Aluminum negative electrode and nonaqueous electrolyte secondary battery

Abstract

This aluminum negative electrode is used in a nonaqueous electrolyte secondary battery. The aluminum negative electrode has a negative electrode body including aluminum as a material, and demonstrates, in a lithiation reaction which is measured under given measurement conditions, a resistance value of 6.5 kΩ·cm2 or less when the lithiation capacity is 1 mAh / cm2.

Description

Aluminum negative electrode and non-aqueous electrolyte secondary battery

[0001] The present invention relates to an aluminum negative electrode and a nonaqueous electrolyte secondary battery. This application claims priority to Japanese Patent Application No. 2022-60259, filed March 31, 2022, the contents of which are incorporated herein by reference.

[0002] Known rechargeable secondary batteries include those that use a nonaqueous electrolyte as the electrolyte (hereinafter referred to as nonaqueous electrolyte secondary batteries) and those that use a solid electrolyte (all-solid-state secondary batteries). Of these, nonaqueous electrolyte secondary batteries have already been put to practical use not only in small power sources for mobile phones and notebook computers, but also in medium- and large-sized power sources for automobiles and power storage.

[0003] Regarding non-aqueous electrolyte secondary batteries, studies are being conducted on electrodes and active materials contained in the electrodes in order to improve their performance. For example, regarding lithium secondary batteries, which are a type of non-aqueous electrolyte secondary battery, studies are being conducted on improving battery performance by using a material with a larger theoretical capacity for the negative electrode constituting the lithium secondary battery than graphite, which is a conventional negative electrode material. As such a material, attention is being paid to, for example, metal materials that can absorb and release lithium ions, similar to graphite.

[0004] As an example of a negative electrode formed from a metal material, for example, Patent Document 1 describes a negative electrode made of a porous aluminum alloy and composed of a negative electrode active material for a secondary battery containing at least one of silicon and tin.

[0005] JP 2011-228058 A

[0006] As the application fields of non-aqueous electrolyte secondary batteries expand, there is a demand for further improvement in the cycle characteristics of non-aqueous electrolyte secondary batteries. There is room for improvement in the cycle characteristics of metal negative electrodes used in non-aqueous electrolyte secondary batteries.

[0007] The "cycle characteristics" of a nonaqueous electrolyte secondary battery are performance evaluated by the rate at which the discharge capacity is maintained when the battery is repeatedly charged and discharged. A nonaqueous electrolyte secondary battery that has a high rate at which the discharge capacity is maintained when the battery is repeatedly charged and discharged is evaluated as having "good cycle characteristics."

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an aluminum negative electrode for a nonaqueous electrolyte secondary battery that can improve the cycle characteristics of the nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery using the same.

[0009] The inventors analyzed the behavior of the negative electrode during charge and discharge for a non-aqueous electrolyte secondary battery that uses an aluminum negative electrode (aluminum negative electrode) as the metal negative electrode, and investigated the cause of negative electrode deterioration. As a result, they confirmed that a coating that was not initially present had formed on the surface of the negative electrode of the non-aqueous electrolyte secondary battery that had been charged and discharged several times.

[0010] The inventors believed that the coating film inhibits the insertion and extraction of Li ions into and from the aluminum negative electrode, adversely affecting the physical properties. Based on this belief, the inventors conducted extensive research and completed the present invention.

[0011] That is, in order to solve the above problems, one aspect of the present invention includes the following aspects.

[0012] [1] An aluminum negative electrode for use in a non-aqueous electrolyte secondary battery, having a negative electrode body made of aluminum, and having a lithiation capacity of 1 mAh / cm in a lithiation reaction measured under the following measurement conditions: ２ The resistance value is 6.5 kΩ cm ２ An aluminum negative electrode having the following characteristics: (Measurement conditions) Current density: 0.6 mA / cm ２ Positive electrode: LiCoO ２ Electrolyte: 1 mol / L LiPF ６ Solution (ethylene carbonate: dimethyl carbonate = 1:1 (volume ratio) mixed solvent) Measurement temperature: 25°C C rate: 0.2C

[0013] [2] The aluminum anode according to [1], which has a coating formed on the surface of the anode body, and the coating is made of any one material selected from the group consisting of gold, carbon, and alumina hydrate.

[0014] [3] The aluminum negative electrode according to [2], wherein the thickness of the coating is 1 μm or less.

[0015] [4] The aluminum anode according to [2] or [3], wherein the coating is made of carbon and has an oxygen content of 20 mol % or less.

[0016] [5] The aluminum negative electrode according to [1], wherein the negative electrode body is a rolled material, and in FT-IR analysis of the surface of the negative electrode body, rolling oil is below the detection limit.

[0017] [6] The aluminum negative electrode according to [5], wherein the negative electrode body is a member obtained by treating the surface of a rolled material made of aluminum with either an alkali treatment or an acid treatment, or both.

[0018] [7] The aluminum negative electrode according to any one of [1] to [6], wherein after the lithiation reaction is carried out, the thickness of the deposit of the electrolyte formed on the surface of the aluminum negative electrode is 2 μm or less.

[0019] [8] The aluminum negative electrode according to any one of [1] to [7], wherein the negative electrode body contains aluminum and one or more metal elements selected from the group consisting of Si, Ge, Sn, Ag, Sb, Bi, In, Mn, and Mg, and the content of the metal elements relative to the total amount of the negative electrode body is 0.1 mass % or more and 8 mass % or less.

[0020] [9] The aluminum negative electrode according to any one of [1] to [8], wherein the average crystal grain size of aluminum crystal grains, as determined from a scanning ion microscope image of a cross section of the negative electrode body, is 200 μm or less.

[0021]

[10] A non-aqueous electrolyte secondary battery comprising a positive electrode, the aluminum negative electrode according to any one of [1] to [9], and a non-aqueous electrolyte.

[0022]

[11] The nonaqueous electrolyte is LiBF ４ The nonaqueous electrolyte secondary battery according to

[10] ,

[0023]

[12] A cathode, an aluminum anode, and LiBF ４ and a non-aqueous electrolyte solution containing the aluminum negative electrode, wherein the aluminum negative electrode has a resistance value of a lithiation reaction measured under the following measurement conditions of 6.5 kΩ cm ２ A non-aqueous electrolyte secondary battery having the following characteristics: (Measurement conditions) Lithium capacity: 1 mAh / cm２ Current density: 0.6mA / cm ２ Positive electrode: LiCoO ２ Measurement temperature: 25°C C rate: 0.2C

[0024] According to the present invention, it is possible to provide an aluminum negative electrode for a nonaqueous electrolyte secondary battery that can improve the cycle characteristics of the nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery using the same.

[0025] FIG. 1 is an explanatory diagram showing ideal behavior during charge and discharge of a lithium secondary battery employing a conventional aluminum negative electrode. FIG. 2 is an explanatory diagram showing ideal behavior during charge and discharge of a lithium secondary battery employing a conventional aluminum negative electrode. FIG. 3 is an explanatory diagram showing ideal behavior during charge and discharge of a lithium secondary battery employing a conventional aluminum negative electrode. FIG. 4 is an SEM photograph showing the appearance of the surface of the positive electrode side of an aluminum negative electrode after five charge and discharge cycles. FIG. 5 is an explanatory diagram showing behavior during charge and discharge of a lithium secondary battery taking into account the formation of film X. FIG. 6 is an explanatory diagram showing behavior during charge and discharge of a lithium secondary battery taking into account the formation of film X. FIG. 7 is an explanatory diagram showing behavior during charge and discharge of a lithium secondary battery taking into account the formation of film X. FIG. 8 is a schematic diagram showing an aluminum negative electrode 40A of an embodiment. FIG. 9 is a schematic diagram showing another aluminum negative electrode 40B of an embodiment. FIG. 10 is a schematic diagram showing an example of a nonaqueous electrolyte secondary battery.

[0026] <Aluminum Negative Electrode> The aluminum negative electrode of this embodiment has a negative electrode body made of aluminum, and has a lithiation capacity of 1 mAh / cm in a lithiation reaction measured under the following measurement conditions. ２ The lower limit of the resistance value is 5.8 kΩ cm ２ Preferably, it is 5.9 kΩ cm or more. ２ More preferably, it is 6.0 kΩ cm or more. ２ The upper limit is preferably 6.5 kΩ cm or more. ２ Preferably, it is 6.4 kΩ cm or less. ２ It is more preferable that the current density is 0.6 mA / cm or less. (Measurement conditions) ２Positive electrode: LiCoO ２ Electrolyte: 1 mol / L LiPF ６ Solution (ethylene carbonate: dimethyl carbonate = 1:1 (volume ratio) mixed solvent) Measurement temperature: 25°C C rate: 0.2C

[0027] The above resistance value is calculated based on a voltage (V) of 1 mAh and a current density of 0.6 mA / cm during charging. ２ Therefore, the resistance (Ω cm) can be calculated using Ohm's law using the following formula (1): ２ ) = Voltage at 1 mAh (V) / Current density (A / cm ２ ) … (1)

[0028] The behavior and problems of conventional aluminum negative electrodes will be explained below, followed by an explanation of the present invention.

[0029] 1 to 3 are explanatory diagrams showing ideal behavior during charging and discharging of a lithium secondary battery (nonaqueous electrolyte secondary battery) 100 employing a conventional aluminum negative electrode 50. The aluminum negative electrode 50 is assumed to be made of simple aluminum.

[0030] As shown in FIG. 1 , when a lithium secondary battery 100 employing an aluminum negative electrode 50 (hereinafter, negative electrode 50) is charged, lithium ions (Li ions) move from the positive electrode 60 side to the negative electrode 50 via the electrolyte 70. The Li ions penetrate into the negative electrode 50 from a surface 50 a on the side of the negative electrode 50 facing the positive electrode 60, and form a Li—Al alloy. As a result, as shown in FIG. 2 , in the negative electrode 50 of the lithium secondary battery 100 after charging, a Li—Al alloy layer 51 grows from the surface 50 a in the thickness direction of the negative electrode 50 (the normal direction of the surface 50 a).

[0031] Next, when the lithium secondary battery 100 in the state shown in FIG. 2 is discharged, Li ions are released from the Li-Al alloy layer 51 and inserted into the positive electrode 60. As a result, the Li-Al alloy layer 51 of the negative electrode 50 changes to aluminum. At this time, the volume of the Li-Al alloy layer 51 decreases as the Li ions are released. At this time, the Li-Al alloy layer 51 does not shrink uniformly, but rather the shrinkage rate varies from place to place. As a result, as shown in FIG. 3, cracks occur on the surface of the Li-Al alloy layer 51, and the surface of the negative electrode 50 after discharge becomes a state in which multiple columnar structures 51a are arranged.

[0032] Next, when such a lithium secondary battery 100 is recharged, Li ions are absorbed from the surfaces of the columnar structures 51a, and the Li—Al alloy layer 51 is formed again. This causes the columnar structures 51a to grow (the volume of the columnar structures 51a increases), and ideally, the cracks that occurred during discharge in the negative electrode 50 disappear, resulting in the state shown in FIG. 2. In this way, the negative electrode 50 reversibly changes between the state shown in FIG. 2 (charged state) and the state shown in FIG. 3 (discharged state) as it is charged and discharged.

[0033] However, it is known that in lithium secondary batteries that use conventional aluminum negative electrodes, the ideal reversible reaction described above is unlikely to occur with repeated charge and discharge, and the aluminum negative electrode gradually breaks down. The inventors analyzed the behavior of the aluminum negative electrode in such lithium secondary batteries as it is charged and discharged, and investigated the cause of aluminum negative electrode deterioration. As a result, they confirmed that a coating that was not initially present was formed on the surface of the aluminum negative electrode after several charge and discharge cycles.

[0034] Figure 4 is an SEM photograph (magnification: 10,000 times) showing the surface of the positive electrode side of an aluminum negative electrode that has been subjected to five charge-discharge cycles. Figure 4 shows that a film X with a thickness of 1 to 2 μm is formed on the surface of the aluminum negative electrode 50 in contact with the Li—Al alloy layer 51. Analysis revealed that the material of film X is a decomposition product of a solvent such as ethylene carbonate (EC) or dimethyl carbonate (DMC) contained in the electrolyte.

[0035] It has been known that when a lithium secondary battery is charged and discharged, a solid electrolyte interphase (SEI) film is formed on the surface of the negative electrode. Many reports have been published on SEI films formed when carbon materials are used in the negative electrode, but the thickness of the SEI films known to date is several nanometers to several tens of nanometers. In contrast, film X shown in FIG. 4 is significantly thicker than known SEI films. Based on the results of confirming film X, the inventors have deduced the phenomenon occurring in aluminum negative electrodes.

[0036] 5 to 7 are explanatory diagrams showing the behavior of the lithium secondary battery 100 during charging and discharging, taking into consideration the formation of the film X.

[0037] As shown in Fig. 5, in the negative electrode 50 of the lithium secondary battery 100 after the initial charge, a Li-Al alloy layer 51 grows from the surface 50a in the thickness direction of the negative electrode 50 (the normal direction to the surface 1a), and a film X is formed to cover the Li-Al alloy layer 51. When such a negative electrode 50 is discharged, cracks occur on the surface of the Li-Al alloy layer 51, and a plurality of columnar structures 51a are arranged, as shown in Fig. 6. A new aluminum surface is generated on the cracked surface (side surface B of the columnar structure 51a).

[0038] Decomposition products, which are the material of the film X, are also produced during the second and subsequent charges. Considering the known method of forming an SEI film, it is believed that the film X is formed when the electrolyte is reductively decomposed on the positive electrode 60 side of the negative electrode 50, and the resulting decomposition products accumulate. Therefore, it is expected that the film X is formed thicker at the tip A of the columnar structure 51 a near the positive electrode 60 on the side B where the crack occurs than at the side B of the columnar structure 51 a.

[0039] It is assumed that the film X, which is made of a decomposition product of the electrolyte solution, has high electrical resistance. Therefore, when the lithium secondary battery 100 is further charged with the film X formed thickly at the tip A, Li ions penetrate into the columnar structure 51a from the side surface B, where the film X is relatively thinner than the tip A and has low electrical resistance, and form a Li—Al alloy.

[0040] As a result, the surface through which Li ions enter the negative electrode 50 becomes side surface B, and it is assumed that "cracks on the surface through which Li ions enter" occur on side surface B as shown in Fig. 7, forming cracks 51x in the columnar structure 51a. When the cracks 51x grow, the columnar structure 51a breaks at the cracks 51x, and as a result, it is assumed that the negative electrode 50 collapses and deteriorates.

[0041] After studying the degradation mechanism of the negative electrode as envisioned above, the inventors hypothesized that the cause of the degradation of the aluminum negative electrode was film X, which is formed to a much greater thickness than known SEI films. They then conducted further studies based on the idea that if the formation of film X could be suppressed, the degradation of the aluminum negative electrode could be suppressed, and completed the invention.

[0042] Since it is assumed that the formation of the film X results in a higher electrical resistance than the negative electrode itself, in the present invention, the effect of "suppressing the formation of the film X" is judged by the resistance value of the lithiation reaction described above. In detail, the resistance value of the lithiation reaction is determined as follows.

[0043] (Method for Measuring Resistance Value of Lithium Addition Reaction) (1) Manufacture of Lithium Secondary Battery First, an aluminum negative electrode having a thickness of 50 μm is cut into a disk shape having a diameter of 16 mm as a measurement object.

[0044] Next, LiCoO ２ The resultant was molded into a disk shape with a diameter of 14 mm to serve as a counter electrode (positive electrode).

[0045] Next, LiPF was added to a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of EC:DMC=50:50. ６ The above is dissolved in a proportion of 1.0 mol / L to prepare an electrolyte solution.

[0046] A polyethylene porous separator was placed between the aluminum negative electrode and the counter electrode, and the resultant was housed in a battery case (standard 2032). The above electrolyte solution was poured into the battery case, and the battery case was sealed to produce a coin-shaped (half-cell) lithium secondary battery with a diameter of 20 mm and a thickness of 3.2 mm.

[0047] (2) Measurement of resistance value of lithiation reaction The coin-type lithium secondary battery was left standing at room temperature (25°C) for 10 hours to allow the positive electrode and separator to be sufficiently impregnated with the electrolyte. Then, at room temperature (25°C), a current density of 0.6 mA / cm was applied. ２ The battery was charged at 0.2 C, and a charging curve was created with the horizontal axis representing the charge capacity (unit: mAh) and the vertical axis representing the voltage (unit: V).

[0048] In the obtained charging curve, the voltage at 1 mAh is read, and the resistance value calculated from Ohm's law (V=IR) is taken as the resistance value of the lithiation reaction.

[0049] In the aluminum negative electrode of the present invention, the formation of the film X is suppressed by carrying out the treatments described below. In the obtained aluminum negative electrode, the resistance value of the lithiation reaction is 6.5 kΩ cm ２ If the temperature is below this value, it can be determined that the formation of the film X is suppressed, and an improvement in cycle characteristics (discharge capacity retention rate) can be expected as a result of suppressing deterioration of the aluminum negative electrode.

[0050] The discharge capacity retention rate is measured by the following method. "Good cycle characteristics" means that the discharge capacity retention rate measured by the following method is 80% or more and 100% or less.

[0051] (Method for Measuring Discharge Capacity Retention Rate) A lithium secondary battery manufactured according to the above (1) Manufacturing of Lithium Secondary Battery was used, and initial charge and discharge was performed by constant current charging at 1 mA to 4.2 V at room temperature, followed by constant voltage charging at 4.2 V for 5 hours, and then constant current discharging at 1 mA to 3.4 V. The discharge capacity was measured, and the obtained value was designated as the "initial discharge capacity" (mAh), i.e., the discharge capacity at the first cycle.

[0052] After the initial charge and discharge, charge and discharge were repeated under the same conditions as the initial charge and discharge, with one cycle consisting of charge at 1 mA and discharge at 1 mA. The discharge capacity was measured at each cycle, and the discharge capacity retention rate was calculated as a ratio to the initial discharge capacity.

[0053] The discharge capacity retention rate is evaluated by determining the maximum number of cycles at which the initial discharge capacity is 80% or more. The larger the "maximum number of cycles" determined, the better the cycle characteristics are judged to be.

[0054] (Aluminum negative electrode) Next, the resistance value of the lithiation reaction was 6.5 kΩ cm ２ A specific configuration for achieving the aluminum negative electrode will be described below. In the present invention, by suppressing the formation of the film X as described above, the resistance value of the lithiation reaction is 6.5 kΩ cm ２ The aluminum anode is as follows:

[0055] Fig. 8 is a schematic diagram showing an aluminum negative electrode 40A of this embodiment. The aluminum negative electrode 40A has a negative electrode body 41 and a coating 42 formed on the surface of the negative electrode body 41. In Fig. 8, the coating 42 is formed on one side of the negative electrode body 41, but it may be formed on both sides of the negative electrode body 41.

[0056] (Negative electrode body) The negative electrode body 41 acts as a negative electrode active material in a nonaqueous electrolyte secondary battery. The negative electrode body 41 may be made of only aluminum, except for unavoidable impurities. Alternatively, the negative electrode body 41 may be made of an aluminum alloy produced by intentionally adding other metals (non-aluminum metals) to aluminum as a base material.

[0057] The inevitable impurities include manufacturing residues that are inevitably mixed in during the refining process. Specifically, iron and copper are included. The content of the inevitable impurities is 0.1% by mass or less of the entire base material, preferably 0.05% by mass or less, and more preferably 0.01% by mass or less.

[0058] Aluminum having a purity of 99.9% by mass or more, high-purity aluminum having a purity of 99.99% by mass or more, etc. can be used as the aluminum material of the negative electrode body 41. High-purity aluminum can be produced by appropriately adopting a known method for increasing the purity of aluminum, such as a segregation method, a three-layer electrolysis method, a zone melting refining method, or an ultra-high vacuum melting method.

[0059] The aluminum alloy preferably has a phase of the other metal (non-aluminum metal phase) dispersed in an aluminum phase (aluminum metal phase). That is, the aluminum alloy preferably has a non-aluminum metal phase dispersed in the aluminum metal phase.

[0060] The non-aluminum metal phase preferably has the other metals aggregated in particulate form and dispersed throughout the aluminum metal phase. The term "particulate" refers to the appearance of the non-aluminum metal phase aggregated into round particles when the surface or cross section of the aluminum-containing metal is observed.

[0061] The non-aluminum metal phase refers to a metal phase that does not contain aluminum. The non-aluminum metal phase is preferably composed of one or more metal elements selected from the group consisting of Si, Ge, Sn, Ag, Sb, Bi, In, Mn, and Mg. The content of the metal elements relative to the total amount of the negative electrode body 41 is preferably 0.1% by mass or more and 8% by mass or less. The content of the metal elements relative to the total amount of the negative electrode body 41 is more preferably 2.0% by mass or less, and even more preferably 1.0% by mass or less.

[0062] The "other metals" constituting the non-aluminum metal phase have a very large lithium absorption capacity. Therefore, the non-aluminum metals undergo large volume expansion upon lithium insertion and large volume contraction upon lithium desorption. The strain caused by the expansion and contraction of the non-aluminum metals can lead to cracking of the structure (e.g., anode) composed of the non-aluminum metals, which can result in the structure becoming finer. The finer graining of the non-aluminum metals acting as anode active materials during charge and discharge can shorten the cycle life.

[0063] In contrast, when a non-aluminum metal phase is dispersed in an aluminum metal phase as described above, the particulate non-aluminum metal is surrounded by aluminum, which is relatively less prone to volume expansion than the non-aluminum metal. Therefore, in a negative electrode in which a non-aluminum metal phase is dispersed in an aluminum metal phase, expansion that leads to miniaturization of the non-aluminum metal is easily suppressed. Therefore, even when the lithium secondary battery is repeatedly charged and discharged, the initial discharge capacity is easily maintained.

[0064] (Method for measuring metal element content) The metal element content can be determined by quantifying the amount of metal elements in aluminum using an optical emission spectrometer (model: ARL-4460, manufactured by Thermo Fisher Scientific). Note that metal elements can be more precisely quantified using a glow discharge mass spectrometer.

[0065] The metal element constituting the non-aluminum metal phase is preferably one containing few unavoidable impurities. For example, when Si is used as the metal element, high-purity silicon with a purity of 99.999% by mass or more is used as the material.

[0066] When the negative electrode body 41 is made of an alloy in which a non-aluminum metal phase is dispersed in an aluminum metal phase, the negative electrode body 41 can be obtained by casting a molten alloy of aluminum and the metal elements that constitute the non-aluminum metal phase, and subjecting the resulting alloy ingot to cutting, rolling, extruding, forging, or the like.

[0067] The negative electrode body 41 preferably contains aluminum crystal grains. The aluminum crystal grains preferably have an average crystal grain size of 200 μm or less. The average crystal grain size of the aluminum crystal grains is a value calculated from a scanning ion microscope (SIM) image of a cross section of the negative electrode body 41.

[0068] When the negative electrode body 41 is made of the above aluminum alloy, the aluminum metal phase preferably consists of aluminum crystal grains.

[0069] Cross-sectional SIM observation of the negative electrode body 41 can be performed by the following method.

[0070] (Method for measuring average crystal grain size) First, an uncharged aluminum negative electrode is processed using the focused ion beam processing and observation device described below to prepare a cross section of the negative electrode body 41. Next, the obtained cross section is observed using the focused ion beam processing and observation device also described below. [Measurement conditions] Focused ion beam processing and observation device: FB-2100 (manufactured by Hitachi High-Technologies Corporation) Ion source: gallium liquid metal Acceleration voltage: 40 kV Magnification: 700x to 50,000x

[0071] The average grain size of aluminum crystal grains is determined by the following method. For all crystal grains contained in the SIM image obtained by the above method, whose outlines can be confirmed in their entirety, the distance between parallel lines drawn from a fixed direction around each crystal grain (unidirectional diameter) is measured. The arithmetic mean value of the obtained measurements is taken as the average grain size of the crystal grains.

[0072] When lithium is absorbed into the negative electrode body 41, the aluminum crystal grains change into Li-Al alloy particles, and the volume of the crystal grains increases. When the volume of the crystal grains increases, distortion may occur in the crystal lattice around the crystal grains. In such distorted areas of the crystal lattice, Li is more likely to penetrate into the crystal lattice.

[0073] In contrast, when the average grain size of the aluminum crystal grains is 200 μm or less, the volume increase per crystal grain is small, and distortion is unlikely to form around the crystal grains. Therefore, differences in the ease of Li penetration, i.e., the ease of Li-Al alloy formation, are unlikely to occur in the negative electrode body 41, and uneven formation of Li-Al alloys is unlikely to occur. As a result, deformation such as wrinkles and cracks is unlikely to occur in the aluminum negative electrode during charge and discharge, and deterioration can be suppressed.

[0074] The upper limit of the average grain size of the aluminum crystal grains is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 50 μm or less, and particularly preferably 10 μm or less. The lower limit is preferably 1 μm or more, more preferably 3 μm or more. The upper and lower limits of the average grain size of the aluminum crystal grains can be combined in any manner.

[0075] (Vickers Hardness) The Vickers hardness of the negative electrode body 41 is preferably 10 HV or more and 100 HV or less, more preferably 10 HV or more and 70 HV or less, even more preferably 20 HV or more and 70 HV or less, and even more preferably 30 HV or more and 70 HV or less.

[0076] The Vickers hardness is measured by the following method using a micro Vickers hardness tester (HV0.05).

[0077] (Method for Measuring Vickers Hardness) The Vickers hardness is a value measured in accordance with JIS Z2244:2009 "Vickers Hardness Test - Test Method." To measure the Vickers hardness, a square pyramidal diamond indenter is pressed into the surface of the test piece of the negative electrode body 41, and after the test force is released, the Vickers hardness is calculated from the diagonal length of the indentation remaining on the surface. When the negative electrode body 41 is not exposed on the surface of the aluminum negative electrode 40A, it is advisable to remove the coating 42 as appropriate and then measure the exposed negative electrode body 41.

[0078] The above standard stipulates that the hardness symbol be changed depending on the test force. In this embodiment, the micro Vickers hardness HV0.05 is measured when the test force is 0.05 kgf (=0.4903 N).

[0079] It is presumed that a Vickers hardness of not more than the upper limit can alleviate distortion in the crystalline structure when aluminum absorbs lithium, thereby maintaining the crystalline structure. Therefore, when aluminum negative electrode 40A is used in a lithium secondary battery and repeatedly charged and discharged, the discharge capacity can be maintained.

[0080] (Coating) The coating 42 is made of any one material selected from the group consisting of gold, carbon, and alumina hydrate. The coating 42 made of gold, carbon, or alumina hydrate all has lithium ion conductivity.

[0081] When the material of the coating 42 is gold, the coating 42 can be formed by physical vapor deposition of gold on the surface of the negative electrode body 41 .

[0082] When the coating 42 made of gold is formed on the surface of the negative electrode body 41, it is predicted that decomposition products of organic substances are less likely to adhere to the surface of the coating 42. Therefore, it is thought that decomposition products of the electrolyte solution, which is the material of the film X, are less likely to accumulate, and the formation of the film X is suppressed.

[0083] That is, in the case of an aluminum negative electrode having a negative electrode body made of aluminum and a gold coating formed on the surface of the negative electrode body, the gold coating suppresses decomposition of the electrolyte and suppresses the formation of film X. As a result, in the case of such an aluminum negative electrode, the resistance value of the lithiation reaction measured under the above measurement conditions is 6.5 kΩ cm ２ It is believed that an aluminum anode having a .DELTA..times ...

[0084] When the material of the coating 42 is carbon, the coating 42 can be formed by vapor-depositing carbon on the surface of the negative electrode body 41. The vapor deposition method may be chemical vapor deposition or physical vapor deposition.

[0085] Furthermore, when the material of the coating 42 is carbon, the oxygen content of the coating 42 is preferably 20 mol% or less, more preferably 15 mol% or less, even more preferably 10 mol% or less, and even more preferably 5 mol% or less. The oxygen content of the coating 42 is ideally 0 mol% or more, and may be 0.1 mol% or more.

[0086] (Method for Measuring Oxygen Content) The oxygen content can be measured by calculating the molar ratio of each element contained in the coating 42 by X-ray photoelectron spectroscopy (XPS) analysis. The XPS spectrum of the coating 42 is acquired, and the molar ratio (mol %) of each element constituting the coating 42 can be calculated by multiplying the area value of the peak derived from each element by the relative sensitivity coefficient of the device using XPS data analysis software. The oxygen content is the proportion (mol %) occupied by oxygen when the content of all elements detected by XPS analysis is expressed as a molar fraction (mol %). [Measurement Conditions] Device: Quantera SXM (manufactured by ULVAC-PHI, Inc.) X-ray source: Al-Kα ray Photoelectron take-off angle: 45 degrees Aperture diameter: 100 μm Charge neutralization: None [Analysis Conditions] Analysis software: MuitiPak (manufactured by ULVAC-PHI, Inc.)

[0087] The composition of the electrolyte is often adjusted assuming that the negative electrode is graphite. Therefore, if the surface to which the decomposition product of the electrolyte (film X) adheres is covered with carbon, it is expected that the film X with good Li ion conductivity will be more easily formed than when the decomposition product of the electrolyte adheres directly to the negative electrode body made of aluminum, and that an increase in resistance due to the film X will be less likely to occur.

[0088] That is, in the case of an aluminum negative electrode having a negative electrode body made of aluminum and a coating made of carbon formed on the surface of the negative electrode body, if an electrolyte optimized for a carbon-based negative electrode is used, the film X is unlikely to be formed with an abnormal thickness. As a result, in the case of such an aluminum negative electrode, the resistance value of the lithiation reaction measured under the above measurement conditions is 6.5 kΩ cm ２ It is believed that an aluminum anode having a .DELTA..times ...

[0089] The material of the coating 42 is alumina hydrate (Al ２ O ３ ・nH ２In the case of (O), the coating 42 can be formed by immersing the negative electrode body 41 in hot water at 50 to 100°C for several minutes to several hours. This formation method is known as the boehmite method. The term "boehmite method" has the meaning defined in JIS H 0201:1998 "Terminology for Aluminum Surface Treatment." During the immersion treatment, ammonia or triethanolamine may be added to the hot water as needed. These additives can uniformly generate alumina hydrate, forming a homogeneous coating 42. Alumina hydrate is called bayerite, alumina hydrate, etc., depending on the amount of hydrate, and it is known that this can be controlled by the temperature of the hot water and the immersion time.

[0090] The coating 42 made of alumina hydrate can also be formed by spraying high-temperature steam onto the negative electrode body 41 .

[0091] The alumina hydrate film formed on the surface of the negative electrode body 41 and the natural oxide film on the surface of the negative electrode body 41 can be distinguished by magnification observation using a microscope. The alumina hydrate film can be observed at a magnification of 10,000 times. On the other hand, the natural oxide film is so thin that it cannot be observed at the above magnification, and therefore can be easily distinguished from the alumina hydrate film.

[0092] When the electrolyte solution decomposes on the surface of the negative electrode 40A, it is thought that electrons are supplied from the negative electrode 40A to the electrolyte solution in contact with the surface of the negative electrode 40A, causing the reductive decomposition. On the other hand, the alumina hydrate film is electrically passive and does not easily allow electrons to pass through. Therefore, it is thought that in the portion of the surface of the negative electrode 40A covered with the alumina hydrate film, electron exchange between the electrolyte solution and the negative electrode 40A is unlikely to occur, and reductive decomposition of the electrolyte solution is unlikely to occur.

[0093] That is, in the case of an aluminum negative electrode having a negative electrode body made of aluminum and a coating made of alumina hydrate formed on the surface of the negative electrode body, reductive decomposition of the electrolyte solution is unlikely to occur on the surface, and the film X is unlikely to form. As a result, in the case of such an aluminum negative electrode, the resistance value of the lithiation reaction measured under the above measurement conditions is 6.5 kΩ cm ２ It is believed that an aluminum anode having a .DELTA..times ...

[0094] The thickness of the coating 42 is preferably 1 μm or less, and more preferably 0.5 μm or less. When the thickness of the coating 42 is 1 μm or less, the movement of Li ions is not hindered during charging and discharging, and Li ions can easily permeate the coating 42. This improves battery performance. By making the thickness 1 μm or less, there is almost no increase in thickness during battery manufacturing, and capacity reduction can also be suppressed. The thickness of the coating 42 is preferably 100 nm or more, and more preferably 200 nm or more.

[0095] When the material of the coating 42 is carbon, the thickness of the coating 42 is preferably 1 nm or more and 1 μm or less, and more preferably 1 nm or more and 100 nm or less.

[0096] (Method for Measuring Coating Thickness) The thickness of the coating 42 is measured from an SEM image of a cross section of the aluminum negative electrode 40A that is perpendicular to the surface of the coating 42. For example, the cross section is observed at a magnification of 10,000 times, and a virtual line connecting the intersection of the outer frame in the magnified field of view with the surface of the coating 42 is set as a reference line. Next, a perpendicular line is extended from a reference point set on the reference line toward the negative electrode body 41, and an intersection of the "interface between the negative electrode body 41 and the coating 42" and the "perpendicular line" is set. Next, the length of the line segment connecting the intersection and the reference point is determined. Ten reference points are set at equal intervals on the surface of the coating 42 in one magnified field of view, and the length of the line segment at each reference point is determined in the same manner as described above. The arithmetic mean value of the lengths thus determined is the thickness of the coating 42.

[0097] 9 is a schematic diagram showing another aluminum negative electrode 40B according to this embodiment. The aluminum negative electrode 40B is composed only of a negative electrode body 41. The negative electrode body 41 is similar to the negative electrode body described above.

[0098] The surface of the aluminum negative electrode 40B is pre-treated with alkali and acid. Specifically, the negative electrode body 41 is immersed in alkali (5 mass % NaOH aqueous solution) at 60° C. for 30 seconds, and then immersed in acid (30 mass % HNO ) at 25° C. ３ The aluminum negative electrode 40B was obtained by immersing the aluminum negative electrode 40B in the aqueous solution for 30 seconds and then rinsing it with water.

[0099] A natural oxide film of aluminum oxide is formed on the surface of the negative electrode body 41 (the surface of the rolled aluminum material that is the material of the negative electrode body 41). It is believed that the aluminum oxide present as the natural oxide film catalyzes and promotes the reductive decomposition of the electrolyte.

[0100] Furthermore, the surface of the rolled aluminum material from which the negative electrode body 41 is made may have oil (rolling oil) used in rolling the rolled material during production.

[0101] By subjecting the material (rolled material) of the negative electrode body 41 to an alkali or acid treatment, it is possible to remove a film of organic compounds (typically rolling oil) and natural oxide films adhering to the surface of the rolled material, thereby reducing the electrical resistance value of the surface. Removal of the rolling oil can be confirmed by FT-IR analysis of the surface of the negative electrode body 41, where the rolling oil is below the detection limit.

[0102] That is, in a component in which the surface of a rolled aluminum material is treated with either or both of an alkali treatment and an acid treatment, for example, an aluminum negative electrode in which the surface of the rolled material is treated with an alkali and then an acid, it is assumed that an organic compound film or a natural oxide film is not present. Therefore, catalytic reactions caused by the organic compound film or the natural oxide film are suppressed, and reductive decomposition of the electrolyte is suppressed. This makes it difficult for the film X to be formed. As a result, in such an aluminum negative electrode, the resistance value of the lithiation reaction measured under the above measurement conditions is 6.5 kΩ cm. ２ It is believed that an aluminum anode having a .DELTA..times ...

[0103] Such an aluminum negative electrode can be produced by a method for producing an aluminum negative electrode, which includes a step of producing a rolled material made of aluminum, and a step of treating the surface of the rolled material with either an alkali treatment or an acid treatment, or both.

[0104] Furthermore, the surface of the rolled material may be further treated with a non-chromate treatment after being treated with either or both of an alkali treatment and an acid treatment. The non-chromate treatment suppresses the formation of a natural oxide film on the surface of the rolled material treated with the alkali treatment or the acid treatment. The non-chromate treatment solution may be selected from inorganic Zr-based, Ti-based, Mo-based, Mn-based, and Ce-based solutions, or organic silane coupling agents.

[0105] In the aluminum negative electrodes 40A and 40B described above, after the lithiation reaction is carried out by the above-described method, it is preferable that the thickness of the film X (electrolyte deposit) formed on the surface of the aluminum negative electrode is 2 μm or less. If the formed film X is thin, deterioration of the columnar structures 51 a as described with reference to FIGS. 6 and 7 is unlikely to occur.

[0106] The thickness of the film X is preferably 1 μm or less, more preferably 0.1 μm or less, and even more preferably 0.01 μm or less. The thinner the film X formed on the surface of the aluminum negative electrode after the lithiation reaction is performed, the less the surface resistance of the negative electrode increases, and the easier it is to maintain the performance of the negative electrode. The thickness of the film X is ideally 0 nm, but may be 5 nm or more.

[0107] (Method for measuring thickness of deposit) The thickness of the film X (deposit) can be measured in the same manner as (Method for measuring thickness of coating) described above, except that the object to be measured is changed from the coating 42 to the film X.

[0108] The aluminum negative electrode having the above-described structure is an aluminum negative electrode for a nonaqueous electrolyte secondary battery that can improve the cycle characteristics of the nonaqueous electrolyte secondary battery.

[0109] ≪Nonaqueous electrolyte secondary battery≫

[0110] 10 is a schematic diagram showing an example of a nonaqueous electrolyte secondary battery. The lithium secondary battery (nonaqueous electrolyte secondary battery) 10 has a positive electrode 2, an aluminum negative electrode (negative electrode) 3, and a nonaqueous electrolyte (electrolyte) 6.

[0111] The cylindrical lithium secondary battery 10 is manufactured as follows: First, as shown in Fig. 10 , a pair of strip-shaped separators 1, a strip-shaped positive electrode 2 having a positive electrode lead 21 at one end, and a strip-shaped negative electrode 3 having a negative electrode lead 31 at one end are stacked in this order: separator 1, positive electrode 2, separator 1, negative electrode 3, and then wound to form an electrode group 4.

[0112] Next, the electrode group 4 and an insulator (not shown) are housed in the battery can 5, the bottom of the can is sealed, the electrode group 4 is impregnated with an electrolyte solution 6, and the electrolyte is disposed between the positive electrode 2 and the negative electrode 3. Furthermore, the top of the battery can 5 is sealed with a top insulator 7 and a sealing member 8, whereby a lithium secondary battery 10 can be manufactured.

[0113] The shape of the electrode group 4 can be, for example, a columnar shape such that the cross-sectional shape when the electrode group 4 is cut perpendicular to the winding axis is a circle, an ellipse, a rectangle, or a rectangle with rounded corners.

[0114] The shape of a lithium secondary battery having such an electrode group 4 can be any shape specified in IEC 60086, which is a standard for batteries established by the International Electrotechnical Commission (IEC), or JIS C 8500. Examples of shapes include a cylindrical shape and a rectangular shape.

[0115] Furthermore, the lithium secondary battery is not limited to the above-mentioned wound type configuration, and may be a stacked type configuration in which a stacked structure of a positive electrode, a separator, a negative electrode, and a separator is repeatedly stacked. Examples of stacked lithium secondary batteries include so-called coin type batteries, button type batteries, and paper type (or sheet type) batteries.

[0116] The separator 1, the positive electrode 2, and the negative electrode lead 31 can be made of materials known for use in lithium secondary batteries.

[0117] The aluminum negative electrode of the present embodiment described above can be used for the negative electrode 3. That is, the negative electrode 3 has a negative electrode body made of aluminum, and in the lithiation reaction measured under the measurement conditions described above, has a lithiation capacity of 1 mAh / cm ２ The resistance value is 6.5 kΩ cm ２An aluminum anode can be employed that is:

[0118] The negative electrode 3 may be an aluminum negative electrode having a negative electrode body made of aluminum and a coating formed on the surface of the negative electrode body, the coating being made of any one material selected from the group consisting of gold, carbon, and alumina hydrate.

[0119] The electrolyte 6 is a non-aqueous electrolyte. Examples of organic solvents contained in the electrolytic solution include carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di(methoxycarbonyloxy)ethane; ethers such as 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran; esters such as methyl formate, methyl acetate, propyl propionate, and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfolane, dimethyl sulfoxide, and 1,3-propane sultone; The above organic solvents may further contain fluoro groups (organic solvents in which one or more hydrogen atoms have been substituted with fluorine atoms).

[0120] As the organic solvent, it is preferable to use a mixture of two or more of these. Among them, a mixed solvent containing a carbonate is preferable, and a mixed solvent of a cyclic carbonate and an acyclic carbonate and a mixed solvent of a cyclic carbonate and an ether are more preferable. As a mixed solvent of a cyclic carbonate and an acyclic carbonate, a mixed solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is preferable. An electrolyte solution using such a mixed solvent has many advantages, such as a wide operating temperature range, resistance to deterioration even when charged and discharged at a high current rate, and resistance to deterioration even when used for a long time.

[0121] The electrolyte contained in the electrolytic solution is LiClO ４ , LiPF ６ , LiAsF ６ , LiSbF ６ , LiBF ４ , LiCF ３ SO ３ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiN(SO ２ CF ３ ) (COCF ３ ), Li(C ４ F ９ SO ３ ), LiC(SO ２ CF ３ ) ３ , Li ２ B １０ Cl １０ , LiBOB (wherein BOB is bis(oxalato)borate), LiFSI (wherein FSI is bis(fluorosulfonyl)imide), lithium salts of lower aliphatic carboxylic acids, LiAlCl ４ The electrolyte may be a fluorine-containing lithium salt such as LiPF ６ , LiAsF ６ , LiSbF ６ , LiBF ４, LiCF ３ SO ３ , LiN(SO ２ CF ３ ) ２ and LiC(SO ２ CF ３ ) ３ It is preferable to use a material containing at least one selected from the group consisting of:

[0122] Furthermore, the inventors have investigated LiBF ４ In addition to the lithium ion conductivity as an electrolyte, ６ It has been found that the electrolyte solution has the effect of suppressing the formation of the above-mentioned film X compared to other electrolytes such as LiBF. ４ When the electrolyte contains LiBF ４ From BF ３ For example, when ethylene carbonate (EC) is used as the solvent for the electrolyte, BF ３ It is believed that this protects the unshared electron pair of EC and suppresses decomposition of the electrolyte.

[0123] According to the lithium secondary battery 10 described above, the cycle characteristics can be improved.

[0124] While the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to these examples. The shapes and combinations of the components shown in the above examples are merely examples, and various modifications can be made based on design requirements, etc., without departing from the spirit of the present invention.

[0125] The present invention includes the following aspects.

[0126] <1> An aluminum negative electrode for use in a nonaqueous electrolyte secondary battery, the aluminum negative electrode having an anode body made of aluminum and a coating formed on the surface of the anode body, the coating being made of any one material selected from the group consisting of gold, carbon, and alumina hydrate.

[0127] <2> An aluminum negative electrode for use in a nonaqueous electrolyte secondary battery, the aluminum negative electrode having a negative electrode body made of aluminum and a coating formed on the surface of the negative electrode body, the coating being made of a material selected from the group consisting of gold, carbon, and alumina hydrate, and the coating having a thickness of 1 nm or more and 1 μm or less.

[0128] <3> An aluminum negative electrode for use in a nonaqueous electrolyte secondary battery, the aluminum negative electrode having a negative electrode body made of aluminum and a coating formed on the surface of the negative electrode body, the coating being made of carbon, and the oxygen content of the coating being 0 mol % or more and 20 mol % or less.

[0129] <4> The aluminum negative electrode according to any one of <1> to <3>, wherein the negative electrode body contains aluminum and one or more metal elements selected from the group consisting of Si, Ge, Sn, Ag, Sb, Bi, In, Mn, and Mg, and the content of the metal elements relative to the total amount of the negative electrode body is 0.1 mass% to 8 mass%.

[0130] <5> The aluminum negative electrode according to any one of <1> to <3>, wherein the average crystal grain size of aluminum crystal grains, as determined from a scanning ion microscope image of a cross section of the negative electrode body, is 1 μm or more and 200 μm or less.

[0131] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0132] In this example, the following measurements were carried out as appropriate.

[0133] (Resistance Value in Lithiation Reaction) The resistance value in the lithiation reaction was measured according to the above-mentioned (Method for measuring resistance value in lithiation reaction).

[0134] (Discharge Capacity Retention Rate) The discharge capacity retention rate was measured according to the above-mentioned (Method for measuring discharge capacity retention rate).

[0135] The thickness of the coating was measured as described above in (Method for measuring the thickness of the coating).

[0136] (Oxygen Content of Coating) The oxygen content of the coating was measured according to the above-mentioned (Method for Measuring Oxygen Content).

[0137] (Average Crystal Grain Size of Aluminum Crystal Grains) The average crystal grain size of aluminum crystal grains was measured according to the above-mentioned (Method for measuring average crystal grain size).

[0138] (Thickness of Deposit) The thickness of the deposit was measured according to the above-mentioned (Method for measuring the thickness of the deposit).

[0139] (Metal Element Content) The metal element content was measured according to the above-mentioned (Method for measuring metal element content).

[0140] Example 1 Preparation of Negative Electrode High-purity aluminum (purity: 99.99% by mass or more) and high-purity chemically produced silicon (purity: 99.999% by mass or more) were heated to and maintained at 760°C to obtain a molten aluminum-silicon alloy having a silicon content of 1.0% by mass relative to the total amount of aluminum and silicon.

[0141] Next, the molten alloy was purified by being held at a temperature of 740°C for 2 hours under a vacuum of 50 Pa. The molten alloy was cast into a cast iron mold (22 mm x 150 mm x 200 mm) dried at 150°C to obtain an ingot.

[0142] The rolling was carried out under the following conditions: Both sides of the ingot were machined by 2 mm, and then cold-rolled from a thickness of 18 mm at a processing rate of 99.6%. The thickness of the obtained rolled material was 50 μm.

[0143] Cross-sectional SIM observation (magnification 2000x) of the rolled material revealed aluminum crystal grains. Observation of the size of 50 crystal grains revealed that the crystal grain size was in the range of 1 μm to 20 μm. It was confirmed that the average crystal grain size of the aluminum crystal grains was 200 μm or less.

[0144] A high-purity aluminum-silicon alloy foil (thickness: 50 μm) having an aluminum purity of 99.999% and a silicon content of 1.0 mass % was cut into a disk shape with a diameter of 16 mm.

[0145] Gold was vapor-deposited onto the disk-shaped rolled material to produce the aluminum negative electrode of Example 1. The disk-shaped rolled material corresponds to the negative electrode body of the aluminum negative electrode.

[0146] The gold deposition conditions are shown below. "Film thickness" refers to the thickness of the gold film formed. Equipment: Ion sputter E-101, manufactured by Hitachi Naka Seiki Co., Ltd. Method: A disk-shaped rolled material was placed in a vacuum chamber, and gold was deposited by discharging between it and the target. Conditions: Target: Au-Pd (98:2) (manufactured by Hitachi High-Tech Fielding Co., Ltd., model: 01E-1112, size: 300 x 15 x 0.25 mm) Vacuum level: 15-20 Pa Ion current: Approximately 15 mA Deposition time: 2 minutes Film thickness: 100 Å (10 nm)

[0147] [Preparation of Positive Electrode] 90 parts by mass of lithium cobalt oxide (product name: Cellseed, manufactured by Nippon Chemical Industry Co., Ltd.; average particle size (D50) 10 μm) as a positive electrode active material, 5 parts by mass of polyvinylidene fluoride (manufactured by Kureha Corporation) as a binder, and 5 parts by mass of acetylene black (product name: Denka Black, manufactured by Denka Company, Ltd.) as a conductive material were mixed, and 70 parts by mass of N-methyl-2-pyrrolidone was further mixed to prepare an electrode mixture for the positive electrode.

[0148] The obtained electrode mixture was applied to a 15 μm thick aluminum foil current collector by a doctor blade method. The applied electrode mixture was dried at 60°C for 2 hours and then further vacuum dried at 150°C for 10 hours to volatilize N-methyl-2-pyrrolidone. The coating amount of the positive electrode active material after drying was 21.5 mg / cm. ２ It was.

[0149] The obtained laminate of the electrode mixture layer and the current collector was rolled and then cut into a disk shape with a diameter of 14 mm, thereby producing a positive electrode, which was a laminate of a positive electrode mixture layer containing lithium cobalt oxide as a forming material and a current collector.

[0150] [Preparation of Electrolyte Solution] LiPF 5 was added to a mixed solvent obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of EC:DMC=50:50. ６ The above was dissolved in a proportion of 1 mol / L to prepare an electrolyte solution.

[0151] [Production of Lithium Secondary Battery] A polyethylene porous separator was placed between the negative electrode and the positive electrode, and the resulting battery was housed in a battery case (standard 2032). The above electrolyte solution was poured into the battery case, and the battery case was sealed to produce a coin-shaped lithium secondary battery (lithium secondary battery including the aluminum negative electrode of Example 1) having a diameter of 20 mm and a thickness of 3.2 mm.

[0152] Example 2 An aluminum negative electrode of Example 2 and a lithium secondary battery including the aluminum negative electrode of Example 2 were fabricated in the same manner as in Example 1, except that carbon was vapor-deposited on a disk-shaped rolled material. The oxygen content of the formed carbon coating was 5 mol%.

[0153] The carbon deposition conditions are as follows. The length described in "Deposition amount" corresponds to the thickness of the carbon film to be formed. Apparatus: Vacuum deposition apparatus JEE-420. Manufactured by JEOL Ltd. Conditions: 10 －３ Heat deposition was performed under a vacuum of 0.1 Pa or less. Deposition amount: 15 nm. Carbon source: carbon rod (5φ×100 mm) manufactured by JEOL Ltd.

[0154] Example 3 An aluminum negative electrode of Example 3 and a lithium secondary battery including the aluminum negative electrode of Example 3 were produced in the same manner as in Example 1, except that the disk-shaped rolled material was immersed in hot water at 100°C for 10 minutes to form alumina hydrate.

[0155] Example 4 A disk-shaped rolled material was washed with alkali (5 mass % NaOH aqueous solution) at 60°C for 30 seconds, and then washed with acid (30 mass % HNO ) at 25°C. ３ An aluminum negative electrode of Example 4 and a lithium secondary battery including the aluminum negative electrode of Example 4 were fabricated in the same manner as in Example 1, except that the aluminum negative electrode was washed with a 100% aqueous solution of 1,000 sulphuric acid for 30 seconds, rinsed with water and dried.

[0156] Example 5: The disk-shaped rolled material was used as an aluminum anode, and the electrolyte contained in the electrolytic solution was LiPF ６ From LiBF ４ An aluminum negative electrode of Example 5 and a lithium secondary battery including the aluminum negative electrode of Example 5 were fabricated in the same manner as in Example 1, except that the above-mentioned change was made.

[0157] Example 6: The electrolyte contained in the electrolytic solution was LiPF ６ From LiBF ４ A lithium secondary battery including the aluminum negative electrode of Example 6 was fabricated in the same manner as in Example 2, except for changing the oxygen content of the formed carbon coating to 5 mol %.

[0158] Example 7: The electrolyte contained in the electrolytic solution was LiPF ６ From LiBF ４ A lithium secondary battery including the aluminum negative electrode of Example 7 was fabricated in the same manner as in Example 3, except for changing the above.

[0159] Example 8 An aluminum negative electrode of Example 8 and a lithium secondary battery including the aluminum negative electrode of Example 8 were produced in the same manner as in Example 6, except that a 5 nm thick layer of carbon was vapor-deposited on a disk-shaped rolled material. The oxygen content of the formed carbon coating was 5 mol%.

[0160] Example 9 An aluminum negative electrode of Example 9 and a lithium secondary battery including the aluminum negative electrode of Example 9 were produced in the same manner as in Example 6, except that a 30 nm thick layer of carbon was vapor-deposited on a disk-shaped rolled material. The oxygen content of the formed carbon coating was 5 mol%.

[0161] Example 10 An aluminum negative electrode of Example 10 and a lithium secondary battery including the aluminum negative electrode of Example 10 were produced in the same manner as in Example 3, except that the disk-shaped rolled material was immersed in hot water at 60°C for 5 minutes to form alumina hydrate.

[0162] Example 11 An aluminum negative electrode of Example 11 and a lithium secondary battery including the aluminum negative electrode of Example 11 were produced in the same manner as in Example 3, except that the disk-shaped rolled material was immersed in hot water at 50°C for 30 minutes to form alumina hydrate.

[0163] Example 12: A disk-shaped rolled material was immersed in hot water at 60°C for 5 minutes to form alumina hydrate, and the electrolyte contained in the electrolytic solution was changed to LiPF ６ From LiBF ４An aluminum negative electrode of Example 12 and a lithium secondary battery including the aluminum negative electrode of Example 12 were fabricated in the same manner as in Example 3, except that the above-mentioned change was made.

[0164] Example 13: A disk-shaped rolled material was immersed in hot water at 50°C for 30 minutes to form alumina hydrate, and the electrolyte contained in the electrolytic solution was changed to LiPF ６ From LiBF ４ An aluminum negative electrode of Example 13 and a lithium secondary battery including the aluminum negative electrode of Example 13 were fabricated in the same manner as in Example 3, except that the above-mentioned change was made.

[0165] Comparative Example 1 An aluminum negative electrode of Comparative Example 1 and a lithium secondary battery including the aluminum negative electrode of Comparative Example 1 were fabricated in the same manner as in Example 1, except that the disk-shaped rolled material was used as the aluminum negative electrode as is.

[0166] The evaluation results are shown in Table 1. In the "Surface Treatment" column of Table 1, the value in parentheses after "Carbon" indicates the film thickness of the carbon coating. Similarly, the value in parentheses after "Alumina Hydrate" indicates the formation conditions for forming the alumina hydrate (the conditions for immersing the disk-shaped rolled material in hot water).

[0167]

[0168] As a result of the evaluation, the resistance value in the lithiation reaction in all of Examples 1 to 13 was lower than the result of Comparative Example 1, suggesting that the formation of film X made from decomposition products of the electrolyte solution was suppressed. Furthermore, the cycle characteristics of all of Examples 1 to 13 were improved compared to the cycle characteristics of Comparative Example 1.

[0169] In Examples 6 to 9, 12, and 13, the negative electrode body was an aluminum negative electrode coated with carbon or alumina hydrate, and the electrolyte was LiBF ４ It was confirmed that excellent cycle characteristics could be achieved by combining the electrolyte solution with the aluminum anode. ４ Therefore, the other aluminum anodes shown in Examples 1, 4, and 5 and the electrolyte containing LiBF４ Similarly, excellent cycle characteristics can be expected even when combined with an electrolyte solution that employs the above.

[0170] The above results confirmed that the present invention is useful.

[0171] 2,60...Positive electrode, 3,40A,40B,50...Aluminum negative electrode (negative electrode), 6,70...Nonaqueous electrolyte (electrolyte solution), 10,100...Lithium secondary battery (nonaqueous electrolyte secondary battery), 41...Negative electrode body, 42...Coating

Claims

1. An aluminum negative electrode for use in a non-aqueous electrolyte secondary battery, comprising: The negative electrode body is made of aluminum. In the lithiation reaction measured under the following measurement conditions, the lithiation capacity is 1 mAh / cm ２ The resistance value is 6.5 kΩ cm ２ The aluminum anode is: (Measurement conditions) Current density: 0.6mA / cm ２ Positive electrode: LiCoO ２ Electrolyte: 1 mol / L LiPF ６ Solution (ethylene carbonate: dimethyl carbonate = 1:1 (volume ratio) mixed solvent) Measurement temperature: 25℃ C rate: 0.2C

2. A coating is formed on the surface of the negative electrode body, 2. The aluminum negative electrode according to claim 1, wherein the coating is made of any one material selected from the group consisting of gold, carbon, and alumina hydrate.

3. 3. The aluminum negative electrode according to claim 2, wherein the coating has a thickness of 1 μm or less.

4. The coating is made of carbon, 4. The aluminum negative electrode according to claim 2, wherein the coating has an oxygen content of 20 mol % or less.

5. The negative electrode body is a rolled material, 2. The aluminum negative electrode according to claim 1, wherein rolling oil is below the detection limit in FT-IR analysis of the surface of the negative electrode body.

6. 4. The aluminum negative electrode according to claim 1, wherein after the lithiation reaction is carried out, a deposit of the electrolyte formed on the surface of the aluminum negative electrode has a thickness of 2 μm or less.

7. The negative electrode body includes aluminum and at least one metal element selected from the group consisting of Si, Ge, Sn, Ag, Sb, Bi, In, Mn, and Mg; 4. The aluminum negative electrode according to claim 1, wherein the content of the metal element relative to the total amount of the negative electrode body is 0.1 mass % or more and 8 mass % or less.

8. 4. The aluminum negative electrode according to claim 1, wherein the average crystal grain size of aluminum crystal grains is 200 μm or less as determined from a scanning ion microscope image of a cross section of the negative electrode body.

9. A positive electrode and The aluminum negative electrode according to any one of claims 1 to 3, A non-aqueous electrolyte secondary battery having a non-aqueous electrolyte.

10. The non-aqueous electrolyte is LiBF ４ The nonaqueous electrolyte secondary battery according to claim 9 .

11. A positive electrode and An aluminum negative electrode; LiBF ４ and a non-aqueous electrolyte solution containing The aluminum negative electrode has a lithiation reaction resistance of 6.5 kΩ cm when measured under the following conditions: ２ The nonaqueous electrolyte secondary battery is as follows: (Measurement conditions) Lithium capacity: 1 mAh / cm ２ Current density: 0.6mA / cm ２ Positive electrode: LiCoO ２ Measurement temperature: 25℃ C rate: 0.2C