JP5749034B2 - battery - Google Patents

Description

  Embodiments described herein relate generally to a battery.

  In recent years, due to rapid technological development in the electronics field, electronic devices are becoming smaller and lighter. As a result, electronic devices have become more portable and cordless, and a secondary power source serving as a driving source thereof is desired to be smaller, lighter, and have higher power density. In response to such demands, lithium secondary batteries with high output density have been developed.

  In order to improve the current collecting performance of the secondary battery, the non-coating end of the positive electrode protrudes at one end of both ends in the winding axis direction of the wound electrode group, and the other end Projecting the non-coated end portion of the negative electrode is performed. The positive and negative electrodes having non-coated end portions are produced, for example, by applying a slurry containing an active material to a strip-shaped current collector, excluding the end portions parallel to the long sides, drying, and pressing. . The end that is not coated with the slurry and that is parallel to the long side is the non-coated end.

  However, when the positive and negative electrodes are produced by such a method, the width direction of the electrode (short) is caused by the press pressure difference that occurs in the coating part and the non-coating part, which is generated in the pressing process for the purpose of improving the conductivity of the electrode. Distortion occurs in the side direction. In the electrode group produced using the positive and negative electrodes in which distortion occurs, the internal resistance of the battery is large because of the large variation in the distance between the positive and negative electrodes.

  For this reason, a plurality of strip-shaped tabs are punched from the current collector of the non-coated portion, and the electrode group and the positive and negative electrode terminals are electrically connected by welding the tabs to leads or the like. ing. In this case, when the tab is positioned at the curved portion of the wound electrode group, three-dimensional distortion occurs in the tab, so that stress is concentrated on the tab during welding work or battery use, and the tab is easily cut. Moreover, in order to match the welding position with the lead or the like, it is desirable to align the tab positions. Therefore, in order to arrange the tabs at locations that do not cover the curved portion of the wound electrode group and to align the positions, it has been studied to adjust the distance between the tabs with a varying pitch.

  However, if the pitch size varies depending on the distance between the tabs, the rotary blade cannot be used when the tabs are punched from the current collector, and the electrode processing becomes very complicated.

JP-A-2005-93242

  A battery with high productivity and high output characteristics is provided.

According to the embodiment, a battery including an electrode group, a plurality of positive electrode tabs, and a plurality of negative electrode tabs is provided. The electrode group has a structure in which a positive electrode and a negative electrode are wound in a flat spiral shape via a separator. The plurality of positive electrode tabs are electrically connected to the positive electrode. The plurality of negative electrode tabs are electrically connected to the negative electrode. At least one of the positive electrode tab and the negative electrode tab is a tab between the first tab located on the innermost peripheral side of the electrode group and the second and subsequent tabs so that the distance between adjacent tabs is equal. The interval increases at an equal pitch from the inner periphery to the outer periphery, has a width of less than (−bm ² + 2a) / 2, and protrudes from one or both end faces of the electrode group. Moreover, an electrode group satisfy | fills following (1) Formula.

bm ² -2a <0 (1)
Where a is the length of the linear portion of the electrode group, b is π (T ₁ + T ₂ + 2T ₃ ) / 2 , T ₁ is the thickness of the positive electrode, T ₂ is the thickness of the negative electrode, and T ₃ is The thickness of the separator, π is the circumferential ratio, and m is the number of wrinkles of the electrode group.

The expanded view of the positive electrode, the negative electrode, and separator which are contained in the electrode group of the battery of embodiment. The top view of the positive electrode shown in FIG. The top view of the negative electrode shown in FIG. The schematic diagram which shows the state which has arrange | positioned the several tab to the linear part of the electrode group in embodiment, aligning a position. Graph showing the relationship between the number and the distance L _1, L _2, L ₃ wound. The top view which looked at the electrode group used for the battery of embodiment from the outermost periphery side. The top view of one end surface orthogonal to the winding axis | shaft in the electrode group shown in FIG. The top view of the other end surface orthogonal to the winding axis | shaft in the electrode group shown in FIG. The perspective view which shows the square battery provided with the electrode group shown in FIG. FIG. 10 is a partially exploded perspective view of the battery of FIG. 9. The top view which looked at the electrode group used for the battery of embodiment from the outermost periphery side. The top view of one end surface orthogonal to the winding axis | shaft of the electrode group shown in FIG.

  Hereinafter, embodiments will be described with reference to the drawings.

According to the embodiment, a battery including an electrode group, a plurality of positive electrode tabs, and a plurality of negative electrode tabs is provided. In the electrode group, a positive electrode and a negative electrode are wound in a flat spiral shape via a separator. The plurality of positive electrode tabs are electrically connected to the positive electrode. The plurality of negative electrode tabs are electrically connected to the negative electrode. At least one of the positive electrode tab and the negative electrode tab is a tab between the first tab located on the innermost peripheral side of the electrode group and the second and subsequent tabs so that the distance between adjacent tabs is equal. The interval increases at an equal pitch from the inner periphery to the outer periphery, has a width of less than (−bm ² + 2a) / 2, and protrudes from one or both end faces of the electrode group. Moreover, an electrode group satisfy | fills following (1) Formula.

bm ² -2a <0 (1)
Where a is the length of the linear portion of the electrode group, b is π (T ₁ + T ₂ + 2T ₃ ) / 2 , T ₁ is the thickness of the positive electrode, T ₂ is the thickness of the negative electrode, and T ₃ is the thickness of the separator. Here, π is the circumference ratio, and m is the number of times of wrinkling of the electrode group.

The equal pitch includes not only the case where the pitch deviation width is 0 but also the case where the pitch deviation width is (bm ² −2a) or less. The pitch deviation width is desirably in the range of -1 mm to 1 mm.

FIG. 1 is a development view of a positive electrode, a negative electrode, and a separator included in the electrode group. FIG. 2 is a plan view of the positive electrode, and FIG. 3 is a plan view of the negative electrode. As shown in FIG. 1, the electrode group 1 includes, for example, a separator 4 interposed between a positive electrode 2 and a negative electrode 3, these are wound into a flat shape using a core 5, and then pressed as necessary. It is produced by applying. The positive electrode 2 includes a strip-shaped positive electrode current collector 2a and an active material-containing layer 2b formed on both surfaces of the positive electrode current collector 2a. Although not shown in FIG. 1, the positive electrode 2 has a plurality of positive electrode tabs 2c as shown in FIG. Each of the positive electrode tabs 2c has a band shape and extends from the long side of the positive electrode current collector 2a. The distances D ₁ and D ₂ between the positive electrode tabs 2c increase from the inner circumference toward the outer circumference at an equal pitch. The positive electrode tab 2c is formed by punching from the positive electrode current collector 2a, for example. On the other hand, the negative electrode 3 includes a strip-shaped negative electrode current collector 3a and active material-containing layers 3b formed on both surfaces of the negative electrode current collector 3a. Although not shown in FIG. 1, the negative electrode 3 has a plurality of negative electrode tabs 3c as shown in FIG. Each of the negative electrode tabs 3c has a belt shape and extends from the long side of the negative electrode current collector 3a. The distances d ₁ and d ₂ between the negative electrode tabs 3c increase from the inner periphery toward the outer periphery at equal pitches. The negative electrode tab 3c is formed by punching from the negative electrode current collector 3a, for example.

  Of the two separators 4, one separator 4 is arranged between the active material-containing layer 2 b of the positive electrode 2 and the active material-containing layer 3 b of the negative electrode 3, and the other separator 4 is the other active material of the negative electrode 3. It arrange | positions on the content layer 3b. These are wound into a flat shape using two flat cores 5 having a flat shape. Here, of the pair of short sides of the positive electrode 2, the side close to the core 5, that is, the innermost peripheral side is the short side 2 d of the winding start, and the opposite side is the short side 2 e of the winding end. Of the pair of short sides of the negative electrode 3, the side close to the core 5, that is, the innermost peripheral side is the short side 3 d at the start of winding, and the opposite side is the short side 3 e at the end of winding. In FIG. 1, the positive electrode 2 is wound before the negative electrode 3, but the negative electrode 3 can be wound before the positive electrode 2.

  FIG. 4 is a schematic diagram showing a state in which a plurality of tabs are arranged at the same position on the linear portion of the electrode group. FIG. 4 schematically shows an end surface orthogonal to the winding axis of the electrode group 1, and only the positive electrode 2 of the electrode group 1 is displayed for convenience of explanation. The following description uses the positive electrode as an example, but the same applies to the negative electrode. When the end surface is viewed from the winding axis direction of the electrode group 1, the curved portions X are portions where the positive and negative electrodes 2 and 3 are curved at both ends of the end surface. A portion located between the curved portions X is a straight portion. Here, the length of the straight line portion is a. Since the length of the bending portion X is equal to the radius of the bending portion X, the total value of the lengths of both the bending portions X is equal to the diameter of the bending portion X, that is, the thickness of the electrode group. Therefore, a value obtained by subtracting the thickness of the electrode group from the width of the electrode group 1 (width in the direction perpendicular to the winding axis of the electrode group 1) can be used as the length a of the straight line portion.

(1) It is assumed that the position of the positive electrode tab 2c is aligned with the starting end of the straight line portion of the positive electrode 2 in order to represent the position of the straight line portion of the electrode group 1 using the number of turns (the number of turns) of the electrode group 1. To do. This position is the last position where the positive electrode tab 2 c does not reach the curved portion X of the electrode group 1. When the positive electrode tabs 2c are arranged at the start end of the straight line every other turn, the distance of the positive electrode tab 2c from the short side 2d at the start of winding of the positive electrode 2 is as shown in Table 1 below. Here, b is π (T ₁ + T ₂ + 2T ₃ ) / 2 . T ₁ is the thickness of the positive electrode, T ₂ is the thickness of the negative electrode, T ₃ is the thickness of the separator, and π is the circumference. The method for measuring the thickness T _{1 of} the positive electrode, the thickness T ₂ of the negative electrode, and the thickness T ₃ of the separator is as follows. Ten positive electrodes, negative electrodes, and separators are stacked, and the thickness when a load of 500 g / 25 cm ² is applied is measured, and one-tenth of this thickness is defined as the thickness of each of the positive and negative electrodes and the separator.

When the positive electrode tab 2c is positioned on the short side 2d at the start of winding of the positive electrode 2, the number of wrinkles is 0 and the distance is 0. If the positive electrode tab 2c is located at the starting end of the linear portion Y ₁ of the first lap winding number 1, the distance is 2a + 3b. If the positive electrode tab 2c is located at the starting end of the linear portion Y ₂ of the second round, winding number 2, the distance is 4a + 10b. Further, when the positive electrode tab 2c is located at the start end of the straight portion of the third turn, the number of wrinkles is 3, and the distance is 6a + 21b. The distance between the tabs increases at an equal pitch of 4b, such as 2a + 3b, 2a + 7b, 2a + 11b, every time the number of times of wrinkles increases. Therefore, an arithmetic progression relationship is established for the distance between the tabs. For this reason, the distance L ₁ from the short side 2 d of the winding start of the positive electrode tab 2 c located at the start end of the n-th straight line portion is equal to the sum of the arithmetic sequence of the distance between the tabs. (A) It represents with a type | formula.

L ₁ = 2an + bn + 2n ² b (A)
Further, the distance L ₂ from the short side 2d of the positive electrode 2 at the beginning of the positive electrode 2 of the positive electrode tab 2c located at the end of the nth straight line portion is the sum of the distance L ₁ and the length a of the straight portion. And represented by the following formula (B).

L ₂ = 2an + bn + 2n ² b + a = (2n + 1) a + bn + 2n ² b (B)
(2) When the distance between the positive electrode tabs 2c is increased from the inner periphery to the outer periphery at an equal pitch, the distance L ₃ from the short side 2d at the beginning of winding of the positive electrode 2 to the positive electrode tab 2c located on the nth periphery is: It is represented by a linear function as shown in equation (C).

L ₃ = kn + p (C)
Here, k and p are arbitrary integers.

(3) The conditions for arranging these tabs in the straight portion of the electrode group while increasing the distance between the positive electrode tabs 2c from the inner periphery to the outer periphery at an equal pitch will be described. FIG. 5 is a graph showing the relationship between the number of wrinkles and the distances L ₁ , L ₂ , L ₃ . As shown in FIG. 5, the distance defining the L ₃ straight (hereinafter, referred to as straight line distance L ₃₎ is a quadratic function curve which defines the distance L ₂ (hereinafter, referred to as a quadratic function curve of the distance L ₂ ) And a quadratic function curve that defines the distance L ₁ (hereinafter referred to as a quadratic function curve of the distance L ₁ ), and the positive electrode tab 2c is positioned at the straight line portion of the electrode group. In addition, the distance between the tabs increases from the inner periphery to the outer periphery at an equal pitch. The conditions for the presence of a straight line with the distance L _{3 in} the region are as follows.

(D) The straight line having the distance L ₃ has intersections α and β with the quadratic function curve having the distance L _{1 at} the number of wrinkles of 0 and m (final circumference). That is, the straight line has no intersection with the quadratic function curve in the range where the number of wrinkles is 1 or more and (m−1) or less.

(E) The straight line with the distance L ₃ has no intersection with the quadratic function curve with the distance L ₂ .

To satisfy the requirements of (E), with a linear gradient of L ₃ plus (obvious), and if the y-intercept (p) is the minus direction, is certainty. On the other hand, in order to satisfy the condition (D), it is advantageous that the y-intercept (p) is large. First, a linear function that satisfies the condition (D) will be described.

The linear function passes through the first point of L ₁ and the point passing through the last m times of winding. In terms of coordinates, a straight line passes through α (0, 0) and β (m, 2 am+bm+2m ² b).

L ₃ = kn + p = (2a + b + 2mb) n. (P is 0)
Next, the condition (E) will be described. Whether or not the quadratic function (L ₂ ) and the linear function (L ₃ ) have an intersection point needs to be negative in the discriminant of the solution of the quadratic equation (F) set up to obtain the intersection point.

L ₂ = L ₃ = (2n + 1) a + bn + 2n ² b = (2a + b + 2mb) n (F)
Rearranging this equation gives 2n ² b-2mnb + a = 0. The solution discriminant is as shown in equation (G).

(-2 mb) ² -4 (2ba) <0 (G)
When the equation (G) is rearranged, 4b (bm ² −2a) <0. Since b> 0 is self-explanatory,
bm ² −2a <0.

Therefore, if bm ² −2a <0, the straight line L ₃ can simultaneously satisfy the conditions (D) and (E), the distance between the tabs increases from the inner periphery to the outer periphery at equal pitches, and these tabs Can be arranged every other round in the linear portion of the electrode group. By increasing the distance between the tabs at an equal pitch, it becomes possible to use a high-speed electrode tab forming apparatus such as a rotary blade. In addition, since the tab is not located at the curved portion of the electrode group, it is possible to avoid three-dimensional distortion in the tab, to prevent the tab from being cut during welding work or battery use, and to obtain a high output density. be able to. In addition, since at least one tab can be arranged per turn, the internal resistance can be lowered and a high output battery can be provided at low cost.

  One form of the structure of the electrode group with which a positive electrode tab and a negative electrode tab satisfy | fill Formula (1) is shown in FIGS. FIG. 6 is a plan view of the electrode group as viewed from the outermost periphery. FIG. 7 shows a plan view of one end face of both end faces orthogonal to the winding axis of the electrode group, and FIG. 8 shows a plan view of the other end face. 9 is a perspective view showing a prismatic battery including the electrode group shown in FIG. 6, and FIG. 10 is a partially exploded perspective view of the battery shown in FIG.

  As shown in FIG. 6, the positive electrode tab 2c protrudes from one end surface orthogonal to the winding axis of the electrode group 1, and the negative electrode tab 3c protrudes from the other end surface. As shown in FIG. 7, the positive electrode tab 2 c is arranged at a rate of one sheet per one turn of the winding circumference, and has a quadratic function curve (parabola) above the space 6 located on the innermost circumference of the electrode group 1. Arranged to draw. Further, as shown in FIG. 8, the negative electrode tab 3c is disposed at a rate of one sheet per one turn of the winding circumference, and is a quadratic function curve (parabolic curve) below the space 6 located in the innermost circumference of the electrode group 1. ).

  A battery including the electrode group 1 shown in FIG. 6 is shown in FIGS. The battery 11 is a square nonaqueous electrolyte secondary battery. The battery 11 includes an outer can 12, an electrode group 1 accommodated in the outer can 12, positive and negative electrode leads 13 and 14 positioned in the outer can 12, and a lid 15 attached to an opening of the outer can 12. And positive and negative terminals 16 and 17 provided on the lid 15. The positive and negative terminals 16 and 17 are caulked and fixed to the lid 15 via an insulating member 18.

  The outer can 12 has a bottomed rectangular tube shape, and is formed of a metal such as aluminum, an aluminum alloy, iron, or stainless steel, for example. An electrolytic solution (not shown) is accommodated in the outer can 12 and impregnated in the electrode group 1. The lid 15 is made of, for example, a metal such as aluminum, an aluminum alloy, iron, or stainless steel. The lid 15 and the outer can 1 are preferably formed of the same type of metal.

  As shown in FIG. 10, one end of the positive electrode lead 13 is electrically connected to the positive electrode current collecting tab 2 c of the electrode group 1. The other end (not shown) of the positive electrode lead 13 is electrically connected to the positive electrode terminal 16. On the other hand, one end of the negative electrode lead 14 is electrically connected to the negative electrode current collecting tab 3 c of the electrode group 1. The other end (not shown) of the negative electrode lead 4 is electrically connected to the negative electrode terminal 17.

  In the case of a lithium ion secondary battery using a carbon-based material for the negative electrode active material, the positive electrode terminal is generally made of aluminum or an aluminum alloy, and the negative electrode terminal is made of a metal such as copper, nickel, or nickel-plated iron. used. When lithium titanate is used as the negative electrode active material, in addition to the above, aluminum or an aluminum alloy may be used for the negative electrode terminal. When aluminum or an aluminum alloy is used for the positive and negative electrode terminals, the positive and negative current collecting tabs and the positive and negative electrode leads are preferably formed from aluminum or an aluminum alloy.

  A thicker tab can reduce the resistance. Further, the shorter the tab length, the lower the resistance, but it is desirable that the tab protrude at least outside the electrode group than the separator. The range of the tab length is preferably 2 mm to 25 mm. By setting it to 2 mm or more, the tab can protrude outside the electrode group. Moreover, the resistance of a tab can be made small by setting it as 25 mm or less.

  The arrangement of the tabs in the electrode group is not limited to those shown in FIGS. 6 to 8, and for example, the form shown in FIGS. 11 to 12 can be adopted. FIG. 11 is a plan view showing another form of the structure of the electrode group in which the positive electrode tab and the negative electrode tab satisfy the expression (1), and FIG. 12 is a plan view of one end surface orthogonal to the winding axis of the electrode group.

  FIG. 11 is an example in which the positive and negative electrode tabs 2 c and 3 c protrude from one surface orthogonal to the winding axis of the electrode group 1. FIG. 11 is a plan view seen from the negative electrode tab 3c side. As shown in FIG. 12, the positive electrode tab 2 c is arranged so as to draw a quadratic function curve (parabola) on the upper side with the space located in the innermost circumference of the electrode group 1 as a boundary. Moreover, the negative electrode tab 3c is arranged on the lower side so as to draw a quadratic function curve (parabola). Each of the positive electrode tab 2c and the negative electrode tab 3c is arranged at a rate of one per winding circumference. Since the tabs extend in the same direction for both the positive and negative electrodes, the internal resistance can be lowered and the battery capacity can be increased, so that a battery with a high output density can be provided at low cost.

  According to the embodiment described above, a high-speed electrode tab forming apparatus such as a rotary blade can be used. In addition, since the tab is not positioned at the curved portion of the electrode group, it is possible to avoid three-dimensional distortion in the tab, and to prevent the tab from being cut during welding work or battery use. Further, since at least one tab can be arranged for each turn, the internal resistance can be lowered, and a high-power battery can be provided at low cost.

  Hereinafter, a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, and an outer container that can be used in the embodiment will be described.

(Positive electrode)
The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer that is supported on one or both surfaces of the positive electrode current collector and includes an active material, a conductive material, and a binder.

Examples of the positive electrode active material include various oxides and sulfides. For example, manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (eg, Li _x Mn ₂ O ₄ or Li _x MnO ₂ ), lithium nickel composite oxide (eg, Li _x NiO ₂ ) , lithium-cobalt composite oxide (Li _x CoO _2), lithium nickel cobalt composite oxide (e.g., _{LiNi 1-y Co y O 2} ), lithium manganese cobalt composite oxides (e.g. _{LiMn y Co 1-y O 2} ), spinel type lithium-manganese-nickel composite oxide _{(Li x Mn 2-y Ni} y O 4), lithium phosphates having an olivine structure _{(Li x FePO 4, Li x} Fe 1-y Mn y PO 4, Li x CoPO 4 etc. ), Iron sulfate (Fe ₂ (SO ₄ ) ₃ ), vanadium oxide (for example, V ₂ O ₅ ), and the like. In addition, conductive polymer materials such as polyaniline and polypyrrole, disulfide-based polymer materials, organic materials such as sulfur (S) and carbon fluoride, and inorganic materials are also included. More preferable positive electrodes for secondary batteries include lithium manganese composite oxide (Li _x Mn ₂ O ₄ ), lithium nickel composite oxide (Li _x NiO ₂ ), and lithium cobalt composite oxide (Li _x CoO ₂ ) having a high battery voltage. ), Lithium nickel cobalt composite oxide (Li _x Ni _1-y Co _y O ₂ ), spinel type lithium manganese nickel composite oxide (Li _x Mn _{2 -y} Ni _y O ₄ ), lithium manganese cobalt composite oxide (Li _{x Mn y Co 1-y O} 2), lithium iron phosphate (Li _x FePO _4), and the like. X and y are preferably in the range of 0 to 1.

  Examples of the conductive agent include acetylene black, carbon black, and graphite. In addition, when the active material itself has high conductivity, a conductive material may be unnecessary.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine-based rubber.

  Examples of the positive electrode current collector include aluminum or an aluminum alloy.

  The mixing ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by weight of the positive electrode active material, 3 to 18% by weight of the conductive agent, and 2 to 17% by weight of the binder.

(Negative electrode)
The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer that is supported on one or both surfaces of the negative electrode current collector and includes an active material, a conductive material, and a binder.

Examples of the negative electrode active material that can be used include iron sulfide, iron oxide, titanium oxide, lithium titanate, nickel oxide, cobalt oxide, tungsten oxide, molybdenum oxide, titanium sulfide, and carbonaceous material. In particular, lithium titanate has excellent cycle characteristics, and is represented by the chemical formula Li _{4 + x} Ti ₅ O ₁₂ (x can vary within the range of 0 ≦ x ≦ 3 by charge / discharge reaction), and has a spinel structure. Lithium titanate is preferred.

The lithium titanate preferably has a surface area of 1 to 10 m ² / g. By setting it to 1 m ² / g or more, an effective area contributing to the electrode reaction can be sufficiently secured and excellent large current discharge characteristics can be obtained. By setting it to 10 m < ² > / g or less, the reaction amount of a negative electrode and electrolyte solution can be decreased, high charging / discharging efficiency can be obtained, and the gas generation at the time of storage can be suppressed.

  A carbonaceous material is used as the conductive agent. In addition, when the active material itself has high conductivity, a conductive material may be unnecessary.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine-based rubber.

  Examples of the negative electrode current collector include aluminum, copper, nickel, an aluminum alloy, a copper alloy, and a nickel alloy.

  The mixing ratio of the negative electrode active material, the conductive agent and the binder is preferably in the range of 70 to 96% by weight of the negative electrode active material, 2 to 28% by weight of the conductive agent, and 2 to 28% by weight of the binder. By setting the amount of the conductive agent to 2% by weight or more, excellent current collecting performance and high large current characteristics can be obtained. However, when the negative electrode active material has very high conductivity, a conductive material may be unnecessary. In that case, the blending ratio is preferably 2 to 29% by weight of the binder. By setting the amount of the binder to 2% by weight or more, the binding property between the mixture layer and the current collector becomes sufficient, and excellent cycle performance can be obtained. On the other hand, from the viewpoint of increasing the capacity, the amount of the conductive agent and the binder is preferably 28% by weight or less.

  The negative electrode is produced by suspending a conductive agent and a binder in a negative electrode active material in a suitable solvent, applying the suspension to a current collector such as an aluminum foil, drying, and pressing to form a strip electrode. .

(Separator)
A porous separator is used as the separator. Examples of the porous separator include a porous film containing polyethylene, polypropylene, cellulose, or polyvinylidene fluoride (PVdF), and a synthetic resin nonwoven fabric. Among these, a porous film made of polyethylene, polypropylene, or both is preferable because it can improve the safety of the secondary battery.

(Nonaqueous electrolyte)
Examples of the electrolytic solution include a non-aqueous electrolytic solution. The nonaqueous electrolytic solution is prepared by dissolving an electrolyte in an organic solvent. Also, a room temperature molten salt containing lithium ions can be used as the non-aqueous electrolyte.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), and trifluorometa. Examples thereof include lithium salts such as lithium sulfonate (LiCF ₃ SO ₃ ) and bistrifluoromethylsulfonylimitolithium [LiN (CF ₃ SO ₂ ) ₂ ]. The electrolyte is preferably dissolved in the range of 0.5 to 2 mol / L with respect to the organic solvent.

  Examples of the organic solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC); chains such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC). Cyclic carbonates such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (2MeTHF); chain ethers such as dimethoxyethane (DME); γ-butyrolactone (BL); acetonitrile (AN); sulfolane (SL) Can do. These organic solvents can be used alone or in the form of a mixture of two or more.

  The room temperature molten salt refers to a salt that is at least partially in a liquid state at room temperature, and the room temperature refers to a temperature range in which a power supply is assumed to normally operate. The temperature range in which the power supply is assumed to normally operate has an upper limit of about 120 ° C. and in some cases about 60 ° C., and a lower limit of about −40 ° C. and in some cases about −20 ° C.

  The room temperature molten salt is composed of a combination of a lithium salt and an organic cation.

As the lithium salt, a lithium salt having a wide potential window, which is generally used for lithium secondary batteries, is used. For example, LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ), LiNCF ₃ SC (C ₂ F ₅ SO ₂ ) _{3 and the} like can be mentioned. However, it is not limited to these. These may be used alone or in combination of two or more.

  The lithium salt content is preferably 0.1 to 3.0 mol / L, and particularly preferably 1.0 to 2.0 mol / L. When the lithium salt content is 0.1 mol / L or more, the resistance of the electrolyte is reduced, and the large current / low temperature discharge performance is improved. By setting the content to 3.0 mol / L or less, the melting point of the electrolyte is lowered. Thus, it becomes possible to maintain a liquid state at room temperature.

The room temperature molten salt is, for example, one having a quaternary ammonium organic cation having a skeleton represented by Chemical Formula 1 or having an imidazolium cation having a skeleton represented by Chemical Formula 2.

However, in Chemical Formula 2, R1, R2: C _n H _{2n + 1} (n = 1 to 6), R3: H or C _n H _{2n + 1} (n = 1 to 6)
In addition, the normal temperature molten salt which has these cations may be used independently, or may be used in mixture of 2 or more types.

  Examples of the quaternary ammonium organic cation having a skeleton represented by Chemical Formula 1 include imidazolium ions such as dialkylimidazolium and trialkylimidazolium, tetraalkylammonium ions, alkylpyridinium ions, pyrazolium ions, pyrrolidinium ions, and piperidinium ions. Um ion etc. are mentioned. In particular, an imidazolium cation having a skeleton represented by Chemical Formula 2 is preferred.

  Examples of the tetraalkylammonium ion include, but are not limited to, trimethylethylammonium ion, trimethylethylammonium ion, trimethylpropylammonium ion, trimethylhexylammonium ion, and tetrapentylammonium ion.

  Examples of the alkyl pyridinium ion include N-methyl pyridinium ion, N-ethyl pyridinium ion, N-propyl pyridinium ion, N-butyl pyridinium ion, 1-ethyl-2methyl pyridinium ion, 1-butyl-4-methyl. Examples thereof include, but are not limited to, pyridinium ions and 1-butyl-2,4 dimethylpyridinium ions.

  The imidazolium cation having a skeleton represented by Chemical Formula 2 is not particularly limited. Examples of the dialkylimidazolium ion include 1,3-dimethylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1-methyl-3-ethylimidazolium ion, 1-methyl-3-butylimidazolium ion, 1 -Butyl-3-methylimidazolium ion etc. are mentioned. Examples of the trialkylimidazolium ion include 1,2,3-trimethylimidazolium ion, 1,2-dimethyl-3-ethylimidazolium ion, 1,2-dimethyl-3-propylimidazolium ion, and 1-butyl-2. , 3-dimethylimidazolium ion and the like. However, it is not limited to these.

(Exterior container)
Instead of the outer can shown in FIG. 9, an outer container made of a laminate film can be used.

  Moreover, the application to the charging / discharging system of the battery which concerns on embodiment can mention the use as a power supply of the control system which drives the drive motor of an electric vehicle.

  Examples will be described below.

( Reference Example 1)
First, 90% by weight of lithium cobalt oxide (LiCoO ₂ ) powder, 3% by weight of acetylene black, 3% by weight of graphite and 4% by weight of polyvinylidene fluoride (PVdF) are added to N-methylpyrrolidone (NMP) as a positive electrode active material. The slurry was mixed to form a slurry. The slurry was applied to both surfaces of a current collector made of 15 μm aluminum foil, dried, and pressed to prepare a positive electrode having an electrode density of 3.0 g / cm ³ . The thickness T _{1 of the} positive electrode was 60 μm.

Li ₄ Ti ₅ O ₁₂ as the negative electrode active material, coke having an average particle size of 1.12 μm and a specific surface area of 82 m ₂ / g as the conductive material, and polyvinylidene fluoride (PVdF) in a weight ratio of 90: 5: 5 Thus, it added to the N-methylpyrrolidone (NMP) solution, it mixed, and the obtained slurry was apply | coated to the 15-micrometer-thick aluminum foil, it dried, and the negative electrode was produced by pressing. The negative electrode thickness T ₂ was 100 μm.

A positive electrode, a separator made of a polyethylene porous film having a thickness of T ₃ 20 μm, a negative electrode, and a separator were laminated in this order, and then wound in a spiral shape. The total thickness (T ₁ + T ₂ + 2T ₃ ) of the positive electrode thickness, the negative electrode thickness, and the thickness of the two separators was 200 microns. The value of b is shown in Table 2 below.

  The positive and negative electrode tabs were formed by a rotary mold. The increasing pitches of the tab width and the distance between the tabs of the positive electrode and the negative electrode are shown in Table 2 below. For each of the positive electrode tab and the negative electrode tab, the tabs were combined into one by ultrasonic welding. This was heated and pressed at 90 ° C. to produce a flat electrode group having a width of 53.1 mm, a thickness of 10 mm, and a height of 80 mm. Table 2 below shows the length a of the linear portion of the electrode group and the number m of wrinkles.

After housing the electrode group in the outer can, a non-aqueous electrolyte (PC: EC = 1: 1 (volume ratio), LiPF ₆ concentration 1.0 mol / l) was injected, and FIG. 9 and FIG. A prismatic nonaqueous electrolyte secondary battery having the structure shown was manufactured.

( Reference Examples 2 and 3 and Examples 4 to 8 and Comparative Example)
a, b, m, positive and negative tab arrangement, tab width, number of tabs, electrode group width, square pitch in the same manner as in Reference Example 1 except that any one of pitches between positive and negative electrode tabs is changed. A non-aqueous electrolyte secondary battery was manufactured.

The output density of the obtained battery in the SOC 50% state was measured, and the result is shown in Table 2 below.

As is clear from Table 2, the batteries of Reference Examples 1 to 3 and Examples 4 to 8 had a higher output density than the batteries of the comparative examples. Since Reference Examples 1 to 3 and Examples 4 to 8 satisfy the formula (1), it is considered that tab breakage is reduced. On the other hand, in the comparative example, since the positive and negative tabs were arranged in the curved portion of the electrode group, the tabs were cut in the manufacturing process and the like, and the output was lowered.

  According to the above embodiments and examples, it is possible to provide a high-power-density battery in which tab breakage is suppressed.

Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.
The invention described in the scope of claims at the beginning of the filing of the present application will be appended.
[1] An electrode group in which a positive electrode and a negative electrode are wound in a flat spiral shape via a separator, a plurality of positive electrode tabs electrically connected to the positive electrode, and a plurality of electrodes electrically connected to the negative electrode A battery comprising a negative electrode tab, wherein at least one of the positive electrode tab and the negative electrode tab has a tab interval that changes at an equal pitch, and protrudes from one or both end faces of the electrode group, A battery characterized by satisfying the following formula (1).
bm ² -2a <0 (1)
Where a is the length of the straight portion of the electrode group, b is 2π (T ₁ + T ₂ + 2T ₃ ), T ₁ is the thickness of the positive electrode, T ₂ is the thickness of the negative electrode, and T ₃ is the separator. , Π is the circumferential ratio, and m is the number of wrinkles of the electrode group.
[2] The battery according to [1], wherein at least one of the positive electrode tab and the negative electrode tab has a quadratic function curve as viewed from the winding axis direction of the electrode group.

  DESCRIPTION OF SYMBOLS 1 ... Electrode group, 2 ... Positive electrode, 2a ... Positive electrode collector, 2b ... Positive electrode active material containing layer, 2c ... Positive electrode tab, 3 ... Negative electrode, 3a ... Negative electrode collector, 3b ... Negative electrode active material containing layer, 3c ... Negative electrode tab, 4 ... separator, 5 ... core, 11 ... battery, 12 ... outer can, 13 ... positive electrode lead, 14 ... negative electrode lead, 15 ... lid, 16 ... positive electrode terminal, 17 ... negative electrode terminal.

Claims (3)

A group of electrodes in which a positive electrode and a negative electrode are wound in a flat spiral shape via a separator;
A plurality of positive electrode tabs electrically connected to the positive electrode;
A battery comprising a plurality of negative electrode tabs electrically connected to the negative electrode,
At least one of the positive electrode tab and the negative electrode tab is a distance between the first tab located on the innermost side of the electrode group and the second and subsequent tabs so that the distance between adjacent tabs is equal. The tab spacing increases at equal pitches from the inner periphery to the outer periphery, has a width of less than (−bm ² + 2a) / 2, and projects from one or both end faces of the electrode group, A battery characterized by satisfying the following formula (1).
bm ² -2a <0 (1)
Where a is the length of the linear portion of the electrode group, b is π (T ₁ + T ₂ + 2T ₃ ) / 2, T ₁ is the thickness of the positive electrode, T ₂ is the thickness of the negative electrode, and T ₃ is The thickness of the separator, π is the circumferential ratio, and m is the number of wrinkles of the electrode group. (-Bm ² The battery according to claim 1, wherein the width which is less than + 2a) / 2 is in the range of 3 mm to 45 mm.   2. The battery according to claim 1, wherein at least one of the positive electrode tab and the negative electrode tab has a quadratic function curve as viewed from a winding axis direction of the electrode group.