JP5509561B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. In particular, the present invention relates to an improvement for improving durability and long-term reliability of a nonaqueous electrolyte secondary battery.

  In recent years, hybrid vehicles, electric vehicles, and fuel cell vehicles have been manufactured and sold from the viewpoints of environment and fuel efficiency, and new developments are continuing. In these so-called electric vehicles, it is indispensable to use a power supply device capable of discharging and charging. As the power supply device, a secondary battery such as a lithium ion battery or a nickel metal hydride battery, an electric double layer capacitor, or the like is used. In particular, a lithium ion secondary battery, which is one of the nonaqueous electrolyte secondary batteries, is considered suitable for electric vehicles because of its high energy density and durability against repeated charge and discharge, and various developments are underway. It has been. However, in order to apply to the power sources for driving motors of various automobiles as described above, it is necessary to use a plurality of secondary batteries connected in series in order to ensure a large output.

  However, when a battery is connected via the connection portion, the output is reduced due to the electrical resistance of the connection portion. Further, the battery having the connection portion has a disadvantage in terms of space. That is, the connection portion causes a reduction in the output density and energy density of the battery.

  As a solution to this problem, a bipolar lithium ion secondary battery (bipolar battery) has been developed (see, for example, Patent Document 1). A bipolar battery includes a battery element having a configuration in which a plurality of bipolar electrodes each having a positive electrode active material layer formed on one surface and a negative electrode active material layer formed on the other surface are stacked via an electrolyte layer. In order to prevent a short circuit between adjacent unit cell layers, the outer peripheral portion of a unit cell (unit cell layer) in which a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer are stacked in this order is provided. Generally, a seal portion is provided. Such battery elements are usually vacuum-packed in an exterior made of a laminate film.

  In the bipolar battery, since a plurality of single battery layers are electrically connected in series in the stacking direction of the battery elements, the battery can be increased in voltage and resistance. Furthermore, since such a series connection is made without going through a connection portion, the battery can be made compact and the output density can be improved.

  By the way, the battery usually exhibits a self-discharge phenomenon in which the electromotive force decreases when it is left unattended. From the viewpoint of battery efficiency, such a self-discharge amount is preferably small. The main factor of self-discharge is the presence of a micro short circuit due to a conductive path formed inside the battery. Such a short-circuit is most likely to occur inside the separator, which is the facing portion between the positive electrode active material layer and the negative electrode active material layer. That is, when the positive electrode active material protrudes from the positive electrode active material layer to the separator side and comes into contact with the negative electrode active material that also protrudes from the negative electrode side, a conductive path is generated inside the single cell (single cell), and a micro short circuit occurs. Occur.

In bipolar batteries, which are being developed with the miniaturization in mind as a power source for automobiles, in order to improve the energy density of the batteries, thinning of the separator is intensively studied. Therefore, in such a bipolar battery, the above-described problem of self-discharge (reduction in electromotive force) due to the micro short-circuit appears more remarkably.
JP-A-11-204136

  Then, an object of this invention is to provide the means which can suppress generation | occurrence | production of the micro short circuit inside a single battery layer in a nonaqueous electrolyte secondary battery.

  In order to solve the above problems, the present inventors have conducted intensive research. In the process, an attempt was made to control the size of the active material contained in the active material layer of the electrode. As a result, it has been found that controlling the maximum particle size of the active material according to the thickness of the active material layer or the separator can extremely effectively prevent the occurrence of a micro short circuit inside the single cell layer, leading to the completion of the present invention. It was.

The nonaqueous electrolyte secondary battery of the present invention has a battery element including at least one single battery layer. The single cell layer includes a positive electrode active material layer that includes a positive electrode active material and is formed on the surface of the current collector, an electrolyte layer in which an electrolyte is held in a separator, and a negative electrode active material that is formed on the surface of the current collector. The formed negative electrode active material layer is laminated in this order. In the at least one single cell layer, the maximum value (D _max (+)) of the particle size of the positive electrode active material and the maximum value (D _max (−)) of the particle size of the negative electrode active material are expressed by the following formula 1:

Where _Te is the thickness of the active material layer, T _s is the thickness of the separator, and N is the number of cell layers.
Satisfy the relationship.

  According to the nonaqueous electrolyte secondary battery of the present invention, the product of the respective protrusion existence probabilities in the active material layer of the positive and negative electrodes in the single cell layer is extremely small, so that the micro short circuit inside the single cell layer is reduced. Occurrence can be effectively suppressed. As a result, it is possible to provide a nonaqueous electrolyte secondary battery that can prevent a decrease in electromotive force due to self-discharge caused by a micro short circuit and can maintain a high electromotive force over a long period of time.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  FIG. 1 is a schematic cross-sectional view schematically showing an outline of a bipolar lithium ion secondary battery which is a typical embodiment of the bipolar secondary battery of the present invention. In the present specification, a bipolar lithium ion secondary battery will be described in detail as an example, but the technical scope of the present invention is not limited to such a form.

  The bipolar secondary battery 10 of this embodiment shown in FIG. 1 has a structure in which a substantially rectangular battery element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is a battery exterior material. .

  As shown in FIG. 1, the battery element 21 of the bipolar secondary battery 10 of the present embodiment has a positive electrode active material layer 13 that is electrically coupled to one surface of a current collector 11, and the current collector 11 has a plurality of bipolar electrodes formed with a negative electrode active material layer 15 electrically coupled to the opposite surface. Each bipolar electrode is laminated via an electrolyte layer 17 to form a battery element 21. At this time, each bipolar type is formed such that the positive electrode active material layer 13 of one bipolar electrode and the negative electrode active material layer 15 of another bipolar electrode adjacent to the one bipolar electrode face each other through the electrolyte layer 17. Electrodes and electrolyte layers 17 are alternately stacked. That is, the electrolyte layer 17 is disposed between the positive electrode active material layer 13 of one bipolar electrode and the negative electrode active material layer 15 of another bipolar electrode adjacent to the one bipolar electrode.

  The adjacent positive electrode active material layer 13, electrolyte layer 17, and negative electrode active material layer 15 constitute one unit cell layer 19. Therefore, it can be said that the bipolar secondary battery 10 has a configuration in which the single battery layers 19 are stacked. In the form shown in FIG. 1, the battery element 21 has a configuration in which 96 single battery layers 19 are laminated. In other words, the stack number (N) of the single battery layers 19 constituting the battery element 21 is 96. However, there is no particular limitation on the number of layers (N).

  A seal portion 31 is disposed around the unit cell layer 19 in order to prevent a liquid junction due to leakage of the electrolyte from the electrolyte layer 17. By providing the seal portion 31, the adjacent current collectors 11 can be insulated and a short circuit due to contact between adjacent electrodes can be prevented. The positive electrode active material layer 13 is formed only on one side of the positive electrode side outermost current collector 11a located in the outermost layer of the battery element 21. Further, the negative electrode active material layer 15 is formed on only one side of the negative electrode side outermost current collector 11 b located in the outermost layer of the battery element 21.

  Furthermore, in the bipolar secondary battery 10 shown in FIG. 1, the positive electrode side outermost layer current collector 11a is extended to form a positive electrode tab 25, which is led out from a laminate sheet 29 which is a battery outer packaging material. On the other hand, the negative electrode side outermost layer current collector 11b is extended to form a negative electrode tab 27, which is similarly derived from a laminate sheet 29 which is a battery exterior material.

[Current collector]
The current collector 11 is made of a conductive material, and an active material layer is formed on both sides thereof to serve as a battery electrode, and finally forms a battery. In the present embodiment, the current collector is used for a battery (bipolar battery) in which active material layers having different polarities (positive electrode and negative electrode) are formed on the surface of each layer. As shown in FIG. 1, in the battery having a power generation element formed by laminating a plurality of single battery layers, the electrode located in the outermost layer does not participate in the battery reaction, so in the current collector located in the outermost layer, The active material layer only needs to exist inside the power generation element.

  Further, the size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used.

  There is no restriction | limiting in particular in the material which comprises the electrical power collector 11. FIG. For example, a metal or a conductive polymer can be employed. Specifically, metal materials, such as aluminum, nickel, iron, stainless steel, titanium, copper, are mentioned, for example. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, and copper are preferable from the viewpoints of electronic conductivity and battery operating potential.

  There is no particular limitation on the thickness of the current collector 11. The thickness of the current collector is usually about 1 to 100 μm.

[Positive electrode active material layer and negative electrode active material layer]
The active material layers 13 and 15 contain an active material, and further contain other additives as necessary.

The positive electrode active material layer 13 includes a positive electrode active material. As the positive electrode active material, for example, LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Co—Mn) O _2, and lithium-such as those in which a part of these transition metals are substituted with other elements Examples include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material. Of course, positive electrode active materials other than those described above may be used.

The negative electrode active material layer 15 includes a negative electrode active material. Examples of the negative electrode active material include carbon materials such as graphite, soft carbon, and hard carbon, lithium-transition metal composite oxides (for example, Li ₄ Ti ₅ O ₁₂ ), metal materials, and lithium-metal alloy materials. . In some cases, two or more negative electrode active materials may be used in combination. Preferably, a carbon material or a lithium-transition metal composite oxide is used as the negative electrode active material. Of course, negative electrode active materials other than those described above may be used.

In the battery of the present invention, the particle size of the active material contained in the active material layer is controlled. More specifically, the maximum value of the particle size of the active material (maximum particle size, D _max ) is controlled so as to satisfy a predetermined relationship with the thickness of the active material layer and the separator. Specifically, in the bipolar secondary battery 10 of the form shown in FIG. 1, the maximum particle size (D _max (+)) of the positive electrode active material and the negative electrode active material The maximum value of particle size (D _max (−)) is expressed by the following formula 1:

Where _Te is the thickness of the active material layer (μm), T _s is the thickness of the separator (μm), and N is the number of cell layers.
It is controlled to satisfy the relationship. Hereinafter, Formula 1 will be described in detail.

FIG. 2 is a graph plotting the frequency with respect to the particle diameter of active material particles having an average particle diameter (D ₅₀ ) of about 10 μm. Here, the average particle diameter (D ₅₀ ) is obtained by plotting the frequency with respect to the particle diameter of the active material on the basis of the volume of the active material particles (in the case of a single composition, the weight may be used). Is the particle size corresponding to the time point when the cumulative value from the small particle size side becomes 50%. As shown in FIG. 2, in the powder, such as active materials, when plotting the volume of the active material particles as a reference, usually it shows a normal distribution having a peak near D _50. On the other hand, the number per unit volume increases as the particle size decreases. For this reason, when the frequency with respect to the particle diameter of an active material particle is plotted on the basis of the number of active material particles, a peak shifts to a smaller particle diameter side as shown in FIG. In addition, the plot of the graph shown in FIG. 2 was performed using the data shown in Table 1 below (particle size profile for a specific negative electrode active material).

As shown in Table 1, in this model, the active material particles were divided into 14 zones from the smaller particle size side according to the particle size. Specifically, as shown in Table 1, D _{x serving} as a delimiter was set. Here, “D _x ” shown in Table 1 is a ratio obtained by accumulating the volume-based frequencies of the active material particles from the smaller particle diameter side to a certain zone (j). For example, as shown in Table 1, the particle size corresponding to D ₄₀ is 8.4 μm, and the particle size corresponding to D ₅₀ is 9.9 μm. Therefore, particles having a particle size larger than 8.4 μm and smaller than 9.9 μm belong to the zone of j = 9. The number-based frequency calculated for the active material particles distributed to a certain zone (j) is “number frequency r _j ” shown in Table 1. For example, particles belonging to the zone of j = 9 occupy 4.01% based on the number.

FIG. 3 is an enlarged schematic view of a portion including the active material layer and separator of the battery electrode. In the model used in the present application, as shown in FIG. 3, it is assumed that the active material particles are stacked in a close-packed state in the active material layer. Then, the thickness (T _e (−)) of the negative electrode active material layer was assumed to be 15 μm, and the thickness (T _s ) of the separator was assumed to be 10 μm. As shown in FIG. 3, among the active material particles contained in the active material layer, the active material particles having a particle size larger than T _e + T _s / 2 are opposed across the center line of the separator (broken line shown in FIG. 3). It protrudes to the active material layer side. In the model of the present application, since T _e (−) + T _s / 2 = 15 + 10/2 = 20 μm, among the 14 zones shown in Table 1, particles in the zones of j = 13 and 14 shown in bold are shown. , Considered to have the possibility of protruding to the side of the active material layer facing. Therefore, for the particles in the zone of j = 13 and 14, the probability of the particles protruding beyond the separator center line to the facing active material side was calculated. Specifically, first, the area of the portion where the particles in the zone of j = 13, 14 protrude to the side of the active material facing the center line of the separator (broken line shown in FIG. 3) (the total area A of the protruding portion). ) Was estimated according to Equation 3 below. At this time, the area of the protruding portion was estimated to be a little wider by assuming that the area of the protruding active material particle is the maximum area (that is, protruding on the surface passing through the center).

In the formula, the definitions of D _j and r _j are as shown in Table 1, and n is the total number of active material particles contained in the active material layer.

  N in the above formula 3 is calculated according to the following formula 4.

In the formula, W is the total weight of the active material particles contained in the active material layer, and ρ is the density of the active material particles.

  By dividing the total protrusion area (A) calculated in this way by the total area of the electrode, the ratio of the total area of the protrusion to the total area of the electrode (that is, the protrusion existence probability) is calculated. .

  When the existence probability of the protrusions was calculated through the above process, the protrusion existence probability in the positive electrode active material layer was calculated to be 12% in the model of the present application. Similarly, the protrusion existence probability in the negative electrode active material layer was calculated to be 18%.

The micro short circuit occurs when the protruding portion in the positive electrode active material layer and the protruding portion in the negative electrode active material layer overlap. That is, the probability of occurrence of a micro short circuit in a single cell layer is the product of the respective protrusion existence probabilities in the positive and negative active material layers, and is calculated as 0.12 × 0.18 = 2.16%. Then, for example, as shown in FIG. 1, the probability that a micro short circuit occurs in at least one single cell layer of the battery element having a stacking number N of 96 layers is 1− (0.0216) ⁹⁶ ≈100%. That is, when a bipolar secondary battery having a battery element of N = 96 is produced using an active material having a particle size profile adopted in the model of the present application, there is almost no treatment for the particle size of the active material particles. A minute short circuit will occur in any single cell layer with a probability of 100%.

Based on such knowledge, the present inventors have determined that the maximum value (D _max ) of the active material particle size is half the thickness (T _e ) of the active material layer and half the thickness (T _s ) of the separator. An attempt was made to control the sum (T _e + T _s / 2) so as not to exceed a value obtained by integrating a numerical value smaller than 1 as a constant safety coefficient α. In the process, the change in the probability of occurrence of a short-circuit when the safety factor α was changed was investigated. The results are shown as a graph in FIG. Surprisingly, as shown in FIG. 4, when the value of the safety coefficient α integrated with respect to the sum (T _e + T _s / 2) is gradually reduced, the probability of occurrence of a short-circuit is exponential. It was confirmed that it decreased. In particular, in the region where the occurrence probability is reduced to about 50%, a significant decrease in the occurrence probability was observed.

  Subsequently, the present inventors made a study by paying attention to the relationship between the above-described safety factor α and the number of cell layers (stacking number N) in the battery element. Specifically, it was tracked how the safety factor α required to change the probability of occurrence of a micro short circuit to a certain value when the number of stacked layers N is changed. As reference values at that time, two values of 50%, in which a remarkable decrease in the probability of occurrence of a micro short-circuit was observed, and 10% considered sufficient for practical use were adopted. As a result, as shown in the graph (solid line) in FIG. 5, it was found that the required value of the safety coefficient α gradually decreases as the number of layers increases. It was also unexpectedly found that linearity is observed between the number N of layers and the safety factor α in a region where the number N is large (particularly, N ≧ 48). This is shown in FIG. As shown in FIG. 6, the approximate straight line in the case where the probability of occurrence of a micro short circuit is 50% was y = 0.94-0.0008x. Further, the approximate straight line in the case where the probability of occurrence of a short-circuit is 10% was y = 0.5333-0.0046x. In the area below this approximate straight line, it means that the probability of occurrence of a micro short circuit is not more than a reference value (50% or 10%).

Based on the above knowledge, the present inventors, in at least one single cell layer constituting the battery element of the non-aqueous electrolyte secondary battery, the maximum value (D _max (+)) of the positive electrode active material particle size and the negative electrode The maximum value (D _max (−)) of the particle size of the active material is expressed by the following formula 1:

Where _Te is the thickness of the active material layer, T _s is the thickness of the separator, and N is the number of cell layers.
The present inventors have found that control is performed so as to satisfy the above relationship, and have completed the present invention. Satisfying the above formula 1 means that the probability of occurrence of a micro short circuit is 50% or less when the maximum value (D _max ) of the particle size of the active material takes into account the safety factor α that can vary depending on the number N of layers. It means that it is controlled as small as possible. When satisfying the above mathematical formula 1, when N = 96, α ≦ 0.873.

In a more preferred embodiment of the present invention, an approximate straight line when the probability of occurrence of a micro short circuit is 10% is adopted. Specifically, in at least one single cell layer constituting the battery element of the non-aqueous electrolyte secondary battery, the maximum particle size (D _max (+)) of the positive electrode active material and the maximum particle size of the negative electrode active material The value (D _max (−)) is expressed by the following formula 2:

Where _Te is the thickness of the active material layer, T _s is the thickness of the separator, and N is the number of cell layers.
If the control is performed so as to satisfy this relationship, the probability of occurrence of a micro short circuit can be suppressed to 10% or less, which is a standard that can withstand practical use, and is more preferable. Note that when Expression 2 is satisfied, α ≦ 0.408 when N = 96.

Here, as can be seen by comparing FIG. 5 and FIG. 6, the two approximate lines shown in FIG. 6 are included in the lower region of the graph shown in FIG. In other words, in the region where the number N of layers is large, the approximate line overlaps the graph shown in FIG. 5, but in the region where the number N of layers is small, the approximate line is gradually separated from the graph shown in FIG. It does not pass above the graph shown in FIG. As described above with reference to FIG. 4, the probability of occurrence of a micro short circuit decreases as the safety factor α decreases. Therefore, by controlling the maximum value (D _max ) of the particle size of the active material according to Equation 1 (preferably Equation 2) described above, it is possible to effectively prevent the occurrence of a micro short circuit regardless of the number N of layers. is there.

Note that the value of the safety coefficient α described above may be set to a smaller value regardless of the above-described rules of Formula 1 and Formula 2. As an example, regardless of the above formulas 1 and 2, when N = 96, α ≦ 0.9 is preferable, α ≦ 0.8 is more preferable, and α ≦ 0.8 is more preferable. 0.7. There is no particular limitation on the lower limit value of the safety coefficient α. However, if α is too small, the active material contained in the active material layer has only a small particle size, and efficient charging / discharging may not be performed. From such a viewpoint, α> 0.1 is preferable, α> 0.2 is more preferable, and α> 0.5 is still more preferable. Note that the value of alpha, the maximum value of the active material particles contained in the active material layer and (D _max), the value of the thickness of the active material layer (T _e) and the thickness of the separator (T _s), the It can be calculated based on the mathematical formula (D _max = α (T _e + T _s / 2)). In addition, whether or not a certain cell layer satisfies the above formula 1 and formula 2 is determined by the value of α obtained as described above and the number of cell layers (the number N of stacked layers). What is necessary is just to investigate whether the said Numerical formula 1 and Numerical formula 2 are satisfy | filled.

  In addition, the relationship of the above-mentioned numerical formula 1 and numerical formula 2 should just be satisfy | filled in the at least 1 cell layer which comprises a battery element. However, when the effect of the present invention is to be further exhibited, it is preferable to increase the number of single battery layers satisfying the relationship of Formula 1 and Formula 2 among the single cell layers constituting the battery element. Most preferably, as shown in FIG. 1, all the single battery layers satisfy the relations of the above formulas 1 and 2. The number of single battery layers (the number N of stacked layers) is not particularly limited, but preferably N ≧ 48, more preferably N ≧ 72, and most preferably N = 96 as shown in FIG. . Here, the electromotive force that can be exhibited by the unit cell layer 19 is 4.2 V per layer. Therefore, according to the embodiment of N = 96, a bipolar secondary battery having an electromotive force of about 400 V can be manufactured. This is a voltage sufficient to operate a motor, an inverter, and other electronic devices when mounted on an electric vehicle.

  The specific form of the particle size profile of each of the positive electrode active material and the negative electrode active material is not particularly limited as long as the relationship of Equation 1 and Equation 2 described above is satisfied. However, from the viewpoint of improving the output characteristics of the battery, the average particle diameter of at least one (preferably both) of the positive electrode active material and the negative electrode active material is 0.5 to 20 μm, preferably 1.0 to 15 μm. More preferably, it is 5.0 to 10 μm.

In addition, there is no restriction | limiting in particular about the method of obtaining the active material which satisfy | fills the relationship of the largest particle size ( _Dmax ) said Numerical formula 1 and Numerical formula 2. As an example, from the values of the active material layer thickness (T _e ), the separator thickness (T _s ), and the number of single battery layers (number of stacked layers N) in the single battery layer to be manufactured, D An allowable upper limit value of _max is calculated. Then, the active material may be subjected to classification treatment such as sieving, dry classification, and wet classification so that the maximum particle size (D _max ) of the active material is equal to or less than the allowable upper limit value. When a graph as shown in FIG. 1 is drawn for the active material that has been subjected to such classification processing, the peak position is not changed, and particles having a particle size of a predetermined value or more are cut. Therefore, according to a preferred embodiment of the present invention, the maximum particle diameter (D _max ) of at least one of the positive electrode active material and the negative electrode active material in at least one single cell layer constituting the battery element is the average particle diameter (D ₅₀ ) is preferably 2.0 times or less, and more preferably 1.5 times or less. In the present invention, the “particle diameter” means the maximum distance L among the distances between any two points on the contour line of the active material particles.

Conventionally, for the purpose of obtaining a desired battery performance, the particle size distribution of the active material, technique for overall size and D _50, including are known. However, there is no known technique that uses an active material in which the particle size of a predetermined value or more is cut as in the present invention. In addition, the knowledge that such a configuration dramatically reduces the probability of occurrence of a micro short circuit in the single cell layer is notable even by those skilled in the art.

  Although the characteristic configuration of the present invention has been described in detail above, other modes will be briefly described below.

  Examples of the additive that can be included in the positive electrode active material layer 13 and the negative electrode active material layer 15 include a binder, a conductive additive, an electrolyte salt (lithium salt), and an ion conductive polymer.

  Examples of the binder include polyvinylidene fluoride (PVdF), a synthetic rubber binder, and an epoxy resin.

  The conductive assistant refers to an additive that is blended in order to improve the conductivity of the positive electrode active material layer 13 or the negative electrode active material layer 15. Examples of the conductive assistant include carbon materials such as carbon black such as acetylene black, graphite, and vapor grown carbon fiber. When the active material layer (13, 15) contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to the improvement of the output characteristics of the battery.

Examples of the electrolyte salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N), LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The compounding ratio of the components contained in the positive electrode active material layer 13 and the negative electrode active material layer 15 is not particularly limited. The blending ratio can be adjusted in consideration of the intended use of the battery (emphasis on output, emphasis on energy, etc.) and ion conductivity by appropriately referring to known knowledge about the bipolar secondary battery.

The thickness (T _e ) of each of the active material layers 13 and 15 is not particularly limited, and conventionally known knowledge about the battery can be appropriately referred to. From the viewpoint of improving the output characteristics of the battery, the thickness (T _e ) of each active material layer (13, 15) is preferably 50 μm or less, more preferably 5 to 50 μm, and still more preferably. It is 10-40 micrometers, Most preferably, it is 15-30 micrometers.

[Electrolyte layer]
In the bipolar secondary battery of the present invention, the electrolyte layer 17 includes a separator. The separator functions as a spatial partition (spacer) between the positive electrode active material layer 13 and the negative electrode active material layer 15. In addition, it also has a function of holding an electrolyte that is a lithium ion transfer medium between the positive and negative electrodes during charging and discharging. That is, the electrolyte layer 17 includes a separator and an electrolyte held by the separator. Specific examples of the separator include a microporous film made of polyolefin such as polyethylene or polypropylene. The thickness (T _s ) of the separator is not particularly limited, but from the viewpoint of improving the output characteristics of the battery, the thickness (T _s ) of the separator is preferably 5 to 30 μm, more preferably 10 ˜20 μm.

  In the present invention, a liquid electrolyte or a gel electrolyte can be used as the electrolyte. The liquid electrolyte has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent that can be used as the plasticizer include carbonates such as ethylene carbonate (EC) and propylene carbonate (PC). Further, as the supporting salt (lithium salt), a compound that can be added to the active material layer of the electrode, such as LiBETI, can be similarly employed.

  On the other hand, the gel electrolyte is a polymer electrolyte containing an electrolytic solution, and specifically has a configuration in which the liquid electrolyte is injected into a matrix polymer made of an ion conductive polymer. Examples of the ion conductive polymer used as the matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved. The matrix polymer of gel electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

[Seal part]
The seal portion 31 is a member peculiar to the bipolar secondary battery, and is disposed on the peripheral portion of the single cell layer 19 for the purpose of preventing leakage of the electrolyte layer 17. In addition to this, it is possible to prevent current collectors adjacent in the battery from coming into contact with each other and a short circuit due to a slight unevenness at the end of the laminated electrode. In the form shown in FIG. 1, the seal portion 31 is disposed at the peripheral portion of the unit cell layer 19 while penetrating the separator in the stacking direction of the battery elements 21. Examples of the constituent material of the seal portion 31 include polyolefin resins such as PE and PP, epoxy resins, rubber, and polyimide. Of these, polyolefin resins are preferred from the viewpoints of corrosion resistance, chemical resistance, film-forming properties, economy, and the like.

[Positive electrode and negative electrode tab]
In the bipolar secondary battery 10, the tabs (the positive electrode tab 25 and the negative electrode tab 27) electrically connected to the outermost current collector (11 a, 11 b) are exterior materials for the purpose of taking out current to the outside of the battery. It is taken out of the laminate sheet 29. Specifically, the positive electrode tab 25 electrically connected to the positive electrode outermost layer current collector 11 a and the negative electrode tab 27 electrically connected to the negative electrode outermost layer current collector 11 b are formed on the laminate sheet 29. Take out to the outside.

  The material constituting the tabs (the positive electrode tab 25 and the negative electrode tab 27) is not particularly limited, and a known highly conductive material conventionally used as a tab for a bipolar secondary battery can be used. As a constituent material of the tab, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable, and aluminum, copper, and the like are more preferable from the viewpoint of light weight, corrosion resistance, and high conductivity. Is preferable, and aluminum is particularly preferable. Note that the same material may be used for the positive electrode tab 25 and the negative electrode tab 27, or different materials may be used. Further, the outermost layer current collector (11a, 11b) may be extended to form a tab (25, 27), or a separately prepared tab may be connected to the outermost layer current collector.

[Positive electrode and negative electrode terminal plate]
The positive electrode and the negative electrode terminal plate are used as necessary. For example, when the positive electrode tab 25 and the negative electrode tab 27 are directly taken out from the outermost current collectors 11a and 11b, the positive electrode and the negative electrode terminal plate may not be used.

  As a material for the positive electrode and the negative electrode terminal plate, a material used in a conventionally known lithium ion battery can be used. For example, aluminum, copper, titanium, nickel, stainless steel, and alloys thereof can be used. Aluminum is preferably used from the viewpoints of corrosion resistance, ease of production, economy, and the like. Furthermore, from the viewpoint of suppressing internal resistance at the terminal portion, the thickness of the positive electrode and the negative electrode terminal plate is usually preferably about 0.1 to 2 mm.

[Positive electrode and negative electrode lead]
A positive electrode and a negative electrode can also be used as needed. For example, when the output electrode terminals (the positive electrode tab 25 and the negative electrode tab 27) are directly taken out from the outermost current collectors 11a and 11b, the positive electrode and the negative electrode lead may not be used.

  As a material for the positive electrode and the negative electrode lead, a lead used in a known lithium ion battery can be used. In addition, the parts removed from the battery exterior material should be heat-insulating so that they do not affect products (for example, automobile parts, especially electronic devices) by touching peripheral devices or wiring and causing leakage. It is preferable to coat with a heat shrinkable tube or the like.

[Exterior material]
A conventionally known metal can case can be used as the exterior material. In addition, the battery element 21 may be packed using a laminate sheet 29 as shown in FIG. The laminate sheet 29 can be composed of, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order.

  The bipolar secondary battery 10 of the present invention is not limited to the stacked flat shape as shown in FIG. 1, but the wound bipolar secondary battery has a cylindrical shape. It may be a thing, and the thing of such a cylindrical shape may be deform | transformed and made into the rectangular flat shape. In the cylindrical shape, there is no particular limitation such as using a laminate sheet or a conventional cylindrical can (metal can) as the exterior material.

  The battery of the present invention is suitably used as a power source for driving a vehicle or an auxiliary power source that requires a high volume energy density and a high volume output density as a large capacity power source for an electric vehicle, a hybrid electric vehicle, a fuel cell vehicle, a hybrid fuel cell vehicle, etc. Can be used.

  The preferred embodiment of the present invention has been described in detail by taking the bipolar secondary battery of the form shown in FIG. 1 as an example, but the technical scope of the present invention is not limited to such a form. For example, the non-aqueous electrolyte secondary battery of the present invention may be a non-bipolar (parallel) secondary battery. For reference, a schematic cross-sectional view of a non-aqueous electrolyte secondary battery (stacked secondary battery) that is not bipolar is shown in FIG. As shown in FIG. 7, the laminated secondary battery 10 ′ of the present embodiment has a structure in which the power generation element 21 is sealed inside a laminate film 29 that is a battery exterior material.

  The power generation element 21 includes a positive electrode in which a positive electrode active material layer 13 is formed on both surfaces of a positive electrode current collector 11 ′, an electrolyte layer 17, and a negative electrode active material layer 15 on both surfaces of a negative electrode current collector 12. It has a configuration in which a plurality of unit cell layers 19 made of a negative electrode are stacked. At this time, the positive electrode, the electrolyte layer, and the positive electrode active material layer 13 on one side of one positive electrode and the negative electrode active material layer 15 on one side of one negative electrode adjacent to the one positive electrode face each other through the electrolyte layer 17. 17, The negative electrode is laminated in this order. In addition, there is no restriction | limiting in particular about the lamination | stacking number N of the cell layer 19, Preferably it is 5-40 layers, More preferably, it is 10-30 layers.

  With the above-described configuration, the adjacent positive electrode current collector 11 ′, positive electrode active material layer 13, electrolyte layer 17, negative electrode active material layer 15, and negative electrode current collector 12 constitute one single battery layer 19. Therefore, it can be said that the stacked secondary battery 10 of the present embodiment has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel. Note that the positive electrode active material layer 13 is formed on only one side of the outermost positive electrode current collector located in both outermost layers of the power generation element 21.

  Further, the positive electrode tab 25 and the negative electrode tab 27 that are electrically connected to the respective electrodes (positive electrode and negative electrode) are connected to the positive electrode current collector 33 and the negative electrode current collector 35 of each electrode through the positive electrode terminal lead and the negative electrode terminal lead. It is attached by sonic welding or resistance welding. Thereby, the positive electrode tab 25 and the negative electrode tab 27 have a structure exposed outside from the part joined by the heat sealing | fusion of the peripheral part of the said laminate film 29. FIG.

The battery of the form shown in FIG. 7 has the same characteristics as the bipolar secondary battery of the form shown in FIG. That is, in all the single cell layers constituting the battery element, a maximum particle size of the positive electrode active material contained in the positive electrode active material layer _{(D max (+))} and the negative electrode active maximum particle size of the material _{(D max (-))} However, the relationship of Formula 1 is satisfied. With such a configuration, as described above, the occurrence of a micro short circuit in the single cell layer can be effectively suppressed. As a result, a battery having excellent long-term reliability can be provided.

  In addition, there is no restriction | limiting in particular about the manufacturing method of the nonaqueous electrolyte secondary battery (bipolar type secondary battery / stacked type secondary battery) of this invention, and conventionally well-known knowledge can be referred suitably. However, in order to control the maximum particle diameter of the active material, which is a characteristic configuration of the present invention, classification processing such as sieving as described above may be performed on the active material.

[Battery]
A plurality of the nonaqueous electrolyte secondary batteries (10, 10 ′) of the present invention may be connected to form an assembled battery. Specifically, an assembled battery can be configured by connecting at least two batteries in series, parallel, or both. At this time, it is possible to freely adjust the capacity and voltage by serialization and parallelization.

  The number of nonaqueous electrolyte secondary batteries constituting the assembled battery of the present invention and the manner of connection can be determined according to the output and capacity required of the battery. When the assembled battery of this invention is comprised, the stability as a battery increases compared with a secondary battery single (unit cell). Further, by configuring the assembled battery of the present invention, it is possible to reduce the influence on the entire assembled battery due to deterioration of one single battery layer (single cell) in the assembled battery of the present invention.

  FIG. 8 is an external view of a typical embodiment of an assembled battery according to the present invention, FIG. 8A is a plan view of the assembled battery, FIG. 8B is a front view of the assembled battery, and FIG. 8C is an assembled battery. FIG.

  In the form shown in FIG. 8, a small assembled battery 35 that can be attached and detached is formed by connecting a plurality of the nonaqueous electrolyte secondary batteries (10, 10 ') of the present invention in series and / or in parallel. A plurality of small assembled batteries 35 that can be attached and detached are connected in series and / or in parallel to form an assembled battery 37. As a result, the assembled battery 37 is an assembled battery 37 having a large capacity and a large output suitable for a vehicle driving power source and an auxiliary power source that require high volume energy density and high volume output density. The assembled and removable small assembled batteries 35 are connected to each other using an electrical connection means such as a bus bar, and the assembled batteries 35 are stacked in a plurality of stages using a connection jig 39. How many non-aqueous electrolyte secondary batteries are connected to create the assembled battery 35, and how many assembled batteries 35 are stacked to create the assembled battery 37 depends on the mounted vehicle (electric vehicle). Depending on the battery capacity and output.

[vehicle]
The non-aqueous electrolyte secondary battery (10, 10 ′) and the assembled battery 37 of the present invention can be used as a power source for driving a vehicle. The secondary battery or the assembled battery of the present invention may be, for example, a hybrid vehicle, a fuel cell vehicle, an electric vehicle (all are four-wheeled vehicles (commercial vehicles such as passenger cars, trucks, buses, light vehicles, etc.) as well as two-wheeled vehicles. (Including motorcycles and tricycles). Thereby, a long-life and highly reliable automobile can be provided. However, the application is not limited to automobiles. For example, if it is another vehicle, it can be applied to various power sources for moving bodies such as trains, and it can be used for mounting uninterruptible power supplies and the like. It can also be used as a power source.

  FIG. 9 is a conceptual diagram of a vehicle equipped with the assembled battery 37 of the present invention.

  As shown in FIG. 9, in order to mount the assembled battery 37 in a vehicle such as the electric vehicle 40, the battery pack 37 is mounted under the seat at the center of the vehicle body of the electric vehicle 40. This is because if it is installed under the seat, the interior space and the trunk room can be widened. The place where the assembled battery 37 is mounted is not limited to the position under the seat, but may be a lower part of the rear trunk room or may be mounted in an engine room in front of the vehicle. The electric vehicle 40 using the assembled battery 37 as described above has excellent durability and can provide a sufficient output even when used for a long time. Furthermore, it is possible to provide electric vehicles and hybrid vehicles that are excellent in fuel efficiency and running performance.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited to only the forms shown in the following examples.

<Example 1>
A non-polar lithium ion secondary battery having a battery element including 30 single battery layers was manufactured by the following method. Therefore, according to Equation 1, α <0.95-0.0008 × 30 = 0.926, and according to Equation 2, α <0.85-0.0046 × 30 = 0.712.

In this example, the thickness (T _e (+)) of the positive electrode active material layer constituting the single battery layer was 36 μm, the thickness (T _e (−)) of the negative electrode active material layer was 30 μm, and the thickness of the separator The thickness (T _s ) was 20 μm. Therefore, according to Equation 1, D _max (+) = α (T _e (+) + T _s /2)<0.926(36+20/2)=0.926×46=42.6 μm. Similarly, D _max (−) = α (T _e (−) + T _s /2)<0.926 (30 + 20/2) = 0.926 _× 40 ₌ 37.0 μm. Further, according to Equation 2, D _max (+) = α (T _e (+) + T _s /2)<0.712(36+20/2)=0.712×46=32.8 μm. Similarly, D _max (−) = α (T _e (−) + T _s /2)<0.712(30+20/2)=0.712×40=28.5 μm.

(Preparation of positive electrode)
LiMn ₂ O ₄ (average particle diameter (D ₅₀ ) 10 μm) was prepared as a positive electrode active material. Next, the prepared LiMn ₂ O ₄ was sieved so that the maximum particle size (D _max (+)) was 33 μm.

Next, LiMn ₂ O ₄ (85% by mass) sieved above, acetylene black (5% by mass) as a conductive auxiliary agent, and polyvinylidene fluoride (PVdF) (10% by mass) as a binder are mixed, and then An appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to prepare a positive electrode active material slurry.

  The positive electrode active material slurry prepared above was applied to both sides of an aluminum foil (thickness 20 μm) as a positive electrode current collector in a size of 150 mm length × 150 mm width and dried. Thereafter, the obtained laminate was subjected to press treatment so that the thickness of the positive electrode active material layer was 36 μm on one side to complete the positive electrode.

(Preparation of negative electrode)
As the negative electrode active material, hard carbon (average particle size (D ₅₀ ) 10 μm) was prepared. Next, the prepared hard carbon was sieved so that the maximum particle size (D _max (−)) was 25 μm.

  Next, hard carbon (90% by mass) sieved above and PVdF (10% by mass) as a binder are mixed, and then an appropriate amount of NMP as a solvent for adjusting the slurry viscosity is added to prepare a negative electrode active material slurry. did.

  The negative electrode active material slurry prepared above was applied to both sides of a copper foil (thickness 20 μm) as a negative electrode current collector in a size of 155 mm long × 155 mm wide and dried. Thereafter, the obtained laminate was subjected to press treatment so that the thickness of the negative electrode active material layer was 30 μm on one side to complete the negative electrode.

(Preparation of electrolyte)
An equivalent volume mixture of propylene carbonate (PC) and ethylene carbonate (EC) containing LiPF ₆ at a concentration of 1.0 M was prepared and used as an electrolyte.

(Production of battery)
The positive electrode prepared above, a separator (polypropylene microporous membrane, thickness 20 μm), the negative electrode prepared above, and the same separator as described above were sequentially laminated in this order to obtain 30 single cell layers. A battery element was prepared. In addition, the active material layer was not formed on the outermost surface (uppermost surface and lowermost surface) of the negative electrode located in the outermost layer, and the current collector was exposed. Further, each current collector was connected with a current extraction tab so as to be derived from the same side of the battery element.

  The battery element produced as described above was inserted into a pack made of an aluminum laminate sheet with a three-side seal as an exterior material. At this time, the current extraction tab was led out from the pack. Next, the electrolyte prepared above was injected, and the remaining side of the pack was sealed in a vacuum to complete the battery.

<Example 2>
Sieving was performed so that the maximum particle size (D _max (+)) of the positive electrode active material was 24 μm, and sieving was performed so that the maximum particle size (D _max (−)) of the negative electrode active material was 17 μm. Except for this, a battery was fabricated in the same manner as in Example 1 described above.

<Example 3>
Sieving was performed so that the maximum particle size (D _max (+)) of the positive electrode active material was 14 μm, and sieving was performed so that the maximum particle size (D _max (−)) of the negative electrode active material was 10 μm. Except for this, a battery was fabricated in the same manner as in Example 1 described above.

<Example 4>
A 12-series gel electrolyte type / bipolar type lithium ion secondary battery module was produced by the following method. Therefore, according to Equation 1, α <0.95-0.0008 × 12 = 0.940, and according to Equation 2, α <0.85-0.0046 × 12 = 0.955.

In this example, the thickness (T _e (+)) of the positive electrode active material layer constituting the single battery layer was 36 μm, the thickness (T _e (−)) of the negative electrode active material layer was 30 μm, and the thickness of the separator The thickness (T _s ) was 20 μm. Therefore, according to Equation 1, D _max (+) = α (T _e (+) + T _s /2)<0.940(36+20/2)=0.940×46=43.2 μm. Similarly, D _max (−) = α (T _e (−) + T _s /2)<0.940 (30 + 20/2) = 0.940 _× 40 ₌ 37.6 μm. Further, according to Equation 2, D _max (+) = α (T _e (+) + T _s /2)<0.795 (36 + 20/2) = 0.955 _× 46 ₌ 36.6 μm. Similarly, D _max (−) = α (T _e (−) + T _s /2)<0.795 (30 + 20/2) = 0.955 _× 40 ₌ 31.8 μm.

(Production of bipolar electrode)
As the positive electrode active material and the negative electrode active material, the same materials as in Example 1 described above (after sieving) were used, and active material slurries were prepared by the same method.

  The positive electrode active material slurry was applied to one surface of a stainless foil (thickness 20 μm) as a current collector in a size of 200 mm in length and 150 mm in width and dried. Thereafter, the obtained laminate was subjected to press treatment so that the thickness of the positive electrode active material layer was 36 μm.

  Similarly, the negative electrode active material slurry was applied to the other surface of the current collector in a size of 200 mm long × 150 mm wide and dried. Thereafter, the obtained laminate was pressed so that the thickness of the negative electrode active material layer was 30 μm. Note that the negative electrode active material layer was formed so that the centers of the positive electrode active material layer and the negative electrode active material layer overlapped.

  Next, the current collector coated with the positive electrode active material layer and the negative electrode active material layer is cut into a size of length 130 × width 80 mm, and a current collector having a width of 20 mm is formed on the outer periphery of the positive electrode active material layer and the negative electrode active material layer. An exposed portion (uncoated portion) was provided to produce a bipolar electrode.

(Formation of electrolyte layer)
An electrolyte solution (90% by mass) similar to that of Example 1 described above was prepared. On the other hand, PVdF-HFP (10% by mass) containing 10% by mass of hexafluoropropylene (HFP) was prepared as a matrix polymer. These electrolyte solutions and matrix polymer were mixed, and an appropriate amount of dimethyl carbonate (DMC) was added as a viscosity adjusting solvent to prepare a pregel solution.

  The pregel solution prepared above was applied to the positive electrode active material layer and the negative electrode active material layer of the bipolar electrode prepared above, the DMC was dried, and the gel electrolyte was included in the active material layer.

(Formation of seal part precursor)
The seal part precursor (one-component uncured epoxy resin) was applied to the positive electrode side uncoated part (all four sides) of the bipolar electrode obtained above using a dispenser.

  Next, a polyethylene separator (thickness 20 μm, length 170 mm × width 140 mm) was placed on the positive electrode side of the bipolar electrode provided with the seal portion precursor so as to cover the current collector.

  Then, from the top of the separator, a non-electrode-applied portion (all four sides) (the same portion as the portion where the seal portion precursor is applied) is used with a dispenser, and a seal portion precursor (one-component uncured epoxy resin) ) Was further applied.

(Set to electrode holding mechanism)
With the bipolar electrode-separator laminate obtained above, with the negative electrode face up, the electrodes do not contact and are not displaced in the direction perpendicular to the electrode surface direction. Thirteen sheets were set in a bipolar electrode holding mechanism provided with a clip mechanism capable of chucking the outside of the precursor application portion. Here, the bipolar electrode positioned at the lowermost portion was used without a seal portion precursor applied and without a separator.

(Lamination of electrodes)
While lowering the electrode holding mechanism, the 13 bipolar electrodes were stacked on the electrode base so as not to be displaced. In this way, a battery element in which 12 cell layers were laminated was produced.

(Battery element press)
The battery element produced above was moved together with the electrode cradle to a hot press site in the vacuum chamber under a pressure condition of 1.0 Torr. Thereafter, the battery element was hot pressed at a surface pressure of 1 kg / cm ² at 80 ° C. for 1 hour using the hot press portion. As a result, the seal portion precursor (one-component uncured epoxy resin) was pressed to a predetermined thickness and cured, and a seal portion was formed on the outer peripheral portion of the single cell layer. Moreover, the electrolytic solution penetrated the entire single cell layer (that is, the negative electrode active material layer, the separator, and the positive electrode active material layer) by this hot pressing.

(Encapsulation in exterior)
A total of four battery elements were produced by the same method as described above. And these battery elements were laminated | stacked so that it might become in series. At this time, a current extraction tab (made of aluminum) was sandwiched between the battery elements. Furthermore, the obtained laminate was sandwiched between bakelite plates (thickness 1 mm) having a larger area than the battery element. Next, by inserting the entire laminate into a pack made of an aluminum laminate sheet, which is an exterior material, and packing the interior of the exterior as a vacuum so that the current extraction tab is led out, 12 series gel electrolyte type A bipolar lithium ion secondary battery module was completed.

<Example 5>
Sieving was performed so that the maximum particle size (D _max (+)) of the positive electrode active material was 24 μm, and sieving was performed so that the maximum particle size (D _max (−)) of the negative electrode active material was 17 μm. Except for this, a battery was fabricated in the same manner as in Example 4 described above.

<Example 6>
Sieving was performed so that the maximum particle size (D _max (+)) of the positive electrode active material was 14 μm, and sieving was performed so that the maximum particle size (D _max (−)) of the negative electrode active material was 10 μm. Except for this, a battery was fabricated in the same manner as in Example 4 described above.

<Comparative Example 1>
Sieving was performed so that the maximum particle size (D _max (+)) of the positive electrode active material was 50 μm, and sieving was performed so that the maximum particle size (D _max (−)) of the negative electrode active material was 45 μm. Except for this, a battery was fabricated in the same manner as in Example 1 described above.

<Comparative example 2>
Sieving was performed so that the maximum particle size (D _max (+)) of the positive electrode active material was 50 μm, and sieving was performed so that the maximum particle size (D _max (−)) of the negative electrode active material was 45 μm. Except for this, a battery was fabricated in the same manner as in Example 4 described above.

<Evaluation of micro short circuit>
A predetermined number of batteries were produced for the batteries obtained in each of the above examples and comparative examples, and the presence or absence of a micro short circuit was examined.

  Specifically, first, each of the produced batteries was charged for the first time at a constant current of 0.5 C for 5 hours. Thereafter, aging was performed for one week. Under the present circumstances, about the battery of Examples 1-4 and the comparative example 1, the upper limit voltage was set to 4.2V. Moreover, about the battery of Examples 5-8 and the comparative example 2, the upper limit voltage of each cell layer was set to 4.2V. The voltage was measured after aging, and the presence or absence of a micro short circuit was inspected from the voltage drop at that time. Table 2 below shows the number of prototypes of the batteries and the number of batteries in which a micro short circuit occurred in each of the examples and comparative examples.

  From the results shown in Table 2, it can be seen that according to the present invention, the occurrence of a micro short circuit in the nonaqueous electrolyte secondary battery can be effectively suppressed. Therefore, the nonaqueous electrolyte secondary battery of the present invention has excellent durability and high reliability even when used for a long time. Such a nonaqueous electrolyte secondary battery is extremely useful for applications that require long-term reliability, particularly for in-vehicle use.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view schematically showing an outline of a bipolar lithium ion secondary battery which is a typical embodiment of a nonaqueous electrolyte secondary battery of the present invention. Average particle size (D ₅₀₎ is a graph plotting the frequency for the particle size of the active material particles of about 10 [mu] m. It is an expansion schematic diagram of the site | part containing the active material layer and separator of a battery electrode. It is a graph which shows the result of having investigated the change of the occurrence probability of a micro short circuit when changing safety factor alpha. It is a graph which shows the result of having investigated how safety factor (alpha) required in order to make the generation | occurrence | production probability of a micro short circuit to a fixed value when the number of lamination | stacking N is changed is examined. The solid line is a graph when the probability of occurrence of a micro short circuit is 50%, and the broken line is a graph when the probability of occurrence of a micro short circuit is 10%. It is a graph which shows the linearity between the lamination number N and the safety factor (alpha) in the area | region (N> = 48) with many lamination | stacking numbers. It is the cross-sectional schematic of the nonaqueous electrolyte secondary battery (stacked type secondary battery) which is another type of other embodiment of the nonaqueous electrolyte secondary battery of this invention. FIG. 3A is an external view schematically showing a typical embodiment of a battery pack according to the present invention, FIG. 3A is a plan view of the battery pack, FIG. 3B is a front view of the battery pack, and FIG. It is a side view of a battery. It is a conceptual diagram of the vehicle carrying the assembled battery of this invention.

Explanation of symbols

10 Bipolar secondary battery,
10 'non-bipolar type (parallel type) secondary battery,
11 Current collector,
11a Positive electrode side outermost layer current collector,
11b The negative electrode side outermost layer current collector,
11 'positive electrode current collector,
12 negative electrode current collector,
13 positive electrode active material layer,
15 negative electrode active material layer,
17 electrolyte layer,
19 cell layer,
21 battery elements,
25 positive electrode tab,
27 negative electrode tab,
29 Laminate sheet,
31 seal part,
35 A small assembled battery that can be attached and detached,
37 battery pack,
39 Connecting jig,
40 Electric car.

Claims (10)

A positive electrode active material layer that includes a positive electrode active material and is formed on the surface of the current collector, an electrolyte layer in which an electrolyte is held in a separator, and a negative electrode active material that includes a negative electrode active material and is formed on the surface of the current collector A non-aqueous electrolyte secondary battery having a battery element including at least one single battery layer formed by laminating a material layer in this order,
In at least one single cell layer, the maximum value (D _max (+)) of the particle size of the positive electrode active material and the maximum value (D _max (−)) of the particle size of the negative electrode active material are expressed by the following formula 1:
Where _Te is the thickness of the active material layer, T _s is the thickness of the separator, N is the number of cell layers, and is an integer that satisfies N ≧ 48.
Relationship and satisfy the relationship of _{D max> T e, D max} (+) is not less less 3.3 times the average particle diameter of the positive electrode active material _{(D 50), D max (} -) is the negative active 2.5 times der less of the average particle diameter of material _{(D 50)} is,
In the single cell layer that satisfies the above two relationships, characterized in that T _s is 5 to 30 [mu] m, a non-aqueous electrolyte secondary battery. D _max (+) is 2 times or less of the average particle diameter (D ₅₀ ) of the positive electrode active material, and D _max (−) is 2 times or less of the average particle diameter (D ₅₀ ) of the negative electrode active material. The nonaqueous electrolyte secondary battery according to claim 1.   The nonaqueous electrolyte secondary battery according to claim 1, wherein N = 96 and α ≦ 0.9. D _max (+) and D _max (−) are represented by the following formula 2:
In the formula, definitions of T _e , T _s , and N are the same as those in Formula 1.
The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein:   The nonaqueous electrolyte secondary battery according to claim 1, wherein α> 0.1.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein all the single battery layers constituting the battery element satisfy the above relationship.   The non-aqueous electrolyte secondary battery according to claim 1, wherein N = 96. In the single cell layer that satisfies the relationship of the equation, T _e is 50μm or less, the non-aqueous electrolyte secondary battery according to any one of claims 1 to 7. In the single cell layer that satisfies the relationship of the equation, the positive active material and at least one of an average particle diameter of the negative active material (D ₅₀₎ is 0.5 to 20 [mu] m, any of claims 1-8 1 The nonaqueous electrolyte secondary battery according to item. It is a bipolar lithium ion secondary battery, a nonaqueous electrolyte secondary battery according to any one of claims 1-9.