Secondary batteries, battery packs, vehicle and stationary power supplies

Abstract

To provide an electrolyte capable of realizing a secondary battery that indicates excellent discharge efficiency and a discharge capacity, the secondary battery that indicates the excellent discharge efficiency and the discharge capacity, a battery pack that provides this secondary battery, a vehicle that provides the battery pack and a power supply for fixation.SOLUTION: According to an embodiment, the present invention provides an electrolyte containing an aqueous solvent. The aqueous solvent contains water and phosphate ester. A content amount of the phosphate ester against the aqueous solvent is 1 mol% or more and less than 2.5 mol%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Embodiments of the present invention relate to electrolytes, secondary batteries, battery packs, vehicles, and stationary power supplies. [Background technology]

[0002] Non-aqueous electrolyte batteries, particularly lithium secondary batteries, using carbon materials or lithium titanium oxide as the negative electrode active material and layered oxides containing nickel, cobalt, and manganese as the positive electrode active material, have already been put into practical use as power sources in a wide range of fields. These non-aqueous electrolyte batteries come in a variety of forms, from small ones for various electronic devices to large ones for electric vehicles. Unlike nickel-metal hydride or lead-acid batteries, the electrolyte in these lithium secondary batteries uses a non-aqueous organic solvent mixed with ethylene carbonate or methyl ethyl carbonate. Electrolytes using these solvents have higher oxidation and reduction resistance than aqueous electrolytes, and are less prone to solvent electrolysis. Therefore, non-aqueous lithium secondary batteries can achieve high electromotive forces of 2V to 4.5V.

[0003] On the other hand, since many organic solvents are flammable, the safety of secondary batteries using organic solvents is inherently inferior to that of secondary batteries using aqueous solutions. Although various measures have been taken to improve the safety of lithium secondary batteries using electrolytes containing organic solvents, they are not always sufficient. In addition, non-aqueous lithium secondary batteries require a dry environment in the manufacturing process, which inevitably increases manufacturing costs. Furthermore, electrolytes containing organic solvents have poor conductivity, so the internal resistance of non-aqueous lithium secondary batteries tends to be high. These challenges are major drawbacks for electric vehicles, hybrid electric vehicles, and large-scale storage batteries for energy storage, where battery safety and battery cost are of paramount importance.

[0004] To address the challenges of non-aqueous secondary batteries, secondary batteries using aqueous electrolytes have been proposed. However, because the active material can easily detach from the current collector due to the electrolysis of the aqueous electrolyte, the operation of the secondary battery is unstable, and satisfactory charging and discharging remains a challenge. To achieve satisfactory charging and discharging when using an aqueous electrolyte, this can be addressed by limiting the potential range in which the battery is charged and discharged to a range in which the electrolysis reaction of the water contained as a solvent does not occur. For example, by using lithium manganese oxide as the positive electrode active material and lithium vanadium oxide as the negative electrode active material, electrolysis of the aqueous solvent can be avoided. In the case of these combinations, an electromotive force of about 1V to 1.5V can be obtained, but it is difficult to obtain an energy density sufficient for a battery.

[0005] In contrast, lithium manganese oxide is used as the positive electrode active material, and LiTi2O4 and Li4Ti5O4 are used as the negative electrode active materials. 12 Using lithium titanium oxides such as those mentioned above, theoretically, an electromotive force of around 2.6V to 2.7V can be obtained, making it an attractive battery from the standpoint of energy density. Non-aqueous lithium-ion batteries employing such combinations of positive and negative electrode materials offer excellent lifespan, and such batteries are already in practical use.

[0006] However, in aqueous electrolytes, the lithium insertion / deinsertion potential of lithium titanium oxide is approximately 1.5V (vs. Li / Li) relative to the lithium potential. + Therefore, electrolysis of the aqueous electrolyte is likely to occur. In particular, at the negative electrode, hydrogen generation due to electrolysis is severe on the surface of the negative electrode current collector or the metal casing electrically connected to the negative electrode, and as a result, the active material can easily detach from the current collector. For this reason, such batteries do not operate stably and satisfactory charging and discharging is impossible.

[0007] Spinel-type lithium titanium oxide Li4Ti5O 12The operating potential of many titanium-containing oxides, including TLO, is lower than the electrolysis potential of water. Therefore, in secondary batteries that use titanium-containing oxides such as TLO as the negative electrode active material and contain a large amount of water in the electrolyte, not only does the negative electrode active material detach due to hydrogen bubbles generated by the electrolysis of water, but the insertion reaction of carriers (e.g., alkali metal ions such as lithium ions) into the negative electrode active material and the proton (hydrogen cation; H) reaction by the electrolysis of water can also occur. + This competes with the reduction reaction of ) and, as a result, the charge / discharge efficiency and discharge capacity of the secondary battery decrease. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2020-038818 [Patent Document 2] Japanese Patent Publication No. 2022-049455 [Patent Document 3] Japanese Patent Publication No. 2015-159122 [Patent Document 4] Japanese Patent Publication No. 2017-50148 [Overview of the project] [Problems that the invention aims to solve]

[0009] The problem that this invention aims to solve is to provide an electrolyte capable of realizing a secondary battery exhibiting excellent charge-discharge efficiency and discharge capacity, a secondary battery exhibiting excellent charge-discharge efficiency and discharge capacity, a battery pack equipped with this secondary battery, and a vehicle and stationary power supply equipped with this battery pack. [Means for solving the problem]

[0011] Embodiment According to this, the negative electrode and the positive electrode, electrolyte A secondary battery is provided that has the following features. The electrolyte described above includes an aqueous solvent. The aqueous solvent contains water and a phosphate ester. The phosphate ester content relative to the aqueous solvent is 1 mol% or more and less than 2.5 mol%. The negative electrode described above contains a titanium-containing oxide.

[0012] Furthermore, according to another embodiment, a battery pack comprising the secondary battery according to the above embodiment is provided.

[0013] Furthermore, according to another embodiment, a vehicle is provided that is equipped with the battery pack according to the above embodiment.

[0014] Furthermore, according to another embodiment, a stationary power supply comprising a battery pack according to the above embodiment is provided. [Brief explanation of the drawing]

[0015] [Figure 1] A schematic cross-sectional view showing an example of a secondary battery according to this embodiment. [Figure 2] A cross-sectional view of the secondary battery shown in Figure 1, along the line II-II. [Figure 3] A partially cutaway perspective view schematically showing another example of a secondary battery according to the embodiment. [Figure 4] A partially cutaway perspective view schematically showing yet another example of a secondary battery according to the embodiment. [Figure 5] An enlarged cross-sectional view of part E of one embodiment of the secondary battery shown in Figure 4. [Figure 6] An enlarged cross-sectional view of part E of another embodiment of the secondary battery shown in Figure 4. [Figure 7] A schematic perspective view showing an example of a battery pack according to this embodiment. [Figure 8] A schematic perspective view showing an example of a battery pack according to the embodiment. [Figure 9] An exploded perspective view schematically showing another example of a battery pack according to the embodiment. [Figure 10] A block diagram showing an example of the electrical circuit of the battery pack shown in Figure 9. [Figure 11] A schematic cross-sectional view showing an example of a vehicle according to this embodiment. [Figure 12] A block diagram showing an example of a system including a stationary power supply according to the embodiment. [Modes for carrying out the invention]

[0016] In secondary batteries using aqueous electrolytes, it is known that increasing the concentration of electrolyte salts (e.g., lithium salts) in the electrolyte can suppress water splitting at the electrodes. However, high concentrations of electrolyte salts reduce the wettability of the electrolyte to the electrodes, and also decrease the impregnation of the electrolyte into the electrodes. Insufficient impregnation of the electrolyte into the electrodes contributes to a decrease in battery performance, such as charge / discharge speed, efficiency, and capacity.

[0017] Furthermore, while it is known that providing a highly dense diaphragm on the negative electrode surface to isolate the negative electrode from water is a means of suppressing water splitting, negative electrodes equipped with such diaphragms tend to have lower impregnation properties with high-concentration electrolytes. A solid electrolyte membrane is an example of a diaphragm with particularly high density. A solid electrolyte membrane is a membrane composed solely of ion-conducting solid electrolyte particles. Although a solid electrolyte membrane selectively allows specific ions to pass through, it is difficult for solvents to permeate it, thus exhibiting water-impermeable properties. In addition, polymer composite membranes, in which solid electrolyte particles are bonded together with polymer materials, have been proposed. While polymer composite membranes have lower water-impermeability than solid electrolyte membranes, they possess high density and can retain trace amounts of aqueous electrolytes. Moreover, polymer composite membranes are more flexible than solid electrolyte membranes and can be made into thin films.

[0018] Adding surfactants to the electrolyte is a known method for improving the wettability of liquid electrolytes to electrodes. However, there are concerns that the addition of surfactants may lead to deterioration of battery performance due to changes in the surfactant over time or the decomposition of the surfactant itself at the positive electrode.

[0019] The embodiments will be described below with reference to the drawings as appropriate. Common components throughout the embodiments will be denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, each figure is a schematic diagram intended to illustrate the embodiments and facilitate understanding; their shapes, dimensions, ratios, etc., may differ from those of the actual device. These can be appropriately modified in accordance with the following description and known technology.

[0020] Unless otherwise stated, pH and other measurement values ​​are those obtained at 25°C.

[0021] (First Embodiment) According to the first embodiment, an electrolyte is provided. The electrolyte comprises an aqueous solvent containing water and a phosphate ester. The aqueous solvent contains the phosphate ester in an amount of 1 mol% or more and less than 2.5 mol% relative to the aqueous solvent.

[0022] The electrolyte in question may, for example, be an electrolyte for a secondary battery. More specifically, it may be an aqueous electrolyte for an aqueous electrolyte battery. The secondary battery may, for example, be a lithium secondary battery (lithium-ion secondary battery) or a sodium secondary battery (sodium-ion secondary battery).

[0023] The electrolyte in question may contain an electrolyte salt as a solute. The electrolyte salt may include salts of carrier ions such as lithium ions and sodium ions, for example, lithium salts and sodium salts.

[0024] The electrolyte may be, for example, a liquid aqueous electrolyte. A liquid aqueous electrolyte is an aqueous solution prepared by dissolving an electrolyte salt as a solute in an aqueous solvent. The electrolyte may also be a gel-like aqueous electrolyte. A gel-like aqueous electrolyte is prepared by mixing and compounding the above-mentioned liquid aqueous electrolyte with a polymer compound. Examples of polymer compounds include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

[0025] The electrolyte according to this embodiment exhibits high wettability to electrodes due to the inclusion of a phosphate ester in the solvent. For example, the electrolyte exhibits high wettability to the active material-containing layer of the electrode. Furthermore, even with electrodes having a diaphragm for blocking water, the electrolyte exhibits high wettability to the diaphragm. In other words, regardless of the presence or absence of a diaphragm in the electrode, the electrolyte exhibits high wettability to the electrode.

[0026] High wettability of the electrolyte to the electrode means that the electrolyte has high impregnation properties into the electrode. This allows the electrolyte to penetrate even the finer details of the electrode, improving the contact efficiency between the electrode active material and the electrolyte, thus resulting in higher battery performance. Specifically, for example, it enables the creation of batteries with superior charge-discharge efficiency and discharge capacity.

[0027] Phosphate esters are less prone to degradation compared to surfactants. Furthermore, phosphate esters are more effective than other organic solvents such as N-methyl-2-pyrrolidone and γ-butyrolactone in improving the wettability of electrolytes to electrodes. Examples of phosphate esters include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, and tributyl phosphate. Another example is fluorine-substituted phosphate esters, in which at least one hydrogen atom of the above phosphate esters is substituted with a fluorine atom. The electrolyte in question may contain at least one selected from the group consisting of these phosphate esters and fluorine-substituted phosphate esters.

[0028] The electrolyte in question contains a mixed solvent comprising at least water and a phosphate ester as the solvent. The electrolyte can exhibit the high wettability described above by containing 1 mol% or more of phosphate ester in the total aqueous solvent. The solubility of the electrolyte salt is good when the phosphate ester content is less than 2.5 mol% in the total aqueous solvent. Therefore, even if the concentration of the electrolyte salt is increased, there is no concern about the precipitation of the electrolyte salt, which can cause battery failure, and the electrolysis of water can be suppressed. It is preferable that the molar ratio of phosphate ester to electrolyte salt is 0.03 or more and 0.1 or less.

[0029] Aqueous solvents contain water as their main component. For example, an aqueous solvent may contain water in a proportion of 95 mol% to 99 mol% of the total aqueous solvent.

[0030] As the electrolyte salt, for example, lithium salts, sodium salts, or mixtures thereof can be used.

[0031] Examples of lithium salts include lithium chloride (LiCl), lithium bromide (LiBr), lithium hydroxide (LiOH), lithium sulfate (Li2SO4), lithium nitrate (LiNO3), lithium acetate (CH3COOLi), lithium oxalate (Li2C2O4), lithium carbonate (Li2CO3), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI;LiN(SO2CF)). 3)2 ), lithium bis(fluorosulfonyl)imide (LiFSI;LiN(SO2F)2), and lithium bisoxalate borate (LiBOB:LiB[(OCO)2]2) can be used.

[0032] Examples of sodium salts that can be used include sodium chloride (NaCl), sodium sulfate (Na2SO4), sodium hydroxide (NaOH), sodium nitrate (NaNO3), and sodium trifluoromethanesulfonylamide (NaTFSA).

[0033] The molar concentration of carrier ions (e.g., lithium ions or sodium ions) in the aqueous electrolyte is preferably 4 mol / L or higher, more preferably 9 mol / L or higher, and even more preferably 12 mol / L or higher. When the concentration of carrier ions in the electrolyte is high, the electrolysis of the aqueous solvent at the negative electrode is easily suppressed, and hydrogen generation from the negative electrode tends to be low. Because such electrolytes contain phosphate esters, the wettability to the electrode is high even at high ion concentrations, resulting in good impregnation into the electrode.

[0034] In addition to carrier ion salts, a salt containing one or more elements A selected from the group consisting of B, P, Al, La, Zr, Ge, Zn, Sn, Ga, Pb, In, Bi, Tl, Cu, Cd, and Ag may be added to the electrolyte. By adding such a compound to the electrolyte, a coating layer containing element A as a single element, oxide, hydroxide, basic carbonate compound, or sulfate compound can be formed at the negative electrode. These elements A-containing components exhibit the effect of suppressing hydrogen generation at the electrode on which they are formed.

[0035] The pH of the electrolyte is preferably 3 or more and 14 or less, and more preferably 4 or more and 13 or less. The pH is the value measured at 25°C.

[0036] <<Measurement of electrolyte>> The method for measuring the properties of the electrolyte will be described below.

[0037] When the electrolyte to be measured is contained in, for example, a fabricated battery, the electrolyte is extracted as follows. After discharging the battery, the battery is disassembled, and the electrolyte is extracted to obtain a measurement sample. For example, the battery is disassembled to take out the electrode group. The electrolyte contained in the electrode group is extracted to obtain a measurement sample.

[0038] <Quantification of phosphate ester> The identification and quantification of the phosphate ester in the electrolyte can be carried out, for example, by the method described below. The battery is disassembled and the electrolyte is extracted. The extracted electrolyte is extracted with hexane to separate the organic solvent in the electrolyte. By performing gas chromatography-mass spectrometry (GC-MS) measurement on the separated organic solvent, the phosphate ester in the electrolyte can be identified.

[0039] In addition, by measuring the proton nuclear magnetic resonance ( 1 1H NMR) spectrum, the molar ratio of water and phosphate ester in the electrolyte can be calculated. The extracted electrolyte is directly dissolved in an appropriate deuterated solvent, 1 and the 1H NMR spectrum is measured. 1 In the 1H NMR spectrum, since the peak area is proportional to the number of hydrogen atoms, the molar ratio of water molecules and phosphate ester can be calculated from the area ratio of the peak attributed to the proton (-O“H”) contained in the OH group of water molecules and the peak attributed to the proton (-(C“H2”) n C“H3”) contained in the alkyl group of the phosphate ester.

[0040] <Method for measuring pH> The method for measuring the pH of an electrolyte is as follows: Disassemble the secondary battery, extract the electrolyte, measure the volume of the liquid, and then measure the pH value using a pH meter. pH measurement is performed as follows, for example: For this measurement, use, for example, the F-74 manufactured by Horiba, Ltd. First, prepare standard solutions with pH 4.0, 7.0, and 9.0. Next, calibrate the F-74 using these standard solutions. Prepare an appropriate amount of the electrolyte (electrolyte solution) to be measured, put it in a container, and measure the pH. After measuring the pH, clean the sensor part of the F-74. When measuring a different target, perform the above procedure, i.e., calibration, measurement, and cleaning, each time.

[0041] The electrolyte according to the first embodiment contains an aqueous solvent containing 1 mol% or more and less than 2.5 mol% of a phosphate ester. This electrolyte can realize a secondary battery that exhibits excellent charge-discharge efficiency and excellent discharge capacity.

[0042] (Second Embodiment) According to the second embodiment, a secondary battery is provided. The secondary battery comprises a negative electrode, a positive electrode, and an electrolyte according to the first embodiment.

[0043] The secondary battery in question may be, for example, a lithium secondary battery (lithium-ion secondary battery). Alternatively, the secondary battery may be a sodium secondary battery (sodium-ion secondary battery). Secondary batteries include aqueous electrolyte secondary batteries containing an aqueous electrolyte (e.g., an aqueous solution electrolyte). In other words, the secondary battery may be an aqueous electrolyte lithium-ion secondary battery or an aqueous electrolyte sodium-ion secondary battery.

[0044] The secondary battery may further comprise a diaphragm located between the negative electrode and the positive electrode. In the secondary battery, the negative electrode, the positive electrode, and the diaphragm may constitute an electrode group. The secondary battery may further comprise an outer casing capable of housing the electrode group and the electrolyte. Furthermore, the secondary battery may further comprise a negative electrode terminal electrically connected to the negative electrode and a positive electrode terminal electrically connected to the positive electrode.

[0045] The diaphragm functions as a separator that electrically insulates the negative electrode from the positive electrode. In addition to the diaphragm, the secondary battery may further include other separators independent of the diaphragm. These other separators may, for example, be placed between the diaphragm and the positive electrode. The other separators may also be impregnated with an aqueous electrolyte.

[0046] The following provides a detailed explanation of the negative electrode, positive electrode, diaphragm, other separators, outer casing components, negative electrode terminal, and positive electrode terminal.

[0047] (1) 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 provided on one main surface of the negative electrode current collector or on both the front and back main surfaces. The negative electrode active material-containing layer may optionally include a negative electrode active material, a conductive agent, and a binder.

[0048] The negative electrode may contain a titanium-containing oxide as the negative electrode active material. The titanium-containing oxide used as the negative electrode active material has a lithium ion insertion-desorption potential of 1V (vs.Li / Li) relative to the oxidation-reduction potential of lithium. + ) or more and 3V or less (vs.Li / Li + A compound that is ) can be used. In such a secondary battery, self-discharge and hydrogen generation at the negative electrode can be suppressed by including the electrolyte according to the first embodiment. Therefore, even if the negative electrode active material contains a titanium-containing oxide having a low potential as described above, charging and discharging can be performed appropriately in an aqueous electrolyte.

[0049] As titanium-containing oxides, titanium oxide, lithium titanium composite oxide, monoclinic niobium titanium oxide, sodium niobium titanium composite oxide, etc., can be used. The negative electrode active material may contain one or more titanium-containing oxides.

[0050] Titanium oxides include, for example, monoclinic titanium oxide, rutile titanium oxide, or anatase titanium oxide. Each crystalline structure of titanium oxide has a composition of TiO2 before charging and a composition of Li after charging. xIt can be represented by TiO2 (where x satisfies 0 ≦ x ≦ 1). Also, the structure of the monoclinic titanium oxide before charging can be represented as TiO2(B).

[0051] The lithium titanium oxide includes, for example, lithium titanium oxide with a spinel structure (for example, a compound represented by the general formula Li 4+x Ti5O 12 and -1 ≦ x ≦ 3) and lithium titanium oxide with a lamellarite structure (for example, a compound represented by Li 2+x Ti3O7 and -1 ≦ x ≦ 3, a compound represented by Li 1+x Ti2O4 and 0 ≦ x ≦ 1, a compound represented by Li 1.1+x Ti 1.8 O4 and 0 ≦ x ≦ 1, a compound represented by Li 1.07+x Ti 1.86 O4 and 0 ≦ x ≦ 1, a compound represented by Li x TiO2 and 0 < x ≦ 1), etc. Further, the lithium titanium oxide may be a lithium titanium composite oxide into which a different element is introduced.

[0052] Examples of the monoclinic niobium titanium oxide include compounds represented by Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ 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. Each subscript in the composition formula satisfies 0 ≦ x ≦ 5, 0 ≦ y < 1, 0 ≦ z < 2, -0.3 ≦ δ ≦ 0.3. Specific examples of the monoclinic niobium titanium oxide include Li x Nb2TiO7 (0 ≦ x ≦ 5).

[0053] Other examples of the monoclinic niobium titanium oxide include Li x Ti 1-y M3 y+z Nb 2-z O 7-δCompounds represented by [formula] are included. Here, M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo. Each subscript in the composition formula satisfies 0 ≦ x ≦ 5, 0 ≦ y < 1, 0 ≦ z < 2, and -0.3 ≦ δ ≦ 0.3.

[0054] As yet another example of monoclinic niobium titanate oxide, for example, Nb2TiO7, Nb2Ti2O9, Nb 10 Ti2O 29 Nb 14 TiO 37 And Nb 24 TiO 62 can be mentioned. The monoclinic niobium titanate oxide may be a substituted niobium titanate oxide in which at least a part of Nb and / or Ti is substituted with a different element. Examples of the substitution element include Na, K, Ca, Co, Ni, Si, P, V, Cr, Mo, Ta, Zr, Mn, Fe, Mg, B, Pb, and Al. The substituted niobium titanate oxide may contain one type of substitution element or may contain two or more types of substitution elements.

[0055] Sodium niobium titanium composite oxide is, for example, represented by the general formula Li 2+x Na 2-a M4 b Ti 6-c-d Nb c M5 d O 14+δ and includes an orthorhombic type Na-containing niobium titanium composite oxide where 0 ≦ x ≦ 4, 0 ≦ a < 2, 0 ≦ b < 2, 0 < c < 6, 0 ≦ d < 3, c + d < 6, -0.5 ≦ δ ≦ 0.5, M4 includes one or more selected from the group consisting of Cs, K, Sr, Ba, Ca, and M5 includes one or more selected from the group consisting of Zr, Sn, V, Ta, Mo, W, Fe, Co, Mn, Al.

[0056] As the negative electrode active material, it is preferable to use titanium oxide with an anatase structure, titanium oxide with a monoclinic structure, lithium titanium oxide with a spinel structure, or a mixture thereof. By combining a negative electrode using these oxides as the negative electrode active material with a positive electrode using, for example, a lithium manganese composite oxide as the positive electrode active material, a high electromotive force can be obtained.

[0057] The negative electrode active material is contained in the negative electrode active material-containing layer, for example, in the form of particles. The negative electrode active material particles may be primary particles, secondary particles which are aggregates of primary particles, or mixtures of individual primary and secondary particles. The shape of the particles is not particularly limited and can be, for example, spherical, elliptical, flattened, or fibrous.

[0058] The average particle diameter of the primary particles of the negative electrode active material is preferably 3 μm or less, and a more preferable average primary particle diameter is 0.01 μm or more and 1 μm or less. The average particle diameter of the secondary particles of the negative electrode active material is preferably 30 μm or less, and a more preferable average secondary particle diameter is 5 μm or more and 20 μm or less.

[0059] The primary and secondary particle diameters refer to the particle size at which the integrated volume value in the particle size distribution determined by a laser diffraction particle size distribution analyzer reaches 50%. For example, the Shimadzu SALD-300 is used as the laser diffraction particle size distribution analyzer. During the measurement, the luminosity distribution is measured 64 times at 2-second intervals. The sample used for this particle size distribution measurement is a dispersion of N-methyl-2-pyrrolidone diluted to a concentration of 0.1% to 1% by mass of negative electrode active material particles. Alternatively, the measurement sample may consist of 0.1 g of negative electrode active material dispersed in 1-2 mL of distilled water containing a surfactant.

[0060] Conductive agents are added to enhance current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. In addition, fibrous carbon materials such as carbon nanotubes and carbon nanofibers can be used as conductive agents. 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 active material particles.

[0061] A binder is added to fill the gaps between dispersed active materials and to bond the 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.

[0062] Preferably, the proportions of the negative electrode active material, conductive agent, and binder in the negative electrode active material-containing layer are within the range of 70% to 95% by mass for the negative electrode active material, 3% to 20% by mass for the conductive agent, and 2% to 10% by mass for the binder. A conductive agent content of 3% by mass or more improves the current collection performance of the negative electrode active material-containing layer. A binder content of 2% by mass or more provides sufficient electrode strength. The binder can function as an insulator. Therefore, a binder content of 10% by mass or less reduces the insulating portion within the electrode.

[0063] The density of the negative electrode active material layer (excluding the current collector) is 1.8 g / cm³. 3 More than 2.8g / cm 3The following is preferable. A negative electrode with a density of the negative electrode active material-containing layer 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 More than 2.6g / cm 3 The following is more preferable:

[0064] The negative electrode current collector is preferably a foil containing at least one selected from the group consisting of aluminum (Al), titanium (Ti), and zinc (Zn). Besides foil, other forms of the negative electrode current collector include mesh and porous materials. For improved energy density and output, a foil form with a small volume and large surface area is desirable.

[0065] The thickness of the negative electrode current collector is preferably between 5 μm and 20 μm. A current collector with such a thickness can balance electrode strength and weight reduction.

[0066] Furthermore, the negative electrode current collector may include portions on its surface that do not have a negative electrode active material-containing layer. These portions can function as negative electrode current collector tabs. Alternatively, a separate negative electrode current collector tab may be electrically connected to the negative 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 side 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] (2) Positive electrode The positive electrode can include a positive electrode current collector and a positive electrode active material-containing layer. The positive electrode active material-containing layer can be provided on one main surface or both main surfaces (front and back) of the positive electrode current collector. The positive electrode active material-containing layer can contain a positive electrode active material, and optionally a conductive agent and a binder.

[0070] As the positive electrode active material, for example, an oxide or a sulfide can be used. The positive electrode may contain, as the positive electrode active material, one type of compound alone, or may contain a combination of two or more types of compounds. Examples of the oxide and the sulfide can include compounds into which an alkali metal or an alkali metal ion can be inserted and desorbed.

[0071] Examples of such compounds include, for example, manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (for example, Li x Mn2O4 or Li x MnO2; 0 < x ≦ 1), lithium nickel composite oxide (for example, Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxide (for example, Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxide (for example, Li x Ni 1-y Co y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese cobalt composite oxide (for example, Li x [ Mn y Co 1-y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (for example, Li x Mn 2-y Ni y O4; 0 < x ≦ 1, 0 < y < 2), lithium phosphate having an olivine structure (for example, 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), vanadium oxide (for example, V2O5), and lithium nickel cobalt manganese composite oxide (Lix Ni 1-y-z Co y Mn z O2; where 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, and y + z < 1 is included.

[0072] Among the above, examples of more preferable compounds as the positive electrode active material include lithium manganese composite oxides having a spinel structure (e.g., Li x Mn2O4; 0 < x ≤ 1), lithium nickel composite oxides (e.g., Li x NiO2; 0 < x ≤ 1), lithium cobalt composite oxides (e.g., Li x CoO2; 0 < x ≤ 1), lithium nickel cobalt composite oxides (e.g., Li x Ni 1-y Co y O2; 0 < x ≤ 1, 0 < y < 1), lithium manganese nickel composite oxides having a spinel structure (e.g., Li x Mn 2-y Ni[[ID=X]] y O4; 0 < x ≤ 1, 0 < y < 2), lithium manganese cobalt composite oxides (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 lithium nickel cobalt manganese composite oxides (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, and y + z < 1 is included. Using these compounds as the positive electrode active material can increase the positive electrode potential.

[0073] The primary particle diameter of the positive electrode active material is preferably 100 nm or more and 1 μm or less. A positive electrode active material with a primary particle diameter of 100 nm or more is easy to handle in industrial production. A positive electrode active material with a primary particle diameter of 1 μm or less can allow smooth progress of the solid-state diffusion of lithium ions.

[0074] The specific surface area of the positive electrode active material is 0.1 m 2 / g or more and 10 m2 It is preferable that it is less than or equal to / g. 0.1m 2 A positive electrode active material with a specific surface area of ​​10m or more can adequately secure sites for Li ion intercalation and release. 2 Positive electrode active materials with a specific surface area of ​​less than / g are easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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 internal resistance.

[0079] 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.

[0080] 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.

[0081] The positive electrode current collector is preferably a metal foil such as titanium, aluminum, or stainless steel, or an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si. To prevent corrosion of the current collector due to reaction between the current collector and the electrolyte, the surface of the current collector may be coated with a different element.

[0082] The thickness of the positive electrode current collector is preferably 5 μm or more and 20 μm or less, and more preferably 15 μm or less.

[0083] Furthermore, the positive electrode current collector may include portions on its surface that do not have a positive electrode active material-containing layer. These portions can function as positive electrode current collector tabs. Alternatively, a separate positive electrode current collector tab may be electrically connected to the positive electrode.

[0084] A 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 side 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, a positive electrode is manufactured.

[0085] 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.

[0086] (3) Diaphragm A diaphragm can be placed between the negative and positive electrodes to prevent electrical contact between them. In other words, the diaphragm functions as a separator that electrically insulates the negative and positive electrodes. The diaphragm may also be in contact with at least one of the negative and positive electrodes. The diaphragm may be supported on either the negative or positive electrode. For example, the diaphragm may be formed on the surface of the active material-containing layer of the negative or positive electrode.

[0087] As a diaphragm, a membrane containing inorganic solid particles and polymer materials, such as a composite membrane of inorganic solid particles and polymer materials, or an ion exchange membrane, can be used. The inorganic solid particles may be, for example, particles of a solid electrolyte, and the membrane may be a solid electrolyte membrane. The solid electrolyte membrane may be, for example, a solid electrolyte composite membrane formed by shaping solid electrolyte particles into a membrane using a polymer material.

[0088] From the viewpoint of minimizing internal short circuits, the thickness of the diaphragm is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 7 μm or more. Furthermore, from the viewpoint of increasing ionic conductivity and energy density, the thickness of the diaphragm is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less.

[0089] Examples of inorganic solid particles that can be incorporated into the membrane include oxide ceramics such as alumina, silica, zirconia, yttria, magnesium oxide, calcium oxide, barium oxide, strontium oxide, and vanadium oxide; carbonates and sulfates such as sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lanthanum carbonate, cerium carbonate, calcium sulfate, magnesium sulfate, aluminum sulfate, gypsum, and barium sulfate; phosphates such as hydroxyapatite, lithium phosphate, zirconium phosphate, and titanium phosphate; and nitride ceramics such as silicon nitride, titanium nitride, and boron nitride. The inorganic particles listed above may also be in the form of hydrates.

[0090] The inorganic solid particles preferably include solid electrolyte particles having ionic conductivity for alkali metal ions. More specifically, inorganic solid particles having ionic conductivity for lithium ions and sodium ions are more preferred. Here, lithium ion conductivity means 1 × 10⁻⁶ at 25°C. -6 This refers to exhibiting a lithium-ion conductivity of S / cm or higher. Lithium-ion conductivity can be measured, for example, by the AC impedance method. By using such inorganic solid particles, a diaphragm with lithium-ion conductivity or sodium-ion conductivity can be obtained.

[0091] Examples of inorganic solid particles having lithium ion conductivity include oxide-based solid electrolytes and sulfide-based solid electrolytes. Oxide-based solid electrolytes have a NASICON (Sodium (Na) Super Ionic Conductor) type structure and the general formula Li 1+x It is preferable to use a lithium phosphate solid electrolyte represented by Mα2(PO4)3. In the above general formula, Mα is one or more selected from the group consisting of, for example, titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). The subscript x is in the range of 0 ≤ x ≤ 2.

[0092] Specific examples of the lithium phosphate solid electrolyte having a NASICON structure include Li 1+x Al x Ti 2-x (PO4)3 represented LATP compound where 0.1 ≦ x ≦ 0.5; Li 1+x Al y Mβ 2-y (PO4)3 represented where Mβ is one or more selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Ca and 0 ≦ x ≦ 1 and 0 ≦ y ≦ 1; Li 1+x Al x Ge 2-x (PO4)3 represented where 0 ≦ x ≦ 2; Li 1+x Al x Zr 2-x (PO4)3 represented where 0 ≦ x ≦ 2; Li 1+x+y Al x Mγ 2-x Si y P 3-y O 12 represented where Mγ is one or more selected from the group consisting of Ti and Ge and 0 < x ≦ 2, 0 ≦ y < 3; and Li 1+2x Zr 1-x Ca x (PO4)3 represented where 0 ≦ x < 1 can be mentioned. Li 1+2x Zr 1-x Ca[[ID=​​​​​​​​​​​​​​​​​​​​​​​​A compound represented as follows: A is one or more selected from the group consisting of Ca, Sr, and Ba, and Mδ is one or more selected from the group consisting of Nb and Ta, and 0 ≤ x ≤ 0.5; Li3Mδ 2-x L2O 12 A compound represented by where Mδ is 1 or more selected from the group consisting of Nb and Ta, and L may contain Zr, with 0 ≤ x ≤ 0.5; Li 7-3x Al x La3Zr3O 12 Compounds represented by 0 ≤ x ≤ 0.5; Li 5+x La3MCSR 2-x Zr x O 12 Represented by , where Mδ is 1 or more selected from the group consisting of Nb and Ta, and 0 ≤ x ≤ 2, it is an LLZ compound (e.g., Li7La3Zr2O 12 ); and having a perovskite-type structure La 2 / 3-x Li x Examples include compounds represented as TiO3 with a x-value of 0.3 ≤ x ≤ 0.7. The solid electrolyte may be a single type or a mixture of two or more types.

[0094] Furthermore, a sodium-containing solid electrolyte may be used as the inorganic solid particles having ionic conductivity for sodium ions. Sodium-containing solid electrolytes have excellent ionic conductivity for sodium ions. Examples of sodium-containing solid electrolytes include β-alumina, sodium phosphorus sulfide, and sodium phosphorus oxide. The sodium ion-containing solid electrolyte is preferably in the form of glass ceramics.

[0095] The shape of inorganic solid particles is not particularly limited, but can be spherical, elliptical, flattened, or fibrous, for example.

[0096] The average particle size of the inorganic solid particles is preferably 15 μm or less, and more preferably 12 μm or less. A smaller average particle size of the inorganic solid particles can increase the density of the membrane.

[0097] The average particle size of inorganic solid particles is preferably 0.01 μm or larger, and more preferably 0.1 μm or larger. When the average particle size of inorganic solid particles is large, aggregation of particles tends to be suppressed.

[0098] The average particle size of inorganic solid particles refers to the particle size at which the integrated volume value in the particle size distribution determined by a laser diffraction particle size distribution analyzer becomes 50%. For this particle size distribution measurement, a dispersion of inorganic solid particles diluted in ethanol to a concentration of 0.01% to 5% by mass is used as the sample.

[0099] In the membrane, inorganic solid particles may be of a single type or a mixture of multiple types.

[0100] In the diaphragm, inorganic solid particles are preferably the main component. From the viewpoint of increasing the ionic conductivity of the composite membrane, the proportion of inorganic solid particles in the diaphragm is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more. From the viewpoint of increasing the membrane strength of the diaphragm, the proportion of inorganic solid particles in the diaphragm is preferably 98% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less. The proportion of inorganic solid particles in the diaphragm can be calculated by thermogravimetric (TG) analysis.

[0101] The polymer material contained in the diaphragm enhances the binding properties between inorganic solid particles. The weight-average molecular weight of the polymer material is, for example, 3000 or more. When the weight-average molecular weight of the polymer material is 3000 or more, the binding properties of the inorganic solid particles can be further enhanced. The weight-average molecular weight of the polymer material is preferably 3000 to 5,000,000, more preferably 5000 to 2,000,000, and even more preferably 10,000 to 1,000,000. The weight-average molecular weight of the polymer material can be determined by gel permeation chromatography (GPC).

[0102] Polymeric materials may be polymers consisting of a single monomer unit, copolymers consisting of multiple monomer units, or mixtures thereof. Preferably, polymeric materials contain monomer units composed of hydrocarbons having a functional group containing one or more selected from the group consisting of oxygen (O), sulfur (S), nitrogen (N), and fluorine (F). Preferably, the proportion of the polymeric material composed of monomer units is 70 mol% or more. Hereinafter, these monomer units will be referred to as first monomer units. Furthermore, in copolymers, components other than the first monomer units will be referred to as second monomer units. The copolymer of the first monomer unit and the second monomer unit may be an alternating copolymer, a random copolymer, or a block copolymer.

[0103] In polymer materials, if the proportion of the portion composed of first monomer units is less than 70 mol%, the water-impermeable properties of the composite film may decrease. In polymer materials, it is preferable that the proportion of the portion composed of first monomer units is 90 mol% or more. Most preferably, the polymer material is a polymer composed of 100 mol% first monomer units, that is, a polymer consisting only of first monomer units.

[0104] The first monomer unit may be a compound having a functional group in its side chain containing one or more elements selected from the group consisting of oxygen (O), sulfur (S), nitrogen (N), and fluorine (F), and whose main chain is composed of carbon-carbon bonds. The hydrocarbon may have one or more functional groups containing one or more elements selected from the group consisting of oxygen (O), sulfur (S), nitrogen (N), and fluorine (F). The functional groups in the first monomer unit enhance the conductivity of alkali metal ions passing through the composite film.

[0105] The hydrocarbon constituting the first monomer unit preferably has a functional group containing one or more selected from the group consisting of oxygen (O), sulfur (S), and nitrogen (N). When the first monomer unit has such a functional group, the conductivity of alkali metal ions in the composite film tends to increase and the internal resistance tends to decrease.

[0106] The functional group included in the first monomer unit preferably contains one or more selected from the group consisting of a formal group, a butyral group, a carboxymethyl ester group, an acetyl group, a carbonyl group, a hydroxyl group, and a fluoro group. Furthermore, the first monomer unit more preferably contains at least one of a carbonyl group and a hydroxyl group as a functional group, and even more preferably contains both.

[0107] The first monomer unit can be represented by the following formula.

[0108] [ka]

[0109] In the above formula, R1 is preferably selected from the group consisting of hydrogen (H), alkyl groups, and amino groups. Furthermore, R2 is preferably selected from the group consisting of hydroxyl group (-OH), -OR1, -COOR1, -OCOR1, -OCH(R1)O-, -CN, -N(R1)3, and -SO2R1.

[0110] Examples of the first monomer unit include one or more selected from the group consisting of vinyl formal, vinyl alcohol, vinyl acetate, vinyl acetal, vinyl butyral, acrylic acid and its derivatives, methacrylic acid and its derivatives, acrylonitrile, acrylamide and its derivatives, styrene sulfonic acid, polyvinylidene fluoride, and tetrafluoroethylene.

[0111] The polymer material preferably contains one or more selected from the group consisting of polyvinyl formal, polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polymethyl methacrylate, polyvinylidene fluoride, and polytetrafluoroethylene.

[0112] A second monomer unit is a compound other than the first monomer unit, that is, a compound that does not have a functional group containing one or more selected from the group consisting of oxygen (O), sulfur (S), nitrogen (N), and fluorine (F), or a compound that has such a functional group but is not a hydrocarbon. Examples of second monomer units include ethylene oxide and styrene. Examples of polymers consisting of second monomer units include polyethylene oxide (PEO) and polystyrene (PS).

[0113] The types of functional groups contained in the first and second monomer units can be identified by Fourier Transform Infrared Spectroscopy (FT-IR). Furthermore, the fact that the first monomer unit consists of hydrocarbons can be determined by nuclear magnetic resonance (NMR). In addition, the proportion of the copolymer of the first and second monomer units that is composed of the first monomer unit can be calculated by NMR.

[0114] From the viewpoint of increasing the flexibility of the diaphragm, the proportion of polymer material is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 10% by mass or more. In addition, a higher proportion of polymer material tends to result in a higher density of the diaphragm.

[0115] Furthermore, from the viewpoint of enhancing the carrier ion conductivity of the diaphragm, the proportion of polymer material in the diaphragm is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. The proportion of polymer material in the diaphragm can be calculated by thermogravimetric (TG) analysis.

[0116] The polymer material to be included in the membrane may be a single type or a mixture of multiple types.

[0117] The diaphragm may contain plasticizers and electrolyte salts in addition to inorganic solid particles and polymer materials. For example, if the diaphragm contains electrolyte salts, its alkali metal ion conductivity can be further enhanced.

[0118] The diaphragm can be formed on the electrode, for example, as follows:

[0119] Prepare a slurry for forming a diaphragm. The diaphragm-forming slurry is obtained by mixing inorganic solid particles, polymer material, and a solvent, and then stirring the resulting mixture.

[0120] As a solvent, it is preferable to use one that can dissolve polymer materials. Examples of solvents include alcohols such as ethanol, methanol, isopropyl alcohol, n-propyl alcohol, and benzyl alcohol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and diacetone alcohol; esters such as ethyl acetate, methyl acetate, butyl acetate, ethyl lactate, methyl lactate, and butyl lactate; ethers such as methyl cellosolve, ethyl cellosolve, butyl cellosolve, 1,4-dioxane, and tetrahydrofuran; glycols such as ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, butyl carbitol acetate, and ethyl carbitol acetate; and Glycol ethers such as ethyl carbitol, ethyl carbitol, and butyl carbitol; aprotic polar solvents such as dimethylformamide, dimethylacetamide, acetonitrile, valeronitrile, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and γ-butyrolactam; cyclic carboxylic acid esters such as gamma-butyrolactone, gamma-valerolactone, gamma-macarolactone, and epsilon-caprolactone; and chain-like carbonate compounds such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propylisopropyl carbonate, ethyl methyl carbonate, and methyl-n-propyl carbonate are used.

[0121] A diaphragm-forming slurry is applied to the active material-containing layer on one main surface of the negative or positive electrode, for example, by a doctor blade method, to obtain a coating film. Alternatively, the diaphragm-forming slurry may be applied to the negative electrode active material-containing layer on both the front and back main surfaces of the negative or positive electrode to obtain a coating film on each main surface. The diaphragm-forming slurry applied to each main surface may have the same composition or different compositions. Furthermore, the slurry applied to the negative electrode and the slurry applied to the positive electrode may have the same composition or different compositions. This coating film is dried at a temperature of 50°C to 150°C. In this way, a laminate is obtained in which the dried coating film is provided on the active material-containing layer on one or both sides of the electrode.

[0122] Next, this laminate is subjected to a roll press process. For the roll press process, for example, a press device equipped with two rollers, one above and one below, is used. By using such a press device, if coatings are applied to both sides of the electrode, both coatings can be subjected to pressing simultaneously. In this case, the heating temperature of the rollers can be appropriately changed according to the desired structure.

[0123] As described above, an electrode supporting a diaphragm can be obtained. While the above-described press device allows for simultaneous roll-press processing of the coatings on both sides of the electrode, the roll-press processing may be performed on one side at a time. Even when a coating is applied to only one side of the electrode, the above-described press device with two rollers (one above and one below) can be used.

[0124] Furthermore, the formation of the active material-containing layer and the diaphragm may be carried out simultaneously. For example, after applying a slurry for forming the active material-containing layer to the current collector, a slurry for forming the diaphragm may be applied on top of it before the slurry dries. After drying both slurries, the resulting laminate can be subjected to appropriate pressing to obtain an electrode supporting the diaphragm.

[0125] (4) Other separators Other separators that can be used include, for example, nonwoven fabrics or self-supporting porous membranes. Examples of materials used for nonwoven fabrics or self-supporting porous membranes include polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF). The other separator is preferably a cellulose nonwoven fabric.

[0126] The thickness of the other separators is, for example, 1 μm or more, preferably 3 μm or more. A thicker other separator makes it less likely for internal short circuits to occur in the secondary battery. The thickness of the other separators is, for example, 30 μm or less, preferably 10 μm or less. A thinner other separator tends to result in lower internal resistance of the secondary battery and a higher volumetric energy density of the secondary battery.

[0127] (5) Exterior components The outer casing containing the negative electrode, positive electrode, and electrolyte can be a metal container, a laminated film container, or a resin container.

[0128] Metal containers made of nickel, iron, and stainless steel, in square or cylindrical shapes, can be used. Resin containers made of polyethylene or polypropylene can be used.

[0129] The thickness of the resin container and the metal container is preferably within the range of 0.05 mm to 1 mm. More preferably, the thickness is 0.5 mm or less, and even more preferably 0.3 mm or less.

[0130] Examples of laminate films include multilayer films in which a metal layer is coated with a resin layer. Examples of metal layers include stainless steel foil, aluminum foil, and aluminum alloy foil. Polymers such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET) can be used for the resin layer. The thickness of the laminate film is preferably in the range of 0.01 mm to 0.5 mm. More preferably, the thickness of the laminate film is 0.2 mm or less.

[0131] (6) Negative terminal The negative electrode terminal can be formed from a material that is electrochemically stable at the alkali metal ion insertion-desorption potential of the negative electrode active material described above, and is also conductive. Specifically, examples of materials for the negative electrode terminal include zinc, copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable to use zinc or a zinc alloy as the material for the negative electrode terminal. It is preferable that the negative electrode terminal be made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0132] (7) Positive terminal The positive terminal has a potential range of 3V to 4.5V relative to the oxidation-reduction potential of lithium (vs. Li / Li + The positive electrode terminal can be formed from a material that is electrically stable and conductive. Examples of materials for the positive electrode terminal include titanium, aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable that the positive electrode terminal be formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[0133] The secondary battery according to this embodiment can be used in various forms such as prismatic, cylindrical, flat, thin, and coin-type. Furthermore, the secondary battery may have a bipolar structure. A secondary battery with a bipolar structure has the advantage that multiple series-connected cells can be manufactured from a single cell.

[0134] The details of the secondary battery according to the embodiment will be described below with reference to the drawings. Figure 1 is a schematic cross-sectional view showing an example of the secondary battery according to the embodiment. Figure 2 is a cross-sectional view of the secondary battery shown in Figure 1 along the line II-II.

[0135] The electrode group 1 is housed within an outer casing member 2, which is a rectangular cylindrical metal container. The electrode group 1 includes a negative electrode 3, a separator 4, and a positive electrode 5. The electrode group 1 has a structure in which the positive electrode 5 and the negative electrode 3 are interposed with the separator 4 and wound in a spiral shape to form a flattened shape. The electrolyte (not shown) is held in the electrode group 1. As shown in Figure 1, multiple strip-shaped negative electrode leads 16 are electrically connected to each of the multiple ends of the negative electrode 3 located at the end face of the electrode group 1. Similarly, multiple strip-shaped positive electrode leads 17 are electrically connected to each of the multiple ends of the positive electrode 5 located at the same end face. These multiple negative electrode leads 16 are bundled together and connected to the negative electrode terminal 6, as shown in Figure 2. Similarly, although not shown, the positive electrode leads 17 are also bundled together and electrically connected to the positive electrode terminal 7.

[0136] The metal sealing plate 10 is fixed to the opening of the metal exterior member 2 by welding or the like. The negative terminal 6 and positive terminal 7 are each led out to the outside through outlet holes provided in the sealing plate 10. A negative terminal gasket 8 and a positive terminal gasket 9 are placed on the inner circumferential surface of each outlet hole in the sealing plate 10 to prevent short circuits caused by contact with the negative terminal 6 and positive terminal 7. By placing the negative terminal gasket 8 and the positive terminal gasket 9, the airtightness of the secondary battery 100 can be maintained.

[0137] A control valve 11 (safety valve) is positioned on the sealing plate 10. If the internal pressure in the battery cell increases due to gas generated by the electrolysis of an aqueous solvent, the generated gas can be released to the outside through the control valve 11. As the control valve 11, for example, a reset type can be used that operates when the internal pressure exceeds a set value and functions as a sealing plug when the internal pressure decreases. Alternatively, a non-resettable control valve that does not recover its function as a sealing plug once activated may be used. In Figure 4, the control valve 11 is positioned in the center of the sealing plate 10, but the position of the control valve 11 may also be at the edge of the sealing plate 10. The control valve 11 may be omitted.

[0138] Furthermore, the sealing plate 10 is provided with an injection port 12. The electrolyte can be injected through this injection port 12. After the electrolyte has been injected, the injection port 12 can be sealed with a sealing plug 13. The injection port 12 and the sealing plug 13 may be omitted.

[0139] Figure 3 shows another example of a secondary battery. In this example, instead of a separator 4, a diaphragm 44 is supported on the negative electrode 3. The diaphragm 44 is located between the negative electrode 3 and the positive electrode 5. Other details are the same as in the example shown in Figure 1, so they are omitted from the explanation.

[0140] Figure 4 is a schematic partially cutaway perspective view showing yet another example of a secondary battery according to the embodiment. Figure 5 is an enlarged cross-sectional view of part E of one embodiment of the secondary battery shown in Figure 4. Figure 4 shows an example of a secondary battery 100 using a laminate film exterior member as the exterior member.

[0141] The secondary battery 100 shown in Figure 4 comprises an electrode group 1, an outer casing member 2, and an aqueous electrolyte (not shown). The electrode group 1 and the aqueous electrolyte are housed within the outer casing member 2. The aqueous electrolyte is held within the electrode group 1.

[0142] The exterior component 2 consists of a laminate film comprising two resin layers and a metal layer interposed between them.

[0143] As shown in Figure 5, electrode group 1 is a stacked electrode group. The stacked electrode group 1 has a structure in which negative electrodes 3 and positive electrodes 5 are alternately stacked with separators 4 interposed between them.

[0144] The electrode group 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 comprises a negative electrode current collector 3a and a negative electrode active material-containing layer 3b supported on both sides of the negative electrode current collector 3a. The electrode group 1 also includes a plurality of positive electrodes 5. Each of the plurality of positive electrodes 5 comprises a positive electrode current collector 5a and a positive electrode active material-containing layer 5b supported on both sides of the positive electrode current collector 5a.

[0145] Each negative electrode 3's negative electrode current collector 3a includes a portion on one side where the negative electrode active material-containing layer 3b is not supported on any surface. This portion functions as a negative electrode current collector tab 3c. As shown in Figure 5, the negative electrode current collector tab 3c does not overlap with the positive electrode 5. Furthermore, multiple negative electrode current collector tabs 3c are electrically connected to a strip-shaped negative electrode terminal 6. The tip of the strip-shaped negative electrode terminal 6 is extended to the outside of the outer casing member 2.

[0146] Although not shown in the diagram, the positive electrode current collector 5a of each positive electrode 5 includes a portion on one side where the positive electrode active material-containing layer 5b is not supported on any surface. This portion functions as a positive electrode current collector tab. The positive electrode current collector tab, like the negative electrode current collector tab 3c, does not overlap with the negative electrode 3. Furthermore, the positive electrode current collector tab is located on the opposite side of the electrode group 1 from the negative electrode current collector tab 3c. The positive electrode current collector tab is electrically connected to a strip-shaped positive electrode terminal 7. The tip of the strip-shaped positive electrode terminal 7 is located on the opposite side from the negative electrode terminal 6 and is extended to the outside of the outer casing member 2.

[0147] Figure 6 shows an enlarged cross-sectional view of section E of another embodiment of the secondary battery 100 shown in Figure 4. In this embodiment, instead of including a separator 4, a diaphragm 44 is supported on the negative electrode 3. The negative electrode 3 and the diaphragm 44 constitute a negative electrode complex 500. The electrode group 1 includes a plurality of negative electrode complexes 500. Each negative electrode complex 500 includes a negative electrode 3 and diaphragms 44 supported on both sides of the negative electrode 3. Each negative electrode 3 comprises a negative electrode current collector 3a and a negative electrode active material-containing layer 3b supported on both sides of the negative electrode current collector 3a. Each diaphragm 44 is supported on the negative electrode active material-containing layer 3b of the negative electrode 3. Other details are the same as in the embodiment shown in Figure 5, so their explanation is omitted.

[0148] <Measurement of negative electrode active material> The negative electrode active material contained in the negative electrode can be identified by combining elemental analysis using SEM-EDX, ICP emission spectroscopy, and X-ray diffraction (XRD) measurements. SEM-EDX analysis allows us to determine the shape of the components contained in the active material-containing layer and the composition ratio of the components contained in the active material-containing layer (each element from B to U in the periodic table). ICP measurement allows for the quantification of elements in the active material-containing layer. Finally, XRD measurement allows us to confirm the crystal structure of the material contained in the active material-containing layer.

[0149] First, the rechargeable battery is disassembled. For example, a rechargeable battery that has already undergone its initial charge is discharged, then the battery is disassembled and the negative electrode is removed. The removed negative electrode is washed with pure water for 30 minutes. After that, it is vacuum-dried for 24 hours at a temperature of 80°C. After drying, the temperature is returned to 25°C to obtain the negative electrode sample.

[0150] A cross-section of the negative electrode sample is cut out by Ar ion milling. The cut-out cross-section is observed using a scanning electron microscope (SEM). Sample sampling is also performed in an inert atmosphere such as argon or nitrogen, avoiding contact with the atmosphere. Several particles are selected from the 3000x SEM image. At this time, the selection is made so that the particle size distribution of the selected particles is as broad as possible.

[0151] Next, elemental analysis is performed on each selected particle using EDX. This allows us to identify the types and amounts of elements other than Li contained in each selected particle.

[0152] Regarding Li, information about the Li content in the entire active material can be obtained by ICP emission spectroscopy. ICP emission spectroscopy is performed according to the following procedure.

[0153] From the dried negative electrode, a powder sample is prepared as follows: The negative electrode active material-containing layer is peeled off from the negative electrode current collector and ground in a mortar. The ground sample is dissolved in acid to prepare a liquid sample. Hydrochloric acid, nitric acid, sulfuric acid, hydrogen fluoride, etc., can be used as the acid. By subjecting this liquid sample to ICP emission spectroscopy, the concentrations of elements contained in the active material to be measured can be determined.

[0154] The crystal structure of the compound contained in each particle selected by SEM can be determined by XRD measurement. The XRD measurement is performed using CuKα radiation as the source in the measurement range of 2θ = 5° to 90°. This measurement allows us to obtain the X-ray diffraction pattern of the compound contained in the selected particle.

[0155] For XRD measurements, we will use the Rigaku SmartLab. The measurement conditions will be as follows: X-ray source: Cu target Output: 45kV, 200mA Solar slit: 5° for both incident and received light. Step size (2θ): 0.02deg Scan speed: 20deg / min Semiconductor detector: D / teX Ultra 250 Sample plate holder: Flat glass sample plate holder (thickness 0.5 mm) Measurement range: 5° ≤ 2θ ≤ 90°.

[0156] If other equipment is used, measurements should be performed using standard Si powder for powder X-ray diffraction to find conditions that yield peak intensity, full width at half maximum, and diffraction angle equivalent to those obtained with the above equipment, and then the sample should be measured under those conditions.

[0157] The XRD measurement conditions should be such that an XRD pattern suitable for Rietveld analysis can be obtained. Specifically, to collect data for Rietveld analysis, the step size should be set to 1 / 3 to 1 / 5 of the minimum full width at half maximum of the diffraction peak, and the measurement time or X-ray intensity should be adjusted as appropriate so that the intensity at the peak position of the most intense reflection is 5000 cps or more.

[0158] The XRD patterns obtained as described above are analyzed using the Rietveld method. In the Rietveld method, the diffraction pattern is calculated from a pre-estimated crystal structure model. The crystal structure model is estimated here based on the analysis results from EDX and ICP. By fitting all of these calculated values ​​with the measured values, parameters related to the crystal structure (lattice constants, atomic coordinates, occupancy, etc.) can be precisely analyzed.

[0159] XRD measurements can be performed by directly attaching the negative electrode sample to the glass holder of a wide-angle X-ray diffractometer. In this process, it is necessary to pre-measure the XRD spectrum according to the type of metal foil used for the negative electrode current collector to determine where peaks originating from the current collector appear. It is also important to pre-determine the presence or absence of peaks from composite materials such as conductive agents and binders. If the current collector peak and the active material peak overlap, it is desirable to peel the active material-containing layer from the current collector before measurement. This is to separate the overlapping peaks when quantitatively measuring the peak intensity. Of course, if these factors are known in advance, this step can be omitted.

[0160] The secondary battery according to the second embodiment comprises a negative electrode, a positive electrode, and an electrolyte. The electrolyte is the same as the electrolyte according to the first embodiment. This secondary battery exhibits excellent charge-discharge efficiency and excellent discharge capacity.

[0161] (Third embodiment) According to the third embodiment, a battery pack is provided. This battery pack comprises a plurality of secondary batteries according to the second embodiment.

[0162] In such a battery pack, each individual cell may be arranged in series or parallel connections, or a combination of series and parallel connections may be used.

[0163] Next, an example of a battery pack according to the embodiment will be described with reference to the drawings.

[0164] Figure 7 is a schematic perspective view showing an example of a battery pack. The illustrated battery pack 200 comprises five single cells 100a to 100e, four busbars 21, a positive electrode lead 22, and a negative electrode lead 23. Each of the five single cells 100a to 100e is a secondary battery according to the second embodiment.

[0165] The busbar 21 connects, for example, the negative terminal 6 of one cell 100a to the positive terminal 7 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by four busbars 21. That is, the battery pack 200 in Figure 7 is a battery pack with five cells in series. Although not illustrated, in a battery pack containing multiple cells that are electrically connected in parallel, the multiple cells can be electrically connected, for example, by connecting multiple negative terminals to each other and multiple positive terminals to each other by busbars.

[0166] The positive terminal 7 of at least one of the five single cells 100a to 100e is electrically connected to the positive lead 22 for external connection. In addition, the negative terminal 6 of at least one of the five single cells 100a to 100e is electrically connected to the negative lead 23 for external connection.

[0167] The battery pack according to the third embodiment comprises a secondary battery according to the second embodiment. Therefore, the battery pack can exhibit excellent charge-discharge efficiency and excellent discharge capacity.

[0168] (Fourth Embodiment) According to the fourth embodiment, a battery pack is provided. This battery pack comprises a battery pack according to the third embodiment. This battery pack may also comprise a single secondary battery according to the second embodiment instead of the battery pack according to the third embodiment.

[0169] The battery pack may further include a protection circuit. The protection circuit has the function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., electronic equipment, automobile, etc.) may be used as the protection circuit for the battery pack.

[0170] Furthermore, such a battery pack may also be equipped with external terminals for power supply. These external terminals are for outputting current from the secondary battery to the outside and / or for inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals. Also, when charging the battery pack, the charging current (including regenerative energy from the power of an automobile, etc.) is supplied to the battery pack through the external terminals.

[0171] Next, an example of a battery pack according to the embodiment will be described with reference to the drawings.

[0172] Figure 8 is a schematic perspective view showing an example of a battery pack according to this embodiment.

[0173] The battery pack 300 includes, for example, a battery pack consisting of the rechargeable batteries shown in Figure 4. The battery pack 300 includes a housing 310 and a battery pack 200 housed within the housing 310. The battery pack 200 consists of a plurality (e.g., five) of rechargeable batteries 100 connected electrically in series. The rechargeable batteries 100 are stacked in the thickness direction. The housing 310 has openings 320 on the top and on each of its four sides. The sides from which the negative terminal 6 and positive terminal 7 of the rechargeable battery 100 protrude are exposed to the openings 320 of the housing 310. The output positive terminal 332 of the battery pack 200 is strip-shaped, with one end electrically connected to one of the positive terminals 7 of the rechargeable battery 100, and the other end protruding from the opening 320 of the housing 310 and extending from the top of the housing 310. On the other hand, the output negative terminal 333 of the battery pack 200 is strip-shaped, with one end electrically connected to one of the negative terminals 6 of the secondary battery 100, and the other end protruding from the opening 320 of the housing 310 and extending out from the top of the housing 310.

[0174] Another example of the battery pack will be described in detail with reference to Figures 9 and 10. Figure 9 is an exploded perspective view schematically showing another example of the battery pack according to the embodiment. Figure 10 is a block diagram showing an example of the electrical circuit of the battery pack shown in Figure 9.

[0175] The battery pack 300 shown in Figures 9 and 10 comprises a housing container 31, a lid 32, a protective sheet 33, a battery pack 200, a printed circuit board 34, wiring 35, and an insulating plate (not shown).

[0176] The container 31 shown in Figure 9 is a bottomed rectangular container with a rectangular base. The container 31 is configured to accommodate a protective sheet 33, a battery pack 200, a printed circuit board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the container 31, thereby housing the battery pack 200 and the other components. The container 31 and the lid 32 are provided with openings or connection terminals for connecting to external devices, etc., although these are not shown in the figures.

[0177] The battery pack 200 comprises multiple individual cells 100, a positive electrode lead 22, a negative electrode lead 23, and an adhesive tape 24.

[0178] At least one of the multiple single cells 100 is a secondary battery according to the second embodiment. Each of the multiple single cells 100 is electrically connected in series as shown in Figure 10. The multiple single cells 100 may also be electrically connected in parallel, or they may be connected in a combination of series and parallel connections. When the multiple single cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

[0179] The adhesive tape 24 fastens multiple single cells 100 together. Alternatively, heat-shrinkable tape may be used to secure the multiple single cells 100 instead of the adhesive tape 24. In this case, protective sheets 33 are placed on both sides of the battery pack 200, the heat-shrinkable tape is wrapped around it, and then the heat-shrinkable tape is heat-shrinked to bundle the multiple single cells 100 together.

[0180] One end of the positive lead 22 is connected to the battery pack 200. One end of the positive lead 22 is electrically connected to the positive terminal of one or more single cells 100. One end of the negative lead 23 is connected to the battery pack 200. One end of the negative lead 23 is electrically connected to the negative terminal of one or more single cells 100.

[0181] The printed circuit board 34 is installed along one of the shorter sides of the inner surface of the housing container 31. The printed circuit board 34 includes a positive terminal connector 342, a negative terminal connector 343, a thermistor 345, a protection circuit 346, wiring 342a and 343a, an external terminal 350 for energization, a positive side wiring (positive wiring) 348a, and a negative side wiring (negative wiring) 348b. One main surface of the printed circuit board 34 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed circuit board 34 and the battery pack 200.

[0182] The other end 22a of the positive lead 22 is electrically connected to the positive connector 342. The other end 23a of the negative lead 23 is electrically connected to the negative connector 343.

[0183] The thermistor 345 is fixed to one main surface of the printed circuit board 34. The thermistor 345 detects the temperature of each of the single cells 100 and transmits the detection signal to the protection circuit 346.

[0184] The external power supply terminal 350 is fixed to the other main surface of the printed circuit board 34. The external power supply terminal 350 is electrically connected to equipment located outside the battery pack 300. The external power supply terminal 350 includes a positive terminal 352 and a negative terminal 353.

[0185] The protection circuit 346 is fixed to the other main surface of the printed circuit board 34. The protection circuit 346 is connected to the positive terminal 352 via the positive side wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative side wiring 348b. The protection circuit 346 is also electrically connected to the positive side connector 342 via wiring 342a. The protection circuit 346 is also electrically connected to the negative side connector 343 via wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the multiple single cells 100 via wiring 35.

[0186] The protective sheet 33 is positioned on both inner surfaces in the long-side direction of the housing container 31 and on the inner surface in the short-side direction facing the printed circuit board 34 via the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

[0187] The protection circuit 346 controls the charging and discharging of multiple single cells 100. The protection circuit 346 also disconnects the electrical connection between the protection circuit 346 and the external terminals 350 (positive terminal 352, negative terminal 353) for supplying power to external devices, based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from an individual single cell 100 or a battery pack 200.

[0188] An example of a detection signal transmitted from the thermistor 345 is a signal indicating that the temperature of a single cell 100 is above a predetermined temperature. An example of a detection signal transmitted from an individual single cell 100 or a battery pack 200 is a signal indicating that overcharging, over-discharging, or overcurrent has been detected in a single cell 100. When detecting overcharging, etc., in an individual single cell 100, 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 to be used as a reference electrode is inserted into each individual single cell 100.

[0189] Furthermore, the protection circuit 346 may be a circuit included in a device that uses the battery pack 300 as a power source (for example, an electronic device, an automobile, etc.).

[0190] Furthermore, as described above, the battery pack 300 is equipped with an external terminal 350 for power supply. Therefore, the battery pack 300 can output current from the battery pack 200 to an external device and input current from an external device to the battery pack 200 via the external terminal 350. In other words, when the battery pack 300 is used as a power source, current from the battery pack 200 is supplied to the external device through the external terminal 350. Also, when charging the battery pack 300, charging current from an external device is supplied to the battery pack 300 through the external terminal 350. When this battery pack 300 is used as an on-board battery, the regenerative energy of the vehicle's power can be used as the charging current from the external device.

[0191] The battery pack 300 may comprise multiple battery packs 200. In this case, the multiple battery packs 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed circuit board 34 and wiring 35 may also be omitted. In this case, the positive lead 22 and the negative lead 23 may be used as the positive and negative terminals of the external terminals for energization, respectively.

[0192] Such battery packs are used in applications where excellent cycle performance is required, for example, when drawing high currents. Specifically, these battery packs are used as power supplies for electronic devices, stationary batteries, and on-board batteries for various vehicles. Examples of electronic devices include digital cameras. These battery packs are particularly suitable for use as on-board batteries.

[0193] The battery pack according to the fourth embodiment comprises a secondary battery according to the second embodiment or a battery pack according to the third embodiment. Therefore, the battery pack can exhibit excellent charge and discharge efficiency and excellent discharge capacity.

[0194] (Fifth embodiment) According to the fifth embodiment, a vehicle is provided, which is equipped with a battery pack according to the fourth embodiment.

[0195] In such a vehicle, the battery pack, for example, recovers regenerative energy from the vehicle's power. The vehicle may also include a mechanism (regenerator) that converts the vehicle's kinetic energy into regenerative energy.

[0196] Examples of vehicles include, for example, two-wheeled or four-wheeled hybrid electric vehicles, two-wheeled or four-wheeled electric vehicles, electric assist bicycles, and railway vehicles.

[0197] The mounting location of the battery pack in a vehicle is not particularly limited. For example, when a battery pack is installed in an automobile, it can be mounted in the engine compartment, at the rear of the vehicle, or under the seats.

[0198] A vehicle may be equipped with multiple battery packs. In this case, the batteries contained in each battery pack may be electrically connected in series, in parallel, or a combination of series and parallel connections. For example, if each battery pack contains a battery pack, the battery packs may be electrically connected in series, in parallel, or a combination of series and parallel connections. Alternatively, if each battery pack contains a single battery, the batteries may be electrically connected in series, in parallel, or a combination of series and parallel connections.

[0199] Next, an example of a vehicle according to the embodiment will be described with reference to the drawings.

[0200] Figure 11 is a schematic partial transparency diagram showing an example of a vehicle according to the embodiment.

[0201] The vehicle 400 shown in Figure 11 includes a vehicle body 40 and a battery pack 300 according to the fourth embodiment. In the example shown in Figure 11, the vehicle 400 is a four-wheeled automobile.

[0202] This vehicle 400 may be equipped with multiple battery packs 300. In this case, the batteries contained in the battery pack 300 (for example, single cells or battery packs) may be connected in series, in parallel, or in a combination of series and parallel connections.

[0203] Figure 11 illustrates an example in which the battery pack 300 is mounted in the engine compartment located in front of the vehicle body 40. As described above, the battery pack 300 may also be mounted, for example, in the rear of the vehicle body 40 or under the seats. This battery pack 300 can be used as a power source for the vehicle 400. In addition, this battery pack 300 can recover regenerative energy from the vehicle 400's power.

[0204] The vehicle according to the fifth embodiment is equipped with the battery pack according to the fourth embodiment. Therefore, the vehicle has superior driving performance.

[0205] (Sixth Embodiment) According to the sixth embodiment, a stationary power supply is provided. This stationary power supply is equipped with the battery pack according to the fourth embodiment.

[0206] The stationary power supply may be equipped with a battery pack according to the third embodiment or a secondary battery according to the second embodiment instead of the battery pack according to the fourth embodiment. The stationary power supply according to the embodiment can achieve high efficiency and high capacity.

[0207] Figure 12 is a block diagram showing an example of a system including a stationary power supply according to an embodiment. Figure 12 is a diagram showing an example of the application of battery packs 300A and 300B according to the fourth embodiment to stationary power supplies 112 and 123. In the example shown in Figure 12, a system 110 is shown in which stationary power supplies 112 and 123 are used. System 110 comprises a power plant 111, a stationary power supply 112, a consumer-side power grid 113, and an energy management system (EMS) 115. A power grid 116 and a communication network 117 are also formed in system 110, and the power plant 111, stationary power supply 112, consumer-side power grid 113, and EMS 115 are connected via the power grid 116 and the communication network 117. EMS 115 utilizes the power grid 116 and the communication network 117 to perform control to stabilize the entire system 110.

[0208] Power plant 111 generates a large amount of electricity using fuel sources such as thermal and nuclear power. Electricity is supplied from power plant 111 through the power grid 116, etc. A battery pack 300A is installed in stationary power supply 112. The battery pack 300A can store electricity supplied from power plant 111, etc. The stationary power supply 112 can also supply the electricity stored in the battery pack 300A through the power grid 116, etc. System 110 is equipped with a power converter 118. The power converter 118 includes a converter, inverter, and transformer, etc. Therefore, the power converter 118 can perform conversion between DC and AC, conversion between ACs with different frequencies relative to each other, and voltage transformation (boost and step down). For this reason, the power converter 118 can convert the electricity from power plant 111 into electricity that can be stored in the battery pack 300A.

[0209] The consumer-side power system 113 includes power systems for factories, buildings, and households. The consumer-side power system 113 is equipped with a consumer-side EMS 121, a power converter 122, and a stationary power supply 123. The stationary power supply 123 is fitted with a battery pack 300B. The consumer-side EMS 121 performs control to stabilize the consumer-side power system 113.

[0210] The consumer-side power grid 113 is supplied with power from the power plant 111 and power from the battery pack 300A via the power grid 116. The battery pack 300B can store the power supplied to the consumer-side power grid 113. The power converter 122, like the power converter 118, includes a converter, inverter, and transformer. Therefore, the power converter 122 can perform conversions between DC and AC, conversions between ACs with different frequencies, and voltage transformations (boost and step down). Thus, the power converter 122 can convert the power supplied to the consumer-side power grid 113 into power that can be stored in the battery pack 300B.

[0211] The electricity stored in the battery pack 300B can be used, for example, to charge vehicles such as electric cars. Furthermore, the system 110 may be equipped with a renewable energy source. In this case, the renewable energy source generates electricity using natural energy sources such as wind and solar power. Electricity is then supplied from both the power plant 111 and the renewable energy source through the power grid 116. [Examples]

[0212] Examples are described below, but the embodiments are not limited to those described below.

[0213] (Example 1) <Fabrication of the positive electrode> A slurry was prepared by mixing LiNi5Co2Mn3O2 as the positive electrode active material, graphite powder as the conductive agent, polyvinylidene fluoride (PVdF) as the binder, and N-methyl-2-pyrrolidone (NMP) as the solvent. The mass ratio of the positive electrode active material, conductive agent, and binder in this slurry was 100:5:5. This slurry was coated onto one side of a Ti foil. The solvent was then removed by distillation to obtain a laminate. Next, the positive electrode was obtained by rolling this laminate.

[0214] <Fabrication of the negative electrode> Li4Ti5O is used as the negative electrode active material. 12 A negative electrode mixture slurry was prepared by mixing graphite powder as a conductive agent, PVdF as a binder, and NMP as a solvent. The mass ratio of the negative electrode active material, conductive agent, and binder in this slurry was 100:5:1. 1.3 Al 0.3 Ti 0.3 (PO 0.3 A LATP layer slurry was prepared by mixing 3 (hereinafter abbreviated as LATP) and PVdF with NMP solvent in a mass ratio of 80:20. The negative electrode composite slurry was applied to one side of a Zn foil and dried. The LATP layer slurry was then applied on top and dried. Subsequently, the resulting laminate was rolled to obtain a negative electrode with a supported LATP layer.

[0215] <Preparation of aqueous electrolytes> 9 mL of a 12 mol / L LiCl aqueous solution and 1 mL of trimethyl phosphate (hereinafter abbreviated as TMP) were thoroughly mixed. To the resulting colorless solution, 0.5 g (11.8 mmol) of LiCl was added and thoroughly mixed to obtain a 12 mol / L LiCl aqueous solution containing 10% by volume of TMP. This aqueous solution was used as the aqueous electrolyte in the evaluation cell.

[0216] <Creating evaluation cells> The negative and positive electrodes were punched out into circles with a diameter of 10 mm. Additionally, filter paper (NO. 5C, 21 mm in diameter) manufactured by Kiriyama Seisakusho Co., Ltd. was prepared as a separator.

[0217] An anodized aluminum plate was placed on a plastic plate as the negative electrode lead electrode, and the negative electrode was placed on top of it with the LATP layer facing upwards. Next, an aqueous electrolyte was dropped onto the LATP layer of the negative electrode, a separator was placed on top of that, and more aqueous electrolyte was dropped onto the separator. On top of that, the positive electrode, a Ti plate as the positive electrode lead electrode, and a plastic plate were laminated in this order, with the Ti foil of the positive electrode in contact with the Ti plate. The resulting laminate was fixed with screws to obtain a cell for evaluating battery performance.

[0218] (Example 2) An evaluation cell was prepared in the same manner as described in Example 1, except that the amount of TMP contained in the aqueous electrolyte was changed to 5% by volume.

[0219] (Comparative Example 1) Evaluation cells were prepared in the same manner as described in Example 1, except that the same amount of NMP was used instead of TMP in the aqueous electrolyte.

[0220] (Comparative Example 2) Evaluation cells were prepared in the same manner as described in Example 1, except that the same amount of γ-butyrolactone (hereinafter abbreviated as GBL) was used instead of TMP in the aqueous electrolyte.

[0221] (Comparative Example 3) In an aqueous electrolyte, an evaluation cell was fabricated in the same manner as described in Example 1, except that TMP was omitted and no organic solvent was added instead.

[0222] (Performance Evaluation of Electrolyte) (Measurement of Contact Angle of Aqueous Electrolyte) The contact angle of the aqueous electrolyte on the negative electrode was measured to evaluate the wettability of the electrolyte with respect to the electrode. As the measuring device, an automatic contact angle meter Dme-201 manufactured by Kyowa Interface Science Co., Ltd. was used. The negative electrode was fixed with double-sided tape on a glass plate so that the LATP layer was on top. The syringe attached to the device was filled with the electrolyte, and a liquid droplet with a volume of 1.2 μL was created at the tip of the needle. The created liquid droplet was dropped onto the LATP layer of the negative electrode fixed to the glass plate, and the contact angle 10 seconds after dropping was measured. The above operation was performed 5 times, and the average value of the obtained contact angles was calculated and taken as the contact angle of the electrolyte.

[0223] The measurement results are shown in Table 1 below. In Table 1, in addition to the measurement results of the contact angle, the cell conditions of each example and comparative example include TMP (Example 1) or the organic solvent contained in the electrolyte instead and its content (mole percentage with respect to the aqueous solvent).

[0224]

Table 1

[0225] (Charge-Discharge Test) Charge and discharge tests were performed on each evaluation cell prepared in Example 1 and Comparative Examples 1-3 as follows. Each cycle consisted of one constant-current / constant-voltage (CC / CV) charge followed by one constant-current (CC) discharge, and this was repeated for 10 cycles. Specifically, in CC / CV charging, constant-current charging was first performed at a rate of 0.5C (rate of charge per hour) until the cell voltage reached 2.55V, and then constant-voltage charging was performed until the termination condition was reached. The termination condition was set to whichever came first: when the current value (mA) converged to the equivalent of 0.5C, or when 132 minutes had elapsed from the start of charging. CC discharge was performed at a rate of 0.5C until 132 minutes had elapsed from the start of discharge. The tests were performed twice for each cell condition in Examples 1 and 2, and Comparative Examples 1-3.

[0226] In each of the two tests, the charge-discharge efficiency was calculated for each cycle according to Equation 1 below, and the average value of the charge-discharge efficiency (Equation 1) from the 2nd to the 10th cycle was calculated. The error in charge-discharge efficiency between the two tests was calculated according to Equation 2. If this error was less than 5, the average value of the two tests was taken as the charge-discharge efficiency for that cell condition; if the error was 5 or more, the higher value from the two tests was taken as the charge-discharge efficiency (Coulomb efficiency) for that cell condition. Similarly, the average value of the discharge capacity from the 2nd to the 10th cycle was calculated, and the error in the average value of the discharge capacity between the two tests was calculated according to Equation 3. If this error was less than 5, the average value of the two tests was taken as the discharge capacity for that cell condition; if the error was 5 or more, the higher value from the two tests was taken as the discharge capacity for that cell condition.

[0227] Formula 1: Charge / discharge efficiency (%) = 100% × {Discharge capacity (mAh / g) / Charge capacity (mAh / g)} Formula 2: Error in charge / discharge efficiency (%) = 100% × |Difference in average charge / discharge efficiencies| / Sum of average charge / discharge efficiencies Formula 3: Discharge capacity error (%) = 100% × |Difference in average discharge capacities| / Sum of average discharge capacities.

[0228] The results of the battery performance evaluation are shown in Table 2 below.

[0229] [Table 2]

[0230] First, Table 1 shows that adding an organic solvent to the electrolyte reduces the contact angle compared to a 12 mol / L LiCl aqueous solution without added organic solvent (Comparative Example 3). Furthermore, when TMP is added, the degree of reduction in the contact angle is significantly greater compared to NMP and GBL. This result indicates that phosphate esters like TMP are more effective than other organic solvents such as NMP and GBL in improving the wettability of aqueous electrolytes to electrodes. Also, Table 2 shows that the evaluation cell using the electrolyte of Example 1, which had high wettability to electrodes, showed higher charge-discharge efficiency and discharge capacity compared to the cells under the conditions of Comparative Examples 1-3. This demonstrates that improving the wettability of the electrolyte to electrodes can improve battery performance.

[0231] According to at least one embodiment and example described above, an electrolyte is provided. The electrolyte comprises an aqueous solvent containing a phosphate ester in a content of 1 mol% or more and less than 2.5 mol%. This electrolyte can provide a secondary battery exhibiting excellent charge-discharge efficiency and discharge capacity. It can also provide a battery pack exhibiting excellent charge-discharge efficiency and discharge capacity, and furthermore, a vehicle and a stationary power supply equipped with this battery pack can be provided.

[0232] Furthermore, embodiments of the present invention also include the following aspects.

[0233] [1] A water-based solvent containing water and a phosphate ester, An electrolyte in which the content of the phosphate ester in the aqueous solvent is 1 mol% or more and less than 2.5 mol%. [2] The electrolyte according to [1], comprising water in a proportion of 95 mol% to 99 mol% with respect to the aqueous solvent. [3] The phosphate ester includes at least one selected from the group consisting of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, and a fluorine-substituted phosphate ester in which at least one of the hydrogen atoms is substituted with a fluorine atom, and is the electrolyte according to [1] or [2]. [4] A negative electrode, A positive electrode, [1] to [3] Any one of the electrolyte according to, And a secondary battery comprising the same. [5] The negative electrode contains a titanium-containing oxide, and is the secondary battery according to [4]. [6] Further comprising a separator located between the negative electrode and the positive electrode and having lithium ion conductivity, and is the secondary battery according to [4] or [5]. [7] Further comprising a separator located between the negative electrode and the positive electrode and containing inorganic solid particles and a polymer material, and is the secondary battery according to [4] or [5]. [8] A battery pack comprising the secondary battery according to any one of [4] to [7]. [9] Further including an external terminal for energization and a protection circuit, and is the battery pack according to [8].

[10] Comprising a plurality of the secondary batteries, and the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel, and is the battery pack according to [8] or [9].

[11] A vehicle comprising the battery pack according to any one of [8] to

[10] .

[12] Including a mechanism for converting the kinetic energy of the vehicle into regenerative energy, and is the vehicle according to

[11] .

[13] A stationary power supply comprising the battery pack according to any one of [8] to

[10] .

[0234] 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 of the invention and its equivalents. [Explanation of symbols]

[0235] 1…Electrode group, 2…Outer casing, 3…Negative electrode, 3a…Negative electrode current collector, 3b…Negative electrode active material layer, 4…Separator, 5…Positive electrode, 5a…Positive electrode current collector, 5b…Positive electrode active material layer, 6…Negative electrode terminal, 7…Positive electrode terminal, 8…Negative electrode gasket, 9…Positive electrode gasket, 10…Sealing plate, 11…Control valve, 12…Filling port, 13…Sealing plug, 16…Negative electrode lead, 17…Positive electrode lead, 21…Bus bar, 22…Positive electrode side lead, 23…Negative electrode side lead, 24…Adhesive tape, 31…Housing container, 32…Lid, 33…Protective sheet, 34…Printed circuit board, 35…Wiring, 40…Vehicle body, 44…Diaphragm, 100…Secondary battery, 110…System, 111…Power plant, 112…Stationary power supply, 113…Consumer-side power Grid, 115...Energy management system, 116...Power grid, 117...Communication network, 118...Power converter, 121...Customer-side EMS, 122...Power converter, 123...Stationary power supply, 200...Battery pack, 300...Battery pack, 300A...Battery pack, 300B...Battery pack, 310...Housing, 320...Opening, 332...Output positive terminal, 333...Output negative terminal, 342...Positive side connector, 343...Negative side connector, 345...Thermistor, 346...Protection circuit, 342a...Wiring, 343a...Wiring, 350...External terminal for energization, 352...Positive side terminal, 353...Negative side terminal, 348a...Positive side wiring, 348b...Negative side wiring, 400...Vehicle, 500...Negative electrode complex.

Claims

1. A negative electrode comprising a titanium-containing oxide, Positive electrode and, An electrolyte containing an aqueous solvent containing water and a phosphate ester, It is equipped with, A secondary battery in which the content of the phosphate ester in the aqueous solvent is 1 mol% or more and less than 2.5 mol%.

2. The secondary battery according to claim 1, wherein the water is contained in a proportion of 95 mol% or more and 99 mol% or less relative to the aqueous solvent.

3. The secondary battery according to claim 1 or 2, wherein the phosphate ester comprises at least one selected from the group consisting of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, and fluorine-substituted phosphate esters in which at least one of the hydrogen atoms is substituted with a fluorine atom.

4. The secondary battery according to claim 1 or 2, further comprising a diaphragm located between the negative electrode and the positive electrode and having lithium-ion conductivity.

5. The secondary battery according to claim 1 or 2, further comprising a diaphragm located between the negative electrode and the positive electrode and containing inorganic solid particles and a polymer material.

6. A battery pack comprising the secondary battery described in claim 1 or 2.

7. The battery pack according to claim 6, further comprising an external terminal for power supply and a protection circuit.

8. The battery pack according to claim 6, comprising a plurality of the secondary batteries, wherein the secondary batteries are electrically connected in series, parallel, or a combination of series and parallel.

9. A vehicle equipped with the battery pack described in claim 6.

10. The vehicle according to claim 9, comprising a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

11. A stationary power supply comprising the battery pack described in claim 6.

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