JP5880964B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. Specifically, the present invention relates to a nonaqueous electrolyte secondary battery in which the moisture content of the positive electrode mixture layer is controlled.

  Lithium secondary batteries and other non-aqueous electrolyte secondary batteries are smaller, lighter, and have higher energy density and superior output density than existing batteries. For this reason, it is preferably used as a so-called portable power source such as a personal computer or a portable terminal, or a vehicle driving power source such as a hybrid vehicle. In a typical configuration of this type of nonaqueous electrolyte secondary battery, a positive electrode, a negative electrode, and an electrolytic solution are accommodated in a battery case. Positive and negative electrodes have an electrode mixture layer (active material) mainly composed of a material (active material) capable of reversibly occluding and releasing charge carriers (typically lithium ions) on a corresponding electrode current collector. And charge and discharge are performed by charge carriers moving back and forth between the electrodes.

  By the way, in such a non-aqueous electrolyte secondary battery, internal factors such as contamination of metal powder in the battery manufacturing process, impact such as dropping during use or piercing of metal objects during use, generation of dendrites, etc. A short circuit (internal short circuit) may occur. In this case, Joule heat is generated at the short-circuited portion, so that the active material or the like generates heat, and the temperature of the battery may rapidly increase. In particular, such a temperature rise is remarkable in a battery having a high capacity and a high energy density used for a power source for driving a vehicle, and thus high reliability needs to be ensured.

  A technique for increasing the resistance difference between electrodes (positive and negative electrodes) is known as a technique that can suppress the temperature rise as described above. For example, in Patent Document 1, one of the positive and negative electrodes is electrically connected to the battery case, and the electric resistance of the electrode mixture layer provided in the electrode on the side not connected to the case is significantly larger than the other. A lithium secondary battery characterized by the above is disclosed. According to this configuration, it is possible to make it difficult for a short-circuit current to flow when an internal short circuit occurs.

JP 2011-0965539 A JP 2011-034861 A

  However, in the above technique, since it is necessary to increase the resistance of the electrode, the battery characteristics may be deteriorated. In addition, non-aqueous electrolyte secondary batteries tend to have higher capacities and higher energy densities in recent years, and in such batteries, the short-circuit current that instantaneously flows when an internal short circuit occurs is greater than ever. Further, in a battery with an increased energy density, heat dissipation is generally low because there are few voids inside the battery (for example, in the electrode mixture layer). For this reason, the behavior of the temperature rise at the time of an internal short circuit is different from the conventional one, and there is a risk of causing a rapid temperature rise or a local temperature rise.

  The present invention has been made in view of such a point, and the object thereof is to maintain a highly reliable non-aqueous electrolyte secondary in which a malfunction (temperature increase or the like) at the time of an internal short circuit is suppressed while maintaining excellent battery characteristics. It is to provide a battery.

  As a result of various studies on techniques that can suppress a local temperature increase during an internal short circuit, the present inventor has conceived that the electrode mixture layer contains moisture. However, generally, if moisture is contained in a battery, gas is generated during charge / discharge or battery characteristics are deteriorated. Therefore, it is usual to remove moisture as much as possible when the battery is constructed. Therefore, the present inventor has further studied earnestly, and by adjusting the amount of moisture contained in the electrode mixture layer within a suitable range, excellent battery characteristics and high reliability (resistance at the time of internal short circuit) are achieved. The inventors found that they can be compatible, and completed the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte secondary battery by which the electrode body provided with the positive electrode and the negative electrode and the nonaqueous electrolyte were accommodated in the predetermined battery case is provided. The positive electrode includes a positive electrode current collector and a positive electrode mixture layer including a positive electrode active material formed on the current collector. The positive electrode mixture layer has a water content of 300 ppm or less detected after 30 minutes at 120 ° C. by Karl Fischer method (typically moisture vaporization method-coulometric titration method), and 30 minutes at 300 ° C. The amount of water detected later is 3000 ppm or more and 10,000 ppm or less. In the present specification, “ppm” refers to mass fraction, that is, ppm (mass / mass).

In the battery having the above configuration, the amount of dehydration from the positive electrode mixture layer detected under heating conditions of 120 ° C. for 30 minutes is 300 ppm or less. That is, since the amount of water in the positive electrode mixture layer in the normal use temperature range (typically 100 ° C. or lower) of the battery is reduced, it is high without causing an increase in resistance or a decrease in battery characteristics during normal use. Battery characteristics can be exhibited.
Further, in the battery having the above configuration, the amount of dehydration from the positive electrode mixture layer detected under the heating condition of 300 ° C. for 30 minutes is 3000 ppm or more. For this reason, when the temperature inside the battery rises due to an internal short circuit (for example, a temperature of 200 ° C. to 300 ° C.), moisture contained in the positive electrode active material layer is desorbed, and the rise in battery temperature is effectively suppressed. can do. Furthermore, since heat of vaporization (heat of vaporization) is required when the moisture undergoes phase transition to become water vapor, the temperature rise can be more effectively suppressed. Therefore, even when a short circuit occurs in the battery due to a nail penetration of a metal object and a large current flows instantaneously, a rapid temperature rise can be avoided.
As described above, according to the present invention, it is possible to provide a highly reliable non-aqueous electrolyte secondary battery that can suppress an increase in temperature during an internal short circuit while maintaining excellent battery characteristics.

In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the positive electrode active material has a general formula: Li _{1 + δ} (Ni _a Co _b Mn _c M _d ) O ₂ (where M is a transition metal element) , One or more selected from a typical metal element and boron (B), and δ is a value determined to satisfy the charge neutrality condition when 0 ≦ δ ≦ 0.2, and a, b, c , D satisfies a + b + c + d≈1, and at least one of a, b, and c is greater than 0.
The oxide may contain, in part, an oxyhydroxide (eg, NiOOH, CoOOH, FeOOH) of a metal element (eg, Ni, Co, Mn) constituting the oxide. This oxyhydroxide can decompose at a temperature of about 200 ° C. to 300 ° C. to produce water. For this reason, in the battery provided with the said oxide, when the temperature inside a battery rises by an internal short circuit, the further temperature rise can be suppressed. Furthermore, since the oxide has a high energy density, it is possible to achieve even higher battery characteristics (for example, battery capacity). Therefore, excellent battery characteristics and reliability at the time of internal short circuit can be achieved at a higher level.

In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the electrode body has a positive electrode mixture layer having a predetermined width in the longitudinal direction of the current collector on a long positive electrode current collector. A long positive electrode formed along the long negative electrode current collector, and a negative electrode mixture layer having a predetermined width is formed on the long negative electrode current collector along the longitudinal direction of the current collector. A negative electrode, and the long positive electrode and the long negative electrode are stacked in a state of facing each other and wound in the longitudinal direction.
With the above configuration, the capacity of the battery can be increased. However, particularly in such a configuration, the heat dissipation of the central portion (winding core portion) in the winding axis direction is low, and therefore, when an internal short circuit occurs, a temperature increase due to large current movement is likely to occur in the winding core portion. Therefore, the application of the present invention is particularly useful.

In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the density of the positive electrode mixture layer is 2.5 g / cm ³ or more and 4 g / cm ³ or less.
When the density of the positive electrode mixture layer is higher than the conventional one, there are few voids in the mixture layer. For this reason, it is difficult to dissipate heat generated at the time of an internal short circuit, and a rapid temperature rise is likely to occur. Therefore, the application of the present invention is particularly useful for the battery having the above configuration.

In addition, according to the present invention, there is provided a method for manufacturing a non-aqueous electrolyte secondary battery in which an electrode body having positive and negative electrodes and a non-aqueous electrolyte are accommodated in a predetermined battery case. The manufacturing method includes (1) preparing a composition for forming a positive electrode mixture layer containing at least a positive electrode active material and a binder; (2) applying the composition for forming a positive electrode mixture layer on a positive electrode current collector. And (3) placing the positive electrode in an environment where moisture is supplied; and (4) placing the positive electrode supplied with moisture at 50 ° C. or higher. And drying at a temperature not higher than the melting point of the binder; and (5) constructing a non-aqueous electrolyte secondary battery using the dried positive electrode.
According to this method, the water content of the positive electrode mixture layer can be adjusted to a suitable range. Therefore, a non-aqueous electrolyte secondary battery having both excellent battery characteristics and high reliability (resistance during internal short circuit) can be preferably manufactured.

In a preferred embodiment of the production method disclosed herein, the moisture is supplied to the positive electrode by maintaining the environment in an environment with a relative humidity of 50% or more and 100% or less for 24 hours or more and 240 hours or less.
According to such a method, a suitable amount of moisture can be imparted to the positive electrode (more specifically, the positive electrode mixture layer) by a simple operation of holding the substrate in a predetermined humidity environment for a relatively short time. For this reason, it is preferable also from a viewpoint of work efficiency or manufacturing cost.

In a preferred embodiment of the production method disclosed herein, the positive electrode supplied with moisture is dried in a drying furnace at 60 ° C. or higher and 120 ° C. or lower.
According to such a method, moisture that may deteriorate battery characteristics, that is, moisture present in the positive electrode mixture layer during normal use of the battery can be suitably reduced. In addition, the moisture that can suppress the temperature rise at the time of an internal short circuit, that is, the moisture present in the positive electrode mixture layer when the battery temperature is about 200 ° C. to 300 ° C. can be adjusted to a suitable range.

In a preferred embodiment of the production method disclosed herein, the positive electrode active material has a general formula: Li _{1 + δ} (Ni _a Co _b Mn _c M _d ) O ₂ (where M is a transition metal element, a typical metal element) And one or more selected from boron (B), δ is a value determined to satisfy the charge neutrality condition with 0 ≦ δ ≦ 0.2, and a, b, c, d are a + b + c + d≈1 is satisfied, and at least one of a, b, and c is greater than 0.)
The oxyhydroxide contained in the lithium transition metal oxide can decompose at a temperature of about 200 ° C. to 300 ° C. to generate water. For this reason, in a battery using the oxide as a positive electrode active material, when a temperature rise occurs during an internal short circuit, the oxyhydroxide is decomposed to generate water, and further temperature rise can be suppressed. Moreover, since the said oxide has a high energy density, it can implement | achieve still higher battery characteristics. Therefore, the battery having the above-described configuration can achieve both excellent battery characteristics and reliability at the time of an internal short circuit at an even higher level.

In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the battery capacity of the nonaqueous electrolyte secondary battery is 20 Ah or more. In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the energy density of the nonaqueous electrolyte secondary battery is 230 kWh / m ³ or more.
In such a high-capacity and / or high-energy density non-aqueous electrolyte secondary battery, a large current instantaneously flows through the short-circuited portion, and a problem (for example, a rapid temperature increase) easily occurs due to the movement of the current. For this reason, application of the present invention is particularly useful.

In addition, according to the present invention, an assembled battery in which a plurality of the nonaqueous electrolyte secondary batteries (unit cells) disclosed herein are combined is provided.
Since the non-aqueous electrolyte secondary battery disclosed herein has improved reliability (typically resistance to internal short circuit), it is an assembled battery formed by connecting a plurality of such batteries in series and / or in parallel. It can be preferably used.

Furthermore, according to the present invention, there is provided a vehicle including the assembled battery as a driving power source.
The assembled battery disclosed here can achieve both excellent battery characteristics and resistance at the time of internal short circuit at a high level. Therefore, it can be suitably used in applications that require high battery characteristics and safety. Examples of such applications include a power source (driving power source) for driving a motor mounted on a vehicle (typically, a plug-in hybrid vehicle, a hybrid vehicle, or an electric vehicle).

FIG. 1 is a perspective view schematically showing the outer shape of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing a cross-sectional structure taken along line II-II of the nonaqueous electrolyte secondary battery in FIG. FIG. 3 is a schematic diagram showing a configuration of a wound electrode body of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. FIG. 4 is a perspective view schematically showing an assembled battery in which a plurality of nonaqueous electrolyte secondary batteries (unit cells) according to an embodiment of the present invention are combined. FIG. 5 is a side view schematically showing a vehicle (automobile) provided with the nonaqueous electrolyte secondary battery according to one embodiment of the present invention. FIG. 6 is a graph showing the relationship between the amount of moisture (ppm) detected at a heating temperature of 120 ° C. and the battery capacity (relative value). FIG. 7 is a graph showing the relationship between the amount of moisture (ppm) detected at a heating temperature of 120 ° C. and the battery resistance (relative value). FIG. 8 is a graph showing temperature changes during the nail penetration test in Example 1. FIG. 9 is a graph showing temperature changes during the nail penetration test in Example 2. FIG. 10 is a graph showing the temperature change during the nail penetration test in Example 3. FIG. 11 is a graph showing temperature changes during the nail penetration test in Example 4. FIG. 12 is a graph showing the relationship between the amount of moisture (ppm) detected at a heating temperature of 300 ° C. and the maximum temperature reached (° C.) during the nail penetration test.

  Hereinafter, preferred embodiments of the nonaqueous electrolyte secondary battery disclosed herein will be described. Matters necessary for implementation other than matters specifically mentioned in the present specification can be grasped as design matters of those skilled in the art based on the prior art in this field. The non-aqueous electrolyte secondary battery having such a structure can be implemented based on the contents disclosed in the present specification and common technical knowledge in the field. Hereinafter, the case of a lithium secondary battery may be described in more detail as a typical example, but the application target of the present invention is not intended to be limited to such a battery.

  In the present specification, the “non-aqueous electrolyte secondary battery” refers to a battery including a non-aqueous electrolyte (typically, an electrolytic solution containing a supporting salt in a non-aqueous solvent). The “lithium secondary battery” refers to a secondary battery that uses lithium ions as non-aqueous electrolyte ions and is charged and discharged by movement of lithium ions (transfer of charges) between positive and negative electrodes. A secondary battery generally referred to as a lithium ion secondary battery, a lithium polymer battery, a lithium ion capacitor, or the like is a typical example included in the lithium secondary battery in this specification. In the present specification, the “active material” refers to a substance (compound) capable of reversibly occluding and releasing chemical species (lithium ions in a lithium secondary battery) serving as a charge carrier on the positive electrode side or the negative electrode side.

A nonaqueous electrolyte secondary battery (typically, a lithium ion secondary battery) disclosed herein includes an electrode body including a positive electrode and a negative electrode, and a nonaqueous electrolyte housed in a predetermined battery case. It is a configuration.
Hereinafter, the components of the battery will be described in order.

The positive electrode of the non-aqueous electrolyte secondary battery disclosed herein includes a positive electrode current collector and a positive electrode mixture layer including at least a positive electrode active material formed on the positive electrode current collector. In this embodiment, the positive electrode active material layer includes a positive electrode active material and a conductive material for enhancing conductivity, and these are fixed on the positive electrode current collector by a binder (binder).
As the positive electrode current collector, a conductive member made of a metal having good conductivity (for example, aluminum, nickel, titanium, stainless steel, etc.) is preferably used. The shape of the current collector may be different depending on the shape of the battery to be constructed, and is not particularly limited. For example, a rod-like body, a plate-like body, a foil-like body, a net-like body, or the like can be used. In addition, in the battery provided with the winding electrode body mentioned later, a foil-like body is mainly used. The thickness of the foil-like current collector is not particularly limited, but a thickness of about 5 μm to 50 μm (more preferably 8 μm to 30 μm) can be used in consideration of the capacity density of the battery and the strength of the current collector.

As the positive electrode active material, one type or two or more types of materials conventionally used in non-aqueous electrolyte secondary batteries can be used without any particular limitation. Such a positive electrode active material typically has a general formula:
Li _{1 + δ} (Ni _a Co _b Mn _c M _d ) O ₂
(Where M is one or more selected from transition metal elements, typical metal elements and boron (B); δ satisfies the charge neutrality condition with 0 ≦ δ ≦ 0.2. A, b, c, d satisfy a + b + c + d≈1, and at least one of a, b, c is greater than 0.)
And a layered structure or a spinel structure can be appropriately selected and used. For example, a kind selected from a lithium nickel-based oxide (typically LiNiO ₂ ), a lithium cobalt-based oxide (typically LiCoO ₂ ), and a lithium manganese-based oxide (typically LiMn ₂ O ₄ ). Alternatively, two or more lithium transition metal oxides can be used. In this specification, “a + b + c + d≈1” is generally 0.9 ≦ a + b + c + d ≦ 1.2 (typically 0.9 <a + b + c + d <1.2, for example, 0.95 ≦ a + b + c + d ≦ 1.1). For example, a + b + c + d = 1.

  As shown in the above general formula, the lithium transition metal composite oxide may contain at least one other metal element M in addition to lithium (Li), nickel (Ni), cobalt (Co), and manganese (Mn) as a constituent element. It may be good (that is, d <0) or may not be included (that is, d = 0). The metal element M may be typically one or more selected from transition metal elements other than Ni, Co, and Mn, typical metal elements, and the like. More specifically, magnesium (Mg), calcium (Ca), strontium (Sr), titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo) , Iron (Fe), rhodium (Rh), palladium (Pb), platinum (Pt), copper (Cu), zinc (Zn), boron (B), aluminum (Al), gallium (Ga), indium (In) , Tin (Sn), lanthanum (La), cerium (Ce), and the like. For example, Zr, Mg, and Ca can be preferably used. The amount of M element (the value of d in the above general formula) is not particularly limited, but can be, for example, 0 ≦ d ≦ 0.02.

  Further, a, b, and c in the above general formula are not particularly limited as long as the conditions that a + b + c + d≈1 and at least one of a, b, and c is greater than 0 are satisfied. Any number of c may be the largest. In other words, the first element of Ni, Co, and Mn (the element that is contained most on the basis of the number of atoms) may be any of Ni, Co, and Mn. For example, a can be 0.1 or more (typically 0.3 or more) and less than 1 (typically 0.9 or less, such as 0.6 or less). b can be 0 or more (typically 0.1 or more, for example 0.3 or more) and 0.6 or less (typically 0.5 or less, for example 0.4 or less). c can be 0 or more (typically 0.1 or more, for example 0.3 or more) and 0.6 or less (typically 0.5 or less, for example 0.4 or less).

Among them, a lithium nickel cobalt manganese composite oxide having a layered structure in which a, b, c> 0 (including all elements of Ni, Co, and Mn) can be preferably used. In a preferred embodiment, a> b and a> c (in other words, the first element is Ni). In another preferred embodiment, a, b, and c (that is, amounts of Ni, Co, and Mn) are approximately the same. For example, LiNi _1/3 Co _1/3 Mn _1/3 O _{2 in} which a = b = c and d = 0 can be preferably used. Since such an oxide has a higher theoretical energy density than other compounds, the application of the present invention is particularly useful.

Also, for example, the general formula:
xLi [Li _1/3 Mn _2/3 ] O _2. (1-x) LiMeO ₂
(Here, Me is one or more transition metals, and x satisfies 0 <x ≦ 1.)
It is also possible to use a so-called solid solution type lithium-excess transition metal oxide represented by

Further, for example, the general formula:
LiMAO ₄
(Here, M is at least one metal element selected from the group consisting of Fe, Co, Ni and Mn, and A is an element selected from the group consisting of P, Si, S and V). )
The polyanion type compound represented by these can be used. More specifically, lithium manganese phosphate (LiMnPO ₄ ), lithium iron phosphate (LiFePO ₄ ), or the like can be used.

Such a compound may contain an oxyhydroxide (eg, NiOOH, CoOOH, FeOOH) of a metal element (eg, Ni, Co, Mn) constituting the oxide in a part thereof. Such oxyhydroxide can decompose at a temperature of about 200 ° C. to 300 ° C. to produce water. More specifically, for example, nickel oxyhydroxide can generate water by a reaction of 4NiOOH → 4NiO + 2H ₂ O + O ₂ at around 220 ° C. to 230 ° C. For this reason, in the battery provided with the oxide, when the temperature rises during an internal short circuit, the oxyhydroxide is decomposed to generate water, so that further temperature rise can be suppressed.

  Such a compound can be prepared and prepared by a conventionally known method. For example, raw material compounds (for example, a lithium source and a transition metal element source) selected according to the composition of the target positive electrode active material are mixed at a predetermined ratio, and the mixture is fired by an appropriate means. The desired compound which comprises a positive electrode active material can be prepared by grind | pulverizing, granulating, and classifying this suitably.

Such a compound is typically in the form of particles (powder). Although the properties of the particles are not particularly limited, for example, the particle size can be 20 μm or less (typically 0.1 μm to 20 μm, for example 0.5 μm to 15 μm, preferably 1 μm to 10 μm). For example, the specific surface area of the particles is 0.1 m ² / g or more (typically 0.5 m ² / g or more, for example 1 m ² / g or more), and 30 m ² / g or less (typically 20 m ² / g or less, for example, 10 m ² / g or less). When the properties of the positive electrode active material particles are in the above range, a dense and highly conductive positive electrode mixture layer can be produced. Moreover, since a moderate space | gap can be hold | maintained in this positive electrode compound material layer, a non-aqueous electrolyte can be easily immersed and battery resistance can be reduced.
In this specification, “particle size” means a particle size corresponding to 50% cumulative from the fine particle side in a volume-based particle size distribution measured by particle size distribution measurement based on a general laser diffraction / light scattering method. D ₅₀ particle diameter, also referred to as median diameter). Further, in this specification, the “specific surface area” refers to a specific surface area (BET specific surface area) measured by a BET method (preferably a BET multipoint method) using nitrogen gas.

  The proportion of the positive electrode active material in the entire positive electrode mixture layer is not particularly limited, but may be 50% by mass or more (typically 70% by mass or more and less than 100% by mass, for example, 80% by mass or more and 99% by mass or less). preferable.

As the conductive material, one kind or two or more kinds of substances conventionally used in non-aqueous electrolyte secondary batteries can be used without any particular limitation. For example, carbon black (for example, acetylene black, furnace black, ketjen black, channel black, lamp black, thermal black, etc.), coke, activated carbon, graphite (natural graphite and its modified products, artificial graphite), carbon fiber (PAN) Carbon fiber, pitch-based carbon fiber), carbon nanotubes, fullerenes, graphene, and other carbon materials. Among these, carbon black (typically acetylene black) having a relatively small particle size and a large specific surface area can be preferably used. Or metal fibers (e.g. Al fibers, stainless steel (SUS) fibers), conductive metal powder (e.g. Ag, Ni, metal powder such as Cu), metal oxides (e.g. ZnO, SnO _2, etc.), metal surface coating Synthetic fibers or the like may be used.
The proportion of the conductive material in the entire positive electrode mixture layer is not particularly limited, but is, for example, 0.1% by mass to 15% by mass (typically 1% by mass to 10% by mass, for example, 2% by mass to 7% by mass). Below).

As the binder, one kind or two or more kinds of substances conventionally used in non-aqueous electrolyte secondary batteries can be used without any particular limitation. For example, when the positive electrode mixture layer is formed using an organic solvent-based slurry (a solvent-based slurry in which the main component of the dispersion medium is an organic solvent), a polymer material that is dispersed or dissolved in the organic solvent can be preferably used. . Examples of such a polymer material include polyvinylidene fluoride (PVdF), polyvinylidene chloride (PVdC), and polyethylene oxide. Alternatively, when the positive electrode mixture layer is formed using an aqueous slurry, a polymer material that is dissolved or dispersed in water can be preferably used. Examples of water-soluble (water-soluble) polymer materials include cellulose polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropyl methyl cellulose (HPMC); polyvinyl alcohol (PVA) ), Acrylic polymers such as polymethyl methacrylate (PMMA); urethane polymers such as polyurethane; and the like. Examples of polymer materials that are dispersed in water (water-dispersible) include vinyl polymers such as polyethylene (PE) and polypropylene (PP); ethylene polymers such as polyethylene oxide (PEO) and polytetrafluoroethylene (PTFE). Polymers: Fluororesin such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA); vinyl acetate copolymer; styrene butadiene rubber (SBR), Rubbers such as acrylic acid-modified SBR resin (SBR latex); and the like.
The ratio of the binder in the entire positive electrode composite material layer is not particularly limited, but may be, for example, 0.1% by mass or more and 10% by mass or less (typically 1% by mass or more and 7% by mass or less).

  Various additives can be added to the positive electrode mixture slurry prepared here as long as the effects of the present invention are not significantly impaired. As an example of this, an inorganic compound that generates gas during overcharge (a state where the depth of charge (SOC) exceeds 100%), a material that can function as a dispersant, or the like can be given. Examples of the dispersant include polymer compounds having a hydrophobic chain and a hydrophilic group (for example, alkali salts, typically sodium salts); anionic compounds having sulfates, sulfonates, phosphates, etc .; amines, etc. Cationic compounds; etc. can be used. More specifically, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, butyral, polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, polycarboxylic acid, oxidized starch, phosphoric acid starch, etc. may be used. it can.

Although the manufacturing method of the positive electrode disclosed here is not particularly limited, for example,
(S1) A positive electrode active material, a conductive material, and a binder are mixed in an appropriate solvent to prepare a slurry-like composition (including paste-like and ink-like ones, and so on);
(S2) Applying the prepared slurry onto a positive electrode current collector to produce a positive electrode provided with a positive electrode mixture layer;
(S3) placing the positive electrode including the positive electrode mixture layer in an environment where moisture is supplied;
(S4) drying the positive electrode supplied with moisture at a temperature of 50 ° C. or higher and lower than the melting point of the binder;
Can be produced.

<S1; Preparation of positive electrode mixture slurry>
First, using a positive electrode active material, a conductive material, and a binder as described above, these are mixed in an appropriate solvent to prepare a slurry-like composition (hereinafter referred to as “positive electrode mixture slurry”). For such preparation, various conventionally known stirring / mixing devices such as a ball mill, a mixer, a disper, and a kneader can be appropriately used.

  Patent Document 2 describes a positive electrode active material (lithium composite oxide) having a moisture content of 0.2% by mass or less (2000 ppm or less) detected at 300 ° C. using the Karl Fischer method. The amount of water was set in the above range because when the slurry for forming an electrode mixture layer was prepared, if the water contained in the positive electrode active material was large, it reacted with a slurry preparation solvent (organic solvent) or the like to cause gelation. This is because there is a risk of causing it (paragraph 0039 of Patent Document 2). As described above, when the positive electrode mixture layer is formed (typically, when the slurry is prepared), moisture contained in the positive electrode active material can be a problem. Therefore, the positive electrode active material containing moisture as described in the present invention is generally not used as it is. Even if it is used, it is unlikely that the moisture is retained in the process of forming the positive electrode mixture layer (for example, steps S1 and S2). Therefore, in order to obtain the positive electrode mixture layer as disclosed herein, it is necessary to perform some special process (for example, S3) after the formation of the positive electrode mixture layer.

The solvent is not particularly limited as long as the material used for forming the slurry can be uniformly dispersed or dissolved. For example, one or more of the solvents conventionally used in the production of nonaqueous electrolyte secondary batteries are used. be able to. Such solvents are roughly classified into organic solvents and aqueous solvents. Examples of the organic solvent include amide solvents, alcohol solvents, ketone solvents, ester solvents, amine solvents, ether solvents, nitrile solvents, cyclic ether solvents, and aromatic hydrocarbon solvents. . More specifically, N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, N, N-dimethylacetamide, 2-propanol, ethanol, methanol, acetone, methyl acetate, ethyl acetate, methyl acrylate , Diethyltriamine, N, N-dimethylaminopropylamine, acetonitrile, ethylene oxide, tetrahydrofuran, dioxane, benzene, toluene, ethylbenzene, xylene dimethyl sulfoxide, dichloromethane, trichloromethane, dichloroethane, etc., typically using NMP Can do. The aqueous solvent is preferably water or a mixed solvent mainly composed of water. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. For example, it is preferable to use an aqueous solvent in which 80% by mass or more (more preferably 90% by mass or more, more preferably 95% by mass or more) of the aqueous solvent is water. A particularly preferable example is an aqueous solvent (for example, water) substantially consisting of water.
The solid content concentration (NV) at the time of slurry preparation is not particularly limited, but may be, for example, 50% by mass to 80% by mass (preferably 55% by mass to 65% by mass, more preferably 55% by mass to 60% by mass). it can.

<S2: Formation of positive electrode composite material layer>
Next, the prepared slurry is applied to the surface of the positive electrode current collector as described above to form a positive electrode mixture layer (also referred to as a positive electrode active material layer). Thereby, the positive electrode provided with the positive electrode compound material layer can be produced. For forming such a positive electrode mixture layer, for example, a conventionally known coating apparatus such as a slit coater, a die coater, a comma coater, a gravure coater, or a dip coater can be used. The application of the positive electrode mixture slurry may be performed on the front and back surfaces (both surfaces) of the positive electrode current collector, or may be performed on any one surface (single surface). But are not limited to the mass of the positive electrode mixture slurry for coating (weight per side) is a unit ^{area, 10mg / cm 2 ~50mg / cm} 2 about (typically ^{10mg / cm 2 ~40mg / cm 2} , for example, ^{15mg / cm 2 ~30mg / cm 2} ) and can be.

  The positive electrode provided with the positive electrode mixture layer is dried by an appropriate drying method to remove excess components such as a solvent. As a drying method, for example, an appropriate drying device such as a hot air device, a low-humidity air device, a vacuum device, various infrared devices, an electromagnetic induction device, a microwave device, or a drying promoting means such as a blower can be used alone or in combination. . It is preferable that the drying conditions (for example, drying temperature and required time) are appropriately determined according to the solid content ratio of the positive electrode mixture slurry, the formation thickness of the positive electrode mixture layer, and the like.

Then, typically, the thickness and density of the positive electrode mixture layer can be adjusted by appropriately pressing the positive electrode. For the press treatment, various conventionally known press methods such as a roll press method and a flat plate press method can be employed. The thickness of the positive electrode mixture layer after the press treatment (thickness per side in the structure having the positive electrode mixture layer on both surfaces of the positive electrode current collector) is, for example, 40 μm or more (typically 45 μm or more), and 100 μm or less. (Typically 80 μm or less). The density of the positive electrode mixture layer after the press treatment is, for example, 2 g / cm ³ or more (typically 2.5 g / cm ³ or more), and 4 g / cm ³ or less (typically 3.5 g). / Cm ³ or less). A positive electrode mixture layer satisfying the above range is preferable because high battery characteristics (for example, high energy density and output density) can be realized. Further, when the density of the positive electrode mixture layer is higher than that of the conventional material, there are few voids in the mixture layer. For this reason, it is difficult to dissipate heat generated by an internal short circuit or the like, and a rapid temperature rise is likely to occur. Therefore, the application of the present invention is particularly useful for such a battery.

<S3: Supply of moisture to the positive electrode>
Next, the produced positive electrode is held for a certain period in an environment where moisture is supplied. In general, if moisture is contained in the container of the non-aqueous electrolyte secondary battery, gas is generated at the time of charge / discharge or battery characteristics are deteriorated. In particular, a positive electrode having a positive electrode mixture layer having a porous structure tends to be a major cause of bringing moisture into the container. For this reason, conventionally, after the step S2, the positive electrode is handled under highly dry conditions (for example, an environment having a dew point temperature of −30 ° C. or lower), and the battery is constructed in a state where the amount of water contained in the container is minimized. Was customary. Therefore, this process is characteristic in the manufacturing method disclosed here. That is, in order to obtain the positive electrode disclosed here, it is indispensable to go through some special process such as this process.

  The method for supplying moisture to the positive electrode is not particularly limited. For example, the moisture can be supplied by holding the positive electrode in a constant temperature and humidity chamber maintained at a constant humidity for a certain period of time. According to such a method, a suitable amount of moisture can be applied to the positive electrode (more specifically, the positive electrode mixture layer) by a simple operation of holding (leaving) for a predetermined time in a predetermined humidity environment. . Or the method of hold | maintaining for a fixed time after spraying (spraying) water directly on the surface of a positive electrode compound-material layer is also employable.

  Here, the “environment in which moisture is supplied to the positive electrode” refers to an environment having a higher water concentration (having moisture) than at least the positive electrode mixture layer after the step S2. More specifically, the humidity is 10% RH or more (typically 30% RH or more, such as 40% RH or more, preferably 50% RH or more), and 100% RH or less (typically 95% RH or less, for example, 90% RH or less). In other words, the environment has a dew point temperature of −10 ° C. or higher (typically 5 ° C. or higher, eg, 10 ° C. or higher) and 25 ° C. or lower (typically 24 ° C. or lower, eg, 23 ° C. or lower). obtain. Then, by appropriately adjusting the holding time in such an environment, moisture can be included (humidified) so as to achieve a target moisture content. The suitable holding time may vary depending on the humidity to which the positive electrode is exposed, the degree of hydrophilicity of the material constituting the positive electrode mixture layer, the thickness and density of the positive electrode mixture layer, and the like. Therefore, it is preferable to determine the time required for supplying water by actually collecting a sample from the positive electrode mixture layer and measuring the water content by a conventionally known method. Alternatively, an appropriate holding time can be predicted by performing a simple preliminary experiment or the like. In addition, when supplying moisture, an operation capable of promoting such supply (for example, application of pressure by vacuuming or heating or heating) can be used in combination as appropriate.

  In a preferred embodiment disclosed herein, water is supplied to the positive electrode in an environment having a humidity of 50% RH to 100% RH (dew point temperature of 5 ° C. to 25 ° C.) for 24 hours to 240 hours (preferably 24 hours or more and 120 hours). According to such a method, a suitable amount of moisture can be imparted to the positive electrode (more specifically, the positive electrode mixture layer) by a simple operation of holding the substrate in a predetermined humidity environment for a relatively short time. For this reason, it is preferable also from a viewpoint of work efficiency or manufacturing cost.

<S4: Drying of positive electrode>
Then, the positive electrode supplied with the moisture is dried at a predetermined temperature. For such drying, the above-described method can be used as appropriate, and among these drying apparatuses, those having a heating function can be preferably used. The drying temperature is not particularly limited as long as it is not higher than the melting point of the binder, but is typically 40 ° C. or higher (eg 50 ° C. or higher, preferably 60 ° C. or higher) and 200 ° C. or lower (eg 170 ° C. or lower, preferably 140 ° C. or lower, more preferably 120 ° C. or lower). In addition, melting | fusing point of a binder can be grasped | ascertained by the differential scanning calorimetry (DSC) according to the prescription | regulation of JISK7121, for example. The time required for drying may vary depending on the thickness and density of the positive electrode mixture layer, the amount of moisture supplied to the positive electrode mixture layer in S3, and the like. For this reason, it is preferable to actually collect a sample from the positive electrode mixture layer and measure and determine the moisture content by a conventionally known method. For example, it is 2 hours or more (typically 5 hours or more, for example, 10 hours or more). Thus, it can be 240 hours or less (typically 120 hours or more, for example, 100 hours or less). In addition, operations that can accelerate drying (for example, application of pressure by evacuation or blowing of air at a wind speed of about 1 to 15 m / sec) can be used in combination as appropriate.

  In a preferred embodiment disclosed herein, the positive electrode supplied with moisture is dried in a drying furnace at 50 ° C. or higher (typically 60 ° C. or higher) and 120 ° C. or lower. According to such a method, moisture that may deteriorate the battery characteristics (in other words, the amount of dehydration from the positive electrode mixture layer detected under the heating condition of 120 ° C. for 30 minutes by the Karl Fischer method) is suitably reduced. Can do. For this reason, the amount of moisture present in the positive electrode mixture layer in the normal use temperature range can be suitably reduced. Further, according to such a method, moisture that can suppress the temperature rise at the time of an internal short circuit (in other words, the amount of dehydration from the positive electrode mixture layer detected by the Karl Fischer method under heating conditions of 300 ° C. for 30 minutes) is suitable. Can be adjusted to the range. For this reason, when the temperature inside the battery rises due to an internal short circuit or the like (for example, the inside of the battery becomes 200 ° C. to 300 ° C.), moisture is desorbed from the positive electrode active material layer, and the temperature rise can be suppressed. Therefore, according to such a method, it is possible to manufacture a battery that does not have an increase in resistance or a decrease in battery characteristics during normal use, and that has a resistance against an internal short circuit.

The positive electrode mixture layer disclosed herein has a water content of 300 ppm or less detected after 30 minutes at 120 ° C. by the Karl Fischer method (typically the water vaporization method-coulometric titration method). When the amount of dehydration from the positive electrode mixture layer is suppressed below this value, the amount of water present in the positive electrode mixture layer is reduced in the normal use temperature range of the battery (typically 100 ° C. or less). . For this reason, high battery characteristics can be exhibited without causing an increase in resistance or a decrease in battery characteristics during normal use.
In addition, the positive electrode mixture layer disclosed herein has a water content of 3000 ppm or more and 10,000 ppm or less (typical) detected after 30 minutes at 300 ° C. by the Karl Fischer method (typically, the water vaporization method-coulometric titration method). Is 3000 ppm or more and 7000 ppm or less, for example 3000 ppm or more and 5000 ppm or less. When the amount of dehydration from the positive electrode mixture layer is 3000 ppm or more compared to the conventional case, it is included in the positive electrode active material layer when the battery temperature rises due to an internal short circuit or the like (for example, a temperature of 200 ° C. to 300 ° C.). Moisture is released. And the inside of a battery is cooled with this water | moisture content, and the raise of battery temperature can be suppressed effectively. Furthermore, since heat of vaporization (heat of vaporization) is required when the moisture undergoes phase transition to become water vapor, the temperature rise can be more effectively suppressed. Therefore, even when a short circuit occurs in the battery due to a nail penetration of a metal object and a large current flows instantaneously, a rapid temperature rise can be avoided.

The Karl Fischer method is used here as the moisture detection method. However, for example, substantially the same value can be obtained also by a conventionally known method of differential thermal-thermogravimetric measurement (TG-DTA). be able to. More specifically, using a general TG-DTA apparatus, the measurement target (positive electrode mixture layer) is raised at a predetermined temperature increase rate (for example, 10 ° C./min) in an oxygen gas (O ₂ ) atmosphere. The amount of water (dehydration) can be calculated by subtracting the amount of weight reduction related to factors other than moisture (for example, decomposition of the binder) from the weight reduction (ppm (weight ratio)) at such time.

Next, the negative electrode of the nonaqueous electrolyte secondary battery disclosed herein includes a negative electrode current collector and a negative electrode mixture layer including at least a negative electrode active material formed on the negative electrode current collector. . In this embodiment, the negative electrode active material layer contains a negative electrode active material, and is fixed on the negative electrode current collector by a binder.
As the negative electrode current collector, a conductive material made of a metal having good conductivity (for example, copper, nickel, titanium, stainless steel, etc.) is preferably used. The shape of the negative electrode current collector can be the same as the shape of the positive electrode current collector.

As the negative electrode active material, one kind or two or more kinds of materials conventionally used in non-aqueous electrolyte secondary batteries can be used without any particular limitation. Specific examples include, but are not limited to, carbon materials such as natural graphite (graphite), artificial graphite, hard carbon (non-graphitizable carbon), soft carbon (graphitizable carbon), and carbon nanotubes; silicon oxide , Titanium oxide, vanadium oxide, iron oxide, cobalt oxide, nickel oxide, niobium oxide, tin oxide, lithium silicon composite oxide, lithium titanium composite oxide (LTO, for example, Li ₄ Ti ₅ O ₁₂ , LiTi ₂ O ₄ , Li ₂ Ti ₃ O ₇ ), metal oxide materials such as lithium vanadium composite oxide, lithium manganese composite oxide, lithium tin composite oxide; lithium nitride, lithium cobalt composite nitride, lithium nickel composite nitride Metal nitride materials such as tin, silicon, aluminum, zinc, lithium, etc. And the like; metal material comprising a et of metal elements from metal alloy mainly. Especially, since a high energy density is obtained, a graphite-type material (typically graphite) can be used preferably.
The proportion of the negative electrode active material in the entire negative electrode mixture layer is not particularly limited, but it is usually suitably about 50% by mass or more, and preferably 90% by mass or more and 99% by mass (eg, 95% by mass or more and 99% by mass). Mass% or less).

As the binder, an appropriate material can be selected from the polymer materials exemplified as the binder for the positive electrode mixture layer. Specifically, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE) and the like are exemplified.
The ratio of the binder in the entire negative electrode composite material layer is not particularly limited, but may be, for example, 1% by mass or more and 10% by mass or less (preferably 2% by mass or more and 5% by mass or less).
In addition, the above-mentioned various additives (for example, carboxymethyl cellulose (CMC) as a dispersant), a conductive material, and the like can be used as appropriate.

The method for producing the negative electrode disclosed herein is not particularly limited. For example, a negative electrode active material and a binder are mixed in an appropriate solvent to prepare a slurry composition; the prepared slurry is used as a negative electrode current collector. It is produced by applying on a body and producing a negative electrode provided with a negative electrode mixture layer.
More specifically, first, a negative electrode active material and a binder as described above are mixed in an appropriate solvent to prepare a slurry-like composition (hereinafter referred to as “negative electrode mixture slurry”). To do. The method for preparing the negative electrode mixture slurry may be the same as that for the positive electrode described above. Although the solid content concentration (NV) of the slurry is not particularly limited, it can be, for example, 40% by mass to 65% by mass (preferably 45% by mass to 55% by mass, more preferably 45% by mass to 50% by mass). . Next, the prepared slurry is applied to the surface of the negative electrode current collector as described above and dried to form a negative electrode mixture layer (also referred to as negative electrode active material layer). Thereby, the negative electrode provided with the negative electrode compound material layer can be produced. The method for forming the negative electrode mixture layer and the drying method may be the same as those for the positive electrode described above. It is not particularly restricted but (one surface of the mass on both sides of the negative electrode current collector in a configuration having a mixture layer) weight of the negative electrode mixture slurry is applied per unit ^{area, 5mg / cm 2 ~30mg / cm} 2 about (typically specifically the may be ^{5mg / cm 2 ~20mg / cm 2} ) degree.

Then, typically, the thickness and density of the negative electrode mixture layer can be adjusted by appropriately pressing the negative electrode. The thickness of the negative electrode mixture layer after the press treatment (thickness per side in the configuration having the negative electrode mixture layer on both sides of the negative electrode current collector) is, for example, 40 μm or more (typically 50 μm or more), and 100 μm or less. (Typically 80 μm or less). Further, the density of the negative electrode mixture layer after the press treatment is not particularly limited, but is, for example, 1.0 g / cm ³ or more (typically 1.1 g / cm ³ or more) and 2.0 g / cm ³ or less. (Typically 1.5 g / cm ³ or less). When satisfy | filling the said range, a high energy density is realizable compared with the past.

  The positive electrode and the negative electrode prepared as described above are laminated to prepare an electrode body. The shape of the electrode body is not particularly limited. For example, the electrode body layer having a predetermined width is formed on the long positive electrode current collector along the longitudinal direction of the current collector. The positive electrode and the long negative electrode in which a negative electrode mixture layer having a predetermined width is formed on the long negative electrode current collector along the longitudinal direction of the current collector are laminated and wound. Thus, a wound electrode body can be obtained. High capacity can be realized by the above configuration. In addition, the application of the present invention is particularly useful because such a battery is liable to increase in temperature due to a large current transfer during an internal short circuit.

  In the typical configuration disclosed here, a separator is interposed between the positive electrode and the negative electrode. As the separator, various porous sheets similar to those conventionally used in non-aqueous electrolyte secondary batteries can be used. For example, polyethylene (PE), polypropylene (polypropylene: PP), polyester, cellulose, Examples thereof include a porous resin sheet (film, nonwoven fabric, etc.) made of a resin such as polyamide. Such a porous resin sheet may have a single-layer structure or a plurality of structures of two or more layers. For example, a porous separator sheet having a total thickness of about 5 to 30 μm and a three-layer structure (PP / PE / PP) in which PP layers are laminated on both sides of the PE layer can be preferably used. In addition, in the secondary battery (lithium polymer battery) using a solid nonaqueous electrolyte, it is good also as a structure where the said nonaqueous electrolyte serves as a separator.

And the non-aqueous electrolyte secondary battery is constructed | assembled by accommodating the said winding electrode body in a battery case with a non-aqueous electrolyte, and sealing the opening part of a battery case.
As a battery case, the material and shape conventionally used for a nonaqueous electrolyte secondary battery can be used. Examples of the material of the case include metal materials such as aluminum and steel; resin materials such as polyphenylene sulfide resin and polyimide resin. Among them, a relatively light metal (for example, aluminum or aluminum alloy) can be preferably employed for the purpose of improving heat dissipation and increasing energy density. Further, the shape of the case (outer shape of the container) is not particularly limited. For example, the shape (cylindrical shape, coin shape, button shape), hexahedron shape (cuboid shape, cube shape), bag shape, and the like are processed and deformed. It can be a shape or the like. In addition, the case can be provided with a safety mechanism such as a current interruption mechanism (a mechanism capable of interrupting current in response to an increase in internal pressure when the battery is overcharged).

  As the nonaqueous electrolyte, one containing at least a supporting salt is used. Such a non-aqueous electrolyte typically has a composition in which a supporting salt (a lithium salt in a lithium secondary battery) is contained in a suitable non-aqueous solvent. For example, a polymer is added to a liquid non-aqueous electrolyte to form a solid. It may be in a shape (typically a so-called gel).

  As the non-aqueous solvent, one or two or more of those conventionally used in non-aqueous electrolyte secondary batteries can be used without particular limitation. Typically, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones and lactones can be mentioned. More specifically, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2-diethoxy Examples include ethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol, dimethyl ether, ethylene glycol, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, and γ-butyrolactone. It is done. For example, a nonaqueous solvent mainly composed of carbonates is preferable because a film can be suitably formed on the surface of the negative electrode active material in the initial charge treatment. Among them, EC having a high relative dielectric constant, DMC, EMC, or the like having a high oxidation potential (wide potential window) can be preferably used. For example, the nonaqueous solvent contains one or more carbonates, and the total volume of these carbonates is 60% by volume or more (more preferably 75% by volume or more, and further preferably 90% by volume) of the total volume of the nonaqueous solvent. That is, it may be substantially 100% by volume.) A non-aqueous solvent can be preferably used.

As the supporting salt, various materials known to be able to function as a supporting electrolyte for nonaqueous electrolyte secondary batteries can be appropriately employed. For example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ One or two or more selected from various lithium salts such as LiClO ₄ can be used, and among them, LiPF ₆ can be preferably used. The concentration of the supporting salt is not particularly limited, but if it is too low, the amount of charge carriers (typically lithium ions) contained in the electrolyte is insufficient, and the ionic conductivity tends to decrease. On the other hand, if it is too high, the viscosity of the electrolyte increases in a temperature range below room temperature (for example, 0 ° C. to 30 ° C.), and the internal resistance tends to increase. For this reason, it is preferable that the density | concentration of a support salt shall be 0.1 mol / L or more and 2 mol / L or less (preferably 0.8 mol / L or more and 1.5 mol / L or less), for example.

  The non-aqueous electrolyte in the technique disclosed herein can appropriately contain components other than the above-described supporting salt, gas generating agent, and non-aqueous solvent as long as the effects of the present invention are not significantly impaired. As an example of such an optional component, for example, a film forming agent such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), or fluoroethylene carbonate (FEC); gas at the time of overcharging such as biphenyl (BP) or cyclohexylbenzene (CHB) Various additives such as compounds that can be generated; dispersants such as carboxymethylcellulose (CMC); thickeners;

  In addition, the injection method of electrolyte solution, the sealing method of a battery case, etc. can be performed similarly to the conventional nonaqueous electrolyte secondary battery. Thereafter, operations such as conditioning (initial charge / discharge), degassing, and quality inspection of the battery can be appropriately performed as necessary.

  Although not intended to be particularly limited, as a schematic configuration of the nonaqueous electrolyte secondary battery according to one embodiment of the present invention, a flatly wound electrode body (winding electrode body), and a nonaqueous electrolyte Is taken as an example of a non-aqueous electrolyte secondary battery (unit cell) in a flat rectangular parallelepiped (rectangular) container, and FIGS. In the following drawings, members / parts having the same action are denoted by the same reference numerals, and redundant description may be omitted or simplified. The dimensional relationship (length, width, thickness, etc.) in each figure does not reflect the actual dimensional relationship.

  FIG. 1 is a perspective view schematically showing an outer shape of a nonaqueous electrolyte secondary battery 100 according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing a cross-sectional structure taken along line II-II of the nonaqueous electrolyte secondary battery shown in FIG. The nonaqueous electrolyte secondary battery 100 according to this embodiment includes a wound electrode body 80 and a battery case (outer container) 50. The battery case 50 includes a flat rectangular parallelepiped (square) battery case main body 52 having an open upper end, and a lid 54 that closes the opening. On the upper surface (that is, the lid body 54) of the battery case 50, a positive electrode terminal 70 electrically connected to the positive electrode sheet of the wound electrode body 80 and a negative electrode terminal 72 electrically connected to the negative electrode sheet of the electrode body are provided. It has been. The lid 54 is provided with a safety valve 55 for discharging gas generated inside the battery case to the outside of the case.

  As shown in FIG. 2, in the battery case 50, a long positive electrode sheet 10 and a long negative electrode sheet 20 are wound flatly via a long separator sheet 40. An electrode body (rolled electrode body) 80 is accommodated together with a non-aqueous electrolyte (not shown). The positive electrode sheet 10 is formed such that the positive electrode mixture layer 14 is not provided (or removed) at one end portion along the longitudinal direction, and the positive electrode current collector 12 is exposed. Similarly, the negative electrode sheet 20 to be wound is not provided with (or removed from) the negative electrode mixture layer 24 at one end portion along the longitudinal direction so that the negative electrode current collector 22 is exposed. Is formed.

  FIG. 3 is a diagram schematically showing a long sheet structure (electrode sheet) in a stage before assembling the wound electrode body 80. Of the positive electrode sheet 10 in which the positive electrode mixture layer 14 is formed along the longitudinal direction on one or both surfaces (typically both surfaces) of the long positive electrode current collector 12, and the long negative electrode current collector 22. The negative electrode sheet 20 on which the negative electrode mixture layer 24 is formed along the longitudinal direction on one side or both sides (typically both sides) is overlapped with the long separator sheet 40 and wound in the longitudinal direction. A rotating electrode body is produced. At this time, the positive electrode sheet 10 and the negative electrode sheet 20 are formed so that the positive electrode mixture layer non-formed portion of the positive electrode sheet 10 and the negative electrode composite material layer non-formed portion of the negative electrode sheet 20 protrude from both sides of the separator sheet 40 in the width direction. Are overlapped slightly in the width direction. A flat wound electrode body 80 is obtained by squashing and winding the wound electrode body from the side surface direction.

  A wound core portion 82 (that is, the positive electrode mixture layer 14 of the positive electrode sheet 10, the negative electrode mixture layer 24 of the negative electrode sheet 20, and the separator sheet 40 is densely formed in the central portion of the wound electrode body 80 in the winding axis direction. Laminated portions) are formed. Moreover, the electrode composite material layer non-formation part of the positive electrode sheet 10 and the negative electrode sheet 20 protrudes outward from the winding core part 82 at both ends in the winding axis direction of the wound electrode body 80, respectively. The protruding portion on the positive electrode side (that is, the portion where the positive electrode mixture layer 14 is not formed) and the protruding portion on the negative electrode side (that is, the portion where the negative electrode mixture layer 24 is not formed) are respectively provided with a positive electrode current collector plate and a negative electrode current collector plate. Attached and electrically connected to the positive terminal 70 and the negative terminal 72 described above.

  FIG. 4 shows an example of a battery pack 200 in which nonaqueous electrolyte secondary batteries (unit cells) 100 are connected in series and / or in parallel. The battery (single cell) disclosed herein is characterized by improved reliability (resistance during internal short-circuiting) while maintaining excellent battery characteristics as compared with conventional batteries. Therefore, an assembled battery formed by connecting a plurality of these single cells to each other (typically in series) can exhibit even higher battery characteristics. In the form shown in FIG. 4, the assembled battery 200 includes a plurality of (typically 10 or more, preferably about 10 to 30, for example, 20) non-aqueous electrolyte secondary batteries (unit cells) 100. The wide surfaces of the battery case 50 are arranged in the facing direction (stacking direction) while being reversed one by one so that the positive electrode terminals 70 and the negative electrode terminals 72 are alternately arranged. A cooling plate 110 having a predetermined shape is sandwiched between the arranged unit cells 100. The cooling plate 110 functions as a heat dissipating member for efficiently dissipating heat generated in each unit cell 100 during use, and preferably a cooling fluid (typically between the unit cells 100). Air) (for example, a shape in which a plurality of parallel grooves extending vertically from one side of the rectangular cooling plate to the opposite side are provided on the surface). A cooling plate made of metal having good thermal conductivity or lightweight and hard polypropylene or other synthetic resin is suitable.

  A pair of end plates (restraint plates) 120 are arranged at both ends of the unit cells 100 and the cooling plate 110 arranged as described above. One or a plurality of sheet-like spacer members 150 as length adjusting means may be sandwiched between the cooling plate 110 and the end plate 120. The unit cell 100, the cooling plate 110, and the spacer member 150 arranged in the above manner are applied with a predetermined restraining pressure in the stacking direction by a fastening restraint band 130 attached so as to bridge between both end plates. It is restrained. More specifically, by tightening and fixing the end portion of the restraining band 130 to the end plate 120 with screws 155, the unit cells and the like are restrained so that a predetermined restraining pressure is applied in the arrangement direction. Thereby, restraint pressure is also applied to the wound electrode body 80 housed in the battery case 50 of each unit cell 100. Then, between the adjacent unit cells 100, one positive terminal 70 and the other negative terminal 72 are electrically connected by a connecting member (bus bar) 140. Thus, the assembled battery 200 of the desired voltage is constructed | assembled by connecting each cell 100 in series.

As a preferable application target of the technology disclosed herein, there is a relatively high capacity type non-aqueous electrolyte secondary battery (typically a lithium secondary battery) having a battery capacity of 20 Ah or more. For example, a non-aqueous electrolyte secondary battery having a battery capacity of 20 Ah or more (typically 25 Ah or more, for example, 30 Ah or more) and 100 Ah or less is exemplified. Alternatively, another preferable application object is a non-aqueous electrolyte secondary battery (typically a lithium secondary battery) having an energy density of 230 kWh / m ³ or more. For example, a nonaqueous electrolyte secondary battery having an energy density of 230 kWh / m ³ or more (typically 250 kWh / m ³ or more, for example, 300 kWh / m ³ or more) and 500 kWh / m ³ or less is exemplified. In such a high-capacity type non-aqueous electrolyte secondary battery, a large current instantaneously flows through the short-circuited portion, and a problem (for example, a rapid temperature increase) easily occurs due to the movement of the current. For this reason, application of the present invention is particularly useful.

  As described above, the battery disclosed herein has high resistance at the time of an internal short circuit and exhibits good battery characteristics (for example, battery capacity). Therefore, the battery disclosed herein is preferably used in applications that require high battery characteristics and reliability. obtain. Examples of such applications include power supplies for motors (electric motors) mounted on vehicles such as automobiles. Therefore, according to the present invention, for example, as schematically shown in FIG. 5, there is provided a vehicle 1 provided with a battery pack 200 formed by connecting a plurality of such nonaqueous electrolyte secondary batteries (particularly lithium secondary batteries) as a power source. The type of the vehicle 1 is not particularly limited, and examples thereof include plug-in hybrid vehicles (PHV), hybrid vehicles (HV), electric vehicles (EV), electric trucks, motorbikes, electric assist bicycles, electric wheelchairs, electric railways and the like. Is done. Here, the assembled battery 200 in which a plurality of unit cells 100 are connected in series and / or in parallel is used, but it is of course possible to use the unit cell 100 alone.

  Hereinafter, some examples relating to the present invention will be described. However, the present invention is not intended to be limited to the specific examples.

<Preparation of positive electrode sheet>
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM) as a positive electrode active material powder, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder, these materials The mass ratio of NCM: AB: PVdF = 91: 6: 3 is charged into a kneader and the viscosity is adjusted with N-methylpyrrolidone (NMP) so that the solid content concentration (NV) is 50% by mass. While mixing, a positive electrode active material slurry was prepared. By applying this slurry in a strip shape to a long sheet-like aluminum foil (positive electrode current collector) having a thickness of 15 μm at a basis weight (both sides) of 27.0 mg / cm ² and drying (drying temperature 80 ° C., 5 minutes) A total of four positive electrode sheets in which a positive electrode mixture layer was provided on both surfaces of the positive electrode current collector were produced. And the produced positive electrode sheet was roll-pressed and it adjusted so that the density of a positive electrode compound-material layer might be 2.6-3.0 g / cm < ³ >. The thickness of the positive electrode mixture layer after the rolling press was about 50 μm per side (100 μm on both sides).
Each of the prepared positive electrode sheets was held for a certain period in the environment shown in Table 1, and then Example 1 and Example 3 were dried under the conditions shown in Table 1.

[Measurement of water content of positive electrode mixture layer]
After the positive electrode sheets (Examples 1 to 4) were treated under the conditions shown in Table 1, a part of the positive electrode mixture layer was scraped off from the positive electrode sheet, and a general Karl Fischer method (moisture vaporization method-coulometric titration method) was used. The amount of water contained in the sample was measured. The measurement conditions are as follows. The results are shown in the corresponding column of Table 2.
Measurement conditions: (1) Heating conditions: 30 minutes at 120 ° C
(2) Heating conditions: 30 minutes at 300 ° C

  According to the results of the moisture content measurement shown in Table 2, the humidity in the storage environment of the positive electrode was as high as 50% RH (that is, in the environment where water can be supplied to the positive electrode mixture layer). Temperature: The amount of water detected at 300 ° C. was relatively large and was 3000 ppm or more. In Example 1 where drying was performed after storage in an environment where the humidity was 50% RH and Examples 3 and 4 where the humidity in the storage environment was as low as about 1%, the amount of water detected at a heating temperature of 120 ° C. It was relatively low and was 300 ppm or less (typically 250 ppm or less, for example, 100 ppm or more and 300 ppm or less).

<Preparation of negative electrode sheet>
Next, amorphous coated graphite (C, particle size 25 μm, specific surface area 2.5 m ² / g) as the negative electrode active material, styrene butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the thickener In a kneader so that the mass ratio of these materials is C: SBR: CMC = 98: 1: 1, and the viscosity is adjusted with ion-exchanged water so that the solid content concentration (NV) is 45 mass%. While kneading, a negative electrode active material slurry was prepared. The slurry was applied to a long sheet-like long copper foil (negative electrode current collector) having a thickness of 10 μm in a band shape with a basis weight (both sides) of 14.7 mg / cm ² and dried (drying temperature 80 ° C., 5 minutes). As a result, a total of four negative electrode sheets in which the negative electrode mixture layers were provided on both surfaces of the negative electrode current collector were produced. And the produced negative electrode sheet was rolling-pressed and adjusted so that the density of a negative electrode compound-material layer might be 1.1-1.3 g / cm < ³ >. Note that the thickness of the negative electrode mixture layer after the rolling press was approximately 60 μm per side (120 μm on both sides).

<Construction of non-aqueous electrolyte secondary battery>
The produced positive electrode sheet and negative electrode sheet are divided into two separator sheets (here, a three-layer porous sheet (total thickness 20 μm) in which a polypropylene (PP) layer is laminated on both sides of a polyethylene (PE) layer). And wound on the opposite side, and formed into a flat shape to produce a wound electrode body. A positive electrode terminal is provided at the positive electrode current collector end of the electrode body (uncoated portion of the positive electrode mixture layer), and a negative electrode terminal is provided at the end of the negative electrode current collector (uncoated portion of the negative electrode mixture layer). Joined by welding. Such an electrode body is accommodated in a rectangular battery case, and a non-aqueous electrolyte (here, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are EC: DMC: EMC = 3: 4: 3). In a mixed solvent containing a volume ratio of 1), LiPF ₆ as a supporting salt dissolved at a concentration of 1 mol / L was used. Then, the battery case was sealed (sealed) to construct a rectangular nonaqueous electrolyte secondary battery (Examples 1 to 4).

<Battery characteristics measurement>
For the secondary batteries of Examples 1 to 4 constructed as described above, an appropriate conditioning process (here, until the voltage between the positive and negative terminals reaches 4.1 V at a constant current of 1 C under a temperature environment of 25 ° C.) After charging, an operation of resting for 5 minutes and performing constant voltage charging for 1.5 hours was performed. The battery was discharged at a constant current of 0.3 C until the voltage between the positive and negative terminals reached 3 V, and the initial capacity (mAh / g) was confirmed. The result is shown in the column of “initial capacity” in FIG. In the column of “Initial capacity” in Table 2, “◯” represents that the target battery capacity was obtained, and “×” represents that the target battery capacity was not obtained. Yes.
Next, the input / output characteristics (IV resistance) of the battery were evaluated. Specifically, in a temperature environment of 25 ° C., the batteries of Examples 1 to 4 are first charged at a constant current of 1 C to a SOC of 20%, and then the SOC is adjusted by performing a constant voltage charge for 2 hours. did. Then, this battery was discharged at a constant current of 5 C, and the IV resistance was obtained from the voltage drop after 10 seconds. The results are shown in the column of “input / output characteristics” in FIG. In the column of “input / output characteristics” in Table 2, “◯” represents that the battery resistance was lower than the target, and “×” represents that it was higher than the target battery resistance. Yes. In addition, the SOC is 100% of the state of charge in which a voltage (4.1 V here) can be obtained in the reversibly chargeable / dischargeable voltage range, and a voltage (3.0 V here) which is the lower limit. This shows the state of charge when the state of charge obtained is 0%.

  As apparent from FIGS. 6 and 7 and Table 2, the battery of Example 2 did not reach the target battery characteristics. As a cause of this, it is conceivable that moisture present in the battery (typically in the positive electrode mixture layer) reacts with the electrolyte or the like to form lithium carbonate, thereby forming a high-resistance coating on the surface of the positive electrode mixture layer. In contrast, the batteries of Examples 1, 3, and 4 satisfied the target battery characteristics. Therefore, when the moisture content detected at a heating temperature of 120 ° C. is relatively low, ie, 300 ppm or less (typically 250 ppm or less), that is, in the normal use temperature range (typically 100 ° C. or less) of the battery, It was shown that when the amount of moisture present in the layer is reduced, high battery characteristics can be exhibited without causing an increase in resistance or a decrease in battery characteristics.

<Nail penetration test>
For the non-aqueous electrolyte secondary batteries of Examples 1 to 4, first, the above-described theoretical capacity is charged at a current value (1/5 C) that can be supplied in 5 hours to a charging upper limit voltage (4.2 V), and further, Constant voltage charging was performed until 1/10 of the initial current value. And the nail penetration test was done with respect to the non-aqueous electrolyte secondary battery after the said charge. In the nail penetration test, an iron nail having a diameter of 3 mm was penetrated at a speed of 10 mm / sec near the center of the non-aqueous electrolyte secondary battery after charging (portion indicated by x in FIG. 1) at a test temperature of 25 ° C. . Further, two thermocouples were attached to the outer surface of the battery case, and the battery temperature (maximum temperature reached) at the time of each test was measured.

  The results are shown in FIGS. 8 shows the results of Example 1, FIG. 9 shows the results of Example 2, FIG. 10 shows the results of Example 3, and FIG. 11 shows the results of Example 4. FIG. 12 shows the relationship between the amount of moisture (ppm) detected at 300 ° C. and the maximum temperature reached (° C.) during the nail penetration test. In addition, the arrow shown in FIGS. 8-11 represents the point which penetrated the nail. Furthermore, the presence or absence of the effect of the present invention was examined based on the change in battery temperature, the maximum temperature reached, and the like measured during the test. The results are shown in the “nail penetration test” column of Table 2. In addition, in the column of “nail penetration test-judgment” in Table 2, “◯” indicates that an effect was recognized (typically, the maximum temperature reached was less than 400 ° C.), and “×” Indicates that the effect was not recognized (typically, the maximum temperature reached 400 ° C. or higher).

As is clear from FIG. 12 and Table 2, in the batteries of Examples 3 and 4 that were not exposed to a high humidity environment after the formation of the positive electrode mixture layer (that is, water was not supplied to the positive electrode mixture layer), The maximum temperature reached was as high as 400 ° C or higher. On the other hand, in the batteries of Examples 1 and 2, the maximum temperature was suppressed to 400 ° C. or lower. This is because moisture contained in the positive electrode active material layer is desorbed when the temperature inside the battery rises (for example, 200 ° C. to 300 ° C.), and the rise in battery temperature is suitably suppressed by the moisture. It is thought that it was done. Therefore, it was shown that when the amount of water detected at the heating temperature of 300 ° C. is 3000 ppm or more, which is relatively large compared to the conventional case, the temperature increase during the internal short circuit can be suppressed.
Thus, according to the present invention, it is possible to provide a highly reliable non-aqueous electrolyte secondary battery that can suppress an increase in temperature during an internal short circuit while maintaining excellent battery characteristics.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

1 Automobile (vehicle)
10 Positive electrode sheet (positive electrode)
12 Positive electrode current collector 14 Positive electrode mixture layer 20 Negative electrode sheet (negative electrode)
22 Negative electrode current collector 24 Negative electrode mixture layer 40 Separator sheet (separator)
50 Battery Case 52 Battery Case Body 54 Lid 55 Safety Valve 70 Positive Terminal 72 Negative Electrode 80 Winding Electrode Body 82 Winding Core Part 100 Nonaqueous Electrolyte Secondary Battery 110 Cooling Plate 120 End Plate 130 Restraint Band 140 Connection Member 150 Spacer Member 155 screw 200 battery pack

Claims (12)

An electrode body including a positive electrode and a negative electrode, and a non-aqueous electrolyte are non-aqueous electrolyte secondary batteries housed in a predetermined battery case,
The positive electrode includes a positive electrode current collector, and a positive electrode mixture layer including a positive electrode active material formed on the current collector,
The positive electrode mixture layer is formed by a Karl Fischer method.
The amount of water detected after 30 minutes at 120 ° C. is 300 ppm or less,
A non-aqueous electrolyte secondary battery, wherein a water content detected after 30 minutes at 300 ° C. is 3000 ppm or more and 10,000 ppm or less. The positive electrode active material has the general formula (1):
Li _{1 + δ} (Ni _a Co _b Mn _c M _d ) O ₂ (1)
(Here, M is one or more selected from a transition metal element, a typical metal element, and boron (B), and δ satisfies the charge neutrality condition with 0 ≦ δ ≦ 0.2. (A, b, c, d satisfy 0.9 ≦ a + b + c + d ≦ 1.2, and at least one of a, b, c is greater than 0.)
The nonaqueous electrolyte secondary battery of Claim 1 containing the lithium transition metal oxide represented by these. The electrode body is
On a long positive electrode current collector, a positive electrode mixture layer having a predetermined width is formed along the longitudinal direction of the current collector, and
On the long negative electrode current collector, a negative electrode mixture layer having a predetermined width is formed along the longitudinal direction of the current collector.
The nonaqueous electrolyte secondary according to claim 1, wherein the secondary electrode is a wound electrode body that is laminated in a state where the elongated positive electrode and the elongated negative electrode face each other and wound in the longitudinal direction. battery. 4. The nonaqueous electrolyte secondary battery according to claim 1, wherein a density of the positive electrode mixture layer is 2.5 g / cm ³ or more and 4 g / cm ³ or less. A method for manufacturing a non-aqueous electrolyte secondary battery in which an electrode body including a positive electrode and a negative electrode and a non-aqueous electrolyte are accommodated in a predetermined battery case, comprising:
Preparing a composition for forming a positive electrode mixture layer containing at least a positive electrode active material and a binder;
Applying the composition for forming a positive electrode mixture layer on a positive electrode current collector to produce a positive electrode provided with a positive electrode mixture layer;
Placing the positive electrode in an environment where moisture is supplied;
Drying the positive electrode supplied with moisture at a temperature of 50 ° C. or higher and lower than the melting point of the binder;
Constructing a non-aqueous electrolyte secondary battery using the dried positive electrode;
A method for producing a non-aqueous electrolyte secondary battery.   The production method according to claim 5, wherein the supply of moisture to the positive electrode is performed by maintaining the environment in a relative humidity of 50% or more and 100% or less for 24 hours or more and 240 hours or less.   The manufacturing method according to claim 5 or 6, wherein drying of the positive electrode supplied with moisture is performed in a drying furnace of 60 ° C or higher and 120 ° C or lower. As the positive electrode active material, the general formula (1):
Li _{1 + δ} (Ni _a Co _b Mn _c M _d ) O ₂ (1)
(Here, M is one or more selected from a transition metal element, a typical metal element, and boron (B), and δ satisfies the charge neutrality condition with 0 ≦ δ ≦ 0.2. (A, b, c, d satisfy 0.9 ≦ a + b + c + d ≦ 1.2, and at least one of a, b, c is greater than 0.)
The manufacturing method as described in any one of Claim 5 to 7 using the lithium transition metal oxide represented by these. The nonaqueous battery capacity of electrolyte secondary battery is not less than 20 Ah, nonaqueous electrolyte secondary batteries according to any one of claims 1 to 4. The nonaqueous energy density of electrolyte secondary battery is 230kWh / m ³ or more, the non-aqueous electrolyte secondary batteries according to any one of claims 1 4, 9. Battery pack that combines a plurality of nonaqueous electrolyte secondary batteries according to any one of claims 1 4, 9, 10. A vehicle comprising the assembled battery according to claim 11 as a driving power source.