Lithium-aluminum alloy negative electrode as well as preparation method and application thereof

Abstract

The invention provides a lithium-aluminum alloy negative electrode and a preparation method and application thereof, and the preparation method comprises the following steps: in a protective gas, an aluminum foil, a lithium sheet, a diaphragm and an electrolyte are adopted to prepare a battery cell, the aluminum foil is a positive electrode, and the lithium sheet is a negative electrode; the method comprises the following steps: preparing an aluminum foil on the surface of a battery cell, then discharging the battery cell with the discharging voltage range of 0.03-0.4 V to generate a beta-LiAl alloy layer on the surface of at least one side of the aluminum foil, disassembling the battery cell after discharging is finished, and taking the disassembled aluminum foil loaded with the beta-LiAl alloy layer on the surface as the lithium-aluminum alloy negative electrode. According to the preparation method disclosed by the invention, the lithium-aluminum alloy with a fixed crystal form is formed on the surface of the aluminum foil in advance, and the conversion of the beta-LiAl alloy between a lithium-rich state and a lithium-poor state is realized by regulating and controlling the voltage range in the charging and discharging process, and the conversion between phases is not involved, so that the cycling stability of the battery is improved, and the service life of the battery is prolonged. The problem that the volume change of the lithium-aluminum alloy in the charging and discharging process is large is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries and relates to a lithium aluminum alloy negative electrode and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are one of the main ways of electrochemical energy storage. The market has put forward higher requirements for the use of lithium-ion batteries, among which reducing battery weight, increasing energy density and improving cycle performance are the main directions. At present, commercial negative electrode materials are mainly graphite negative electrode materials, but their specific capacity is low. Although alloyed negative electrode materials such as silicon, aluminum, and tin have high theoretical specific capacity, they have large volume changes during the process of lithium removal / intercalation, poor structural stability, and electrolyte contamination, resulting in rapid failure of the negative electrode during the cyclic charge and discharge process.

[0003] That is, the alloyed negative electrode has a significant volume effect caused by the alloying / de-alloying process (due to the transformation between crystal forms), and often faces severe volume expansion during the charging and discharging process, such as Si's volume expansion of about 300%, Al's expansion of about 97%, and Sn's expansion of about 260%, resulting in poor battery cycle stability. In the prior art, the solution strategies for the volume expansion of alloyed negative electrodes are mainly alloy nano-sizing, surface coating, alloy three-dimensional conductive framework, alloy nanoparticle core-shell structure, and gradient alloyed negative electrode.

[0004] Although the existing technical solutions have a certain mitigating effect on the volume effect, the volume effect of the electrode material itself has not been fundamentally improved. For example, during the charge and discharge cycle, the volume change of the combined electrode material and adhesive during the lithium insertion / de-lithiation process will cause stress accumulation inside the adhesive and active particles, and cause particle breakage. During repeated cycles, the active particles continue to break and pulverize, resulting in the collapse of the electrode structure and battery failure. In addition, the traditional pole piece needs to bond the current collector to the electrode material, and it can only be cut and assembled into batteries after coating, baking, rolling and other processes.

[0005] Based on the above research, it is necessary to provide a lithium aluminum alloy negative electrode, which can reduce the volume effect caused by the alloy phase transformation during the charge and discharge process and improve the electrochemical stability of the negative electrode. Summary of the invention

[0006] The object of the present invention is to provide a lithium aluminum alloy negative electrode and a preparation method and application thereof. The preparation method can form a β-LiAl alloy layer on the aluminum surface, form a lithium aluminum alloy with a fixed crystal form in advance, and realize the transformation of β-LiAl between a lithium-rich state and a lithium-poor state by regulating the voltage range during the charge and discharge process without involving the transformation between phases, thereby improving the cycle stability of the battery and solving the problem of large volume change of the lithium aluminum alloy during the charge and discharge process.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a lithium aluminum alloy negative electrode, the preparation method comprising the following steps:

[0009] In a protective gas, an aluminum foil, a lithium sheet, a separator and an electrolyte are used to prepare a battery cell, wherein the aluminum foil is a positive electrode and the lithium sheet is a negative electrode;

[0010] The battery cell is then discharged at a voltage range of 0.03-0.4V, so that a β-LiAl alloy layer is formed on at least one surface of the aluminum foil. After the discharge, the battery cell is disassembled, and the aluminum foil with a β-LiAl alloy layer on the surface obtained by disassembly is the lithium aluminum alloy negative electrode.

[0011] Preferably, the thickness of the β-LiAl alloy layer is 1-80 μm, preferably 10-60 μm.

[0012] Preferably, the discharge capacity is 1-80 mAh, preferably 8-60 mAh.

[0013] Preferably, the discharging is performed at a scan rate of 0.01-0.5 mV / s.

[0014] Preferably, the discharging is performed within a voltage range of 0.3-0.4V.

[0015] Preferably, in the aluminum foil loaded with the β-LiAl alloy layer, the thickness of the aluminum foil is 10-30 μm, preferably 10-20 μm.

[0016] Preferably, the preparation of the battery cell is carried out in a protective gas with a H2O content of less than 1 ppm and an O2 content of less than 1 ppm.

[0017] In a second aspect, the present invention provides a lithium aluminum alloy negative electrode, wherein the lithium aluminum alloy negative electrode is prepared by the preparation method described in the first aspect;

[0018] The lithium aluminum alloy negative electrode comprises an aluminum foil and a β-LiAl alloy layer on at least one side of the aluminum foil.

[0019] In a third aspect, the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the lithium-aluminum alloy negative electrode as described in the second aspect.

[0020] Preferably, the lithium-ion battery is charged and discharged in the voltage range of 0.5V-1.35V, and the β-LiAl alloy is in the lithium-deficient β-Li a Al alloy and lithium-rich β-Li bAl alloys transform into each other, where 0.916≤a<1, 1<b≤1.16.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention adopts an electrochemical method, firstly uses aluminum foil as a positive electrode and a lithium sheet as a negative electrode to prepare a battery cell, then discharges the battery cell to generate a β-LiAl alloy layer on the surface of the aluminum foil, and then disassembles the battery cell, and uses the aluminum foil loaded with the β-LiAl alloy layer obtained by disassembling the battery cell as a negative electrode plate. On the one hand, the negative electrode plate is directly prepared in one step, which can simplify the preparation steps of the negative electrode compared with the traditional process steps (mixing, coating, baking), and does not need to add a conductive agent and a binder. On the other hand, a β-LiAl alloy layer with a fixed crystal form is formed in advance, which can enable the lithium-aluminum alloy negative electrode to achieve the transition between a lithium-rich state and a lithium-poor state during the charge and discharge process, without involving a phase change between the β-LiAl alloy and α-Al, which greatly alleviates the volume effect caused by the phase change when the lithium-aluminum alloy is used as the negative electrode, thereby improving the cycle stability of the lithium-aluminum alloy negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the formation process of the lithium aluminum alloy negative electrode of the present invention;

[0024] Figure 2 It is a schematic diagram of the transformation of the lithium-aluminum alloy negative electrode during charging and discharging of the lithium-ion battery of the present invention;

[0025] Figure 3 This is a schematic diagram of the cell structure of the lithium-ion battery of the present invention;

[0026] Among them, 1-negative electrode current collector, 2-β-LiAl alloy layer, 3-separator, 4-positive electrode active material layer, 5-positive electrode current collector. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0028] In a first aspect, a specific embodiment of the present invention provides a method for preparing a lithium aluminum alloy negative electrode, the preparation method comprising the following steps:

[0029] In a protective gas, an aluminum foil, a lithium sheet, a separator and an electrolyte are used to prepare a battery cell, wherein the aluminum foil is a positive electrode and the lithium sheet is a negative electrode;

[0030] The battery cell is then discharged at a voltage range of 0.03-0.4V, so that a β-LiAl alloy layer is formed on at least one surface of the aluminum foil. After the discharge, the battery cell is disassembled, and the aluminum foil with a β-LiAl alloy layer on the surface obtained by disassembly is the lithium aluminum alloy negative electrode.

[0031] The preparation method of the present invention uses aluminum foil as the positive electrode and lithium sheet as the negative electrode. After assembling into a battery cell, since aluminum and lithium have a voltage difference, after discharging in the voltage range of 0.03-0.4V, lithium ions will be deposited on the surface of the aluminum foil and react with aluminum to form a specific β-type lithium-aluminum alloy on the surface of the aluminum foil. In addition, the present invention is that lithium ions enter the aluminum foil to react. Therefore, when lithium ions react with aluminum, aluminum is excessive relative to lithium. Therefore, the present invention obtains a low-energy LiAl alloy, and finally a β-LiAl alloy layer (such as Figure 1 As shown, the formation process of the lithium aluminum alloy negative electrode is schematically shown), and the structure of the aluminum foil and the β-LiAl alloy layer loaded on the surface of the aluminum foil is obtained. Then, after the battery cell is disassembled, the aluminum foil loaded with the β-LiAl alloy layer obtained by disassembling can be directly used as the negative electrode plate. Therefore, the present invention adopts an electrochemical method. On the one hand, the negative electrode plate is directly prepared in one step. Compared with the traditional process steps (mixing, coating, baking), the preparation steps of the negative electrode can be simplified, and there is no need to add a conductive agent and a binder, which can improve the energy density of the battery.

[0032] On the other hand, the preparation method of the present invention also obtains a β-LiAl alloy layer with a fixed crystal form. Specifically, the obtained lithium-aluminum alloy negative electrode includes an aluminum foil and a β-LiAl alloy layer on at least one side of the aluminum foil. The aluminum foil is a negative electrode current collector, and the working layer is a β-LiAl alloy layer; that is, the lithium-aluminum alloy negative electrode is formed into a battery cell first, and a lithium-aluminum alloy with a fixed crystal form is formed in advance and then used as a negative electrode, so that the lithium-aluminum alloy negative electrode can realize the transition between the lithium-rich state and the lithium-poor state of the β-LiAl alloy during the charge and discharge process (such as Figure 2 As shown in the figure, during the charge and discharge process, the Li-poor β-LiAl alloy and the Li-rich β-LiAl alloy transform into each other), without involving the phase change between the β-LiAl alloy and α-Al, which greatly alleviates the volume effect caused by the phase change when the lithium-aluminum alloy is used as the negative electrode, thereby improving the cycle stability of the lithium-aluminum alloy negative electrode.

[0033] In addition, in the lithium aluminum alloy negative electrode of the present invention, aluminum foil with a lower density can also be used as the negative electrode current collector, although aluminum is generally not used as the negative electrode current collector for the following reasons: the size of the lattice octahedron voids of metal aluminum is similar to that of the lattice octahedron voids of lithium, and it is very easy to form an intermetallic compound with Li, such as Li and Al can form LiAl, Li3Al2, Li4Al3 alloys, and when metal Al is used in the negative electrode, a large amount of Li is consumed. +At the same time, it will also be accompanied by a large volume effect, and finally it will be pulverized under the action of stress, and the surface structure will be destroyed, so aluminum generally cannot be used as a negative electrode current collector; however, in the lithium-aluminum alloy negative electrode described in the present invention, a β-LiAl alloy layer is provided on the surface of the aluminum foil, and the β-LiAl alloy layer is used as a working layer to release or embed lithium, and the aluminum foil will not consume lithium. Therefore, the present invention can use aluminum foil as a negative electrode current collector. The density of aluminum is about 30% of the density of copper. Aluminum replaces copper as a negative electrode current collector, which can not only ensure the conductivity of the current collector, but also improve the energy density of the lithium-ion battery, and at the same time save a lot of material costs.

[0034] In some embodiments, the thickness of the β-LiAl alloy layer is 1-80 μm, for example, 1 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm or 80 μm, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 10-60 μm.

[0035] The thickness of the β-LiAl alloy layer of the present invention is within the preferred range, which is beneficial to improving the performance of the lithium-ion battery. If the thickness of the β-LiAl alloy layer is too thin, the capacity provided is too small, and other phases of LiAl alloy layer will be generated during the charge and discharge process; if the thickness of the β-LiAl alloy layer is too thick, Li + The diffusion path in the β-LiAl alloy layer is too long to achieve rapid diffusion.

[0036] In some embodiments, the discharge capacity is 1-80mAh, for example, it can be 1mAh, 10mAh, 20mAh, 30mAh, 40mAh, 50mAh, 60mAh, 70mAh or 80mAh, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 8-60mAh.

[0037] The present invention controls the thickness of the β-LiAl alloy layer by controlling the discharge amount. If the discharge amount is too little, the thickness of the β-LiAl alloy layer will be too thin. If the discharge amount is too much, the thickness of the β-LiAl alloy layer will be too thick. Therefore, the present invention preferably ensures the thickness of the β-LiAl alloy layer within a specific discharge amount range.

[0038] In some embodiments, the discharge is performed at a scan rate of 0.01-0.5 mV / s, for example, 0.01 mV / s, 0.1 mV / s, 0.2 mV / s, 0.3 mV / s, 0.4 mV / s or 0.5 mV / s, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] The scanning rate during discharge of the present invention affects the uniformity of the formed β-LiAl alloy layer. The present invention preferably performs discharge at a specific scanning rate. If the scanning rate is too high, the formed β-LiAl alloy layer will be uneven. If the scanning rate is too low, the discharge efficiency will be affected.

[0040] In some embodiments, the discharge is performed within a voltage range of 0.3-0.4 V, such as 0.3 V, 0.35 V or 0.4 V, but is not limited to the listed values, and other values ​​not listed within the value range are also applicable.

[0041] In some embodiments, the thickness of the aluminum foil loaded with the β-LiAl alloy layer is 10-30 μm, for example, 10 μm, 20 μm or 30 μm, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 10-20 μm.

[0042] In the aluminum foil loaded with the β-LiAl alloy layer of the present invention, the aluminum foil is the aluminum foil remaining after the β-LiAl alloy layer is formed, which is directly used as the current collector. Therefore, its thickness is the thickness of the negative electrode current collector in the lithium aluminum alloy negative electrode of the present invention.

[0043] In some embodiments, when preparing the battery cell, the process is carried out in a protective gas with a H2O content of less than 1ppm, such as 0.8ppm, 0.6ppm, 0.4ppm or 0.2ppm, and an O2 content of less than 1ppm, such as 0.8ppm, 0.6ppm, 0.4ppm or 0.2ppm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] In some embodiments, the shielding gas includes argon.

[0045] In some embodiments, before preparing the battery cell, the aluminum foil is first cleaned and dried using alcohol and acetone before use.

[0046] When preparing the battery cell according to the present invention, the types of the separator and the electrolyte used are not specifically limited in the present invention. For example, the separator can be a polypropylene or polyethylene separator, and the electrolyte can be a commercial electrolyte HR-9212.

[0047] In a second aspect, a specific embodiment of the present invention provides a lithium aluminum alloy negative electrode, wherein the lithium aluminum alloy negative electrode is prepared by the preparation method described in the first aspect;

[0048] The lithium aluminum alloy negative electrode comprises an aluminum foil and a β-LiAl alloy layer on at least one side of the aluminum foil.

[0049] In a third aspect, a specific embodiment of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the lithium-aluminum alloy negative electrode as described in the second aspect.

[0050] The lithium-ion battery of the present invention comprises a battery cell, the structural schematic diagram of which is shown in Figure 3 As shown, it includes a negative electrode current collector 1, a β-LiAl alloy layer 2, a separator 3, a positive electrode active material layer 4 and a positive electrode current collector 5 which are stacked in sequence, wherein the negative electrode current collector 1 is aluminum foil, and the positive electrode current collector 5 is also aluminum foil.

[0051] In some embodiments, the lithium-ion battery is charged and discharged in the voltage range of 0.5V-1.35V (for example, 0.5V, 1V, or 1.35V), and the β-LiAl alloy is in the lithium-poor state. a Al alloy and lithium-rich β-Li b Al alloys transform into each other, wherein 0.916≤a<1, for example, it can be 0.916, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98 or 0.99, and 1<b≤1.16, for example, it can be 1.02, 1.05, 1.1, 1.15 or 1.16, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0052] After the lithium-aluminum alloy negative electrode of the present invention is applied to a lithium-ion battery, during the charge and discharge process, the negative electrode only undergoes a transformation process from a lithium-poor lithium-aluminum alloy to a lithium-rich lithium-aluminum alloy, such as a Li-poor β-Li 0.916 Al alloy (specific capacity 910 mAh / g) and Li-rich β-Li 1.16 The mutual transformation of Al alloy (specific capacity 1152 mAh / g) can provide a specific capacity of 242 mAh / g, and the volume change is less than 2%, which greatly alleviates the volume effect caused by the phase transformation between β-LiAl alloy and α-Al.

[0053] The technical solution of the present invention is further illustrated by specific embodiments below.

[0054] Example 1

[0055] This embodiment provides a method for preparing a lithium aluminum alloy negative electrode, the preparation method comprising the following steps:

[0056] After the surface of the aluminum foil was cleaned and dried with alcohol and acetone respectively, the cleaned aluminum foil was combined with a lithium sheet, a polypropylene separator and a commercial electrolyte HR-9212 in an argon atmosphere (H2O < 1ppm, O2 < 1ppm) to prepare a battery cell, wherein the aluminum foil was the positive electrode and the lithium sheet was the negative electrode;

[0057] The cells were then discharged on an electrochemical workstation at 0.3-0.4V versus Li / Li + Under the conditions of a scan rate of 0.01 mV / s and a discharge capacity of 8 mAh, a β-LiAl alloy layer is generated on one side of the aluminum foil. After the discharge, the battery cell is disassembled, and the aluminum foil with a β-LiAl alloy layer on the surface obtained by disassembly is the lithium aluminum alloy negative electrode. The thickness of the aluminum foil in the lithium aluminum alloy negative electrode is 10 μm, and the thickness of the β-LiAl alloy layer is 10 μm.

[0058] Example 2

[0059] This embodiment provides a method for preparing a lithium aluminum alloy negative electrode, the preparation method comprising the following steps:

[0060] After the surface of the aluminum foil was cleaned and dried with alcohol and acetone respectively, the cleaned aluminum foil was combined with a lithium sheet, a polypropylene separator and a commercial electrolyte HR-9212 in an argon atmosphere (H2O < 1ppm, O2 < 1ppm) to prepare a battery cell, wherein the aluminum foil was the positive electrode and the lithium sheet was the negative electrode;

[0061] The cells were then discharged on an electrochemical workstation at 0.3-0.4V versus Li / Li + Under the conditions of a scan rate of 0.2 mV / s and a discharge capacity of 18 mAh, a β-LiAl alloy layer is generated on one side of the aluminum foil. After the discharge, the battery cell is disassembled, and the aluminum foil with a β-LiAl alloy layer on the surface obtained by disassembly is the lithium aluminum alloy negative electrode. The thickness of the aluminum foil in the lithium aluminum alloy negative electrode is 10 μm, and the thickness of the β-LiAl alloy layer is 20 μm.

[0062] Example 3

[0063] This embodiment provides a method for preparing a lithium aluminum alloy negative electrode, the preparation method comprising the following steps:

[0064] After the surface of the aluminum foil was cleaned and dried with alcohol and acetone respectively, the cleaned aluminum foil was combined with a lithium sheet, a polypropylene separator and a commercial electrolyte HR-9212 in an argon atmosphere (H2O < 1ppm, O2 < 1ppm) to prepare a battery cell, wherein the aluminum foil was the positive electrode and the lithium sheet was the negative electrode;

[0065] The cells were then discharged on an electrochemical workstation at 0.3-0.4V versus Li / Li +Under the conditions of a scan rate of 0.1 mV / s and a discharge capacity of 40 mAh, a β-LiAl alloy layer is generated on one side of the aluminum foil. After the discharge, the battery cell is disassembled, and the aluminum foil with a β-LiAl alloy layer on the surface obtained by disassembly is the lithium aluminum alloy negative electrode. The thickness of the aluminum foil in the lithium aluminum alloy negative electrode is 10 μm, and the thickness of the β-LiAl alloy layer is 40 μm.

[0066] Example 4

[0067] This embodiment provides a method for preparing a lithium aluminum alloy negative electrode, the preparation method comprising the following steps:

[0068] After the surface of the aluminum foil was cleaned and dried with alcohol and acetone respectively, the cleaned aluminum foil was combined with a lithium sheet, a polypropylene separator and a commercial electrolyte HR-9212 in an argon atmosphere (H2O < 1ppm, O2 < 1ppm) to prepare a battery cell, wherein the aluminum foil was the positive electrode and the lithium sheet was the negative electrode;

[0069] The cells were then discharged on an electrochemical workstation at 0.3-0.4V versus Li / Li + Under the conditions of a scan rate of 0.5 mV / s and a discharge capacity of 60 mAh, a β-LiAl alloy layer is generated on one side of the aluminum foil. After the discharge, the battery cell is disassembled, and the aluminum foil with the β-LiAl alloy layer loaded on the surface obtained by disassembly is the lithium aluminum alloy negative electrode. The thickness of the aluminum foil in the lithium aluminum alloy negative electrode is 10 μm, and the thickness of the β-LiAl alloy layer is 60 μm.

[0070] Example 5

[0071] This embodiment provides a method for preparing a lithium aluminum alloy negative electrode, the preparation method comprising the following steps:

[0072] After the surface of the aluminum foil was cleaned and dried with alcohol and acetone respectively, the cleaned aluminum foil was combined with a lithium sheet, a polypropylene separator and a commercial electrolyte HR-9212 in an argon atmosphere (H2O < 1ppm, O2 < 1ppm) to prepare a battery cell, wherein the aluminum foil was the positive electrode and the lithium sheet was the negative electrode;

[0073] The cells were then discharged on an electrochemical workstation at 0.3-0.4V versus Li / Li + Under the conditions of a scan rate of 0.01 mV / s and a discharge capacity of 8 mAh, a β-LiAl alloy layer is generated on one side of the aluminum foil. After the discharge, the battery cell is disassembled, and the aluminum foil with a β-LiAl alloy layer on the surface obtained by disassembly is the lithium aluminum alloy negative electrode. The thickness of the aluminum foil in the lithium aluminum alloy negative electrode is 20 μm, and the thickness of the β-LiAl alloy layer is 10 μm.

[0074] Example 6

[0075] This embodiment provides a method for preparing a lithium aluminum alloy negative electrode, the preparation method comprising the following steps:

[0076] After the surface of the aluminum foil was cleaned and dried with alcohol and acetone respectively, the cleaned aluminum foil was combined with a lithium sheet, a polypropylene separator and a commercial electrolyte HR-9212 in an argon atmosphere (H2O < 1ppm, O2 < 1ppm) to prepare a battery cell, wherein the aluminum foil was the positive electrode and the lithium sheet was the negative electrode;

[0077] The cells were then discharged on an electrochemical workstation at 0.3-0.4V versus Li / Li + Under the conditions of a scan rate of 0.2 mV / s and a discharge capacity of 18 mAh, a β-LiAl alloy layer is generated on one side of the aluminum foil. After the discharge, the battery cell is disassembled, and the aluminum foil with a β-LiAl alloy layer on the surface obtained by disassembly is the lithium aluminum alloy negative electrode. The thickness of the aluminum foil in the lithium aluminum alloy negative electrode is 20 μm, and the thickness of the β-LiAl alloy layer is 20 μm.

[0078] Example 7

[0079] This embodiment provides a method for preparing a lithium aluminum alloy negative electrode, the preparation method comprising the following steps:

[0080] After the surface of the aluminum foil was cleaned and dried with alcohol and acetone respectively, the cleaned aluminum foil was combined with a lithium sheet, a polypropylene separator and a commercial electrolyte HR-9212 in an argon atmosphere (H2O < 1ppm, O2 < 1ppm) to prepare a battery cell, wherein the aluminum foil was the positive electrode and the lithium sheet was the negative electrode;

[0081] The cells were then discharged on an electrochemical workstation at 0.3-0.4V versus Li / Li + Under the conditions of a scan rate of 0.1 mV / s and a discharge capacity of 40 mAh, a β-LiAl alloy layer is generated on one side of the aluminum foil. After the discharge, the battery cell is disassembled, and the aluminum foil with the β-LiAl alloy layer on the surface obtained by disassembly is the lithium aluminum alloy negative electrode. The thickness of the aluminum foil in the lithium aluminum alloy negative electrode is 20 μm, and the thickness of the β-LiAl alloy layer is 40 μm.

[0082] Example 8

[0083] This embodiment provides a method for preparing a lithium aluminum alloy negative electrode, the preparation method comprising the following steps:

[0084] After the surface of the aluminum foil was cleaned and dried with alcohol and acetone respectively, the cleaned aluminum foil was combined with a lithium sheet, a polypropylene separator and a commercial electrolyte HR-9212 in an argon atmosphere (H2O < 1ppm, O2 < 1ppm) to prepare a battery cell, wherein the aluminum foil was the positive electrode and the lithium sheet was the negative electrode;

[0085] The cells were then discharged on an electrochemical workstation at 0.3-0.4V versus Li / Li + Under the conditions of a scan rate of 0.5 mV / s and a discharge capacity of 60 mAh, a β-LiAl alloy layer is generated on one side of the aluminum foil. After the discharge, the battery cell is disassembled, and the aluminum foil with a β-LiAl alloy layer on the surface obtained by disassembly is the lithium aluminum alloy negative electrode. The thickness of the aluminum foil in the lithium aluminum alloy negative electrode is 20 μm, and the thickness of the β-LiAl alloy layer is 60 μm.

[0086] Example 9

[0087] This embodiment provides a method for preparing a lithium aluminum alloy negative electrode. The preparation method is the same as that of Embodiment 1 except that the discharge capacity is 80 mAh and the thickness of the β-LiAl alloy layer is 80 μm.

[0088] Example 10

[0089] This embodiment provides a method for preparing a lithium aluminum alloy negative electrode. The preparation method is the same as that of Embodiment 1 except that the discharge capacity is 1 mAh and the thickness of the β-LiAl alloy layer is 1 μm.

[0090] Embodiment 11

[0091] This embodiment provides a method for preparing a lithium aluminum alloy negative electrode. The preparation method is the same as that of Embodiment 1 except that the discharge scan rate is 0.005 mV / s.

[0092] Example 12

[0093] This embodiment provides a method for preparing a lithium aluminum alloy negative electrode. The preparation method is the same as that of Embodiment 1 except that the discharge scan rate is 0.7 mV / s.

[0094] Example 13

[0095] This embodiment provides a method for preparing a lithium aluminum alloy negative electrode. The preparation method includes the following steps: + Except for the discharge within the range, the rest is the same as Example 1.

[0096] Comparative Example 1

[0097] This comparative example provides a method for preparing a lithium aluminum alloy negative electrode, which adopts the preparation method in CN101280434A, including: using aluminum foil as a cathode material, immersing it in an electrolyte containing KCl and LiCl to carry out an electrolytic reaction, so that lithium atoms are reduced and deposited on the cathode material, and under high temperature conditions, the lithium atoms diffuse into the cathode material to form a lithium aluminum compound, and the lithium content in the lithium aluminum compound is 50wt%.

[0098] Comparative Example 2

[0099] The present comparative example provides a method for preparing a lithium aluminum alloy negative electrode, which adopts the preparation method of CN102127660A, comprising: placing a metal lithium particle and an aluminum particle into a ceramic spherical ink tank in dry air with a relative humidity of less than 2%, adding a certain number of corundum balls, filling with inert gas argon, ball milling, taking out the mixture, filling it into a mold, pressing it into a cake shape on a hydraulic press, placing it in an electrolyte and letting it stand, and then washing it with a solvent to obtain a lithium aluminum alloy.

[0100] Comparative Example 3

[0101] This comparative example provides a method for preparing a lithium aluminum alloy negative electrode. The preparation method includes the following steps: + Except for the discharge within the range, the rest is the same as Example 1.

[0102] Comparative Example 4

[0103] This comparative example provides a method for preparing a lithium aluminum alloy negative electrode. The preparation method includes the following steps: + Except for the discharge within the range, the rest is the same as Example 1.

[0104] The lithium-aluminum alloy negative electrode obtained in the above embodiments and comparative examples is prepared into a lithium-ion battery with a lithium iron phosphate positive electrode plate, a commercial electrolyte HR-9212 and a polyethylene separator, wherein the positive electrode active material layer in the lithium iron phosphate positive electrode plate includes 90wt% lithium iron phosphate, 3wt% polyvinylidene fluoride, 3wt% carbon nanotubes and 4wt% conductive carbon black.

[0105] The prepared lithium-ion battery was tested at 25°C, in the voltage range of 0.5V to 1.35V, for a capacity retention rate of 0.1C and 200 cycles. The test results and the alloy layer thickness of the embodiment and the comparative example are shown in Table 1:

[0106] Table 1

[0107]

[0108]

[0109] The test results are shown in Table 1:

[0110] It can be seen from Example 1 and Comparative Examples 1-2 that the lithium aluminum alloy negative electrode obtained by the preparation method of the present invention first generates a layer of β-LiAl alloy layer with a fixed crystal form on the surface of the aluminum foil, and no phase change is involved in the charge and discharge process, and only the lithium-poor state and the lithium-rich state of the lithium aluminum alloy are transformed. Therefore, the volume change of the negative electrode is small, and the cycle performance of the lithium ion battery can be significantly improved; It can be seen from Example 1, Example 13 and Comparative Examples 3-4 that the present invention has a 0.03-0.4V versus Li / Li + The discharge is carried out within a voltage range of 0.3-0.4V to ensure the formation of a β-type LiAl alloy, and it is further preferred that the discharge is carried out within a voltage range of 0.3-0.4V, while the discharge within the voltage range of Comparative Examples 3-4 forms other crystalline alloys, and the lithium aluminum alloy involves phase conversion during charge and discharge, thereby causing the negative electrode of the battery to fail and the overall performance to decline; it can be seen from Examples 1-8 and 9-10 that the present invention can control the thickness of the β-LiAl alloy layer by controlling the discharge capacity, and it is preferred that the thickness of the β-LiAl alloy layer is within a specific range, which can further improve the cycle performance of the lithium ion battery; it can be seen from Examples 1 and 11-12 that the scan rate during discharge of the present invention affects the uniformity of the β-LiAl alloy layer. Under the premise of ensuring the generation efficiency of the β-LiAl alloy layer, the scan rate of the discharge is not easy to be too large, otherwise it will affect the role of the β-LiAl alloy layer, thereby affecting the cycle performance of the battery.

[0111] In summary, the present invention provides a lithium aluminum alloy negative electrode and a preparation method and application thereof. The preparation method can form a β-LiAl alloy layer on the aluminum surface, form a lithium aluminum alloy with a fixed crystal form in advance, and realize the transformation of β-LiAl between a lithium-rich state and a lithium-poor state without involving transformation between phases, thereby improving the cycle stability of the battery and solving the problem of large volume change of the negative electrode during charging and discharging.

[0112] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a lithium aluminum alloy negative electrode, characterized in that: The preparation method comprises the following steps: In a protective gas, an aluminum foil, a lithium sheet, a separator and an electrolyte are used to prepare a battery cell, wherein the aluminum foil is a positive electrode and the lithium sheet is a negative electrode; The battery cell is then discharged at a voltage range of 0.03-0.4V, so that a β-LiAl alloy layer is formed on at least one surface of the aluminum foil. After the discharge, the battery cell is disassembled, and the aluminum foil with a β-LiAl alloy layer on the surface obtained by disassembly is the lithium aluminum alloy negative electrode.

2. The preparation method according to claim 1, characterized in that: The thickness of the β-LiAl alloy layer is 1-80 μm, preferably 10-60 μm.

3. The preparation method according to claim 1 or 2, characterized in that: The discharge capacity is 1-80 mAh, preferably 8-60 mAh.

4. The preparation method according to claim 3, characterized in that: The discharge was performed at a scan rate of 0.01-0.5 mV / s.

5. The preparation method according to claim 3, characterized in that: The discharge was performed in the voltage range of 0.3-0.4V.

6. The preparation method according to claim 1 or 2, characterized in that: In the aluminum foil loaded with the β-LiAl alloy layer, the thickness of the aluminum foil is 10-30 μm, preferably 10-20 μm.

7. The preparation method according to claim 1 or 2, characterized in that: When preparing the battery core, the process is carried out in a protective gas with a H2O content of less than 1 ppm and an O2 content of less than 1 ppm.

8. A lithium aluminum alloy negative electrode, characterized in that: The lithium aluminum alloy negative electrode is prepared by the preparation method according to any one of claims 1 to 7; The lithium aluminum alloy negative electrode comprises an aluminum foil and a β-LiAl alloy layer on at least one side of the aluminum foil.

9. A lithium ion battery, characterized in that: The lithium-ion battery comprises the lithium-aluminum alloy negative electrode as claimed in claim 8.

10. The lithium ion battery according to claim 9, characterized in that: The lithium-ion battery is charged and discharged in the voltage range of 0.5V-1.35V, and the β-LiAl alloy is in the lithium-poor state β-Li a Al alloy and lithium-rich β-Li b Al alloys transform into each other, where 0.916≤a<1, 1<b≤1.16.

Images