Battery and battery pack

Abstract

Provided is a battery according to an embodiment of the present invention. The battery comprises a positive electrode, a negative electrode, and an electrolyte. The positive electrode contains a first oxide. In a hard X-ray photoelectron spectroscopy spectrum of the surface of the positive electrode, the ratio B / A of the area B of a peak having a peak top in the range of 683 eV to 686 eV inclusive to the area A of a peak having a peak top in the range of 851 eV to 868 eV inclusive is 0.07 to 0.20 inclusive. The negative electrode contains a lithium titanium-containing oxide. In a hard X-ray photoelectron spectroscopy spectrum of the surface of the negative electrode, the ratio D / C of the area D of a peak having a peak top in the range of 685 eV to 687.5 eV inclusive to the area C of a peak having a peak top in the range of 455 eV to 469 eV inclusive is 0.75 to 1.8 inclusive. The electrolyte contains a carboxylic acid ester and a cyclic carbonate. The volume of the carboxylic acid ester is not less than 2.3 times the volume of the cyclic carbonate.

Description

Batteries and battery packs

[0001] Embodiments of the present invention relate to batteries and battery packs.

[0002] Non-aqueous electrolyte batteries have recently been attracting attention for their potential applications in electric vehicles (EVs) and hybrid electric vehicles (HEVs) as a replacement for gasoline-powered vehicles, as well as in large-scale systems such as electric aircraft and power storage. Therefore, improvements in capacity characteristics, high-current output performance, and safety are required.

[0003] Lithium nickel-cobalt manganese oxide is used as a positive electrode active material for non-aqueous electrolyte batteries. By increasing the proportion of nickel (Ni) contained in lithium nickel-cobalt manganese oxide, a high-capacity positive electrode active material can be obtained.

[0004] To improve the safety of non-aqueous electrolyte batteries, methods have been proposed that use flame-retardant solvents such as fluorine-containing solvents or solvents with high flash points as the solvent for the electrolyte.

[0005] International Publication No. 2021 / 199485, Japanese Patent Publication No. 2016-38997

[0006] The problem that this invention aims to solve is to provide a battery that is highly safe and has high input / output performance.

[0007] According to the embodiment, a battery is provided. The battery comprises a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises an oxide containing a transition metal. The transition metals include nickel, cobalt, and manganese. The number of nickel atoms in the oxide is A, where the total number of transition metal atoms is 1. ＮｉThe ratio of the area of ​​peaks with peak tops in the range of 683 eV to 686 eV to the area of ​​peaks with peak tops in the range of 851 eV to 868 eV in the hard X-ray photoelectron spectroscopy spectrum of the positive electrode surface is 0.07 to 0.20. The negative electrode contains a lithium titanium-containing oxide. The ratio of the area of ​​peaks with peak tops in the range of 685 eV to 687.5 eV to the area of ​​peaks with peak tops in the range of 455 eV to 469 eV in the hard X-ray photoelectron spectroscopy spectrum of the negative electrode surface is 0.75 to 1.8. The ratio of the area of ​​peaks with peak tops in the range of 685 eV to 687.5 eV to the area of ​​peaks with peak tops in the range of 455 eV to 469 eV in the hard X-ray photoelectron spectroscopy spectrum of the negative electrode surface is 0.75 to 1.8.

[0008] According to another embodiment, a battery pack is provided. The battery pack includes a battery according to the embodiment.

[0009] Figure 1 is a cross-sectional view of one example of a battery according to the embodiment, cut in the thickness direction. Figure 2 is an enlarged cross-sectional view of part A in Figure 1. Figure 3 is a partially cutaway perspective view of another example of a battery according to the embodiment. Figure 4 is a perspective view showing another example of the electrode group included in another example of a battery according to the embodiment. Figure 5 is an exploded perspective view of one example of a battery pack according to the embodiment. Figure 6 is a block diagram showing the electrical circuit of the battery pack shown in Figure 5. Figure 7 is an example of a hard X-ray photoelectron spectroscopy spectrum of the positive electrode included in the battery according to the embodiment. Figure 8 is another example of a hard X-ray photoelectron spectroscopy spectrum of the positive electrode included in the battery according to the embodiment. Figure 9 is an example of a hard X-ray photoelectron spectroscopy spectrum of the negative electrode included in the battery according to the embodiment. Figure 10 is another example of a hard X-ray photoelectron spectroscopy spectrum of the negative electrode included in the battery according to the embodiment. Embodiment

[0010] The embodiments will be described below with reference to the drawings. Common components throughout the embodiments will be denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, each drawing is a schematic diagram intended to illustrate the embodiments and facilitate understanding; their shapes, dimensions, and ratios may differ from those of the actual device. These can be appropriately modified in accordance with the following description and known technology.

[0011] (First Embodiment) According to the first embodiment, a battery is provided. The battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes an oxide containing a transition metal. The transition metals include nickel, cobalt, and manganese. The number of nickel atoms in the oxide is A, where the total number of transition metal atoms is 1. Ｎｉ The ratio of the area of ​​peaks with peak tops in the range of 683 eV to 686 eV to the area of ​​peaks with peak tops in the range of 851 eV to 868 eV in the hard X-ray photoelectron spectroscopy spectrum of the positive electrode surface is 0.07 to 0.20. The negative electrode contains a lithium titanium-containing oxide. The ratio of the area of ​​peaks with peak tops in the range of 685 eV to 687.5 eV to the area of ​​peaks with peak tops in the range of 455 eV to 469 eV in the hard X-ray photoelectron spectroscopy spectrum of the negative electrode surface is 0.75 to 1.8. The ratio of the area of ​​peaks with peak tops in the range of 685 eV to 687.5 eV to the area of ​​peaks with peak tops in the range of 455 eV to 469 eV in the hard X-ray photoelectron spectroscopy spectrum of the negative electrode surface is 0.75 to 1.8.

[0012] In this specification, "an oxide containing nickel, cobalt, and manganese, wherein the number of nickel atoms A is defined as the total number of transition metal atoms in the oxide being 1." Ｎｉ Oxides with a value of 0.7 or higher are sometimes referred to as primary oxides.

[0013] An oxide containing nickel, cobalt, and manganese, where the number of nickel atoms A is defined as the total number of transition metal atoms in the oxide being 1. ＮｉOxides with a coefficient of 0.7 or higher (first oxides) have high capacity. However, while first oxides have high capacity, they also have low thermal stability. Therefore, positive electrodes containing first oxides tend to generate heat.

[0014] Conventionally, solvents containing a mixture of linear carbonates and cyclic carbonates have been used as the solvent for electrolytes. Cyclic carbonates have a high dielectric constant, which promotes the dissociation of lithium ions and contributes to lithium ion conduction, but they also have a low decomposition initiation temperature and are easily decomposed.

[0015] Therefore, when a positive electrode containing a primary oxide is combined with a conventional electrolyte, the decomposition of the electrolyte is likely to proceed. In particular, the decomposition of cyclic carbonates is likely to proceed. This leads to the problem of gas generation. In addition, heat can be generated during the decomposition reaction of the electrolyte, and this heat further accelerates the decomposition reaction of the electrolyte. This problem is likely to occur, for example, when the battery is overcharged. When a battery is overcharged, the energy of the positive electrode containing a primary oxide can become excessively high. When such a positive electrode comes into contact with the electrolyte, the decomposition reaction of the electrolyte is particularly likely to proceed.

[0016] In contrast, the electrolyte contained in the battery according to this embodiment includes a carboxylic acid ester and a cyclic carbonate. The volume of the carboxylic acid ester is 2.3 times or more the volume of the cyclic carbonate.

[0017] Carboxylic acid esters have high dielectric constants and low viscosity. Therefore, even when the proportion of carboxylic acid esters in the electrolyte is high, the ionic conductivity of the electrolyte can be maintained at a high level. Thus, electrolytes containing carboxylic acid esters and cyclic carbonates have high ionic conductivity and can therefore achieve high input / output performance.

[0018] Furthermore, carboxylic acid esters have a higher decomposition initiation temperature compared to cyclic carbonates. In electrolytes, the more carboxylic acid esters are included relative to the cyclic carbonate, the more the stability of the electrolyte tends to improve. In this embodiment, the volume of carboxylic acid esters in the electrolyte is 2.3 times or more than the volume of cyclic carbonate. Therefore, the stability of the electrolyte can be improved, and even when this electrolyte is combined with a positive electrode containing a first oxide, the generation of gas and heat can be reduced. Thus, safety can be improved. However, from the viewpoint of maintaining a high ionic conductivity of the electrolyte, the electrolyte needs to contain cyclic carbonates.

[0019] Carboxylic acid esters have low stability at low potentials and are therefore easily reductively decomposed at the negative electrode. The battery according to this embodiment contains a lithium titanium-containing oxide with a relatively high potential at the negative electrode, which can prevent the negative electrode potential from becoming too low. Therefore, gas generation caused by the reductive decomposition of carboxylic acid esters at the negative electrode can be suppressed, thereby improving input / output performance.

[0020] In the hard X-ray photoelectron spectroscopy (HAXPES) spectrum of the positive electrode surface, the ratio B / A of the area B of the peaks with peak tops in the range of 683 eV to 686 eV to the area A of the peaks with peak tops in the range of 851 eV to 868 eV may be an indicator of the degree of exposure of the first oxide on the positive electrode surface.

[0021] For example, a small B / A ratio may mean that the proportion of the primary oxide on the surface of the positive electrode is large. In other words, it may mean that the degree of exposure of the primary oxide on the surface of the positive electrode is large.

[0022] Conversely, a large B / A ratio may mean that the proportion of the primary oxide on the positive electrode surface is small. For example, it may mean that the degree of exposure of the primary oxide is small because a coating is formed on at least a portion of the positive electrode surface. Therefore, contact and reaction between the carboxylic acid ester contained in the electrolyte and the primary oxide can be suppressed. As a result, the oxidative decomposition of the carboxylic acid ester can be suppressed. As a result, the heat generated by the battery due to the decomposition of the electrolyte can be reduced, and gas generation can be suppressed. Therefore, for example, the progression of gas generation can be suppressed even in high-temperature environments.

[0023] In the battery according to this embodiment, the B / A ratio is 0.07 or higher. Therefore, the exposure of the primary oxide on the surface of the positive electrode is suppressed. As a result, the oxidative decomposition of the carboxylic acid ester can be suppressed. In addition, the amount of heat generated by the battery can be reduced, thus improving safety. Furthermore, since the B / A ratio is 0.20 or lower, the amount of film formed on the surface of the positive electrode is not excessive. Therefore, the movement of charge within the battery can be kept smooth, and the resistance can be kept low.

[0024] In the hard X-ray photoelectron spectroscopy spectrum of the negative electrode surface, the ratio D / C of the area D of peaks with peak tops in the range of 685 eV to 687.5 eV to the area C of peaks with peak tops in the range of 455 eV to 469 eV may be an indicator of the degree of exposure of lithium titanium-containing oxide on the negative electrode surface.

[0025] For example, a small D / C ratio may mean that the proportion of lithium titanium-containing oxide on the surface of the negative electrode is large. In other words, it may mean that the degree of exposure of lithium titanium-containing oxide on the surface of the negative electrode is large.

[0026] On the contrary, a large D / C may mean that the proportion of the lithium titanium-containing oxide occupying the negative electrode surface is small. For example, since a film is formed on at least a part of the surface of the negative electrode, it may mean that the degree of exposure of the lithium titanium-containing oxide is small. Therefore, it is possible to suppress the contact and reaction between the carboxylic acid ester contained in the electrolyte and the lithium titanium-containing oxide. Therefore, since the reduction decomposition of the carboxylic acid ester can be suppressed, gas generation can be suppressed.

[0027] In the battery according to the embodiment, D / C is 0.75 or more. Therefore, the exposure of the lithium titanium-containing oxide on the surface of the negative electrode is suppressed. Therefore, the reduction decomposition of the carboxylic acid ester can be suppressed. Further, since D / C is 1.8 or less, the amount of the film formed on the negative electrode surface is not too large. Therefore, since the movement of charges in the battery can be made smooth, the resistance can be kept low. Therefore, the battery according to the embodiment can improve safety and input / output performance.

[0028] The battery according to the embodiment will be further described.

[0029] The battery according to the embodiment can be, for example, a lithium battery or a lithium ion battery having lithium ions as a carrier. The battery according to the embodiment may be a secondary battery. The secondary battery may be a nonaqueous electrolyte secondary battery in which the electrolyte is a nonaqueous electrolyte.

[0030] The first oxide is represented by the general formula Li x Ni 1-y-z Co y Mn z O₂, where x satisfies 0 < x ≤ 1, y satisfies 0 < y < 0.3, and z satisfies 0 < z < 0.3, and is preferably an oxide.

[0031] When the first oxide is an oxide represented by the general formula Li x Ni 1-y-z Co y Mn z O₂, the transition metals contained in the first oxide are nickel, cobalt, and manganese.

[0032] As explained earlier, the first oxide is the number of nickel atoms A when the total number of transition metal atoms is set to 1. Ｎｉ The above general formula Li x Ni 1-y-z Co y Mn z In O2, the sum of the subscripts of the transition metals nickel, cobalt, and manganese is 1. In other words, the first oxide is of the general formula Li x Ni 1-y-z Co y Mn z In the case of an oxide represented by O2, the number of nickel atoms A is calculated by taking the total number of transition metal atoms as 1. Ｎｉ This corresponds to the subscript 1-y-z for nickel in the general formula. General formula Li x Ni 1-y-z Co y Mn z In O2, 1-y-z is 0.7 or greater.

[0033] The positive electrode according to the embodiment may include positive electrode active material particles containing a first oxide. In the particle size distribution chart obtained by laser diffraction scattering for the positive electrode active material particles, it is preferable that the ratio of d90 to d10, d90 / d10, is 4 or less. Here, the particle size distribution is a volume-based cumulative frequency distribution accumulated from the smallest particle size. d10 is the particle size at which the cumulative frequency from the smallest particle size side of the cumulative frequency distribution becomes 10%. d90 is the particle size at which the cumulative frequency from the smallest particle size side of the cumulative frequency distribution becomes 90%. A small value of d90 / d10 may mean that there is little variation in particle size. When there is little variation in the particle size of the positive electrode active material particles, grain boundaries that can cause an increase in resistance are less likely to occur. Therefore, the resistance of the positive electrode can be lowered.

[0034] Furthermore, when the first oxide contained in the positive electrode active material particles is a single crystal, the d90 / d10 of the positive electrode active material particles may be 4 or less.

[0035] Generally, when active material particles crack, the surface area of ​​the active material particles increases, which can alter the performance of the battery containing those particles. For example, active material particles can crack due to expansion and contraction during charging and / or discharging. The more charge-discharge cycles are repeated, the more likely the particles are to crack.

[0036] If the primary oxide contained in the positive electrode active material particles is a single crystal, cracking of the positive electrode active material particles can be reduced. As a result, the increase in the surface area occupied by the primary oxide due to particle cracking can be suppressed, thus suppressing contact between the primary oxide and the electrolyte. Therefore, the decomposition of the electrolyte can be further suppressed.

[0037] When the primary oxide contained in the positive electrode active material particles is a single crystal, the d90 / d10 of the positive electrode active material particles may be 4 or less. Furthermore, the average particle diameter may be between 2 μm and 8 μm. Also, the fracture strength may be between 30 MPa and 300 MPa. In other words, when the d90 / d10, average particle diameter, and / or fracture strength of the positive electrode active material particles are within the above range, the primary oxide contained in the positive electrode active material particles may be a single crystal, thus suppressing the increase in the specific surface area occupied by the primary oxide due to cracking of the positive electrode active material particles. Therefore, the decomposition of the electrolyte can be suppressed. Consequently, heat generation and gas generation due to electrolyte decomposition can be suppressed. Therefore, the safety and input / output performance of the battery can be improved.

[0038] Positive electrode active material particles are prone to cracking when repeated charge-discharge cycles are performed. Therefore, when the battery according to this embodiment is a secondary battery, it is preferable that the d90 / d10, average particle diameter, and / or fracture strength of the positive electrode active material particles are within the above-mentioned range, as this can more effectively suppress the decomposition of the electrolyte.

[0039] The battery according to the embodiment will be described in more detail below.

[0040] The carboxylic acid ester contained in the electrolyte preferably does not contain fluorine atoms. Compared to carboxylic acid esters containing fluorine atoms, carboxylic acid esters that do not contain fluorine atoms can reduce gas generation and reduce resistance.

[0041] An example of a carboxylic acid ester that does not contain a fluorine atom is represented by the structural formula R-COO-R', where R and R' are each C ｘ H ｙ Examples include carboxylic acid esters, which are hydrocarbon groups represented by the formula. It is preferable that the subscripts x and y satisfy y = 2x + 1. In other words, it is preferable that R and R' each be a saturated hydrocarbon group. A saturated hydrocarbon group consists only of x carbon atoms and y hydrogen atoms, and therefore does not contain fluorine atoms. Furthermore, saturated hydrocarbon groups are preferred because they are considered to have lower reactivity compared to unsaturated hydrocarbon groups that contain unsaturated bonds such as double bonds.

[0042] Examples of carboxylic acid esters that do not contain a fluorine atom and are represented by the structural formula R-COO-R', where R and R' are both saturated hydrocarbon groups, include propyl propionate, ethyl propionate, methyl propionate, ethyl acetate, methyl acetate, propyl butyrate, ethyl butyrate, and methyl butyrate.

[0043] The fewer carbon atoms a single carboxylic acid ester molecule contains, the higher its dielectric constant and the lower its viscosity tends to be. The higher the dielectric constant of a carboxylic acid ester, or the lower its viscosity, the better its conductivity tends to be. Therefore, the fewer carbon atoms a single carboxylic acid ester molecule contains, the better the input / output performance can be. However, it is preferable that a single carboxylic acid ester molecule contains six or more carbon atoms. Carboxylic acid esters with six or more carbon atoms per molecule are less flammable than carboxylic acid esters with five or fewer carbon atoms. Therefore, they are easier to handle and improve the safety of batteries. It is preferable that a single carboxylic acid ester molecule contains six carbon atoms. Among carboxylic acid esters with six carbon atoms per molecule, propyl propionate is the most preferred.

[0044] In hard X-ray photoelectron spectroscopy of the positive electrode surface, within the range of 851 eV to 868 eV, for example, Ni2p, which is attributed to nickel atoms, is present. ３／２ A peak may be detected. Ni2p is attributed to nickel atoms. ３／２The range in which the peak may be detected is between 851.0 eV and 868.0 eV. (Ni2p) ３／２ The peak may have its peak top within the range of 851 eV to 868 eV. A peak with its peak top within the range of 683 eV to 686 eV may be, for example, an F1s peak attributed to lithium fluoride (LiF). The range in which an F1s peak attributed to lithium fluoride (LiF) has its peak top may be between 683.0 eV and 686.0 eV.

[0045] In other words, the ratio B / A of the area B of peaks with peak tops in the range of 683 eV to 686 eV to the area A of peaks with peak tops in the range of 851 eV to 868 eV can be an indicator of the degree of lithium fluoride presence relative to nickel atoms on the surface of the positive electrode. On the surface of the positive electrode, nickel atoms may be contained in, for example, the first oxide. Lithium fluoride may be contained in, for example, the coating.

[0046] A high B / A ratio may indicate a high degree of lithium fluoride relative to the nickel atoms exposed on the positive electrode surface. In other words, it may indicate a large amount of film formed on the positive electrode surface. More specifically, for example, a high B / A ratio may occur when a large amount of lithium fluoride-containing film is formed, or when lithium fluoride makes up a high proportion of the film. Alternatively, the B / A ratio may also increase when the amount of nickel atoms exposed on the positive electrode surface decreases due to the formation of a film on the positive electrode surface.

[0047] Conversely, a small B / A ratio may mean that the amount of film formed on the surface of the positive electrode is small. In this case, resistance can be reduced, which contributes to improved input / output performance.

[0048] In the hard X-ray photoelectron spectroscopy spectrum of the negative electrode surface, within the range of 455 eV to 469 eV, for example, Ti2p, which is attributed to titanium atoms, is present. １／２ Peak and Ti2p ３／２ A peak may be detected. Ti2p is attributed to titanium atoms. １／２ Peak and Ti2p ３／２The range in which the peak may be detected is between 455.0 eV and 469.0 eV. (Ti2p) １／２ Peak and Ti2p ３／２ The peak may have its peak top within the range of 455 eV to 469 eV. A peak with its peak top within the range of 685 eV to 687.5 eV may be, for example, an F1s peak attributed to lithium fluoride (LiF). The lower limit of the range in which an F1s peak attributed to lithium fluoride (LiF) has its peak top may be 685.0 eV.

[0049] In other words, the ratio D / C of the area D of peaks with peak tops in the range of 685 eV to 687.5 eV to the area C of peaks with peak tops in the range of 455 eV to 469 eV can be an indicator of the degree of lithium fluoride presence relative to titanium atoms on the surface of the negative electrode. On the surface of the negative electrode, titanium atoms may be contained in, for example, lithium titanium-containing oxides. Lithium fluoride may be contained in, for example, coatings.

[0050] A high D / C ratio may indicate a high degree of lithium fluoride relative to the titanium atoms exposed on the negative electrode surface. In other words, it may mean a large amount of coating formed on the negative electrode surface. More specifically, for example, a high D / C ratio can occur when a large amount of lithium fluoride-containing coating is formed, or when lithium fluoride makes up a high proportion of the coating. Alternatively, the D / C ratio can also increase when the amount of titanium atoms exposed on the negative electrode surface decreases due to the formation of a coating on the negative electrode surface.

[0051] Conversely, a low D / C ratio may mean that the amount of film formed on the surface of the negative electrode is small. In this case, resistance can be reduced, which contributes to improved input / output performance. The upper limit of the D / C ratio may be, for example, 1.80.

[0052] Next, the battery according to the embodiment will be described in more detail with reference to the drawings.

[0053] An example of such a battery will be described with reference to Figures 1 and 2. The flat-type battery shown in Figure 1 comprises a flat electrode group 1, an outer casing member 2, a positive electrode terminal 7, a negative electrode terminal 6, and an electrolyte (not shown). The outer casing member 2 is a bag-shaped outer casing member made of laminate film. The electrode group 1 is housed in the outer casing member 2.

[0054] The electrode group 1 included in the battery shown in Figures 1 and 2 is a wound electrode group. As shown in Figure 2, the wound electrode group includes a positive electrode 3, a negative electrode 4, and a separator 5, and is formed by winding a laminate made by stacking the negative electrode 4, separator 5, positive electrode 3, and separator 5 in that order from the outside in, in a spiral shape, and then press molding. The electrolyte is held in the electrode group.

[0055] The positive electrode 3 includes a positive electrode current collector 3a and a positive electrode active material containing layer 3b. The positive electrode active material containing layer 3b contains positive electrode active material. The positive electrode active material containing layer 3b is formed on both sides of the positive electrode current collector 3a. The negative electrode 4 includes a negative electrode current collector 4a and a negative electrode active material containing layer 4b. The negative electrode active material containing layer 4b contains negative electrode active material. In the outermost part of the negative electrode 4, the negative electrode active material containing layer 4b is formed only on one side of the inner surface of the negative electrode current collector 4a. In the rest of the negative electrode 4, the negative electrode active material containing layer 4b is formed on both sides of the negative electrode current collector 4a.

[0056] As shown in Figure 1, near the outer edge of the electrode group 1, the positive electrode terminal 7 is electrically connected to the positive electrode 3. The negative electrode terminal 6 is electrically connected to the negative electrode 4 in the outermost layer. The positive electrode terminal 7 and the negative electrode terminal 6 extend to the outside through an opening in the outer casing member 2. Such a battery is not limited to the configurations shown in Figures 1 and 2, but can also have configurations such as that shown in Figure 3.

[0057] In the rectangular battery shown in Figure 3, the electrode group 10 is housed in a bottomed rectangular cylindrical metal container 12, which serves as the outer casing. A rectangular lid 13 is welded to the opening of the container 12. The flattened electrode group 10 may have a configuration similar to that of the electrode group 1 described with reference to Figures 1 and 2, for example.

[0058] The negative lead 14 has one end electrically connected to the negative current collector and the other end electrically connected to the negative terminal 15. The negative terminal 15 is fixed to the rectangular cover 13 with a hermetic seal interposed with a glass material 16. The positive lead 17 has one end electrically connected to the positive current collector and the other end electrically connected to the positive terminal 18 fixed to the rectangular cover 13.

[0059] The negative electrode lead 14 is manufactured from a material such as aluminum or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, or Si. It is preferable that the negative electrode lead 14 be made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0060] The positive electrode lead 17 is manufactured from a material such as aluminum or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, or Si. It is preferable that the positive electrode lead 17 be made of the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[0061] Although the battery shown in Figure 3 uses a wound electrode group (wound electrode group) in which the separator is wound together with the positive and negative electrodes, a stacked electrode group (stacked electrode group) may be used as the electrode group 10 instead of the wound electrode group. An example of such a stacked electrode group is shown in Figure 4. The electrode group 11 shown in Figure 4 is constructed by folding the separator 5 in a zigzag pattern and arranging the positive electrode 3 and negative electrode 4 alternately at the folded parts. Specifically, the positive electrode 3, negative electrode 4, positive electrode 3, and negative electrode 4 are arranged in this order, sandwiched between the separators 5 in the zigzag pattern. The positive electrode current collector tab 3c and the negative electrode current collector tab 4c protrude from one of the long sides of the zigzag pattern folded separator 5. The positive electrode current collector tab 3c and the negative electrode current collector tab 4c are arranged so as not to overlap each other.

[0062] Note that the order of the positive electrode 3 and the negative electrode 4 is not limited to the order shown in Figure 4; they may also be arranged in the order of negative electrode 4, positive electrode 3, negative electrode 4, positive electrode 3.

[0063] When the stacked electrode group 11 described above with reference to Figure 4 is applied as the electrode group 10 of the battery shown in Figure 3, each of the multiple positive electrode current collector tabs 3c can be electrically connected to the positive electrode lead 17. In addition, each of the multiple negative electrode current collector tabs 4c can be electrically connected to the negative electrode lead 14.

[0064] (Manufacturing Method) An example of a battery manufacturing method according to the embodiment includes preparing a positive electrode and a negative electrode, housing the positive electrode and negative electrode in an outer casing, injecting an electrolyte into the outer casing, sealing the outer casing to obtain a battery precursor, and aging the battery precursor to obtain a battery. The battery precursor may be charged for the first time before aging. The gas inside the battery may be removed after aging.

[0065] The positive electrode can be manufactured, for example, by the following method. First, a slurry is prepared by suspending the positive electrode active material, conductive agent, and binder in a solvent. This slurry is applied to one or both sides of the positive electrode current collector. Next, the applied slurry is dried to obtain a laminate of the positive electrode active material-containing layer and the positive electrode current collector. After that, this laminate is pressed. In this way, the positive electrode is manufactured.

[0066] Alternatively, the positive electrode may be manufactured by the following method: First, a positive electrode active material, a conductive agent, and a binder are mixed to obtain a mixture. Next, this mixture is formed into pellets. Then, these pellets are placed on a positive electrode current collector to obtain the positive electrode.

[0067] The negative electrode can be manufactured, for example, by the following method. First, a slurry is prepared by suspending the negative electrode active material, conductive agent, and binder in a solvent. This slurry is applied to one or both sides of the negative electrode current collector. Next, the applied slurry is dried to obtain a laminate of the negative electrode active material-containing layer and the negative electrode current collector. After that, this laminate is pressed. In this way, the negative electrode is manufactured.

[0068] Alternatively, the negative electrode may be manufactured by the following method: First, a negative electrode active material, a conductive agent, and a binder are mixed to obtain a mixture. Next, this mixture is formed into pellets. Then, these pellets are placed on a negative electrode current collector to obtain the negative electrode.

[0069] An electrode group can be fabricated by placing a separator between the positive electrode and the negative electrode prepared as described above. Within the electrode group, the positive electrode can be electrically connected to the positive terminal, and the negative electrode to the negative terminal.

[0070] An electrode group having positive and negative terminals is placed inside a bag-shaped outer casing made of laminate film. The remaining portion is then sealed by heat sealing, leaving an opening for electrolyte injection. Next, the electrolyte is injected into the bag-shaped outer casing through the opening, and the opening is sealed by heat sealing. Heat sealing may be performed under reduced pressure. This yields a battery precursor.

[0071] Next, the battery precursor is subjected to aging at a temperature above room temperature. Before aging, an initial charge may be performed at room temperature (e.g., 25°C). Alternatively, the battery may be discharged after the initial charge before aging is performed.

[0072] As the aging process progresses, the electrolyte decomposes, resulting in the formation of a film on at least a portion of the surfaces of the positive and negative electrodes. Specifically, for example, the reaction between the positive and / or negative electrodes and the electrolyte can cause the electrolyte to decompose, and the resulting decomposition products can adhere to at least a portion of the surfaces of the positive and negative electrodes, forming a film. The decomposition of the electrolyte and the formation of the film can also occur during the initial charging.

[0073] Specifically, in the positive electrode, a film may be formed on at least a portion of the surface of the primary oxide. As a result, the proportion of the primary oxide on the positive electrode surface may be reduced. Therefore, the ratio B / A in HAXPES for the positive electrode surface can be set to 0.07 or more and 0.20 or less. In the negative electrode, a film may be formed on at least a portion of the surface of the lithium titanium-containing oxide. As a result, the proportion of the lithium titanium-containing oxide on the negative electrode surface may be reduced. Therefore, the ratio D / C can be set to 0.75 or more and 1.8 or less.

[0074] Details of the manufacturing conditions are described below.

[0075] Aging can be performed, for example, on a battery precursor in an environment with a temperature of 40°C to 80°C for a period of 12 to 100 hours. It is preferable to bring the battery voltage to a range of 2.05V to 2.3V by initial charging or discharging after initial charging before performing aging.

[0076] The higher the temperature during aging, or the longer the aging time, the more likely the electrolyte decomposition will progress. Furthermore, the higher the battery voltage at the time of aging, the more likely the electrolyte decomposition will progress.

[0077] As will be explained in more detail later, the electrolyte may contain substances containing lithium atoms and fluorine atoms. Substances containing lithium atoms and fluorine atoms tend to decompose during aging, forming a lithium fluoride-containing film on the positive and / or negative electrodes.

[0078] The negative electrode, positive electrode, and electrolyte will be described below. Separators, casing members, positive electrode terminals, and negative electrode terminals that the battery of this embodiment may include in addition to these components will also be described below.

[0079] (Negative Electrode) The negative electrode may include a negative electrode current collector and a negative electrode active material-containing layer. The negative electrode active material-containing layer may be formed on one or both sides of the negative electrode current collector. The negative electrode active material-containing layer may include a negative electrode active material and optionally a conductive agent and a binder. Lithium titanium-containing oxide may be included in the negative electrode as the negative electrode active material, for example.

[0080] The negative electrode of the battery according to this embodiment contains a lithium titanium-containing oxide, which allows for a high lithium storage potential. A higher lithium storage potential of the negative electrode is preferable because it is easier to suppress the decomposition of the electrolyte. The negative electrode has a lithium storage potential of 1.5 V (vs. Li / Li) relative to the oxidation-reduction potential of lithium. ＋ It is preferable to exhibit a Li storage potential of ) or higher.

[0081] A coating may be formed on at least a portion of the surface of the negative electrode. The coating may contain, for example, fluorine atoms. The fluorine atoms may be included in the coating as, for example, lithium fluoride (LiF). The coating may be present on at least a portion of the surface of the negative electrode active material-containing layer, or it may cover at least a portion of the surface of the negative electrode active material particles. The coating may be in the form of a film or in the form of layers.

[0082] The negative electrode in the battery according to this embodiment may be a modified version of the negative electrode immediately after fabrication. In other words, it may be a modified version of the negative electrode in the battery precursor before it is subjected to initial charging and aging. This is because, for example, as described earlier, the negative electrode and electrolyte may react after the battery precursor is assembled and undergoes initial charging and / or aging. In this reaction, a film may be formed on at least a portion of the surface of the negative electrode.

[0083] The density of the negative electrode active material-containing layer (excluding the negative electrode current collector) is 1.8 g / cm³. 3 2.8g / cm or more 3 The following is preferable. A negative electrode in which the density of the negative electrode active material-containing layer is within this range exhibits excellent energy density and electrolyte retention. The density of the negative electrode active material-containing layer is 2.1 g / cm³. 3 2.6g / cm or more 3 The following is more preferable:

[0084] The negative electrode active material may contain lithium titanium-containing oxide alone, or it may further contain other active materials. From the viewpoint of preventing the negative electrode potential from becoming too low, the negative electrode active material preferably contains 70% by mass or more of lithium titanium-containing oxide, and more preferably 80% by mass or more. The upper limit of the proportion of lithium titanium-containing oxide in the negative electrode active material can be 100% by mass.

[0085] Examples of lithium titanium-containing oxides include lithium titanate (e.g., Li) having a ramsdelite structure. 2+y Li3O7 (for example, Li) has a spinel structure. 4+x Ti5O 12Examples include , 0 ≤ x ≤ 3). The type of lithium titanium-containing oxide can be one or two or more.

[0086] Other active materials besides lithium titanium oxides include titanium dioxide (TiO2), anatase-type titanium dioxide, rutile-type titanium dioxide, niobium pentoxide (Nb2O5), hollandite-type titanium composite oxide, orthorhombic titanium composite oxide, and monoclinic niobium titanium oxide. The other active materials can be one or more types.

[0087] As an example of the above orthorhombic titanium-containing composite oxide, Li 2+a M Ｉ 2-b Ti 6-c M ＩＩ d O 14+σ Examples of compounds represented by are given. Here, M Ｉ It is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb, and K. ＩＩ is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The subscripts in the composition formula are 0 ≤ a ≤ 6, 0 ≤ b < 2, 0 ≤ c < 6, 0 ≤ d < 6, -0.5 ≤ σ ≤ 0.5. A specific example of an orthorhombic titanium-containing composite oxide is Li 2+a Na2Ti6O 14 (0 ≤ a ≤ 6) is one example.

[0088] As an example of the monoclinic type niobium titanium oxide mentioned above, Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ Examples of compounds represented by are: Here, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, -0.3≦δ≦0.3. A specific example of monoclinic titanium niobium oxide is Li xOne example is Nb2TiO7 (0 ≤ x ≤ 5).

[0089] Another example of monoclinic titanium niobium oxide is Li x Ti 1-y M3 y+z Nb 2-z O 7-δ A compound represented by the formula is shown below. Here, M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the compositional formula are 0 ≤ x ≤ 5, 0 ≤ y < 1, 0 ≤ z < 2, and -0.3 ≤ δ ≤ 0.3.

[0090] Conductive agents are added to enhance current collection performance and reduce contact resistance between the negative electrode active material and the negative electrode current collector. Examples of conductive agents include carbonaceous materials such as vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanotubes, and carbon nanofibers. One of these may be used as a conductive agent, or two or more may be used in combination. Alternatively, instead of using a conductive agent, a carbon coating or an electronically conductive inorganic material coating may be applied to the surface of the negative electrode active material particles.

[0091] A binder is added to fill the gaps between dispersed negative electrode active materials and to bond the negative electrode active materials to the negative electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as a binder, or two or more may be used in combination.

[0092] In the negative electrode active material-containing layer, it is preferable that the negative electrode active material, conductive agent, and binder are blended in proportions of 68% to 96% by mass, 2% to 30% by mass, and 2% to 30% by mass, respectively. By setting the amount of conductive agent to 2% by mass or more, the current collection performance of the negative electrode active material-containing layer can be improved. Furthermore, by setting the amount of binder to 2% by mass or more, sufficient bonding between the negative electrode active material-containing layer and the negative electrode current collector can be achieved, and excellent cycle performance can be expected. On the other hand, it is preferable to set the amount of conductive agent and binder to 30% by mass or less, respectively, in order to achieve high capacity.

[0093] The negative electrode current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted into and removed from the negative electrode active material. For example, the negative electrode current collector is preferably made of copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the negative electrode current collector is preferably 5 μm to 20 μm. A negative electrode current collector with such a thickness can balance the strength of the negative electrode with weight reduction.

[0094] Furthermore, the negative electrode current collector may include portions on its surface where the negative electrode active material-containing layer is not formed. These portions can function as negative electrode current collector tabs.

[0095] (Positive electrode) The positive electrode may include a positive electrode current collector and a positive electrode active material-containing layer. The positive electrode active material-containing layer may be formed on one or both sides of the positive electrode current collector. The positive electrode active material-containing layer may include a positive electrode active material and optionally a conductive agent and a binder.

[0096] A coating may be formed on at least a portion of the surface of the positive electrode. The coating may contain, for example, fluorine atoms. The fluorine atoms may be included in the coating as, for example, lithium fluoride (LiF). The coating may be present on at least a portion of the surface of the positive electrode active material-containing layer, or it may cover at least a portion of the surface of the positive electrode active material particles. The coating may be in the form of a film or in the form of layers.

[0097] The positive electrode in the battery according to this embodiment may be a modified version of the positive electrode immediately after fabrication. In other words, it may be a modified version of the positive electrode in the battery precursor before it is subjected to initial charging and aging. This is because, for example, as described earlier, the positive electrode and electrolyte may react after the battery precursor is assembled and undergoes initial charging and / or aging. In this reaction, a film may be formed on at least a portion of the surface of the positive electrode.

[0098] The positive electrode active material may contain the first oxide described above alone, or it may further contain other negative electrode active materials. From the viewpoint of increasing battery capacity, the positive electrode active material preferably contains 80% by mass or more of the first oxide, and more preferably 90% by mass or more. The upper limit of the proportion of the first oxide in the positive electrode active material can be 100% by mass.

[0099] Other positive electrode active materials besides the first oxide can be, for example, sulfides or oxides other than the first oxide. Examples of these sulfides and oxides include compounds that can insert and remove Li or Li ions.

[0100] Examples of such compounds include manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, and lithium manganese composite oxide (e.g., Li x Mn2O4 or Li x MnO2; 0 < x ≤ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≤ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≤ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≤ 1, 0 < y < 1), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; 0 < x ≤ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni yO4; 0 < x ≤ 1, 0 < y < 2), a lithium phosphate oxide having an olivine structure (e.g., Li x FePO4; 0 < x ≤ 1, Li x Fe 1-y Mn y PO4; 0 < x ≤ 1, 0 < y ≤ 1, Li x CoPO4; 0 < x ≤ 1), iron sulfate (Fe2(SO4)3) and vanadium oxide (e.g., V2O5), and, A Ｎｉ is less than 0.7, a lithium nickel cobalt manganese composite oxide is included. More specific examples include a lithium manganese composite oxide having a spinel structure (e.g., Li x Mn2O4; 0 < x ≤ 1), a lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≤ 1), a lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≤ 1), a lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≤ 1, 0 < y < 1), a lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≤ 1, 0 < y < 2), a lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; 0 < x ≤ 1, 0 < y < 1), lithium iron phosphate (e.g., Li x FePO4; 0 < x ≤ 1), and, A Ｎｉ is less than 0.7, a lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, 0.3 < y + z < 1) can be mentioned.

[0101] A binder is added to fill the gaps between dispersed positive electrode active materials and to bond the positive electrode active materials to the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as a binder, or two or more may be used in combination.

[0102] Conductive agents are added to enhance current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as a conductive agent, or two or more may be used in combination. Conductive agents may also be omitted.

[0103] In the positive electrode active material-containing layer, it is preferable that the positive electrode active material and the binder are blended in proportions of 80% to 98% by mass and 2% to 20% by mass, respectively.

[0104] Sufficient electrode strength can be obtained by using a binder amount of 2% by mass or more. Furthermore, the binder can function as an insulator. Therefore, by reducing the binder amount to 20% by mass or less, the amount of insulator contained in the electrode decreases, thus reducing the internal resistance.

[0105] When a conductive agent is added, it is preferable that the positive electrode active material, binder, and conductive agent are blended in proportions of 77% to 95% by mass, 2% to 20% by mass, and 3% to 15% by mass, respectively.

[0106] The above-mentioned effects can be achieved by increasing the amount of conductive agent to 3% by mass or more. Furthermore, by reducing the amount of conductive agent to 15% by mass or less, the proportion of conductive agent in contact with the electrolyte can be reduced. This lower proportion reduces the decomposition of the electrolyte under high-temperature storage conditions.

[0107] The positive electrode current collector is preferably an aluminum foil, or an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.

[0108] The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, and more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

[0109] Furthermore, the positive electrode current collector may include portions on its surface where the positive electrode active material-containing layer is not formed. These portions can function as positive electrode current collector tabs.

[0110] (Electrolyte) For example, a non-aqueous electrolyte can be used as the electrolyte. The composition of the electrolyte contained in the battery of the embodiment may change from the composition of the electrolyte immediately after preparation (initial composition). This is because, for example, after assembling the battery precursor using the electrolyte immediately after preparation, the substances contained in the electrolyte may decompose during aging or the like.

[0111] As the non-aqueous electrolyte, for example, a liquid non-aqueous electrolyte or a gel-type non-aqueous electrolyte can be used.

[0112] Liquid non-aqueous electrolytes are prepared by dissolving an electrolyte salt, which acts as a solute, in an organic solvent.

[0113] Carboxylic acid esters and cyclic carbonates may be included in the electrolyte as organic solvents. The organic solvent may further contain solvents other than carboxylic acid esters and cyclic carbonates.

[0114] As the carboxylic acid ester, the types described above can be used. The electrolyte may contain one or more types of carboxylic acid esters.

[0115] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC). The type of cyclic carbonate can be one or more.

[0116] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium arsenide hexafluoride (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bistrifluoromethylsulfonyliimide (LiN(CF3SO2)2), as well as mixtures thereof. The electrolyte salt is preferably resistant to oxidation even at high potentials, with LiPF6 being the most preferred.

[0117] The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less.

[0118] Other solvents besides carboxylic acid esters and cyclic carbonates include, for example, linear carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC); cyclic ethers such as tetrahydrofuran (THF) and 2-methyl tetrahydrofuran (2MeTHF); linear ethers such as dimethoxyethane (DME); cyclic esters such as γ-butyrolactone (BL); non-aqueous solvents such as acetonitrile (AN) and sulfolane (SL). These non-aqueous solvents can be used individually or as mixtures of two or more.

[0119] The electrolyte preferably contains a substance containing lithium atoms and fluorine atoms. The substance containing lithium atoms and fluorine atoms may function as an electrolyte salt or an organic solvent, or it may function as both an electrolyte salt and an organic solvent.

[0120] It is preferable that the substance containing lithium atoms and fluorine atoms does not function as an electrolyte salt. In other words, it is preferable that the electrolyte contains a substance containing lithium atoms and fluorine atoms in addition to the electrolyte salt. When the electrolyte contains such a substance, the decomposition of the electrolyte salt can be suppressed. As a result, the formation of an excessive film on the positive electrode and / or negative electrode can be suppressed. Examples of substances containing lithium atoms and fluorine atoms that do not function as an electrolyte salt include lithium difluorodifluoridate (DFP) and lithium difluorobisoxalate phosphate (LiDFBOP). The types of substances containing lithium atoms and fluorine atoms can be one or more.

[0121] If the electrolyte contains a large amount of the above-mentioned lithium and fluorine atoms, the amount of coating formed on the positive and negative electrodes may increase. From the viewpoint of setting the ratio B / A in HAXPES for the surface of the positive electrode to 0.07 or more and 0.20 or less, and the ratio D / C in HAXPES for the surface of the negative electrode to 0.75 or more and 1.8 or less, it is preferable that the electrolyte contains 0.1% to 5% by mass of DFP and 0.1% to 5% by mass of LiDFBOP.

[0122] The more LiDFBOP an electrolyte contains, the greater the amount of film that tends to form on the negative electrode.

[0123] LiDFBOP can suppress the decomposition of electrolyte salts, and it can also form a film by decomposing itself. Therefore, the more LiDFBOP the electrolyte contains, the greater the amount of film formed on the negative electrode tends to be. For this reason, when the electrolyte contains LiDFBOP, the amount of film formed on the negative electrode is easily controlled within a desirable range, which is preferable.

[0124] Gel-like non-aqueous electrolytes are prepared by compounding a liquid non-aqueous electrolyte with a polymer material. Examples of polymer materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or mixtures thereof.

[0125] (Separator) The separator is formed from a porous film containing, for example, polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or from a synthetic resin nonwoven fabric. From a safety standpoint, it is preferable to use a porous film made of polyethylene or polypropylene. This is because these porous films can melt at a certain temperature and interrupt the electric current.

[0126] (Exterior components) Exterior components may be formed from laminate film or made of a metal container. When a metal container is used, the lid may be integrated with the container or be a separate component. The wall thickness of the metal container is preferably 0.5 mm or less, and more preferably 0.2 mm or less. Examples of exterior component shapes include flat, rectangular, cylindrical, coin-shaped, button-shaped, sheet-shaped, and laminated types. Exterior components may be used for small batteries mounted in portable electronic devices, as well as for large batteries mounted in two-wheeled or four-wheeled automobiles.

[0127] The thickness of the laminate film exterior component is preferably 0.2 mm or less. Examples of laminate films include multilayer films containing a resin film and a metal layer placed between the resin films. For weight reduction, the metal layer is preferably aluminum foil or aluminum alloy foil. The resin film can be made of polymer materials such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET). The laminate film can be sealed by heat fusion and molded into the shape of the exterior component.

[0128] Metal containers are made from aluminum or aluminum alloys. As aluminum alloys, alloys containing elements such as magnesium, zinc, and silicon are preferred. In aluminum or aluminum alloys, it is preferable to keep the content of transition metals such as iron, copper, nickel, and chromium to 100 ppm or less in order to dramatically improve long-term reliability and heat dissipation in high-temperature environments.

[0129] The metal container made of aluminum or an aluminum alloy preferably has an average crystal grain size of 50 μm or less, more preferably 30 μm or less, and even more preferably 5 μm or less. By setting the average crystal grain size to 50 μm or less, the strength of the metal container made of aluminum or an aluminum alloy can be dramatically increased, making it possible to further thin the container. As a result, it is possible to realize a battery that is lightweight, has high output, and has excellent long-term reliability, making it suitable for automotive applications and other uses.

[0130] (Negative and Positive Terminals) The negative terminal can act as a conductor for electrons to move between the negative electrode and the external terminal by being electrically connected to a portion of the negative electrode. The negative terminal can be connected, for example, to a negative current collector, particularly a negative tab. Similarly, the positive terminal can act as a conductor for electrons to move between the positive electrode and the external circuit by being electrically connected to a portion of the positive electrode. The positive terminal can be connected, for example, to a positive current collector, particularly a positive tab. The negative and positive terminals are preferably made of a material with high electrical conductivity. When connected to a current collector, these terminals are preferably made of the same material as the current collector to reduce contact resistance.

[0131] (Measurement Method) The following describes the methods for measuring HAXPES on the electrode surface, compositional analysis of the electrolyte, compositional analysis of the active material, measurement of average particle size and particle size distribution, and measurement of the fracture strength of the active material particles.

[0132] First, before performing any analysis, we will explain how to remove the electrodes from the battery to be measured.

[0133] (Method for extracting electrodes) First, discharge the battery. For example, discharge it until the battery voltage reaches 1.5V. Then, disassemble the battery in an argon (Ar) atmosphere and extract the electrode group. From the extracted electrode group, cut out the electrode to be analyzed. For example, if analyzing the positive electrode, cut out the positive electrode; if analyzing the negative electrode, cut out the negative electrode. Wash the cut-out electrode with a suitable solvent. For example, ethyl methyl carbonate can be used as a solvent. After washing, immerse the electrode in the solvent for 1 hour, and then dry it for 3 hours under a reduced pressure of -90 kPa. Thus, obtain the electrode to be used as a measurement sample.

[0134] (Analysis of electrode surfaces using HAXPES) Hard X-ray photoelectron spectroscopy (HAXPES) can be used as a method for analyzing the surfaces of the positive and negative electrodes.

[0135] The surface of the electrode used as the measurement sample is measured under vacuum in a beamline equipped with a hard X-ray photoelectron spectrometer. The measurement conditions are an excitation energy of 6 keV, a photoelectron detection angle of approximately 88°, and an energy step of approximately 0.1 eV.

[0136] The analysis method for the HAXPES spectrum obtained as described above is explained below, divided into analysis for the positive electrode and analysis for the negative electrode.

[0137] (Analysis of the HAXPES spectrum of the positive electrode) The method for measuring areas A and B by analyzing the HAXPES spectrum obtained for the surface of the positive electrode will be described below with reference to Figures 7 and 8. Figures 7 and 8 show the HAXPES spectrum obtained for the positive electrode contained in the battery of Example 2, which will be described later, as an example of a positive electrode contained in a battery according to the embodiment. Hereafter, in the HAXPES spectrum, the horizontal axis shows the binding energy (unit: eV) and the vertical axis shows the photoelectron intensity (unit: cps; counts per second).

[0138] First, the method for calculating the area A of a peak having a peak top in the range of 851 eV to 868 eV will be explained with reference to Figure 7. In Figure 7, a portion of the HAXPES spectrum obtained for the positive electrode included in Example 2 is shown by the symbol a0. The background of spectrum a0 is shown by the symbol ab.

[0139] The background is defined as a straight line passing through the right and left ends of the range of the spectrum subject to background subtraction (subtraction range). For example, when calculating area A, the right end of the subtraction range is 851 eV and the left end is 868 eV. The photoelectron intensity at the right and left ends is the average value within a range of ±0.5 eV from the right and left ends, respectively.

[0140] Chart a1 is obtained by subtracting the background ab from spectrum a0. By integrating the intensity of chart a1 with an integration range of 851 eV to 868 eV, the area A of peaks with peak tops within the range of 851 eV to 868 eV can be calculated.

[0141] Next, the method for calculating area B will be explained with reference to Figure 8. When calculating area B, the subtraction range is set to 681 eV or more and 694 eV or less. In Figure 8, a chart obtained by subtracting the background with the subtraction range set to 681 eV or more and 694 eV or less is shown as b1.

[0142] Chart b1 is separated by its peaks. Specifically, fitting is performed assuming that chart b1 contains a first peak with a Gaussian function shape whose maximum value (peak top) is within the range of 683 eV to 686 eV, and a second peak with a pseudo-Voigt function shape. Through fitting, chart b1 is separated into chart b2 containing the first peak and chart b3 containing the second peak. Thus, chart b2 containing the first peak with a maximum value (peak top) within the range of 683 eV to 686 eV can be obtained.

[0143] By integrating the intensity of chart b2 with an integration range of 680 eV to 694 eV, the area B of the peak with its peak top within the range of 683 eV to 686 eV can be calculated.

[0144] By dividing the area B obtained as described above by the area A, the ratio B / A can be obtained. In the positive electrode included in Example 2, illustrated in Figures 7 and 8, the area A was 1,193,741, the area B was 158,801, and the ratio B / A was 0.13.

[0145] (Analysis of the HAXPES spectrum of the negative electrode) A method for measuring area C and area D by analyzing the HAXPES spectrum obtained for the surface of the negative electrode will be described below with reference to Figures 9 and 10. Figures 9 and 10 show the HAXPES spectrum obtained for the negative electrode contained in the battery of Example 2, which will be described later, as an example of a negative electrode contained in a battery according to the embodiment.

[0146] First, the method for calculating the area C of peaks having peak tops within the range of 455 eV to 469 eV will be explained with reference to Figure 9. In Figure 9, a portion of the HAXPES spectrum obtained for the negative electrode included in Example 2 is shown by the symbol c0. The background of spectrum c0 is shown by the symbol cb. The background is subtracted from the range of 455 eV to 469 eV. Chart c1 is obtained by subtracting the background cb from spectrum c0. By integrating the intensity of chart c1 with the integration range of 455 eV to 469 eV, the area C of peaks having peak tops within the range of 455 eV to 469 eV can be calculated.

[0147] Next, the method for calculating area D will be explained with reference to Figure 10. When calculating area D, the subtraction range is set to 681 eV or more and 694 eV or less. Figure 10 shows a chart with the background subtracted using a subtraction range of 681 eV or more and 694 eV or less, labeled as d1.

[0148] Chart d1 is separated by its peaks. Specifically, fitting is performed assuming that chart d1 contains a first peak with a Gaussian function shape whose maximum value (peak top) is within the range of 685 eV to 687.5 eV, and a second peak with a pseudo-Voigt function shape. Through fitting, chart d1 is separated into chart d2 containing the first peak and chart d3 containing the second peak. Thus, chart d2 containing the first peak with a maximum value (peak top) within the range of 685 eV to 687.5 eV can be obtained.

[0149] By integrating the intensity of chart d2 with an integration range of 680 eV to 694 eV, the area D of the peak with its peak top within the range of 685 eV to 687.5 eV can be calculated.

[0150] By dividing the area D obtained as described above by the area C, the ratio D / C can be obtained. In the negative electrode included in Example 2, illustrated in Figures 9 and 10, the area C was 758510.8, the area D was 908960.0, and the ratio D / C was 1.2.

[0151] (Electrolyte composition analysis) The composition of electrolytes can be measured by gas chromatography-mass spectrometry (GC-MS). GC-MS can, for example, determine the volume of carboxylic acid esters and cyclic carbonates contained in the electrolyte.

[0152] First, the battery to be measured is disassembled and the electrolyte is extracted. The extracted electrolyte is analyzed by gas chromatography-mass spectrometry and ion chromatography. This analysis allows for the identification of each component (solvent and solute) contained in the non-aqueous electrolyte. Furthermore, each component can be quantified from the peak area of ​​the chart obtained from this analysis. The ratio of each component is calculated from the quantified values. (Analysis of active material composition) The composition of the active material contained in the electrodes can be measured by powder X-ray diffraction (XRD), as described below. In other words, it can be determined that the positive electrode contains a primary oxide and the negative electrode contains a lithium titanium-containing oxide.

[0153] From the electrode used as a measurement sample, the active material-containing layer is peeled off using, for example, a spatula, to obtain a powdered sample.

[0154] The crystal structure of the active material is identified by powder X-ray diffraction (XRD) measurement of a powder sample. The measurement is performed using CuKα radiation as the source, within the measurement range of 2θ between 10° and 90°. This measurement allows us to obtain the X-ray diffraction pattern of the compound contained in the selected particles.

[0155] For powder X-ray diffraction measurements, for example, a SmartLab manufactured by Rigaku is used. The measurement conditions are as follows: X-ray source: Cu target output: 45kV, 200mA Solar slit: 5° for both incident and receiving Step width: 0.02deg Scan rate: 20deg / min Semiconductor detector: D / teX Ultra 250 Sample plate holder: Flat glass sample plate holder (thickness 0.5mm) Measurement range: 10°≦2θ≦90°.

[0156] If other equipment is used, measurements should be performed using standard Si powder for powder X-ray diffraction to obtain measurement results equivalent to those described above, and the conditions should be adjusted so that the peak intensity and peak top position match those of the above equipment.

[0157] (Measurement of average particle size and particle size distribution) The average particle size and particle size distribution of the active material contained in the electrode can be measured by the laser diffraction / scattering method described below.

[0158] To obtain a sample of active material particles, the electrode used as the measurement sample is separated from the current collector by, for example, using a spatula to separate the active material-containing layer. Next, the powdered sample is placed into a measurement cell filled with N-methylpyrrolidone (NMP) until a measurable concentration is reached. Note that the capacity of the measurement cell and the measurable concentration will vary depending on the particle size distribution analyzer. The measurement cell containing the NMP and the sample dissolved in it is irradiated with ultrasound for 5 minutes. The output of the ultrasound should be, for example, in the range of 35W to 45W. For example, if approximately 50 ml of NMP is used as the solvent, the solvent mixed with the measurement sample is irradiated with ultrasound at an output of approximately 40W for 300 seconds. Such ultrasound irradiation can dissolve the aggregation of conductive particles and active material particles. The measurement cell is inserted into a particle size distribution analyzer using laser diffraction / scattering to measure the particle size distribution. Examples of particle size distribution measuring devices include the Microtrac 3100 and Microtrac 3000 II (both manufactured by Microtrac-Bell Co., Ltd.), or devices with equivalent functionality. Thus, the particle size distribution of the electrode can be obtained.

[0159] The particle size distribution obtained by the above method is a volume-based cumulative frequency distribution accumulated from the smallest particle size to the smallest. In the particle size distribution, we determine the particle size d10 at which the volume-based cumulative frequency from the smallest particle size side is 10%, the particle size d50 at which the volume-based cumulative frequency from the smallest particle size side is 50%, and the particle size d90 at which the volume-based cumulative frequency from the smallest particle size side is 90%.

[0160] The obtained d50 is taken as the average particle diameter. Furthermore, the ratio d90 / d10 is calculated from the obtained d10 and d90.

[0161] (Measurement of fracture strength of active material particles) The positive electrode is removed from the battery to be measured using the method described above and used as a measurement sample. The positive electrode active material-containing layer is peeled off from the current collector by immersing and stirring the positive electrode in an N-methyl-2-pyrrolidone solution. Particles with a diameter of 2 μm or more and 6 μm or less are selected from the peeled positive electrode active material-containing layer. Particles with such a diameter in the positive electrode active material-containing layer can be positive electrode active material particles. The selected particles are used as test particles for the fracture strength test.

[0162] The Shimadzu micro-compression tester MCT-510 can be used as the testing equipment. A very small amount of test particles is scattered on the pressure plate of the testing equipment, and each particle is compressed one by one. The fracture strength is calculated using the following formula.

[0163] Cs = 2.8P / πd 2 Here, Cs represents the breaking strength (numerical unit: N / mm²). ２ The test force (P) is indicated by the force (or MPa), where P is the test force (numerical unit: N) and d is the particle size (numerical unit: mm). Whether the test particles contain the first oxide can be confirmed by performing elemental analysis such as ICP emission spectroscopy on the test particles.

[0164] A battery is provided according to the first embodiment described above. The battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes an oxide containing a transition metal. The transition metals include nickel, cobalt, and manganese. The number of nickel atoms in the oxide is A, where the total number of transition metal atoms is 1. ＮｉThe ratio of the area of ​​peaks with peak tops in the range of 683 eV to 686 eV to the area of ​​peaks with peak tops in the range of 851 eV to 868 eV in the hard X-ray photoelectron spectroscopy spectrum of the positive electrode surface is 0.07 to 0.20. The negative electrode contains a lithium titanium-containing oxide. In the hard X-ray photoelectron spectroscopy spectrum of the negative electrode surface, the ratio of the area of ​​peaks with peak tops in the range of 685 eV to 687.5 eV to the area of ​​peaks with peak tops in the range of 455 eV to 469 eV in the range of 685 eV to 687.5 eV in hard X-ray photoelectron spectroscopy spectrum of the negative electrode surface is 0.75 to 1.8. The electrolyte contains a carboxylic acid ester and a cyclic carbonate. The volume of the carboxylic acid ester is 2.3 times or more the volume of the cyclic carbonate. Therefore, a battery with high safety and high input / output performance can be provided.

[0165] (Second Embodiment) According to the second embodiment, a battery pack is provided. This battery pack includes the battery according to the first embodiment.

[0166] The battery pack according to the second embodiment may comprise one or more of the batteries (single cells) according to the first embodiment described above. Multiple batteries that may be included in such a battery pack can be electrically connected to each other in series or parallel to form a battery pack. Such a battery pack may include multiple battery packs.

[0167] Next, an example of a battery pack according to the second embodiment will be described with reference to the drawings.

[0168] Figure 5 is an exploded perspective view of an example battery pack according to the embodiment. Figure 6 is a block diagram showing the electrical circuit of the battery pack in Figure 5.

[0169] The battery pack 20 shown in Figures 5 and 6 comprises a plurality of individual cells 21. Each individual cell 21 may be a flat-type battery, as described in the embodiment with reference to Figure 1.

[0170] Multiple individual cells 21 are stacked so that their outwardly extending negative terminals 51 and positive terminals 61 are aligned in the same direction, and then fastened together with adhesive tape 22 to form a battery pack 23. These individual cells 21 are electrically connected in series with each other, as shown in Figure 6.

[0171] The printed circuit board 24 is positioned opposite the side from which the negative terminal 51 and positive terminal 61 of the single cell 21 extend. As shown in Figure 6, the printed circuit board 24 is equipped with a thermistor 25, a protection circuit 26, and terminals 27 for supplying power to external devices. An insulating plate (not shown) is attached to the side of the printed circuit board 24 that faces the battery pack 23 to avoid unnecessary connections with the wiring of the battery pack 23.

[0172] The positive lead 28 is connected to the positive terminal 61 located at the bottom layer of the battery pack 23, and its tip is inserted into the positive connector 29 of the printed circuit board 24 for electrical connection. The negative lead 30 is connected to the negative terminal 51 located at the top layer of the battery pack 23, and its tip is inserted into the negative connector 31 of the printed circuit board 24 for electrical connection. These connectors 29 and 31 are connected to the protection circuit 26 through wiring 32 and 33 formed on the printed circuit board 24.

[0173] The thermistor 25 detects the temperature of the individual cell 21, and the detection signal is transmitted to the protection circuit 26. The protection circuit 26 can shut off the positive side wiring 34a and the negative side wiring 34b between the protection circuit 26 and the terminal 27 for supplying power to external devices under predetermined conditions. An example of a predetermined condition is when the temperature detected by the thermistor 25 exceeds a predetermined temperature. Another example of a predetermined condition is when overcharging, over-discharging, overcurrent, etc., of the individual cell 21 is detected. This detection of overcharging, etc., is performed for individual cell 21 or for the entire battery pack 23. When detecting individual cell 21, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each individual cell 21. In the battery pack 20 of Figures 5 and 6, wiring 35 for voltage detection is connected to each individual cell 21. Detection signals are transmitted to the protection circuit 26 through these wirings 35.

[0174] Protective sheets 36 made of rubber or resin are placed on three sides of the battery pack 23, excluding the side from which the positive terminal 61 and negative terminal 51 protrude.

[0175] The battery pack 23 is housed in a storage container 37 together with each protective sheet 36 and the printed circuit board 24. Specifically, the protective sheets 36 are placed on both inner surfaces in the long direction and on each inner surface in the short direction of the storage container 37, and the printed circuit board 24 is placed on the inner surface opposite to the short direction. The battery pack 23 is located in the space enclosed by the protective sheets 36 and the printed circuit board 24. The lid 38 is attached to the top surface of the storage container 37.

[0176] Alternatively, heat-shrinkable tape may be used instead of adhesive tape 22 to secure the battery pack 23. In this case, protective sheets are placed on both sides of the battery pack, the heat-shrinkable tape is wrapped around it, and then the heat-shrinkable tape is heat-shrinked to secure the battery pack.

[0177] Figures 5 and 6 show a configuration in which the single cells 21 are connected in series, but they may be connected in parallel to increase the battery capacity. Furthermore, assembled battery packs can also be connected in series and / or in parallel.

[0178] Furthermore, the configuration of the battery pack can be appropriately modified depending on the application. Preferably, the battery pack is designed for applications where good cycle performance is desired when drawing high current. Specific applications include power supplies for digital cameras, and in-vehicle use in two-wheeled or four-wheeled hybrid electric vehicles, two-wheeled or four-wheeled electric vehicles, and electric assist bicycles. Such a battery pack is particularly suitable for in-vehicle use.

[0179] The battery pack according to the second embodiment includes the battery according to the first embodiment. Therefore, it is possible to provide a battery pack that is highly safe and has high input / output performance.

[0180] The present invention will be further explained with the following examples, but the present invention is not limited to the embodiments listed below unless it exceeds the spirit of the invention.

[0181] (Example 1) <Fabrication of the positive electrode> LiNi as the positive electrode active material ０．８ Co ０．１ Mn ０．１ O ２ A lithium-containing nickel-cobalt-manganese oxide (NCM811), represented by [formula], was prepared with acetylene black (AB) as a conductive agent and polyvinylidene fluoride (PVdF) as a binder.

[0182] The prepared positive electrode active material was single-crystal NCM811 particles. The d90 / d10 ratio measured for these NCM811 particles was 3, the average particle diameter was 4 μm, and the fracture strength was 174 MPa. These measurements were performed using the method described above.

[0183] A positive electrode slurry was prepared by dispersing the positive electrode active material, conductive agent, and binder in N-methyl-2-pyrrolidone (NMP) as a dispersion medium, with a mass ratio of 90:5:5. The positive electrode slurry was applied to a positive electrode current collector made of 15 μm aluminum foil and dried. Thus, a single-sided basis weight of 80 g / m² was obtained. ２ We obtained the positive electrode.

[0184] <Fabrication of the negative electrode> As the negative electrode active material, Li ４ Ti ５ O １２A lithium titanium oxide (TLO) represented by [formula] was prepared, acetylene black (AB) as the conductive agent, and polyvinylidene fluoride (PVdF) as the binder. The negative electrode slurry was prepared by dispersing the negative electrode active material, conductive agent, and binder in N-methyl-2-pyrrolidone (NMP) as the dispersion medium in a mass ratio of 90:5:5. The negative electrode slurry was applied to a negative electrode current collector made of 15 μm aluminum foil and dried. Thus, a single-sided basis weight of 80 g / m² was obtained. ２ We obtained the negative electrode.

[0185] <Preparation of Electrolyte> Propylene carbonate (PC) was prepared as solvent 1, and propyl propionate (PP) was prepared as solvent 2, a carboxylic acid ester. Solvent 1 was mixed in a ratio of 30% by volume and solvent 2 in a ratio of 70% by volume. LiPF was added to this mixture as the electrolyte salt. ６ The solution was dissolved to a concentration of 1 mol / L. Furthermore, lithium difluorophosphate (DFP) was dissolved to a concentration of 0.5% by mass, and lithium difluorobisoxalate phosphate (LiDFBOP) was dissolved to a concentration of 1.0% by mass.

[0186] <Battery Assembly> A resin separator with a thickness of 15 μm was prepared as the separator. The positive electrode and negative electrode were placed in the space defined by the zigzag-folded separator so that the positive electrode active material-containing layer and the negative electrode active material-containing layer faced each other with the separator in between. Thus, the electrode group was fabricated.

[0187] The fabricated electrode group was sandwiched between laminate films, and three sides were sealed by heat sealing to house the electrode group in a bag-shaped laminate film outer casing. At this time, one side of the laminate film was left open without heat sealing. This was placed in a dryer and vacuum dried at 95°C for 12 hours. After vacuum drying, the electrolyte was injected into the outer casing in a glove box where the dew point was controlled to below -50°C. After injection, the open side of the laminate film was heat-sealed and sealed under a reduced pressure environment of -90 kPa. This was used as the battery precursor.

[0188] The battery precursor was initially charged to 2.2V at 1C (the current value at which the battery's State of Charge (SOC) drops to 0% in one hour when discharged from 100% SOC), and then aged for 48 hours in a constant temperature bath at 60°C. After aging, one side of the outer casing was opened to allow degassing. After degassing, the opened side was resealed under a reduced pressure environment of -90kPa. Thus, the battery of Example 1 was fabricated.

[0189] (Examples 2-4) Batteries were prepared in the same manner as in Example 1, except that the proportions of solvent 1 and solvent 2 were set to the values ​​shown in Table 1.

[0190] (Comparative Example 1) A battery was prepared in the same manner as in Example 1, except that solvent 2 was changed to diethyl carbonate (DEC), which is a linear carbonate, and the proportions of solvent 1 and solvent 2 were set to the values ​​shown in Table 1.

[0191] (Comparative Examples 2 and 3) Batteries were prepared in the same manner as in Example 1, except that the proportions of solvent 1 and solvent 2 were set to the values ​​shown in Table 1. In Comparative Example 3, solvent 1 was not mixed, and the proportion of propyl propionate (PP) as solvent 2 was set to 100% by volume.

[0192] (Comparative Examples 4 and 7) Batteries were prepared in the same manner as in Example 1, except that the proportions of solvent 1 and solvent 2, and the aging time were set to the values ​​shown in Table 1.

[0193] (Comparative Example 5) The proportions of solvent 1, solvent 2, DFP concentration, and LiDFBOP concentration were set to the values ​​shown in Table 1. Except for the above, a battery was prepared in the same manner as in Example 1.

[0194] (Comparative Example 6) The negative electrode active material was changed to graphite. Also, the proportions of solvent 1 and solvent 2 were set to the values ​​shown in Table 1. Except for the above, the battery was manufactured in the same manner as in Example 1.

[0195] (Comparative Example 8) A battery was prepared in the same manner as in Example 1, except that the addition of LiDFBOP was omitted.

[0196] (Performance Evaluation) The initial DC resistance and heat generation of the batteries in the examples and comparative examples were tested as follows.

[0197] (DC Resistance Evaluation) The battery under test was charged to 2.75V using CCCV (Constant Current, Constant Voltage) at 25°C. CCCV charging was terminated when the charge rate converged to 0.02C. Next, the battery was discharged to a capacity equivalent to 50% of its 0.2C capacity. After that, it was discharged for 10 seconds at a current of 10C while recording the voltage. The DC resistance (mΩ) was calculated by dividing the voltage difference before and after 10C discharge by the current value.

[0198] (Differential Scanning Calorimeter (DSC) Evaluation) A glass cell was assembled using the positive electrode taken from the battery under test and a lithium metal electrode as the counter electrode. The glass cell was CCCV charged to 4.2V at a charge rate of 0.1C. The glass cell was then disassembled and the positive electrode was removed. The positive electrode removed from the glass cell was washed with ethyl methyl carbonate and then immersed in ethyl methyl carbonate for 1 hour. Next, it was dried for 3 hours under a reduced pressure of -90 kPa. A powdered sample was obtained by separating the active material-containing layer from the current collector of the dried positive electrode. 5 μg of the sample was weighed out and sealed in a pan with 60 μL of electrolyte. The electrolyte used had the same composition as the electrolyte contained in the battery under test. Under conditions of a starting temperature of 30°C and a heating rate of 5°C / min, the heat generation (mJ / mg) was recorded until 300°C was reached, and the positive electrode DSC heat generation was obtained.

[0199] Tables 1 and 2 show the manufacturing conditions and performance evaluation results for the batteries of the above examples and comparative examples. For Comparative Example 1, in which DEC was used instead of the carboxylic acid ester as solvent 2, the "volume ratio of carboxylic acid ester to the volume of cyclic carbonate" is listed as 0.00. In Comparative Example 3, the addition of solvent 1 was omitted, so the "solvent 1" column and the "volume ratio of carboxylic acid ester to the volume of cyclic carbonate" column are indicated as "-". In Comparative Example 6, the ratio D / C could not be measured, so the D / C column is indicated as "-".

[0200]

[0201]

[0202] Examples 1 to 4 all exhibited low DC resistance and low heat generation. In other words, they demonstrated high safety and high input / output performance.

[0203] Comparative Example 1, which used a linear carbonate as solvent 2 instead of a carboxylic acid ester, had a lower D / C ratio than Examples 1-4. This is thought to be because the linear carbonate is less prone to decomposition during aging than the carboxylic acid ester, resulting in less formation of electrolyte decomposition products in Comparative Example 1. As a result of suppressing the formation of electrolyte decomposition products, the amount of film that adheres to and forms on the surface of the negative electrode is reduced. Therefore, in the negative electrode contained in Comparative Example 1, the titanium atoms exposed on the negative electrode surface are less likely to be covered by the film, so the ratio of C to D becomes relatively larger, and the D / C value becomes smaller. In addition, Comparative Example 1 had higher DC resistance and higher positive electrode DSC heat generation compared to Examples 1-4. This is thought to be due to the lower ionic conductivity of the linear carbonate contained in Comparative Example 1 compared to the carboxylic acid ester, resulting in lower resistance.

[0204] Comparative Example 2, in which the volume ratio of solvent 2 / solvent 1, i.e., the ratio of the volume of carboxylic acid ester to the volume of cyclic carbonate was low at 1.00, showed a higher positive electrode DSC heat generation compared to Examples 1-4. This is thought to be because the greater volume of cyclic carbonate, which has a lower decomposition onset temperature compared to carboxylic acid ester, resulted in lower electrolyte stability, making it easier for heat generation associated with gas generation to proceed.

[0205] Comparative Example 3, which did not contain cyclic carbonates, had a higher DC resistance compared to Examples 1-4. This is thought to be because the ionic conductivity of the electrolyte was lower due to the absence of cyclic carbonates in the electrolyte.

[0206] Comparative Example 4, in which the aging time was extended to 120 hours, and Comparative Example 5, in which the electrolyte contained a large amount of LiDFBOP (6% by mass), had a B / A value greater than 0.20 and a D / C value greater than 1.8. Comparative Examples 4 and 5 had higher DC resistance than Examples 1 to 4.

[0207] In Comparative Example 4, it is believed that the aging time was too long, causing excessive decomposition of the electrolyte, resulting in the formation of an excessive film containing lithium fluoride on the surfaces of the positive and negative electrodes. Furthermore, Comparative Example 4 is LiPO ２ F ２ It is thought that the decomposition of the electrolyte salt was not suppressed because it did not contain lithium fluoride. This is also thought to have led to the excessive formation of a film containing lithium fluoride.

[0208] In Comparative Example 5, it is believed that an excessive amount of LiDFBOP resulted in the formation of a lithium fluoride-containing coating on the surfaces of both the positive and negative electrodes. This excessive coating is thought to have caused the resistance to increase.

[0209] In Comparative Example 6, where a carbon material was used instead of a lithium titanium-containing oxide as the negative electrode active material, the D / C ratio could not be measured. This is thought to be because, since the negative electrode did not contain titanium atoms, no peak was detected within the range of 455 eV to 469 eV. Furthermore, Comparative Example 6 had a higher DC resistance than Examples 1 to 4. This is thought to be because, because a carbon material was used instead of a lithium titanium-containing oxide as the negative electrode active material, the negative electrode potential became too low, and as a result, the carboxylic acid ester was more easily reduced and decomposed. This is thought to be due to the formation of an excessive film during the decomposition reaction.

[0210] Comparative Examples 7 and 8, in which LiDFBOP was not added, had a B / A value less than 0.07 and a D / C value less than 0.75. Furthermore, in Comparative Example 7, where the aging time was shortened to 10 hours, the B / A and D / C values ​​were even lower. This is thought to be because the amount of lithium fluoride-containing film formed on the surfaces of the positive and negative electrodes decreased due to the lower content of lithium and fluorine atoms in the electrolyte and the shorter aging time. Comparative Examples 7 and 8, as described above, had a higher positive electrode DSC heat generation than Examples 1 to 4.

[0211] A battery is provided according to at least one embodiment or example described above. The battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes an oxide containing a transition metal. The transition metals include nickel, cobalt, and manganese. The number of nickel atoms in the oxide is A, where the total number of transition metal atoms is 1. Ｎｉ The ratio of the area of ​​peaks with peak tops in the range of 683 eV to 686 eV to the area of ​​peaks with peak tops in the range of 851 eV to 868 eV in the hard X-ray photoelectron spectroscopy spectrum of the positive electrode surface is 0.07 to 0.20. The negative electrode contains a lithium titanium-containing oxide. In the hard X-ray photoelectron spectroscopy spectrum of the negative electrode surface, the ratio of the area of ​​peaks with peak tops in the range of 685 eV to 687.5 eV to the area of ​​peaks with peak tops in the range of 455 eV to 469 eV in the range of 685 eV to 687.5 eV in hard X-ray photoelectron spectroscopy spectrum of the negative electrode surface is 0.75 to 1.8. The electrolyte contains a carboxylic acid ester and a cyclic carbonate. The volume of the carboxylic acid ester is 2.3 times or more the volume of the cyclic carbonate. Therefore, a battery with high safety and high input / output performance can be provided.

[0212] The invention according to the embodiment is described below.

[0213] [1] A positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises an oxide containing a transition metal, the transition metals comprising nickel, cobalt, and manganese, and the number of nickel atoms in the oxide is A when the total number of transition metal atoms is 1. Ni A battery wherein the ratio of the area B of peaks having peak tops in the range of 683 eV to 686 eV to the area A of peaks having peak tops in the range of 851 eV to 868 eV in the hard X-ray photoelectron spectroscopy spectrum of the surface of the positive electrode is 0.7 or more, the ratio B / A of the area B of peaks having peak tops in the range of 683 eV to 686 eV to the area A of peaks having peak tops in the range of 851 eV to 868 eV is 0.07 or more and 0.20 or less, the negative electrode contains a lithium titanium-containing oxide, the ratio D / C of the area D of peaks having peak tops in the range of 685 eV to 687.5 eV to the area C of peaks having peak tops in the range of 455 eV to 469 eV in the hard X-ray photoelectron spectroscopy spectrum of the surface of the negative electrode is 0.75 or more and 1.8 or less, the electrolyte contains a carboxylic acid ester and a cyclic carbonate, and the volume of the carboxylic acid ester is 2.3 times or more the volume of the cyclic carbonate.

[0214] [2] The oxide is characterized in that the transition metal consists of nickel, cobalt and manganese, and the general formula is Li ｘ Ni １－ｙ－ｚ Co ｙ Mn ｚ O ２ It is expressed as follows, where x satisfies 0 < x ≤ 1, y satisfies 0 < y < 0.3, and z satisfies 0 < z < 0.3, and among the above general formula, A Ｎｉ The battery described in [1], wherein the corresponding value 1-y-z is 0.7 or greater.

[0215] [3] The battery according to [1] or [2], wherein the positive electrode includes positive electrode active material particles containing the oxide, and in a particle size distribution chart obtained by a laser diffraction scattering method for the positive electrode active material particles, the ratio of d90 to d10, d90 / d10, is 4 or less.

[0216] [4] The battery according to any one of [1] to [3], wherein the positive electrode includes positive electrode active material particles containing the oxide, and the average particle diameter of the positive electrode active material particles is 2 μm or more and 8 μm or less.

[0217] [5] The battery according to any one of [1] to [4], wherein the positive electrode includes positive electrode active material particles containing the oxide, and the fracture strength of the positive electrode active material particles is 30 MPa or more and 300 MPa or less.

[0218] [6] A battery pack containing a battery as described in any one of items [1] to [5].

[0219] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

[0220] 1...Electrode group, 2...Outer casing, 3...Positive electrode, 3a...Positive electrode current collector, 3b...Positive electrode active material-containing layer, 3c...Positive electrode current collector tab, 4...Negative electrode, 4a...Negative electrode current collector, 4b...Negative electrode active material-containing layer, 5...Separator, 6...Negative electrode terminal, 7...Positive electrode terminal, 11...Wound electrode group, 12...Container, 13...Lid, 14...Negative electrode lead, 15...Negative electrode terminal, 16...Glass material, 17...Positive electrode lead, 18...Positive electrode terminal, 20...Battery pack, 21...Single cell 22...Adhesive tape, 23...Battery pack, 24...Printed circuit board, 25...Thermistor, 26...Protection circuit, 27...Power supply terminal, 28...Positive lead, 29...Positive connector, 30...Negative lead, 31...Negative connector, 32...Wiring, 33...Wiring, 34a...Positive wiring, 34b...Negative wiring, 35...Wiring, 36...Protective sheet, 37...Storage container, 38...Lid, 51...Negative terminal, 61...Positive terminal.

Claims

1. A positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises an oxide containing a transition metal, the transition metals comprising nickel, cobalt, and manganese, and the number of nickel atoms in the oxide is A when the total number of transition metal atoms is 1. Ｎｉ A battery wherein the ratio of the area B of peaks having peak tops in the range of 683 eV to 686 eV to the area A of peaks having peak tops in the range of 851 eV to 868 eV in the hard X-ray photoelectron spectroscopy spectrum of the surface of the positive electrode is 0.7 or more, the ratio B / A of the area B of peaks having peak tops in the range of 683 eV to 686 eV to the area A of peaks having peak tops in the range of 851 eV to 868 eV is 0.07 or more and 0.20 or less, the negative electrode contains a lithium titanium-containing oxide, the ratio D / C of the area D of peaks having peak tops in the range of 685 eV to 687.5 eV to the area C of peaks having peak tops in the range of 455 eV to 469 eV in the hard X-ray photoelectron spectroscopy spectrum of the surface of the negative electrode is 0.75 or more and 1.8 or less, the electrolyte contains a carboxylic acid ester and a cyclic carbonate, and the volume of the carboxylic acid ester is 2.3 times or more the volume of the cyclic carbonate.

2. The oxide is such that the transition metal consists of nickel, cobalt, and manganese, and the general formula is Li x Ni 1-y-z Co y Mn z Represented by O2, where x satisfies 0 < x ≤ 1, y satisfies 0 < y < 0.3, and z satisfies 0 < z < 0.3, and among the above general formula, A Ｎｉ The battery according to claim 1, wherein the value 1-y-z, which corresponds to the value, is 0.7 or greater.

3. The battery according to claim 1, wherein the positive electrode comprises positive electrode active material particles containing the oxide, and in a particle size distribution chart obtained by laser diffraction scattering of the positive electrode active material particles, the ratio of d90 to d10, d90 / d10, is 4 or less.

4. The battery according to claim 1, wherein the positive electrode includes positive electrode active material particles containing the oxide, and the average particle diameter of the positive electrode active material particles is 2 μm or more and 8 μm or less.

5. The battery according to claim 1, wherein the positive electrode comprises positive electrode active material particles containing the oxide, and the fracture strength of the positive electrode active material particles is 30 MPa or more and 300 MPa or less.

6. A battery pack comprising the battery described in any one of claims 1 to 5.

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