JP5526368B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery, in particular, using a specific positive electrode active material, having an initial charge capacity per unit area of positive electrode of 40 mAh / 10 cm ² or less, and containing titanium oxide on the surface of the negative electrode An insulating coating layer is formed, and even when charging / discharging at a current of 60 A or more, an increase in IV resistance value at a low charging depth is suppressed, and load characteristics and output regeneration characteristics are excellent. The present invention relates to a non-aqueous electrolyte secondary battery optimal for an electric vehicle (EV), a hybrid electric vehicle (HEV) and the like.

  Emission regulations such as carbon dioxide gas have been strengthened against the backdrop of an increasing environmental protection movement, and the automobile industry is actively developing EVs and HEVs as well as automobiles that use fossil fuels such as gasoline, diesel oil and natural gas. Has been done. In addition, the rapid rise in fossil fuel prices in recent years is a tailwind for the development of these EVs and HEVs. In the field of batteries for EVs and HEVs, nonaqueous electrolyte secondary batteries represented by lithium ion secondary batteries having a higher energy density than other batteries have attracted attention. The share is showing a big growth.

  Here, an example of a specific configuration of the nonaqueous electrolyte secondary battery 10 used for such EV or HEV will be described with reference to FIGS. FIG. 4 is a perspective view of a cylindrical nonaqueous electrolyte secondary battery. FIG. 5 is an exploded perspective view of a wound electrode body in a cylindrical nonaqueous electrolyte secondary battery. FIG. 6 is a perspective view of a current collector plate used in a cylindrical nonaqueous electrolyte secondary battery. FIG. 7 is a partially broken perspective view showing a state before the current collector plate is pressed against the wound electrode body. Further, FIG. 8 is a partially broken front view showing a state in which a current collector plate is pressed against the wound electrode body and a laser beam is irradiated.

  As shown in FIG. 4, the non-aqueous electrolyte secondary battery 10 has a cylindrical battery outer can 13 formed by welding and fixing lids 12 to both ends of the cylindrical body 11 as shown in FIG. A wound electrode body 20 is accommodated. A pair of positive and negative electrode terminal mechanisms 14 is attached to the lid 12. The wound electrode body 20 and the electrode terminal mechanism 14 are connected within the battery outer can 13, and the power generated by the wound electrode body 20 can be taken out from the pair of electrode terminal mechanisms 14. Yes. Each lid 12 is provided with a pressure open / close gas discharge valve 15.

As shown in FIG. 5, the wound electrode body 20 is configured by interposing a strip-shaped separator 23 between a strip-shaped positive electrode 21 and a negative electrode 22 and winding them in a spiral shape. The positive electrode 21 has a positive electrode active material mixture layer 21 ₂ that are formed by coating a positive electrode mixture slurry on both surfaces of the belt-shaped core member 21 ₁ made of an aluminum foil, the negative electrode 22 is strip-shaped core 22 ₁ made of copper foil and a negative electrode active material mixture layer 22 ₂ that are formed by applying a negative electrode mixture slurry containing a carbon material on both sides. The separator 23 is impregnated with a non-aqueous electrolyte. In order to secure the output characteristics of the battery, the electrode plate is thin and is designed so that the opposing area between the positive electrode and the negative electrode is large.

The cathode 21 is parallel to uncoated portions and the coating portion of the positive electrode active material mixture layer 21 ₂ is formed, the uncoated portion constitutes a positive electrode substrate edge portion 21 ₃ protruding from an end of the separator 23 ing. Similarly, the negative electrode 22 are parallel to uncoated portion forming a coating of the active material mixture layer 22 _2, the uncoated portion of the negative electrode core body end projecting from the end edge 22 ₃ of the separator 23 It is composed.

Each collector plate 30 at both end portions of the wound electrode body 20 is installed, these collector plates 30 laser welding or electron beam welding to the positive electrode substrate edge portion 21 ₃ and the negative electrode substrate edge portion 22 ₃ Is attached by. The tip of the lead part 31 protruding from the end of the current collector plate 30 is connected to the electrode terminal mechanism 14.

As shown in FIGS. 5 and 6, the current collecting plate 30 includes a circular flat plate-like main body 32, and a plurality of arc-shaped convex portions 33 extending radially are integrally formed on the flat plate-like main body 32. And protrudes toward the wound electrode body 20. The current collector plate 30, as shown by an arrow P in FIG. 7, after pressing in the direction of the positive electrode substrate edge portion 21 ₃ or the negative electrode substrate edge portion 22 _3, as indicated by the thick arrows in FIG. 8 In addition, welding is performed by irradiating a laser beam (or electron beam). Longitudinal While direction is moved is performed by sequentially spot welding, bottom and the positive electrode substrate edge portion 21 ₃ or the negative electrode substrate edge of the arc-shaped convex portion 33 of the welding laser beam arcuate protrusion 33 the part 22 ₃ is welded at welds 34. In this way, the positive electrode 21 and the negative electrode 22 are electrically connected to the separate current collecting plates 30 for current collection.

And as a positive electrode active material in such a non-aqueous electrolyte secondary battery, Li _x MO ₂ capable of reversibly occluding and releasing lithium ions (where M is at least one of Co, Ni, and Mn) A lithium transition metal composite oxide represented by: LiCoO ₂ , LiNiO ₂ , LiNi _y Co _1-y O ₂ (y = 0.01 to 0.99), LiMnO ₂ , LiMn ₂ O ₄ , _{LiCo x Mn y Ni z O 2} (x + y + z = 1), or the like LiFePO ₄ is used as a mixture of one kind alone or in combination.

  In addition, as the negative electrode active material, natural graphite, artificial graphite, carbon black, coke, glassy carbon, carbon fiber, or a mixture of one or more of these fired bodies, such as those mainly composed of carbon, is used. ing.

  By the way, as described above, high energy density non-aqueous electrolyte secondary batteries that are lightweight and have high output are being used as batteries for EVs and HEVs. It is also required to achieve advanced driving ability. In order to enhance the driving ability, not only does the battery capacity increase to enable long-distance driving of the car, but also the battery output is increased to significantly affect the acceleration performance and climbing performance of the car. That is, it is necessary to improve the rapid discharge characteristics.

  In addition to this, in order to suppress the energy consumption of the entire EV or HEV, the battery can be quickly recovered using the electric brake at the time of deceleration, that is, in order to improve the regenerative characteristics, the battery It is also necessary to improve the rapid charging characteristics. As is apparent from the driving pattern of the 10-15 mode running test method shown in FIG. 9 for example, this is because there are many deceleration zones as well as acceleration zones when driving an actual vehicle. This is because how the electric energy can be recovered in the case leads to the suppression of the energy consumption of the entire EV or HEV.

  When such rapid discharge or rapid charge is performed, a large current flows through the battery, so that the influence of the internal resistance of the battery greatly appears in the battery characteristics. In particular, in batteries for EV or HEV, in order to obtain sufficient output characteristics and output regeneration characteristics, the internal resistance is required to be low and constant even when the state of charge changes.

JP 2008-53206 A JP 2008-41465 A

By the way, as a positive electrode active material in a nonaqueous electrolyte secondary battery, as described above, LiCoO ₂ , LiNiO ₂ , LiNi _y Co _1-y O ₂ (y = 0.01 to 0.99), LiMnO ₂ , LiMn ₂ O ₄ , LiCo _x Mn _y Ni _z O ₂ (x + y + z = 1), LiFePO ₄ or the like is used singly or in combination. Among these, LiCoO ₂ , LiMn ₂ O _{4 and the} like have high electrode potential and high efficiency, so a battery with high voltage and high energy density can be obtained, and output characteristics are excellent, but output regeneration characteristics are inferior. have.

Therefore, as a positive electrode active material in a nonaqueous electrolyte secondary battery as a battery for EV or HEV, Li _{1 + a} Ni _x Co _y Mn having excellent output regeneration characteristics in consideration of the characteristics of the positive electrode active material as described above. _{z M b O 2 (M =} Al, Ti, Zr, Nb, B, Mg, at least one element selected from Mo, 0 ≦ a ≦ 0.3,0.1 ≦ x ≦ 1,0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.9, 0 ≦ b ≦ 0.01, a + b + x + y + z = 1) are preferably used. However, such a positive electrode active material has low initial charge / discharge efficiency, and the discharge curve of a non-aqueous electrolyte secondary battery using such a positive electrode active material is the initial charge / discharge such as LiCoO ₂ , LiMn ₂ O _4, etc. Compared to the case of a non-aqueous electrolyte secondary battery using a highly efficient positive electrode active material, the internal resistance at the end of discharge gradually increases, so that the output voltage of the battery is relatively gently lowered. This is considered to be because when lithium ions released from the positive electrode during charging return to the positive electrode during discharge, if lithium ions return to the positive electrode to some extent, it becomes difficult for more lithium ions to return to the positive electrode.

Further, as the negative electrode active material, a carbon material such as graphite having a high initial charge / discharge efficiency is generally used. A negative electrode using such a carbon material as a negative electrode active material releases lithium ions taken into the negative electrode during charging at the time of discharging, but some lithium ions cannot be released from the negative electrode during discharging and remain in the negative electrode. It becomes irreversible capacity. And the capacity | capacitance of a negative electrode becomes large, and this irreversible capacity | capacitance becomes large. Using such a carbon material as a negative electrode active material, a low initial charge-discharge efficiency as described above _{Li 1 + a Ni x Co y} Mn z M b O 2 (M = Al, Ti, Zr, Nb, B, Mg, Mo At least one element selected from: 0 ≦ a ≦ 0.3, 0.1 ≦ x ≦ 1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.9, 0 ≦ b ≦ 0.01, a + b + x + y + z = 1) When the lithium transition metal composite oxide represented by 1) is used as the positive electrode active material, the carbon material as the negative electrode active material has high charge / discharge efficiency (the negative electrode has a small irreversible capacity), Because the charge / discharge efficiency of the positive electrode is low, at the end of discharge, the negative electrode can still release lithium ions, but the positive electrode is difficult to take in lithium ions, and the internal resistance of the positive electrode increases. . At the end of the discharge, since the positive electrode discharge is progressing, the charge depth of the positive electrode is in a low region. Thus, when a region where the charge depth of the positive electrode is low is used during discharge, the IV resistance of the battery is high. Problem arises.
For this reason, by increasing the capacity of the negative electrode, the irreversible capacity of the negative electrode with respect to the positive electrode capacity is increased, and the amount of lithium ions that can return from the negative electrode to the positive electrode during discharge is reduced, thereby increasing the internal resistance of the positive electrode. It is conceivable that the increase in the internal resistance of the positive electrode can be mitigated by making it impossible to discharge the positive electrode up to the charging depth. However, in this case, since the negative electrode active material mixture layer becomes too thick, there is a problem that output characteristics are deteriorated.

  Patent Document 1 discloses that a non-aqueous electrolyte secondary battery having excellent cycle characteristics and storage characteristics at high temperatures can be obtained by providing a coating layer containing rutile-type titania on the negative electrode surface. Yes. However, Patent Document 1 does not describe the initial charge capacity per unit area of the positive electrode, and does not suggest an increase in IV resistance value at a low charge depth.

Patent Document 2 discloses that a non-aqueous electrolyte secondary battery excellent in high input / output density and cycle characteristics is obtained by improving the ion diffusibility by containing TiO ₂ in the negative electrode. Has been. However, Patent Document 2 does not describe the formation of a coating layer containing titanium oxide on the negative electrode surface. Further, there is no description of the initial charge capacity per unit area in the positive electrode, and there is no description that suggests an increase in IV resistance value at a low charge depth.

The inventor has made various studies to suppress an increase in IV resistance value at a low charging depth in the nonaqueous electrolyte secondary battery as described above, and as a result, Li is capable of inserting and extracting lithium ions as a positive electrode active material. _{1 + a} Ni _x Co _y Mn _z M _b O ₂ (M = at least one element selected from Al, Ti, Zr, Nb, B, Mg, Mo, 0 ≦ a ≦ 0.3, 0.1 ≦ x ≦ 1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.9, 0 ≦ b ≦ 0.01, a + b + x + y + z = 1) The initial charge capacity per area is 40 mAh / 10 cm ² or less, and by forming an insulating coating layer containing titanium oxide on the surface of the negative electrode, it is not necessary to use a region where the internal resistance at the end of discharge of the positive electrode is high I found out.

  According to the present invention, even when charging / discharging with a large current, it is possible to maintain the IV resistance value at a low constant value within a charge depth region where charging / discharging is possible, and the electric characteristics are excellent in load characteristics and output regeneration characteristics. A non-aqueous electrolyte secondary battery optimal for automobiles (EV), hybrid electric vehicles (HEV), and the like can be obtained.

It is a figure which shows the relationship between the charging depth in the nonaqueous electrolyte secondary battery of Example 1 and Comparative Example 1, and the measured value of IV resistance measured by the electric current value to 10A-60A. It is a figure which shows the relationship between the charging depth in the nonaqueous electrolyte secondary battery of Example 1 and Comparative Example 1, and the measured value of IV resistance measured with the electric current value to 5A-20A. The initial charge capacity per unit area of the positive electrode in the nonaqueous electrolyte secondary batteries of Example 1, Example 2, and Comparative Examples 1 to 4, and the IV resistance value at a charge depth of 10% measured in the range of 10 to 60A It is a figure which shows the relationship with IV resistance value of the charge depth 50% measured in the range of / 10-60A. It is a perspective view of a cylindrical nonaqueous electrolyte secondary battery, It is a disassembled perspective view of the winding electrode body in a cylindrical nonaqueous electrolyte secondary battery. It is a perspective view of a current collecting plate used in a cylindrical nonaqueous electrolyte secondary battery. It is a partially broken perspective view which shows the state before pressing a current collecting plate to a winding electrode body. It is a partially broken front view which shows the state which presses a current collector plate to a winding electrode body, and irradiates a laser beam. It is a figure which shows the driving | running pattern of a 10-15 mode running test method.

In order to achieve the above object, the non-aqueous electrolyte secondary battery of the present invention is Li _{1 + a} Ni _x Co _y Mn _z M _b O ₂ (M = Al, Ti, capable of occluding and releasing lithium ions as a positive electrode active material. At least one element selected from Zr, Nb, B, Mg, Mo, 0 ≦ a ≦ 0.3, 0.1 ≦ x ≦ 1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.9, 0 ≦ b ≦ 0.01, a + b + x + y + z = 1), a positive electrode including a lithium transition metal composite oxide, a negative electrode including a negative electrode active material, a non-aqueous electrolyte, and the positive and negative electrodes. In the non-aqueous electrolyte secondary battery having a separator, the initial charge capacity per unit area of the positive electrode is 40 mAh / 10 cm ² or less, and an insulating coating layer containing titanium oxide is formed on the surface of the negative electrode. It is characterized by.

In the nonaqueous electrolyte secondary battery of the present invention, Li _{1 + a} Ni _x Co _y Mn _z M _b O ₂ (M = Al, Ti, Zr, Nb, B, Mg, which can occlude / release lithium ions as a positive electrode active material) At least one element selected from Mo, 0 ≦ a ≦ 0.3, 0.1 ≦ x ≦ 1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.9, 0 ≦ b ≦ 0.01 , A + b + x + y + z = 1) is used.
Since such a positive electrode active material is excellent in output regeneration characteristics, a nonaqueous electrolyte secondary battery having optimal characteristics as a battery for EV or HEV can be obtained. However, as described above, such a positive electrode active material has low initial charge and discharge efficiency, and the discharge curve of a nonaqueous electrolyte secondary battery using such a positive electrode active material is LiCoO ₂ , LiMn ₂ O _4, or the like. Compared to the case of a non-aqueous electrolyte secondary battery using a positive electrode active material with high initial charge / discharge efficiency, the internal resistance at the end of discharge gradually increases, so the output voltage of the battery decreases relatively gently. There is.

In the nonaqueous electrolyte secondary battery of the present invention, the initial charge capacity per unit area of the positive electrode is 40 mAh / 10 cm ² or less, and an insulating coating layer containing titanium oxide is formed on the surface of the negative electrode.

According to the above configuration, the presence of the insulating coating layer containing titanium oxide on the surface of the negative electrode causes the titanium oxide to slightly react with lithium ions during charging. Since the reaction product of titanium oxide and lithium ions does not participate in the discharge reaction, an irreversible capacity is generated at the negative electrode due to the reaction of titanium oxide. This titanium oxide and the reaction product of titanium oxide and lithium ions are insulative. At the time of initial charging, titanium oxide receives electrons and reacts with lithium ions only in the portion located on the negative electrode surface in contact with the active material layer having electron conductivity. For this reason, the irreversible capacity resulting from the reaction of the titanium oxide becomes a substantially constant amount per unit area of the negative electrode regardless of the thickness of the titanium oxide.
Therefore, it is possible to increase the irreversible capacity on the negative electrode side more efficiently and accurately than increasing the thickness of the negative electrode active material mixture layer to increase the irreversible capacity of the negative electrode, and the area where the internal resistance of the positive electrode is high at the end of discharge. Is not used, and the IV resistance value can be maintained at a low constant value from a low charging depth to a high charging depth.

  In addition, when the irreversible capacity of the negative electrode is simply adjusted by the amount of the active material mixture layer of the negative electrode, it is necessary to increase the amount of the active material mixture layer of the negative electrode, and the thickness of the negative electrode is increased. The capacity is reduced due to the above restrictions, and the output characteristics are also lowered. Furthermore, since the ratio of SEI growth on the negative electrode surface during high-temperature storage increases as the amount of the negative electrode increases, capacity deterioration during storage increases.

Here, when the charge capacity per unit area of the positive electrode is large and the electrode area is small, the irreversible capacity due to titanium oxide contained in the coating layer formed on the negative electrode surface with respect to the charge capacity per unit area of the positive electrode The ratio becomes smaller. In this case, since the region where the internal resistance of the positive electrode becomes high at the end of discharge is used, the IV resistance value becomes relatively high at a low charging depth. Therefore, in order to obtain the effect of the present invention, the initial charge capacity per unit area of the positive electrode needs to be 40 mAh / 10 cm ² or less.

In the present invention, when the initial charge capacity per unit area of the positive electrode is 10 mAh / 10 cm ² or more, the battery capacity can be sufficiently increased. Therefore, the initial charge capacity per unit area of the positive electrode is preferably 10 mAh / 10 cm ² or more.

Further, in the non-aqueous electrolyte secondary battery of the present invention, the output regenerative properties superior to all of the positive electrode active material contained in the positive electrode, the internal resistance increases as the end of discharge _{Li 1 + a Ni x Co y} Mn z M b It is considered that the effect of the present invention can be obtained when the proportion of the positive electrode active material made of O ₂ is 20% by mass or more. The content is preferably 50% by mass or more, and more preferably 70% or more.

  In addition, in the nonaqueous electrolyte secondary battery of the present invention, the irreversible capacity of the completed battery when the insulating coating layer containing titanium oxide is not formed on the negative electrode surface (the difference between the initial charge capacity of the positive electrode and the initial discharge capacity of the completed battery). It is preferable that (the initial charge capacity of the positive electrode−the initial discharge capacity of the finished battery) be 30% or less of the initial charge capacity of the positive electrode. Here, the initial charge capacity of the positive electrode is the initial charge capacity of the entire positive electrode included in the completed battery. The initial discharge capacity of the completed battery is the initial discharge capacity of the completed battery manufactured using a negative electrode in which an insulating coating layer containing titanium oxide is not provided on the negative electrode surface.

  When the irreversible capacity (the initial charge capacity of the positive electrode−the discharge capacity of the completed battery) of the completed battery when the insulating coating layer containing titanium oxide is not formed on the negative electrode surface is greater than 30% of the initial charge capacity of the positive electrode The ratio of the irreversible capacity of titanium oxide to the irreversible capacity of the negative electrode is decreased, and the effect of suppressing the increase of the IV resistance value at a low charging depth is reduced, and at the same time, the capacity of the battery that can be charged and discharged is decreased, which is not preferable .

When the insulating coating layer containing titanium oxide is not formed on the negative electrode surface, the irreversible capacity of the completed battery can be controlled by changing the irreversible capacity of the negative electrode.
In order to increase the irreversible capacity of the completed battery when the insulating coating layer containing titanium oxide is not formed on the surface of the negative electrode, for example, the amount of the negative electrode active material is increased relative to the amount of the positive electrode active material, or irreversible. A large-capacity active material can be used. Further, in order to reduce the irreversible capacity of the finished battery when the insulating coating layer containing titanium oxide is not formed on the negative electrode surface, for example, the amount of the negative electrode active material is decreased with respect to the amount of the positive electrode active material. Alternatively, a negative electrode active material having a small irreversible capacity can be used.
The irreversible capacity of the negative electrode active material can be controlled by changing the crystallinity and specific surface area.
Generally, when the crystallinity is low or the specific surface area is large, the irreversible capacity tends to increase.

  In the nonaqueous electrolyte secondary battery of the present invention, the coating layer formed on the negative electrode surface is preferably a layer made of titanium oxide and a binder.

  According to the said structure, since the layer which consists of an insulating titanium oxide and a binder is formed in the negative electrode surface, generation | occurrence | production of an internal short circuit can be prevented even if it is a case where a separator is damaged.

  The proportion of titanium oxide in the coating layer provided on the negative electrode surface is preferably 95 to 99% by mass with respect to the total mass of the coating layer.

Moreover, as a kind of titanium oxide, it is preferable that a rutile degree is 80 to 99.5%. Here, the rutile ratio is measured by X-ray diffraction measurement, and the peak area (Ir) of the strongest diffraction line (surface index 110) of rutile crystal titanium oxide and the strongest diffraction line (surface index) of anatase crystal titanium oxide. The peak area (Ia) of (101) is calculated by the following formula (1), and is an index indicating the ratio of the rutile and anatase type crystal structures in titanium oxide.
Rutile ratio (% by weight) = 100-100 / (1 + 1.2 × Ir / Ia) (1)

  If the rutile ratio is higher than 99.5%, the irreversible capacity of titanium oxide becomes too small, so that the effect of suppressing the increase of the IV resistance value at a low charging depth becomes small. If the rutile ratio is lower than 80%, the irreversible capacity of titanium oxide becomes too large, and therefore the capacity of the nonaqueous electrolyte secondary battery becomes small.

  Moreover, it is preferable that the average particle diameter of a titanium oxide is 0.1 micrometer-1.0 micrometer.

  When the average particle diameter of titanium oxide is smaller than 0.1 μm, it becomes bulky and handling of the powder cake becomes difficult, and when it is larger than 1.0 μm, the active material surface of the negative electrode is uniformly coated with a layer composed of titanium oxide and a binder. Is not preferable because it becomes difficult.

  Binders include copolymers containing acrylonitrile structures, polyimide resins, styrene butadiene rubber latex (SBR), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene resin (PTFE). Carboxymethyl cellulose (CMC) and the like can be used.

  In the nonaqueous electrolyte secondary battery of the present invention, it is preferable that the thickness of the insulating coating layer containing titanium oxide is 1 μm to 5 μm.

  When the thickness of the insulating coating layer containing titanium oxide exceeds 5 μm, the surface layer is too thick, the output characteristics are lowered, and the battery capacity is lowered due to the design restrictions, which is not preferable.

  In the nonaqueous electrolyte secondary battery of the present invention, it is preferable that the filling density of the negative electrode is 1.0 g / cc to 1.4 g / cc. Here, the packing density of the negative electrode is the packing density of the negative electrode active material mixture layer.

  A negative electrode packing density of less than 1.0 g / cc is not preferable because the battery capacity is reduced due to design constraints. When it exceeds 1.4 g / cc, the current collector of the application part is deformed, and there is a possibility of causing wrinkles at the boundary between the application part and the non-application part.

In the nonaqueous electrolyte secondary battery of the present invention, the positive electrode active material is Li _{1 + a} Ni _x Co _y Mn _z M _b O ₂ (M = Zr, 0 ≦ a ≦ 0.15, 0.25 ≦ x ≦ 0.45, 0.25 ≦ y ≦ 0.45, 0.25 ≦ z ≦ 0.35, 0 ≦ b ≦ 0.01, and a + b + x + y + z = 1).

Li _{1 + a} Ni _x Co _y Mn _z M _b O ₂ (M = Zr, 0 ≦ a ≦ 0.15, 0.25 ≦ x ≦ 0.45, 0.25 ≦ y ≦ 0.45, 0 When .25 ≦ z ≦ 0.35, 0 ≦ b ≦ 0.01, a + b + x + y + z = 1), the effects of the present invention are remarkably exhibited and the battery characteristics are also very good.

  In the nonaqueous electrolyte secondary battery of the present invention, a positive electrode core exposed portion is formed at one end of the electrode body, a negative electrode core exposed portion is formed at the other end, and the positive electrode core exposed portion It is preferable that the positive electrode terminal and the negative electrode terminal are connected to each other by current collectors attached to the negative electrode core exposed portions. That is, in the case of a wound electrode body, a core body exposed portion exists in the longitudinal direction of the elongated positive electrode plate and negative electrode plate, and the positive electrode core body exposed portion and the negative electrode core body exposed portion are respectively the ends of the electrode body. The positive electrode plate and the negative electrode plate are wound through a separator so as to be a part, and a current collector is attached to each of the core exposed parts of the positive electrode and the negative electrode, and is connected to the positive electrode terminal and the negative electrode terminal. The In the case of a laminated electrode body, the positive electrode plate and the negative electrode plate each have a core exposed portion at one end, and the positive electrode core exposed portion and the negative electrode core exposed portion are the end portions of the electrode body, respectively. The positive electrode plate and the negative electrode plate are alternately stacked via a separator so that a current collector is attached to the positive electrode core exposed portion and the negative electrode core exposed portion, and is connected to the positive electrode terminal and the negative electrode terminal. The

  The positive electrode core exposed portion and the negative electrode core exposed portion do not exist at each of the end portions of the electrode body, and the current is taken out by the positive electrode tab and the negative electrode tab attached to the positive electrode core and the negative electrode core body. Since the contact area between the positive electrode tab or the negative electrode tab and the positive electrode core or the negative electrode core cannot be increased, the contact resistance of this portion is increased. The negative electrode core may melt.

  On the other hand, according to the above configuration, the positive electrode core exposed portion is formed at one end of the electrode body, the negative electrode core exposed portion is formed at the other end, and the positive electrode core exposed portion and the negative electrode It has a structure connected to the positive electrode terminal and the negative electrode terminal by current collectors attached to the core body exposed portions. Therefore, the contact resistance between the positive electrode core body and the negative electrode core body and the current collector is reduced, and charging and discharging can be easily performed with a large current of 60 A or more. In addition, according to the non-aqueous electrolyte secondary battery of the present invention, the composition of the positive electrode active material and the initial charge / discharge efficiency of the negative electrode are limited as described above. Even when performed, it is possible to remarkably suppress an increase in the IV resistance value at a low charging depth, the output characteristics are not deteriorated, and the non-aqueous electrolyte secondary battery is optimal for EV use, HEV use, and the like.

  In the present invention, as the non-aqueous solvent (organic solvent) constituting the non-aqueous solvent-based electrolyte, carbonates, lactones, ethers, esters and the like generally used in non-aqueous electrolyte secondary batteries are used. Two or more of these solvents can be mixed and used. Among these, carbonates, lactones, ethers, ketones, esters and the like are preferable, and carbonates are more preferably used.

  Specific examples include ethylene carbonate (EC), propylene carbonate, butylene carbonate, fluoroethylene carbonate (FEC), 1,2-cyclohexyl carbonate (CHC), cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethyl. Sulfolane, 3-methyl-1,3-oxazolidine-2-one, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, Dipropyl carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxola , Methyl acetate, ethyl acetate, 1,4-dioxane and the like.

  In the present invention, a mixed solvent such as EC and a chain carbonate such as DMC, MEC, and DEC is preferably used from the viewpoint of increasing the charge / discharge efficiency, but an asymmetric chain carbonate such as MEC is preferable. Moreover, unsaturated cyclic carbonates such as vinylene carbonate (VC) can also be added to the nonaqueous electrolyte.

In addition, as a solute of the nonaqueous electrolyte in the present invention, a lithium salt generally used as a solute in a nonaqueous electrolyte secondary battery can be used. Such lithium salts include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ , LiB (C ₂ O _{4) 2, LiB (C 2} O 4) F 2, LiP (C 2 O 4) 3, LiP (C 2 O 4) 2 F 2, LiP (C 2 O 4) F 4 , etc., and mixtures thereof examples Is done. Among these, LiPF ₆ (lithium hexafluorophosphate) is preferably used. The amount of solute dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / L.

  Hereinafter, the present invention will be described in detail using various examples and comparative examples. However, the following examples show examples of non-aqueous electrolyte secondary batteries for embodying the technical idea of the present invention, and are not intended to specify the present invention to these examples. The present invention can be equally applied to various modifications without departing from the technical idea shown in the claims.

[Example 1 and Comparative Example 1]
First, a method for manufacturing each negative electrode plate of Example 1 and Comparative Example 1 will be described, and then a specific method for manufacturing a nonaqueous electrolyte secondary battery common to Example 1 and Comparative Example 1 and a method for measuring IV resistance Etc. will be described.

[Production of negative electrode plate]
The negative electrode active materials of Example 1 and Comparative Example 1 were prepared as follows. After natural spherical processing of natural graphite having an interplanar spacing d002 of 3.36 mm by X-ray diffraction method, the pitch is coated and impregnated so as to be 5% by mass with respect to 95% by mass of the graphite powder. And baked at 1000 ° C. for 10 hours. In addition, carbon powder having an interplanar spacing d002 of 3.39 mm by X-ray diffractometry was mixed with the obtained spheroidized low crystalline carbon-coated natural graphite at 7% by mass with respect to 93% by mass of the spheroidized low crystalline carbon-coated natural graphite. Thus, a negative electrode active material was obtained. The average particle diameter of the obtained negative electrode active material was 11.7 μm, and the BET specific surface area was 7.2 m ² / g.

  The negative electrode active material obtained as described above, carboxymethyl cellulose (CMC) as a binder and styrene butadiene rubber latex (SBR) are kneaded together with water at a mass ratio of 98: 1: 1. A material mixture slurry was prepared. Next, the prepared negative electrode active material mixture slurry was applied on both sides of a strip-shaped copper foil (thickness: 8 μm) as a negative electrode core, and then dried to form a negative electrode active material mixture layer. Then, it rolled until the filling density became 1.1 g / cc using the rolling roller.

Next, titanium oxide (TiO ₂ ) having a purity of 99.9%, a rutile ratio of 99.1%, and an average particle size of 0.25 μm, a copolymer containing an acrylonitrile structure as a binder, and N-methylpyrrolidone as a solvent (NMP) was mixed at a weight ratio of 30: 0.9: 69.1 and mixed and dispersed by a bead mill to prepare a slurry. Next, a slurry is applied to the entire surface of the negative electrode active material mixture layer surface on one side of the negative electrode plate prepared by the above method using a gravure coating method, and then the solvent is dried and removed, and titanium oxide is applied to the negative electrode surface. And a binder layer was formed. By the same method, a layer composed of titanium oxide and a binder was also formed on the entire surface of the negative electrode active material mixture layer on the other side. Then, it cut | disconnected to the predetermined dimension and produced the negative electrode plate of Example 1. FIG. The thickness of the titanium oxide and binder layer was 2 μm.

In addition, instead of TiO ₂ , aluminum oxide (Al ₂ O ₃ ) having a purity of 99.99% and an average particle diameter of 0.64 μm is used, and a copolymer containing an acrylonitrile structure as a binder and NMP as a solvent in a weight ratio. 30: 0.9: 69.1 The mixture was mixed and subjected to a mixing and dispersing treatment with a bead mill to prepare a slurry. Next, a layer made of aluminum oxide and a binder was formed on the surfaces of the negative electrode active material mixture layers on both sides of the negative electrode plate in the same manner as in Example 1. Then, it cut | disconnected to the predetermined dimension and produced the negative electrode plate of the comparative example 1. The thickness of the aluminum oxide and binder layer was 2 μm.

[Production of positive electrode plate]
Li ₂ CO ₃ , (Ni _0.35 Co _0.35 Mn _0.3 ) ₃ O ₄ and ZrO ₂ , and the molar ratio of Li, (Ni _0.35 Co _0.35 Mn _0.3 ) and Zr is It mixed so that it might be set to 1.07: 0.925: 0.005. This mixture was fired at 900 ° C. for 20 hours in an air atmosphere, and Li _1.07 (Ni _0.35 Co _0.35 Mn _0.3 ) _0.925 Zr _0.005 O _having an average particle diameter of 9.5 μm. _The lithium transition metal composite oxide represented by ₂ was obtained and used as the positive electrode active material. The positive electrode active material obtained as described above, a carbon material as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder are mixed in NMP so that the mass ratio is 88: 9: 3. The mixture was added and kneaded to prepare a positive electrode active material mixture slurry. The prepared positive electrode active material mixture slurry was applied to both sides of a strip-shaped aluminum foil (thickness 12 μm) as a positive electrode core, and then dried to form a positive electrode active material mixture layer. Then, it rolled until it became the predetermined packing density using the rolling roll, it cut | disconnected to the predetermined dimension, and produced the positive electrode plate.

[Preparation of non-aqueous electrolyte]
In preparing the non-aqueous electrolyte, a mixed solvent in which ethylene carbonate (EC) as a cyclic carbonate and ethyl methyl carbonate (EMC) as a chain carbonate were mixed at a volume ratio of 3: 7, As a solute, lithium hexafluorophosphate (LiPF ₆ ) was dissolved at a rate of 1 mol / liter. A non-aqueous electrolyte was prepared by adding 1% by mass of vinylene carbonate (VC) to the solution thus obtained.

[Production of non-aqueous electrolyte secondary battery]
Next, the positive electrode plate prepared as described above and the negative electrode plates of Example 1 and Comparative Example 1 manufactured as described above were respectively used, and a separator made of a polyethylene microporous film was interposed therebetween. After the lamination, each was wound spirally to form a spiral electrode group. An uncoated portion is formed along the longitudinal direction of the positive electrode plate and the negative electrode plate, and the uncoated portion constitutes a core body edge portion protruding from the end of the separator of the spiral electrode group. A current collector plate is attached to each end of the spiral electrode group by laser welding, then inserted into a metal outer can, and the tip of the lead portion protruding from the end of the current collector plate is an electrode terminal mechanism. Connected to.

Next, the non-aqueous electrolyte prepared as described above was poured into a metal outer can. Thereafter, by sealing, a nonaqueous electrolyte secondary battery having the same shape as that of the conventional example shown in FIG. 4 was produced. When various characteristics of the battery thus prepared were measured, the discharge capacity of the completed nonaqueous electrolyte secondary battery in Example 1 was 5.2 Ah, and the discharge of the completed nonaqueous electrolyte secondary battery in Comparative Example 1 was performed. The capacity was 5.4 Ah. In both Example 1 and Comparative Example 1, the initial charge capacity per unit area of the positive electrode was 20 mAh / 10 cm ² . Further, the irreversible capacity of the non-aqueous electrolyte secondary battery produced by the same method as in Example 1 and Comparative Example 1 except that the coating layer was not formed on the negative electrode surface (initial charge capacity of the positive electrode−discharge of the completed non-aqueous electrolyte battery) The capacity) was 23% with respect to the initial charge capacity of the positive electrode.
Here, the discharge capacity of the nonaqueous electrolyte secondary battery, the initial charge capacity of the positive electrode, and the initial charge capacity per unit area of the positive electrode were measured as follows. Also, the same measurement methods are used in the following measurements.

[Measurement method of discharge capacity]
At room temperature of 25 ° C., the non-aqueous electrolyte secondary battery produced by the above-described method was charged with 4.1 V constant current-constant voltage for 2 hours at 1 It, and then charged with 3.0 V constant current at 1/3 It— The constant voltage discharge was performed for 5 hours, and the discharge capacity at this time was defined as the discharge capacity of the nonaqueous electrolyte secondary battery.

[Measurement method of initial charge capacity of positive electrode]
A positive electrode plate having a positive electrode active material mixture layer formed on both sides of the positive electrode core produced by the above-described method is cut out, and the area of the core on which the positive electrode active material mixture layer is formed on both sides is 12.5 cm ² . An electrode was prepared so that a three-electrode cell was prepared using lithium metal as a counter electrode and a reference electrode. After charging to 4.2 V (vs. Li / Li ⁺ ) at a current value of 0.75 mA / cm ² at room temperature of 25 ° C., 4.2 V at a current value of 0.25 mA / cm ^2. The charge capacity when charging was performed in two stages until (vs Li / Li ⁺ ) was measured. The charge capacity thus determined is converted into the charge capacity per total area of the core body in which the positive electrode active material mixture layer is formed on both sides in the positive electrode plate included in the finished battery, and the initial charge capacity of the positive electrode did.

[Measurement method of initial charge capacity per unit of positive electrode]
The initial charge capacity per unit of the positive electrode is the initial charge capacity of the positive electrode determined by the above-described method of measuring the initial charge efficiency of the positive electrode, per 10 cm ² of area of the core body in which the positive electrode active material mixture layer is formed on both surfaces. It calculated by converting into a capacity | capacitance.

Moreover, about the battery of the said Example 1 and the comparative example 1, the relationship between a charge depth and internal resistance was investigated with the method shown below. As the internal resistance, an IV resistance value obtained by measuring a voltage when a battery is charged or discharged at a certain current value for a certain period of time and calculating a slope of the voltage with respect to the current value is adopted. This IV resistance value is an index for knowing how much current can flow through the battery.
[Relationship between charging depth and IV resistance]
At a room temperature of 25 ° C., the battery was charged at a charging current of 5 A until reaching the respective charging depths, and discharged for 10 seconds at a current of 10 A, 20 A, 30 A, 40 A, and 60 A, respectively, and each battery voltage was measured. Each current value and the battery voltage were plotted to obtain the IV characteristics at the time of discharge, and the IV resistance (mΩ) at the time of discharge was obtained from the slope of the obtained straight line. In this way, the IV resistance value at a predetermined charging depth was obtained. In addition, the charging depth shifted by discharging was restored to the original charging depth by charging with a constant current of 5A. The relationship between this charging depth and the measured value of IV resistance is shown in FIG. FIG. 2 shows the relationship between the charging depth and the IV resistance value when the IV resistance is measured with current values of 5A, 10A, 15A, and 20A.

[Example 2]
Example 2 is the same as Example 1 except that when the positive electrode plate and the negative electrode plate were produced, the coating amount of the positive electrode active material mixture slurry and the negative electrode active material mixture slurry was respectively doubled as in Example 1. A non-aqueous electrolyte secondary battery was produced by the same method. The initial charge capacity per unit area of the positive electrode in the nonaqueous electrolyte secondary battery of Example 2 produced in this manner was 40 mAh / 10 cm ² . The completed nonaqueous electrolyte secondary battery of Example 2 had a discharge capacity of 6.7 Ah.
Further, the irreversible capacity of the nonaqueous electrolyte secondary battery produced by the same method as in Example 2 except that the coating layer was not formed on the negative electrode surface (initial charge capacity of the positive electrode−discharge capacity of the completed nonaqueous electrolyte battery) was It was 23% with respect to the initial charge capacity of the positive electrode in Example 2.

[Comparative Example 2]
Comparative Example 1 is Comparative Example 1 except that when the positive electrode plate and the negative electrode plate are produced, the coating amount of the positive electrode active material mixture slurry and the negative electrode active material mixture slurry is respectively doubled in the case of Comparative Example 1. A non-aqueous electrolyte secondary battery was produced by the same method. The initial charge capacity per unit area of the positive electrode in the completed nonaqueous electrolyte secondary battery of Comparative Example 2 was 40 mAh / 10 cm ² . Moreover, the discharge capacity of the completed nonaqueous electrolyte secondary battery of Comparative Example 2 was 6.8 Ah.
Further, the irreversible capacity of the nonaqueous electrolyte secondary battery produced by the same method as in Comparative Example 2 except that no coating layer was formed on the negative electrode surface (initial charge capacity of the positive electrode−discharge capacity of the completed nonaqueous electrolyte battery) is It was 23% with respect to the initial charge capacity of the positive electrode in Comparative Example 2.

[Comparative Example 3]
In Comparative Example 3, when preparing the positive electrode plate and the negative electrode plate, the application amounts of the positive electrode active material mixture slurry and the negative electrode active material mixture slurry were each three times that in Example 1, and A non-aqueous electrolyte secondary battery was produced by the same method. The initial charge capacity per unit area of the positive electrode in the completed nonaqueous electrolyte secondary battery of Comparative Example 3 was 60 mAh / 10 cm ² . Moreover, the discharge capacity of the completed nonaqueous electrolyte secondary battery of Comparative Example 3 was 7.0 Ah.
Further, the irreversible capacity of the nonaqueous electrolyte secondary battery produced by the same method as in Comparative Example 3 except that no coating layer was formed on the negative electrode surface (the initial charge capacity of the positive electrode−the discharge capacity of the completed nonaqueous electrolyte battery) was It was 23% with respect to the initial charge capacity of the positive electrode in Comparative Example 3.

[Comparative Example 4]
Comparative Example 4 was the same as Comparative Example 1 except that when the positive electrode plate and the negative electrode plate were produced, the amount of application of the positive electrode active material mixture slurry and the negative electrode active material mixture slurry was three times that in Comparative Example 1, respectively. A non-aqueous electrolyte secondary battery was produced by the same method. The initial charge capacity per unit area of the positive electrode in the completed nonaqueous electrolyte secondary battery of Comparative Example 4 was 60 mAh / 10 cm ² . Moreover, the discharge capacity of the completed nonaqueous electrolyte secondary battery of Comparative Example 3 was 7.1 Ah.
The irreversible capacity of the nonaqueous electrolyte secondary battery produced by the same method as in Comparative Example 4 except that no coating layer was formed on the negative electrode surface (initial charge capacity of the positive electrode−discharge capacity of the completed nonaqueous electrolyte battery) is It was 23% with respect to the initial charge capacity of the positive electrode in Comparative Example 3.

  For Example 1, Example 2, and Comparative Examples 1 to 4, as an index indicating the dependency of the output characteristics on the charging depth (IV resistance value measured at a charging depth of 10% in the range of 10 to 60 A) / (IV resistance value of 50% charge depth measured in the range of 10-60A) is shown in FIG.

The following can be understood from the results shown in FIGS. In each of Example 1 and Comparative Example 1, when the IV resistance value was measured in the range of 5A to 20A (FIG. 2) and when measured in the range of 10A to 60A (FIG. 1), the charging depth was 20% to 90%. In the% range, substantially the same IV resistance value is provided, and the IV resistance value is as low as 5 mΩ or less. Further, in both Example 1 and Comparative Example 1, it can be seen that when the charging depth is lower than 20%, the IV resistance value increases, and a remarkable difference appears when charging / discharging with a large current of 60 A or more is performed. .
However, in Example 1, compared with Comparative Example 1, the IV resistance value in the range where the charging depth is lower than 20% when charging / discharging with a large current of 60 A or more is low. Then, it turns out that the increase in IV resistance value in a low charge depth can be suppressed.

  In addition, as shown in FIG. 3, when the initial charge capacity per unit area of the positive electrode is small and an insulating coating layer containing titanium oxide is formed on the negative electrode surface, the increase in IV resistance is suppressed at a remarkably low charge depth. I understand that I can do it.

  Therefore, the batteries of Example 1 and Example 2 according to the present invention have a wide charge as compared with relatively non-aqueous electrolyte secondary batteries of 1 to 4 even when charged and discharged at a large current of 60 A or more. Since the IV resistance value is kept low and constant over the depth range, it can be seen that it is optimal as a battery for HE or HEV that requires particularly sufficient output characteristics and output regeneration characteristics.

As described above, the positive electrode active material capable of absorbing and desorbing lithium ions as a _{Li 1 + a Ni x Co y} Mn z M b O 2 (M = Al, Ti, Zr, Nb, at least B, Mg, selected from Mo One element, 0 ≦ a ≦ 0.3, 0.1 ≦ x ≦ 1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.9, 0 ≦ b ≦ 0.01, a + x + y + z = 1) The initial charge capacity per unit area of the positive electrode is 40 mAh / 10 cm ² or less using the lithium transition metal composite oxide to be formed, and an insulating coating layer containing titanium oxide is formed on the negative electrode surface. Even when charging / discharging with current, the IV resistance value can be maintained at a low constant value from a low charging depth to a high charging depth. Therefore, according to the present invention, it is possible to obtain a non-aqueous electrolyte secondary battery that is optimal for an electric vehicle (EV), a hybrid electric vehicle (HEV), and the like having excellent load characteristics and output regeneration characteristics.

10: Nonaqueous electrolyte secondary battery 11: Cylindrical body 12: Lid body 13: Battery outer can 14: Electrode terminal mechanism 20: Winding electrode body 21: Positive electrode 21 ₃ : Edge part of positive electrode core body 22: Negative electrode 22 ₃ : Negative electrode core edge 23: Separator 30: Current collector 31: Lead part 32: Flat body 33: Arc-shaped convex part 34: Welded part

Claims (6)

Li _{1 + a} Ni _x Co _y Mn _z M _b O ₂ (M = Al, Ti, Zr, Nb, B, Mg, Mo, which can occlude / release lithium ions as a positive electrode active material, 0 ≦ a ≦ 0.3, 0.1 ≦ x ≦ 1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.9, 0 ≦ b ≦ 0.01, a + b + x + y + z = 1) In a non-aqueous electrolyte secondary battery having a positive electrode including a metal composite oxide, a negative electrode including a negative electrode active material, a non-aqueous electrolyte, and a separator interposed between the positive and negative electrodes, the unit area of the positive electrode A non-aqueous electrolyte secondary battery having an initial charge capacity of 40 mAh / 10 cm ² or less and an insulating coating layer containing titanium oxide formed on the surface of the negative electrode.   The irreversible capacity (the initial charge capacity of the positive electrode−the initial discharge capacity of the completed battery) of the completed battery when the coating layer is not formed on the surface of the negative electrode is 30% or less with respect to the initial charge capacity of the positive electrode. The non-aqueous electrolyte secondary battery according to claim 1.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the coating layer is made of titanium oxide and a binder.   The thickness of the said coating layer is 1 micrometer-5 micrometers, The nonaqueous electrolyte secondary battery in any one of Claims 1-3 characterized by the above-mentioned.   The non-aqueous electrolyte secondary battery according to claim 1, wherein a filling density of the negative electrode is 1.0 g / cc to 1.4 g / cc. The positive electrode active material is Li _{1 + a} Ni _x Co _y Mn _z M _b O ₂ (M = Zr, 0 ≦ a ≦ 0.15, 0.25 ≦ x ≦ 0.45, 0.25 ≦ y ≦ 0.45, The lithium transition metal composite oxide represented by 0.25 ≦ z ≦ 0.35, 0 ≦ b ≦ 0.01, a + b + x + y + z = 1), according to any one of claims 1 to 5 Non-aqueous electrolyte secondary battery.

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