roller during the rolling process, thereby preventing the lithium foil from directly contacting the roller and alloying. In some embodiments of the present invention, in step S3, the polymer film is selected from polyethylene terephthalate (PET) film or polyimide film.

[0030] In some embodiments of the present invention, the method for controlling the orientation of lithium metal crystal planes specifically includes the following steps:

[0031] S1. Under conditions where the dew point is below -40℃, perform a stretching treatment on the lithium metal foil; the stretching treatment includes 6-11 stretches, and after each stretch, the stretched lithium metal foil is folded in half before the next stretch, that is, after the first stretch, the folding and stretching are repeated 5-10 times; the tensile force applied for each stretch is 2N / cm. 2 -20 N / cm 2 The elongation rate of each stretch is controlled between 50% and 80%.

[0032] S2. The stretched lithium foil is folded in half, then coated with a polymer film, and then rolled. The thickness change rate of the lithium foil before and after the rolling process is controlled within 30%-50%.

[0033] The lithium metal material prepared by the above method of controlling the orientation of lithium metal crystal planes has (110) crystal plane, (211) crystal plane and (200) crystal plane on its surface; the ratio of the characteristic peak intensity of (110) crystal plane to the characteristic peak intensity of (211) crystal plane is greater than or equal to 3, and the ratio of the characteristic peak intensity of (110) crystal plane to the characteristic peak intensity of (200) crystal plane is greater than or equal to 3, and has a high exposure of (110) crystal plane.

[0034] In a third aspect, the present invention provides an electrode made of any of the aforementioned lithium metal materials. Specifically, the electrode can be obtained by dividing the aforementioned lithium metal material.

[0035] In a fourth aspect, the present invention provides a battery comprising a positive electrode, a negative electrode, and a separator, wherein the separator is sandwiched between the positive and negative electrode, and the positive and / or negative electrode employs any of the aforementioned electrode types. Because this battery employs any of the aforementioned electrode types, the risk of internal short circuits under high-current, long-cycle conditions can be effectively reduced. Detailed Implementation

[0036] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0037] Example 1

[0038] A method for controlling the orientation of lithium metal crystal planes, the method comprising the following steps:

[0039] S1. The lithium metal foil is stretched in an environment with a dew point below -40°C.

[0040] Specifically, in an environment with a dew point below -40°C, the lithium foil is fixed at both ends and subjected to a stretching test with a force of 10 N / cm. 2 The tensile force was applied to stretch the lithium foil to 50% elongation. The clamp was then released and the lithium foil was folded in half. The stretching operation was repeated, and the folding and stretching operations were repeated. Specifically, after the first stretching was completed, the folding and stretching were repeated 5 times, and each stretching was performed in the same direction as the lithium foil. A high-intensity (110) crystal plane signal was detected on the surface of the stretched lithium foil.

[0041] S2. Fold the lithium metal foil after stretching in step S1 in half, then cover the lithium metal foil with a polymer film, and then roll the lithium metal foil. After the roll forming process, the thickness of the lithium metal foil is reduced by 50%, resulting in a lithium metal material with uniform thickness and smooth surface.

[0042] Example 2

[0043] A method for controlling the orientation of lithium metal crystal planes, which differs from Example 1 in that: in step S1, during the stretching process, the tensile force applied by the stretching machine each time is changed from 10 N / cm. 2 Adjust 20N / cm 2 The other operations are the same as in Example 1, to produce a lithium metal material with uniform thickness and smooth surface.

[0044] Example 3

[0045] A method for controlling the orientation of lithium metal crystals, the difference between this method and Example 1 is that in step S1, the elongation rate of each stretching process is adjusted from 50% to 80%, and other operations are the same as in Example 1, to produce a lithium metal material with uniform thickness and smooth surface.

[0046] Example 4

[0047] A method for controlling the orientation of lithium metal crystals, the difference between this method and Example 1 is that in step S1, the number of repetitions of folding and stretching after the first stretching is adjusted from 5 to 10, and other operations are the same as in Example 1, to produce a lithium metal material with uniform thickness and smooth surface.

[0048] Example 5

[0049] A method for controlling the orientation of lithium metal crystals, the difference between this method and Example 1 is that in step S2, the rolling process is controlled so that the thickness reduction rate of the lithium metal foil after the rolling process is adjusted from 50% to 30%, and other operations are the same as in Example 1, so as to produce a lithium metal material with uniform thickness and smooth surface.

[0050] Example 6

[0051] A method for controlling the orientation of lithium metal crystal planes, which differs from Example 1 in that: in step S1, during the stretching process, the tensile force applied by the stretching machine each time is changed from 10 N / cm. 2 Adjust 30N / cm 2 Other operations are the same as in Example 1.

[0052] Example 7

[0053] A method for controlling the orientation of lithium metal crystals, the difference between this method and Example 1 is that in step S1, the elongation rate of each stretching process is adjusted from 50% to 30%, and other operations are the same as in Example 1.

[0054] Example 8

[0055] A method for controlling the orientation of lithium metal crystals, the difference between this method and Example 1 is that in step S1, the number of repetitions of folding and stretching after the first stretching is adjusted from 5 to 4, and other operations are the same as in Example 1.

[0056] Example 9

[0057] A method for controlling the orientation of lithium metal crystals, the difference between this method and Example 1 is that in step S2, the rolling process is controlled so that the thickness reduction rate of the lithium metal foil after the rolling process is adjusted from 50% to 60%, and other operations are the same as in Example 1.

[0058] Comparative Example 1

[0059] The untreated lithium foil from Example 1 was used as Comparative Example 1.

[0060] Comparative Example 2

[0061] The difference between this comparative example and Example 1 is that: in this comparative example, the processing of step S1 in Example 1 was not performed, but the original lithium metal foil was directly folded in half according to step S2 in Example 1, and then the lithium metal foil was coated with a polymer film, and then the lithium metal foil was rolled. After the rolling process, the thickness of the lithium metal foil was reduced by 50%, and the product lithium metal material was obtained.

[0062] Performance testing

[0063] 1. The lithium metal material samples obtained in each embodiment and comparative example were cut into 1cm*1cm square pieces. The sample surface was detected by XRD with a scanning angle of 10-80° and a scanning speed of 2° / min. Let the characteristic peak intensity of the (110) crystal plane be x(110), the characteristic peak intensity of the (200) crystal plane be y(200), and the characteristic peak intensity of the (211) crystal plane be z(211). By examining the ratio of the characteristic peak intensities of the (200) crystal plane and the (211) crystal plane of the (110) crystal plane, it was determined whether the sample achieved the expected effect. Specifically, when x(110) / z(211)≥3 and x(110) / y(200)≥3 are simultaneously satisfied, the obtained sample can be considered to have achieved the expected effect. The results obtained by the above method are shown in Table 1.

[0064] 2. Cut the metal foil materials obtained in each embodiment and comparative example into 16mm small circular pieces. Assemble a 2032 symmetrical battery using two identical small circular pieces. The electrolyte formulation is a 1M LiPF6 ethylene carbonate (EC) / ethyl methyl carbonate (EMC) electrolyte, with EC:EMC = 3:7. The separator is a 14μm thick PE membrane. Take 5 of each symmetrical battery and set the current density to 1mAh / cm³. 2 The single-charge capacity is set to 1mAh / cm². 2 The cells were charged and discharged at room temperature until the polarization voltage was greater than 0.2V, and the cycle life of each case was compared.

[0065] The testing steps are as follows:

[0066] a. Let it sit for 5 minutes;

[0067] b. at 1mAh / cm 2 Constant current charging for 1 hour;

[0068] c. Let it sit for 5 minutes;

[0069] d. at 1mAh / cm 2 Constant current discharge for 1 hour;

[0070] e. Repeat steps 1-4 until the polarization voltage is >0.5V;

[0071] f. End.

[0072] The cycle life of the symmetrical batteries assembled using lithium metal materials from each embodiment and comparative example, measured using the above method, is shown in Table 1 below.

[0073] Table 1. Method control and product performance test data for each embodiment and comparative example.

[0074] As shown in Table 1 above, compared to Comparative Example 1, the lithium foil in each embodiment, after stretching treatment, exhibits higher (110) crystal plane strength and exposes more (110) crystal planes in the lithium metal material. Therefore, the method for controlling the orientation of lithium metal crystal planes in this invention, by stretching the lithium foil, can promote the exposure of the (110) crystal plane orientation. Compared to the method of repeatedly exposing the (110) crystal planes of lithium metal through rolling and bonding, this method is simpler to operate, facilitates industrialization, and avoids the problem of material hardening caused by repeated rolling in conventional methods.

[0075] As can be seen from the experimental results of Comparative Example 2, directly rolling the lithium foil results in a large number of (200) crystal planes on the surface of the lithium foil, which cannot achieve the expected effect.

[0076] In addition, by comparing the various embodiments, it can be seen that in the above methods for controlling the orientation of lithium metal crystal planes, the tensile force during the stretching process, the elongation rate of each stretch, the number of repetitions of folding and stretching, and the change rate of the thickness of the lithium metal foil before and after rolling during the rolling process will affect the strength of the (110) crystal plane on the lithium metal material of the product, thereby affecting the cycle life of the battery.

[0077] Specifically, comparing Examples 1, 2, and 6 and their performance test results, it can be seen that the tensile force during the tensile treatment process in Examples 1 and 2 is 10 N / cm. 2 20N / cm 2 The ratios of the characteristic peak intensities of the (110) crystal plane to those of the (211) and (200) crystal planes on the lithium metal material are all greater than 3, resulting in a high battery cycle life; while compared to

[0078] In Examples 1, 2, and 6, the tensile force was relatively large, and the ratio of the characteristic peak intensity of the (110) crystal plane to that of the (200) crystal plane on the lithium metal material was greater than 3, but the ratio of the characteristic peak intensity of the (110) crystal plane to that of the (211) crystal plane was less than 3. The battery cycle life was significantly lower than in Examples 1 and 2. This is because the tensile force affects the tensile speed. Polycrystalline materials require strain time to undergo crystal plane transformation under external force. If the tensile speed is too fast, an orderly evolution of lithium metal texture cannot be formed, thus failing to effectively expose the (110) crystal plane. Conversely, if the tensile force is too small, the lithium metal will not stretch. Therefore, it is advisable to control the tensile force during the stretching process at 2 N / cm. 2 -20 N / cm 2 In order to effectively control the stretching speed, the lithium metal undergoes a crystal plane transformation to form an orderly texture evolution, which is conducive to effectively exposing the (110) crystal plane.

[0079] By comparing Examples 1, 3, and 7, it can be seen that in Examples 1 and 3, the elongation rate of each stretching process was 50% and 80%, respectively. The ratio of the characteristic peak intensity of the (110) crystal plane to the characteristic peak intensity of the (211) crystal plane and the (200) crystal plane on the lithium metal material of the product was greater than 3, and the battery cycle life was high. However, compared with Examples 1 and 3, the elongation rate of stretching in Example 7 was smaller, and the ratio of the characteristic peak intensity of the (110) crystal plane to the characteristic peak intensity of the (211) crystal plane and the (200) crystal plane on the lithium metal material of the product was less than 3. The battery cycle life was significantly lower than that of the battery constructed using the lithium metal foil material of Examples 1 and 3. This is because the elongation rate of stretching mainly affects the evolution effect of the (110) crystal plane. If the stretching elongation rate is too large, it may cause lithium metal band breakage; while if the stretching elongation rate is too small, it may not reach the effective distance for the evolution of the (110) crystal plane, and effective crystal plane deformation cannot be achieved. Therefore, it is advisable to control the elongation of each stretching process within 50%-80%.

[0080] Comparing Examples 1, 4, and 8, it can be seen that in Examples 1 and 4, after the first stretching, the folding-stretching process was repeated 5 times and 10 times respectively. The ratios of the characteristic peak intensities of the (110) crystal plane to those of the (211) and (200) crystal planes on the lithium metal material were all greater than 3, resulting in a high battery cycle life.

[0081] In Examples 1, 4, and 8, the number of folding-stretching repetitions was relatively small. The ratios of the characteristic peak intensities of the (110) crystal plane to those of the (211) and (200) crystal planes on the lithium metal material were all less than 3. Consequently, the battery cycle life was significantly lower than that of batteries constructed using lithium metal foil materials from Examples 1 and 4. This is because repeated stretching is a key process for exposing the (110) crystal plane. When the lithium metal foil is subjected to a specific tensile force, the material itself will undergo crystal plane deformation in order to adapt to the direction of the external stress. Crystal plane deformation tends to occur along crystal planes with tightly packed atoms, thereby causing these planes to align in a specific direction. As the number of stretching repetitions increases, the alignment degree continuously increases, eventually forming lithium metal containing only a single (110) crystal plane. Insufficient stretching repetitions are not conducive to the exposure and orientation of the (110) crystal plane. Furthermore, comparing Example 8 and Comparative Example 1, the cycle life of the symmetrical battery in Example 8 is inferior to that in Comparative Example 1. The reason is that, according to calculations, the peak intensity ratio of the (110):(211):(200) crystal planes of the lithium metal material obtained in Example 8 is 2.3:1:1.64; while the peak intensity ratio of the (110):(211):(200) crystal planes of the lithium metal foil in Comparative Example 1 is 1:1:10. That is to say, the untreated lithium metal foil is mainly composed of the 200 crystal plane, while the peak intensities of each crystal plane of the lithium foil after four folding-stretching treatments are similar. The presence of polycrystalline planes on the surface of the lithium foil will make the lithium deposition behavior more complex and will not improve the cycle life. On the contrary, it may lead to a deterioration trend.

[0082] Furthermore, comparing Examples 1, 5, and 9, it can be seen that in Examples 1 and 5, the thickness change rates before and after the rolling process are 50% and 30%, respectively. The ratios of the characteristic peak intensities of the (110) crystal plane to those of the (211) and (200) crystal planes on the lithium metal material are all greater than 3, resulting in high battery cycle life. However, compared to Examples 1 and 5, the thickness change during the rolling process in Example 9 is too large. The ratios of the characteristic peak intensities of the (110) crystal plane to those of the (211) and (200) crystal planes on the lithium metal material are all less than 3, resulting in a lower battery cycle life than that of batteries constructed using the lithium metal materials of Examples 1 and 5. This is because the final rolling process also generates stress on the lithium metal strip, resulting in smaller crystal size and crystal plane transformation. Therefore, in the product forming process, the thickness change during rolling should be reduced to maintain as many (110) crystal planes as possible in the product. Too small a thickness change cannot form a smooth lithium metal surface. Therefore, the thickness change of the lithium foil before and after the rolling process can be controlled within 30%-50%.

[0083] As can be seen from the above, the exposure degree (or intensity) of the (110) crystal plane significantly affects the cycle life of the battery. Specifically, when the ratio of the characteristic peak intensity of the (110) crystal plane to that of the (211) crystal plane on the lithium metal material is greater than or equal to 3, and the ratio of the characteristic peak intensity of the (110) crystal plane to that of the (200) crystal plane is greater than or equal to 3, the risk of internal short circuit in lithium metal batteries under high current long-cycle conditions can be effectively reduced, and the cycle life of the battery can be significantly improved. This is because the (211) and (200) crystal planes tend to generate one-dimensional whiskers, i.e., lithium dendrites, due to the presence of energy barriers, while the (110) crystal plane tends to deposit into a high-dimensional structure with a smooth surface after deposition. During cycling, the short circuit caused by dendrite growth is often a local behavior. The fewer the (211) and (200) crystal planes, the lower the probability of dendrite growth and puncture of the separator.

[0084] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A lithium metal material, characterized in that, The surface of the lithium metal material has a (110) crystal plane, a (211) crystal plane and a (200) crystal plane; the ratio of the characteristic peak intensity of the (110) crystal plane to the characteristic peak intensity of the (211) crystal plane is greater than or equal to 3, and the ratio of the characteristic peak intensity of the (110) crystal plane to the characteristic peak intensity of the (200) crystal plane is greater than or equal to 3.

2. The lithium metal material according to claim 1, characterized in that, The thickness of the lithium metal material is 8 μm-350 μm; and / or, the density of the lithium metal material is 0.534 g / cm³. 3 -0.545g / cm 3 .

3. A method for controlling the orientation of lithium metal crystal planes, characterized in that, include: The lithium foil was stretched under conditions where the dew point was below -40°C.

4. The method for controlling the orientation of lithium metal crystal planes according to claim 3, characterized in that, The stretching process includes at least two stretches, each stretch being performed in the same direction as the lithium metal foil.

5. The method for controlling the orientation of lithium metal crystal planes according to claim 4, characterized in that, During the stretching process, after each stretching is completed, the stretched lithium foil is folded in half before the next stretching is performed.

6. The method for controlling the orientation of lithium metal crystal planes according to claim 5, characterized in that, During the stretching process, after the first stretching is completed, the folding and stretching are repeated 5-10 times.

7. The method for controlling the orientation of lithium metal crystal planes according to claim 5, characterized in that, During the stretching process, the tensile force applied for each stretch is 2 N / cm. 2 -20N / cm 2 ; and / or, the elongation at each stretch is controlled between 50% and 80%.

8. The method for controlling the orientation of lithium metal crystal planes according to claim 3, characterized in that, The thickness of the lithium foil is 20μm-500μm.

9. The method for controlling the orientation of lithium metal crystal planes according to any one of claims 3 to 8, characterized in that, After the stretching process is completed, the process further includes: coating the stretched lithium foil with a polymer film and then performing a roll forming process.

10. The method for controlling the orientation of lithium metal crystal planes according to claim 9, characterized in that, The thickness change rate of the lithium foil before and after the rolling process is controlled within 30%-50%; and / or, After the stretching process is completed, the stretched lithium foil is first folded in half, then a polymer film is used to cover the folded lithium foil, and then it is rolled.

11. An electrode sheet, characterized in that, The electrode is made of lithium metal material as described in any one of claims 1 to 2 or lithium metal material prepared by the method for controlling the orientation of lithium metal crystal planes as described in any one of claims 3 to 10.

12. A battery, characterized in that, It includes a positive electrode, a negative electrode, and a separator, wherein the separator is sandwiched between the positive electrode and the negative electrode, and the positive electrode and / or the negative electrode is the electrode as described in claim 11.

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