JP5484771B2 - Positive electrode for lithium ion battery - Google Patents

Description

  The present invention relates to a positive electrode for a lithium ion battery and a lithium ion battery using the positive electrode for a lithium ion battery. The positive electrode for a lithium ion battery and the lithium ion battery using the same according to the present invention are used, for example, as a power source for driving a motor of a vehicle such as an electric vehicle, a fuel cell vehicle, and a hybrid electric vehicle.

  In recent years, various electric vehicles are expected to be widely used for solving environmental and energy problems. Secondary batteries have been intensively developed as in-vehicle power supplies such as motor drive power supplies that hold the key to commercialization of these electric vehicles. However, in order to spread widely, it is necessary to make the battery high performance and cheaper. In addition, for electric vehicles, it is necessary to bring the distance for one charge closer to a gasoline engine vehicle, and a battery with higher energy is desired.

In order to make the battery have a high energy density, it is necessary to increase the amount of electricity stored per unit mass of the positive electrode and the negative electrode. A so-called solid solution positive electrode material has been studied as a positive electrode material that may meet this demand. Among them, the solid solution of the electrochemically inactive layered Li ₂ MnO ₃ and the electrochemically active layered LiMO ₂ (where M is a transition metal such as Co or Ni) is 200 mAh / g. Therefore, it is expected as a high-capacity positive electrode candidate material that can exhibit a large electric capacity exceeding (see, for example, Patent Document 1).

JP-A-9-55211

However, the solid solution positive electrode using Li ₂ MnO ₃ , which is a high capacity positive electrode candidate material described in Patent Document 1, has a large discharge capacity. There was a problem that the battery deteriorated immediately after repeated discharge. For this reason, even a lithium ion battery using such a solid solution positive electrode as a high-capacity positive electrode has a problem that the cycle durability under a high-capacity usage condition is poor, and it deteriorates immediately when charging / discharging at a high potential. It was.

  Therefore, an object of the present invention is to provide a positive electrode for a lithium ion battery that has a high capacity and suppresses deterioration due to charge and discharge at a high potential.

  The present inventors discharge a predetermined amount of electricity to a predetermined potential after charging, and repeat the operation of charging with the amount of electricity obtained by adding the predetermined amount of electricity to the discharged amount of electricity until the charging potential reaches a predetermined maximum potential. It has been found that the above-described problems can be solved by performing a pre-charge / discharge pretreatment in which the amount of electricity is regulated. Based on this knowledge, the present invention has been achieved.

That is, an object of the present invention is to perform charge / discharge pretreatment with the charge amount controlled as described above in the positive electrode whose main active material is represented by the general formula: xLiMO ₂ · (1-x) Li ₂ NO _3. This can be achieved by a lithium ion battery positive electrode (hereinafter also simply referred to as a positive electrode).

The positive electrode of the present invention is a solid solution positive electrode using a layered lithium composite oxide that is electrochemically inactive, such as Li ₂ MnO _3. Structural stabilization can be achieved without causing significant structural changes. Therefore, the cycle characteristics in the high capacity charge / discharge at a high voltage of the solid solution system positive electrode can be greatly improved. As a result, a large amount of lithium-ion batteries with high capacity and good cycle durability can be provided efficiently.

1 is a schematic cross-sectional view schematically showing an outline of a laminated flat non-bipolar lithium ion secondary battery which is a typical embodiment of a lithium ion battery of the present invention. It is the cross-sectional schematic which represented typically the outline | summary of the laminated flat bipolar lithium ion secondary battery which is another typical embodiment of the lithium ion battery of this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view schematically showing an appearance of a stacked flat lithium ion secondary battery that is a typical embodiment of a lithium ion battery according to the present invention. 4A and 4B are external views schematically showing typical embodiments of the assembled battery according to the present invention, in which FIG. 4A is a plan view of the assembled battery, FIG. 4B is a front view of the assembled battery, and FIG. It is a side view of a battery. It is a conceptual diagram of the vehicle carrying the assembled battery of this invention. It is a schematic diagram which shows the relationship between charging / discharging electricity amount. A diagram showing charge-discharge curves of _{Li [Ni 0.17 Li 0.2 Co 0.07} Mn 0.56] O 2, the first time (1st), second round (2nd) and the fifth ( It is drawing which showed each charging / discharging curve of 5th). It is an enlarged drawing near the beginning of the flat part of the 1st charge curve of Drawing 7A. In the charge / discharge conditions of the electrode of Example 1 (including the time of pre-charge / discharge treatment), the first time in the pre-charge / discharge pre-treatment and the high-capacity battery usage conditions after the pre-charge / discharge pre-treatment It is drawing which showed each charging / discharging curve of the 5th time. In the constant current charge / discharge test using the electrodes of Example 5 and Comparative Example 4, the potential differentiation of the capacity was calculated using the PC software from the obtained charge / discharge data, and the data of the cell that was subjected to the charge / discharge pretreatment were carried out. It is the figure which showed the dQ / dE curve which each represented the result of the cell which is not. 10 is a comparison of TEM bright field images of the electrode active material particles of Example 6 and Comparative Example 5. FIG.

  In the positive electrode for a lithium ion battery of the present invention, the main active material has a general formula

In the positive electrode for a lithium ion battery represented by the following, charge / discharge pretreatment that regulates the amount of charge electricity is performed as follows.

  Here, x in the general formula is a number satisfying 0 <x <1, M is one or more metal elements having an average oxidation state of 3+, and N is an average oxidation state of 4+. One or more metal elements. In addition, as pre-charge / discharge preconditioning that regulates the amount of charge, the amount of electricity Qd (1) (0 <Qd) is charged to a predetermined positive potential Ed (1) after charging a predetermined positive amount of electricity Qc (1) for the first time. (1) <Qc (1)) is discharged, and the second discharge is charged with an electric quantity Qc (2) obtained by adding a predetermined positive electric quantity ΔQ (2) to the initial discharge electric quantity Qd (1), and so on. The charge / discharge pretreatment is repeated until the potential after charging reaches a predetermined maximum potential. By adopting such a configuration, the positive electrode of the present invention that has been structurally stabilized (completed) can significantly improve cycle deterioration even when used up to a high potential.

That is, a positive electrode material of a so-called solid solution system represented by the general formula: xLiMO ₂ · (1-x) Li ₂ NO ₃ is expected as a high-capacity material, but is charged to a high potential to develop a high capacity. When used, there is a problem that deterioration due to charge and discharge is quick (see FIG. 7A). Of the first, second, and fifth charge / discharge curves when charged to a high potential at this time, the first charge curve is simply referred to as an “initial charge curve”. On the other hand, although the mechanism of the effect is not yet well understood, it has been found that the following charge / discharge pretreatment with regulated charge amount may be performed. That is, the amount of electricity in the vicinity of the beginning of the plateau portion (see FIG. 7B) of the initial charge curve obtained earlier so as not to cause a significant change in the solid solution positive electrode crystal structure from the beginning. It turned out that the said problem will be improved if it charges until it becomes. As a result of further investigation, the amount of charge after the second round is also increased stepwise within a range that does not cause a significant change in the solid solution crystal structure, and finally exceeds the potential at the plateau. Charge / discharge is repeated until the maximum potential is reached, and the charge / discharge pretreatment proceeds. As a result, it has been found that structural stabilization proceeds (completed) by a more stable arrangement of constituent elements and a gentle transition to a stable structure, and cycle deterioration can be significantly improved even after use up to a high potential. . As a result, a positive electrode using the solid solution positive electrode material of the present invention as a main active material can provide a positive electrode for a lithium ion battery having high capacity and good cycle durability. Furthermore, in the lithium ion battery of the present invention, by using a positive electrode for a lithium ion battery having the solid solution positive electrode material of the present invention as a main active material, a battery having high energy density and good cycle durability can be configured. Are better.

  That is, according to the present invention, the cycle durability at a high capacity of concern can be greatly improved. Although the cycle durability mechanism of the present invention cannot be determined yet, it is considered as follows. The plateau part of the initial charge curve is not yet clearly understood, but according to one theory, the process in which the dianion of oxygen in the solid solution cathode crystal is oxidized and lithium ions are released. It is believed that. When this reaction occurs, a significant change in the crystal structure occurs, and it is assumed that the subsequent charge / discharge cycle deterioration occurs as a result. In the present invention, the initial charge electricity amount is regulated and the charge / discharge pretreatment is performed without causing a significant change in the crystal structure from the beginning. After that, the amount of charge electricity is regulated so as not to cause a significant change in the crystal structure, and the pre-charge / discharge pretreatment is performed in stages, thereby allowing more stable arrangement of the constituent elements and a gentle transition to a stable structure. Stabilized structurally (completed). Therefore, in subsequent use, it is thought that it will be able to withstand a charge / discharge cycle including a high potential region in which a high capacity can be developed. The present invention may be applied in the state of a positive electrode active material powder, applied by constituting an electrode, or applied after a battery is assembled with a negative electrode. In the present invention, once the charge / discharge pretreatment pattern in which the amount of electricity is regulated is determined for one positive electrode material, the positive electrode can appropriately perform precharge / discharge pretreatment without using a potential reference such as lithium. Therefore, it is possible to carry out mass treatment of the positive electrode and the positive electrode material, and further, pre-charge / discharge pretreatment of the positive electrode in a battery without using a special potential reference.

  Hereinafter, embodiments of a positive electrode for a lithium ion battery and a lithium ion battery using the same according to the present invention will be described with reference to the drawings. The technical scope of the present invention is defined based on the description of the claims. It should be done and is not limited to the following forms. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  First, since the lithium ion battery according to the present invention can have a high capacity, it can be suitably used as a lithium ion secondary battery for a vehicle drive power source or the like, and can also be used as a lithium ion secondary battery for portable devices such as a mobile phone. Is also fully applicable.

  That is, the lithium ion battery that is the subject of the present invention is not particularly limited as long as it uses the positive electrode for a lithium ion battery of the present invention.

  For example, when the lithium ion battery is distinguished by its form / structure, it can be applied to any conventionally known form / structure, such as a stacked (flat) battery or a wound (cylindrical) battery. is there. By adopting a stacked (flat) battery structure, long-term reliability can be secured by a sealing technique such as simple thermocompression bonding, which is advantageous in terms of cost and workability.

  Moreover, when viewed in terms of electrical connection form (electrode structure) in a lithium ion battery, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries. is there.

  Conventionally known, such as a solution electrolyte type battery using a solution electrolyte such as a non-aqueous electrolyte for the electrolyte layer, a polymer battery using a polymer electrolyte for the electrolyte layer when distinguished by the type of electrolyte layer in the lithium ion battery It can be applied to any electrolyte layer type. The polymer battery is further divided into a gel electrolyte type battery using a polymer gel electrolyte (also simply referred to as a gel electrolyte) and a solid polymer (all solid) type battery using a polymer solid electrolyte (also simply referred to as a polymer electrolyte). It is done.

  Therefore, in the following description, drawings are shown for a non-bipolar (internal parallel connection type) lithium ion secondary battery and a bipolar (internal series connection type) lithium ion secondary battery using the positive electrode for a lithium ion battery of the present invention. It will be explained very simply using it. However, the technical scope of the lithium ion battery of the present invention should not be limited to these.

  FIG. 1 shows a flat type (stacked type) lithium ion secondary battery (hereinafter simply referred to as a non-bipolar lithium ion secondary battery or a non-bipolar type secondary battery), which is a typical embodiment of the lithium ion battery of the present invention. 1 is a schematic cross-sectional view schematically showing the entire structure of a secondary battery.

  As shown in FIG. 1, in the non-bipolar lithium ion secondary battery 10, a battery film 22 is made of a polymer-metal composite laminate film, and the entire periphery thereof is bonded by thermal fusion. Thus, the power generation element (battery element) 17 is housed and sealed. That is, a substantially rectangular power generation element (battery element) 17 in which the charge / discharge reaction actually proceeds has a structure sealed inside the laminate sheet that is the battery outer packaging material 22.

  Here, the power generation element 17 includes a positive electrode plate having a positive electrode (positive electrode active material layer) 12 formed on both surfaces of the positive electrode current collector 11 (one surface for the outermost layer of the power generation element), an electrolyte layer 13, and a negative electrode current collector 14. The negative electrode plate in which the negative electrode (negative electrode active material layer) 15 was formed on both surfaces is laminated. At this time, the positive electrode (positive electrode active material layer) 12 on one surface of one positive electrode plate and the negative electrode (negative electrode active material layer) 15 on one surface of one negative electrode plate adjacent to the one positive electrode plate face each other through the electrolyte layer 13. Thus, a plurality of layers of the positive electrode plate, the electrolyte layer 13, and the negative electrode plate are laminated in this order.

  As a result, the adjacent positive electrode (positive electrode active material layer) 12, electrolyte layer 13, and negative electrode (negative electrode active material layer) 15 constitute one unit cell layer 16. Therefore, it can be said that the lithium ion secondary battery 10 of the present embodiment has a configuration in which a plurality of single battery layers 16 are stacked and electrically connected in parallel. Note that the positive electrode (positive electrode active material layer) 12 is formed only on one side of the outermost layer positive electrode current collector 11 a located in both outermost layers of the power generation element (battery element; laminate) 17. In addition, by changing the arrangement of the positive electrode plate and the negative electrode plate in FIG. 1, the outermost negative electrode current collector (not shown) is positioned in both outermost layers of the power generation element (battery element) 17, and the outermost layer negative electrode Also in the case of the current collector, the negative electrode (negative electrode active material layer) 15 may be formed only on one side.

  Further, the positive electrode tab 18 and the negative electrode tab 19 that are electrically connected to the respective electrode plates (positive electrode plate and negative electrode plate) are connected to the positive electrode current collector 11 and the negative electrode of each electrode plate via the positive electrode terminal lead 20 and the negative electrode terminal lead 21. It is attached to the current collector 14 by ultrasonic welding or resistance welding. Accordingly, the positive electrode tab 18 and the negative electrode tab 19 that are electrically connected to the positive electrode current collector 11 and the negative electrode current collector 14 are sandwiched between the heat fusion portions and exposed to the outside of the battery exterior material 22. It has a structure.

  FIG. 2 shows another typical embodiment of the lithium ion battery of the present invention, a bipolar flat type (stacked type) lithium ion secondary battery (hereinafter simply referred to as a bipolar lithium ion secondary battery, or bipolar). 1 is a schematic cross-sectional view schematically showing the entire structure of a secondary battery.

  As shown in FIG. 2, the bipolar lithium ion secondary battery 30 has a structure in which a substantially rectangular power generation element (battery element) 37 in which a charge / discharge reaction actually proceeds is sealed inside a battery exterior member 42. Have The power generation element 37 of the bipolar secondary battery 30 according to the present embodiment has an electrolyte layer 35 sandwiched between one or two or more bipolar electrodes 34, and a positive electrode (positive electrode active material layer) of adjacent bipolar electrodes 34. ) 32 and the negative electrode (negative electrode active material layer) 33 are opposed to each other. Here, the bipolar electrode 34 has a structure in which a positive electrode (positive electrode active material layer) 32 is provided on one surface of the current collector 31 and a negative electrode (negative electrode active material layer) 33 is provided on the other surface. That is, in the bipolar secondary battery 30, a bipolar electrode having a positive electrode (positive electrode active material layer) 32 on one surface of the current collector 31 and a negative electrode (negative electrode active material layer) 33 on the other surface. A power generation element (battery element) 37 having a structure in which a plurality of 34 are stacked via an electrolyte layer 35 is provided.

  The adjacent positive electrode (positive electrode active material layer) 32, electrolyte layer 35, and negative electrode (negative electrode active material layer) 33 constitute one single battery layer (= battery unit or single cell) 36. Therefore, it can be said that the bipolar secondary battery 30 has a configuration in which the single battery layers 36 are stacked. Further, a seal portion (insulating layer) 43 is disposed around the unit cell layer 36 in order to prevent liquid junction due to leakage of the electrolyte from the electrolyte layer 35. By providing the seal portion (insulating layer) 43, the adjacent current collectors 31 can be insulated and a short circuit due to contact between the adjacent electrodes (the positive electrode 32 and the negative electrode 33) can be prevented.

  In addition, the positive electrode side electrode 34a and the negative electrode side electrode 34b located in the outermost layer of the power generation element (battery element) 37 may not have a bipolar electrode structure. For example, a structure in which the positive electrode (positive electrode active material layer) 32 or the negative electrode (negative electrode active material layer) 33 only on one side necessary for the current collectors 31a and 31b (or terminal plates) may be provided. A positive electrode (positive electrode active material layer) 32 may be formed on only one side of the positive electrode side outermost layer current collector 31 a located in the outermost layer of the power generation element (battery element) 37. Similarly, a negative electrode (negative electrode active material layer) 33 may be formed only on one side of the outermost current collector 31b on the negative electrode side located in the outermost layer of the power generation element (battery element) 37. In the bipolar lithium ion secondary battery 30, the positive electrode tab 38 and the negative electrode tab 39 are provided on the positive electrode side outermost layer current collector 31 a and the negative electrode side outermost layer current collector 31 b at both the upper and lower ends, respectively. 40 and the negative terminal lead 41 are joined. However, the positive electrode side outermost layer current collector 31 a may be extended to form a positive electrode tab 38, and may be derived from a laminate sheet that is the battery exterior material 42. Similarly, the negative electrode side outermost layer current collector 31b may be extended to form a negative electrode tab 39, which may be similarly derived from a laminate sheet that is the battery outer packaging material 42.

  Also, in the bipolar lithium ion secondary battery 30, the power generation element (battery element; laminate) 37 portion is sealed in a battery exterior material (exterior package) 42, and the positive electrode tab 38 and the negative electrode tab 39 are connected to the battery exterior material 42. It is preferable to have a structure taken out to the outside. This is because such a structure can prevent external impact and environmental degradation during use. The basic configuration of the bipolar lithium ion secondary battery 30 can be said to be a configuration in which a plurality of stacked single battery layers (single cells) 36 are connected in series.

  As described above, regarding each constituent requirement and manufacturing method of the non-bipolar lithium ion secondary battery and the bipolar lithium ion secondary battery, the electrical connection form (electrode structure) in the lithium ion secondary battery is different. Except for this, it is basically the same. Therefore, the following description will be made mainly on the respective constituent requirements of the above-described non-bipolar lithium ion secondary battery, but the same constituent requirements and manufacturing method are appropriately used for each constituent requirement and manufacturing method of the bipolar lithium ion secondary battery. And can be constructed or manufactured. Moreover, an assembled battery and a vehicle can also be comprised using the non-bipolar lithium ion secondary battery and / or bipolar lithium ion secondary battery of this invention.

First, in the present invention, as a characteristic configuration, in a positive electrode for a lithium ion battery of a so-called solid solution system in which a main active material is represented by a general formula: xLiMO _2. (1-x) Li ₂ NO ₃ , The charge / discharge pretreatment which regulated the amount of charge electricity shown in FIG.

  Here, x in the above formula may be a number satisfying 0 <x <1.

Moreover, as the M of LiMO ₂ which is electrochemically active in the solid solution represented by the general formula: xLiMO ₂ · (1-x) Li ₂ NO ₃ , one or more kinds having an average oxidation state of 3+ Any metal element may be used as long as it is not particularly limited. M in the above formula may be one or more elements selected from Mn, Ni, Co, Fe, V, and Cr, but preferably selected from Mn, Ni, Co, and Fe. One or more transition metal elements are desirable. This is because when these transition metal elements are used, a positive electrode for a lithium ion battery having a higher capacity and better cycle durability can be produced. In particular, a solid solution positive electrode using electrochemically active layered LiMO ₂ has a low meaning as an active material of a high-capacity positive electrode candidate material unless Ni is contained. Therefore, M in the above formula is preferably one containing Ni. When Ni is included, other elements such as Co may not be included.

The general _{formula: xLiMO 2 · (1-x} ) Li 2 NO 3 in an electrochemically inert of solid solution represented as the N of _Li 2 NO _3, 1 kind average oxidation state is 4+ The metal elements are not particularly limited as long as they are the above metal elements. N in the above formula may be one or more elements selected from Mn, Zr and Ti. This is because when these transition metal elements are used, a positive electrode for a lithium ion battery having a higher capacity and better cycle durability can be produced.

In the positive electrode for a lithium ion battery according to the present invention, the following pre-charge / discharge treatment is performed on the solid solution positive electrode represented by the above general formula: xLiMO ₂ · (1-x) Li ₂ NO ₃ , which regulates the amount of charge. It is characterized by being.

Here, FIG. 6 is a schematic diagram showing the relationship between the charge and discharge electric quantity. 7A and 7B are drawings showing charge / discharge curves of Li [Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ] O ₂ . Hereinafter, the pre-charging / discharging pretreatment in which the amount of charge electricity is regulated will be described in detail with reference to FIGS. 6, 7A, and 7B.

  As shown in FIG. 6, in the charge / discharge pretreatment that regulates the amount of charge as described above, first a predetermined positive amount of electricity Qc (1) is charged for the first time, and then the charge is discharged to a predetermined positive potential Ed (1). The quantity Qd (1) (0 <Qd (1) <Qc (1)) is discharged. In the second time, an electric quantity Qc (2) = Qd (1) + ΔQ (2) obtained by adding a predetermined positive electric quantity ΔQ (2) to the initial discharge electric quantity Qd (1) is charged. Thereafter, the same charge / discharge operation is repeated (charge / discharge pretreatment) until the charged potential Ec (n) (n is an integer of 2 or more) reaches a predetermined maximum potential Ec (max). Here, the unit of electricity is mAh / g (milliampere hour / gram), and the unit of potential is V (volt). The amount of electricity refers to the amount of electricity per gram of the positive electrode active material. The potential refers to the potential per unit cell (single cell) (hereinafter, unless otherwise specified, the same unit).

  Here, the same charge / discharge operation is repeated until the charged potential Ec (n) (n is an integer of 2 or more) reaches a predetermined maximum potential Ec (max) in detail as follows.

  After the second charge described above, first, a second discharge is performed to a predetermined potential Ed (2). Next, a third charge is performed to charge an electric quantity Qc (3) = Qd (2) + ΔQ (3) obtained by adding a predetermined electric quantity ΔQ (3) to the second discharge electric quantity Qd (2). . Such a series of charging / discharging operations is defined as one cycle, and this charging / discharging cycle is repeated until the charged potential Ec (n) (n is an integer of 2 or more) reaches a predetermined maximum potential Ec (max). That is, in a certain arbitrary charging / discharging cycle, after the (n-1) th charging (n is an integer of 2 or more) for charging the quantity of electricity Qc (n-1), the battery is first charged to a predetermined positive potential Ed (n-1). The (n-1) th discharge for discharging the quantity Qd (n-1) (0 <Qd (n-1) <Qc (n-1)) is performed. Next, an electric quantity Qc (n) = Qd (n−1) + ΔQ (n) obtained by adding a predetermined positive electric quantity ΔQ (n) to the (n−1) th discharge electric quantity Qd (n−1) is charged. This charging and discharging cycle may be repeated until the nth charge is performed and the charged potential Ec (n) reaches a predetermined maximum potential Ec (max). The above is an explanation for assisting in understanding when n is 3 or more, and is of course unnecessary when Ec (2) reaches Ec (max).

  At this time, the charge / discharge pretreatment may be completed at the stage of performing the nth charge when the charge potential Ec (n) has reached a predetermined maximum potential Ec (max). Alternatively, the nth charge is performed until the charge potential Ec (n) reaches a predetermined maximum potential Ec (max), and then the nth discharge is performed to the predetermined potential Ed (n) to complete the pre-charge / discharge processing. May be. These may be properly used according to the intended use. For example, in the former case, after the pre-charge / discharge pretreatment, if necessary, the battery may be charged to full charge so that it can be used anytime. In the latter case, there may be a case where the remaining capacity that can be discharged is discharged until it becomes empty (discharge end voltage) if necessary.

(1) Predetermined amount of electricity Qc (1) in the first (first) charging The prescribed amount of electricity Qc (1) in the first (first) charging does not impair the operational effects of the present invention. There is no particular limitation as long as it is within the range. In other words, the reaction at the flat part of the initial charge curve does not cause a significant change in the crystal structure in the solid solution cathode crystal from the beginning, and the constituent elements are more stably arranged and stabilized by charging and discharging in a lower potential region. Any material can be used as long as it can be structurally stabilized by gentle transition to the structure. Here, among the charge / discharge curves in FIG. 7, the charge conditions used in the first charge curve are the same as the first charge conditions of the pre-charge / discharge pretreatment. That is, the same electrode configuration (the same composition for both the positive electrode and the counter electrode (negative electrode)), and the one obtained by constant current charging using the same current value (for example, a current rate of 0.5 C or less) under the same temperature environment. Shall be used. This is because even if the temperature and the material of the negative electrode are different, the charge curves obtained are different.

  Preferably, in the initial charge curve (see 1st in FIG. 7A and the charge curve in FIG. 7B), it is desirable to set the quantity of electricity Qcp near the beginning (start point P) of the flat portion (plateau portion). The start of this flat part (start point P) corresponds to the part of the arrow in the figure. Specifically, a portion of the dotted line A extrapolating the flat portion of the initial charging curve and a portion where the slope of the electric potential in the vicinity of the flat portion is constant before reaching the flat portion of the initial charging curve. Indicates a point (capacitance Qcp, potential Ecp) on the charging curve immediately below the intersection C with the one-dot broken line B extrapolated.

(A) Lower limit value of the predetermined amount of electricity Qc (1) at the first charge However, the predetermined amount of electricity Qc (1) at the first charge does not necessarily need to be the amount of electricity Qcp near the beginning of the flat portion. . In other words, the lower limit of the predetermined amount of electricity Qc (1) in the initial charge may be an amount of electricity smaller than the amount of electricity Qcp. Even in this case, the operational effects of the present invention are not impaired. In other words, if the charge amount after the second time is increased stepwise and the charge / discharge pretreatment is repeated until the maximum potential Ec (max) is reached, the amount of electricity until the beginning of the flat part is surely reached in the middle of the process. This is because Qcp is reached. In other words, the maximum potential Ec (max) is set to be equal to or higher than the potential Ec ′ of the flat portion, more preferably higher than the potential Ec ′ of the flat portion, so that the constituent elements can be more stably arranged and the stable structure can be relaxed. This is because the structure can be stabilized by the migration. When the maximum potential Ec (max) is lower than the potential Ec ′ of the flat portion, the constituent elements are not more stably arranged and the transition to the stable structure is not sufficient, and the structural stabilization is not sufficiently performed. Therefore, subsequent use at a high potential (charging / discharging) causes a reaction in a flat portion for the first time, and a significant change in the crystal structure occurs at that time, resulting in deterioration of the charging / discharging cycle.

(B) The upper limit value of the predetermined electric quantity Qc (1) in the first (first) charge The upper limit value of the predetermined electric quantity Qc (1) in the first charge is a significant increase in the crystal structure in the solid solution positive electrode crystal. In order not to cause a change from the beginning, it can be said that it is not necessary to charge significantly beyond the beginning P of the flat portion of the initial charging curve (see the arrow portion in FIGS. 7A and 7B). That is, as described above, the reaction at the plateau portion seen in the initial charge curve is not related to the oxidation and reduction of the metal elements M and N, and the elimination of Li ^{+ in} the crystal and the accompanying oxygen dianion. It is oxidation. Therefore, it is a point of the present invention that the reaction in this part is performed mildly. That is, this plateau is considered to be a process in which the dianion of oxygen in the solid solution positive crystal is oxidized and Li ions are released. When this reaction occurs vigorously, the crystal structure undergoes a significant change. For this reason, it can be said that it is desirable to limit the amount of electricity (charge amount) of the reaction at the plateau portion so as not to increase in the initial charge.

As a result of the examination, the capacity before the plateau part of the initial charge curve is considered to be the contribution of the metal element M in LiMO ₂ . Then, if the capacity Qcp at which the plateau part starts is greatly exceeded, Li ⁺ is released from the Li ₂ NO _{3 part} (Li ₂ MnO _{3 in} FIGS. 7A and 7B) and the oxidation of O ²⁻ constituting the crystal. Occurs violently and the crystals are greatly damaged. Therefore, it is considered that deterioration occurs rapidly in the subsequent cycles. That is, the plateau portion of the initial charging curve is considered to be the release of Li ⁺ from the Li ₂ NO ₃ portion and the oxidation of O ²⁻ constituting the crystal, so the capacity region before this plateau portion It is appropriate to perform the charge / discharge pretreatment within a range not significantly exceeding (0 to Qcp). Therefore, as will be described in detail below, the first charge is performed using the contribution ratio of the element M (Ni, Co in FIGS. 7A and 7B) corresponding to the capacity region before the plateau portion to the theoretical capacity. It defines the amount of electricity.

Specifically, the capacity region before the plateau portion of the initial charge curve corresponds to the amount of electricity that contributes to the theoretical capacity when M is a one-electron reaction in LiMO ₂ . Therefore, charged electricity quantity of first-time, it is desirable electric quantity not exceeding 130% of the contribution to the theoretical capacity when a one-electron reaction of M with LiMO _2. The reason why it is set to 130% is that the effect is reduced when the vicinity is exceeded. That is, it can be said that a sufficient effect of the present invention can be obtained if the amount of electricity is 130% or less of the contribution to the theoretical capacity of the element M (see the comparison between the example and the comparative example). However, even if it exceeds 130%, it is included in the technical scope of the present invention as long as it has an effect of suppressing deterioration at a high potential charge / discharge as compared with a battery using a positive electrode not subjected to the charge / discharge pretreatment of the present invention. It can be said. This is because if the amount of electricity in the initial charge increases beyond the capacity Qcp where the potential Ec ′ of the flat portion starts, the reaction corresponding to the amount of electricity exceeding the Qcp proceeds in the crystal, and the crystal structure Change will also increase. As a result, more stable arrangement of the constituent elements in the crystal by charge / discharge pretreatment, and the crystal region that can be structurally stabilized by gentle transition to the structure will gradually decrease, suppressing charge / discharge cycle deterioration. The effect will be reduced.

If the initial amount of electricity is before the start of the flat part, the effect of the first charge / discharge treatment will not be effective. However, since the second positive charge is applied by adding a predetermined amount of electricity. As a result, pre-processing is performed, but it takes time. From the above viewpoint, it is desirable that the initial charge electric quantity is 80% or more and 130% or less of the contribution to the theoretical capacity when M is a one-electron reaction in LiMO ₂ , more preferably 80%. The amount of electricity is ~ 120%.

The theoretical capacity when M is a one-electron reaction in LiMO ₂ is described as follows by taking as an example the case where Ni and Mn in M are the same amount as described in the examples. Ni is a two-electron reaction, Co is a one-electron reaction, Mn in M is a zero-electron reaction, and the active material of Example 1 is calculated as follows. In the calculation formula, the Faraday constant was 96487 (coulomb / mol).

Composition formula: Li [Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ] O ₂ (formula weight: 85.2)
Another example (general formula): A positive electrode active material of 0.5 [Li (Ni _0.4175 Co _0.165 Mn _0.4175 ) O ₂ ] · 0.5 [Li ₂ MnO ₃ ] is taken as an example.

Theoretical capacity (mAh / g) of these elements calculated as Ni: 2 electrons, Co: 1 electron reaction
= 1000 × 96487 mC / mol × (2 × 0.17 + 1 × 0.07) / (3600 s / h × 85.2 g / mol)
= 129 mAh / g
(2) Predetermined potential Ed (1) at the first discharge For the predetermined potential Ed (1) at the first discharge, confirm that the effect of the present invention is not sufficient only by holding at least the initial charge potential. And below 1.5 V at a potential converted to lithium metal or lithium metal (also simply referred to as Li counter electrode, which corresponds to a potential based on the potential of lithium metal in an electrolyte solution in which 1 mol of lithium ion is dissolved). Then, another deterioration reaction may start. Therefore, the predetermined potential Ed (1) is preferably in the range of 1.5 V to 4.0 V in terms of lithium metal or a potential converted to lithium metal. This is because within this range, the effects of the present invention are sufficiently obtained, and another deterioration reaction does not start. A more preferable range is 2.0V to 3.5V. This is because, within this range, mild charge / discharge pretreatment can be performed without side reactions, and a much longer time is not required.

(3) Predetermined electric quantity ΔQ (n) applied after the second time The predetermined electric quantity ΔQ (n) to be added to the immediately preceding discharge electric quantity Qd (n−1) in the second and subsequent chargings is It is desirable to have an electric quantity that does not cause a significant change in the crystal structure even in the second and subsequent charging / discharging, can continue a more stable arrangement of constituent elements and a gentle transition to a stable structure, and can be more structurally stable. That is, if the predetermined amount of electricity ΔQ (n) is too small, the effect is large to some extent, but the processing required to reach the maximum potential Ec (max) takes too long (the number of times of repeated charge / discharge increases too much). become. On the other hand, if the predetermined amount of electricity ΔQ (n) is too large, the effect is reduced. If the predetermined amount of electricity ΔQ (n) is too large, the second and subsequent charging / discharging causes a significant change in the crystal structure and the effect may be lost. For the above reasons, the predetermined amount of electricity ΔQ (n) is 30% of the amount of electricity after the flat portion in the initial charging curves of FIGS. 7A and 7B (70 mAh / g in this positive electrode active material example). The following is desirable. To determine the beginning of the flat part, between the two points of the initial charge curve corresponding to the start point and the end point of the part where the slope of the differential curve is constant in the vicinity of the flat part (plateau part) of the initial charge curve To draw a one-dot broken line B. In the same manner, a one-dot broken line A is drawn connecting two points of a starting point and a flat part (plateau part) of the initial charging curve corresponding to the end point where the slope of the differential curve becomes zero. A point on the initial charging curve immediately below the intersection C between the dashed lines A and B can be the beginning (start point P) of the flat portion (plateau portion) of the initial charging curve (see FIGS. 7A and 7B). .

  Accordingly, when the constant amount of electricity ΔQ is successively added, a range of 3 to 30% of the amount of electricity after the flat portion of the initial charge curve (10 to 70 mAh / g in the example of FIG. 7) is preferable. . Further, the amount of electricity ΔQ (n) to be applied is not constant but may be changed every time. If the amount of electricity to be added ΔQ (n) is not constant, the amount of electricity after the flat portion of the initial charging curve is appropriately selected from the range of 0 to 30% (0 to 70 mAh / g in the example of FIG. 7). It is preferred to do so. Within these ranges, the crystal structure is not significantly changed even during the second and subsequent charge / discharge cycles, and the more stable arrangement of the constituent elements and the gentle transition to the stable structure can be continued, resulting in more structural stability. Because. When the amount of electricity ΔQ (n) to be applied is 0 mAh / g, that is, when the nth charge is performed with the amount of electricity immediately before discharge Qd (n−1) + ΔQ (n) = the amount of electricity Qd (n−1). Means that it may be included in part. However, when the amount of electricity ΔQ (n) to be applied is 0 mAh / g in all the charging after the second time, the constituent elements in the crystal structure due to the second and subsequent charging and discharging are more stably arranged and stable. Since it becomes difficult to shift to the structure, it is not included in the present invention.

  The feature of the present invention is that the pretreatment for improving the cycle durability can be performed by regulating the amount of electricity for charging without determining the upper limit potential for charging. It has realistic meaning (dominance) when the changing negative electrode and battery are assembled. That is, even if the battery voltage changes slightly due to the negative electrode, if there is no problem such as a side reaction in the discharged state, the positive electrode can be reliably and gradually charged on the flat portion. Therefore, it is possible to provide a lithium ion battery that can be structurally stabilized without causing a significant change in the crystal structure from the beginning and that has good cycle durability.

(4) Predetermined potential Ed (n) in the second and subsequent discharges In the present invention, the following is applied so that it is not necessary to define the discharge end potential Ed (n−1) in the second and subsequent discharges. In the calculation of the amount of charged electricity Qc (n), a predetermined amount of electricity ΔQ (n) is added to the value of the previous amount of discharged electricity Qd (n−1). This is because, when a battery is assembled using this material as the positive electrode active material, the charge / discharge pretreatment can be performed without any problem even when the potential of the negative electrode is not clearly known. Therefore, it can be said that it is not necessary to set a condition that the discharge end potential Ed (n−1) is set to a strictly constant value after the second time. However, as in the case of the predetermined potential Ed (1) in the first discharge described above, if the voltage is significantly lower than 2V, another deterioration reaction may start. Therefore, the predetermined potential Ed (n) is also preferably in the range of 1.5V to 4.0V for the Li counter electrode. A more preferable range is 2.0V to 3.5V. Within this range, there is no side reaction, and mild can be pre-charged / discharged and does not require much time. Therefore, in the embodiment, the predetermined potential Ed (n) in the second and subsequent discharges is also discharged to 2 V with respect to Li.

In FIG. 7, each discharge is set at the potential Ed = 2V (constant), but the capacity (electricity) at the end of the discharge gradually increases by repeating the charge / discharge pretreatment. It can be said that this is because. In initial charging curve of FIG. 7, the charge reaction of a flat portion is from _Li 2 NO ₃ (e.g. _{Li 2} MnO _{3) Li} 2 O escapes reaction. In the discharge after this reaction, the remaining NO ₂ (eg, MnO ₂ ) is reduced and Li ⁺ is inserted. This is because this amount is added to the charge / discharge capacity of the previous M (for example, Ni, Co) and the discharge capacity Qd is increased.

(5) Predetermined maximum potential Ec (max) The predetermined maximum potential Ec (max) is a flat portion around 4.5 V as seen from the initial charging curve of FIG. The potential may be set higher than the potential Ec ′. However, by increasing the temperature during charging, the potential Ec ′ of the flat portion is increased, and in addition to the basic characteristics of the active material, it varies depending on the size of the active material particles. Therefore, in consideration of the fluctuation range of the potential Ec ′ of such a flat portion, 4.8 V at which the charging curve starts to rise suddenly can be said to be a particularly preferable value. Beyond this, the charging curve suddenly rises (that is, the charging potential suddenly increases with a small amount of charge), so there is no significant difference between 4.9V and 5.0V. That is, regardless of whether the predetermined maximum potential Ec (max) is set to 4.8 V or higher, the number of charge / discharge cycles in the pre-charge / discharge pretreatment does not increase, or even if it increases, one extra cycle is performed. The potential Ec (max) is reached. Therefore, it can be said that there is no significant difference in the time required for the pre-charge / discharge treatment. That is, the predetermined maximum potential is 4.6 V or more, preferably 4.7 V to 5.0 V, which is higher than the potential Ec ′ of the flat portion in the vicinity of 4.5 V in terms of lithium metal or lithium metal. The range is more preferably 4.8 V to 5.0 V, particularly preferably 4.8 V. When the voltage is less than 4.6 V, the difference from the potential of the flat portion is small, and depending on the temperature condition, the type of active material, and the type of negative electrode, the maximum potential is obtained within the range of potential fluctuation of the flat portion. Therefore, there is a possibility that sufficient charge / discharge pretreatment is not performed. Because of this tolerance, even when a battery is assembled in combination with an appropriate negative electrode, the same processing can be performed for the positive electrode of the battery by estimating the maximum charge potential Ec (max) of the battery from the charge / discharge curve of the negative electrode.

  In the pre-charging / discharging pretreatment according to the present invention, it is preferable to end the charging when a predetermined maximum potential Ec (max) is reached during charging. For example, when a predetermined maximum potential Ec (max) is reached during the nth charge, the nth charge electricity amount Qc (n) (= Qd (n−1) + ΔQ (n)) can be charged. If not, it is desirable to finish charging. This is because if charging is continued beyond a predetermined maximum potential Ec (max), a so-called overcharge state may occur. From this point of view, the upper limit value of the predetermined maximum potential Ec (max) is about 5.0 V as the upper limit for the Li metal counter electrode, and no further charging is performed beyond this potential. It can be said that it is desirable. This is also true when a battery is assembled in combination with an appropriate negative electrode, and the maximum charge potential Ec (max) of the battery is estimated from the charge / discharge curve of the negative electrode and the same treatment is performed on the positive electrode of the battery. is there.

(6) Charging / Discharging Conditions for Charge / Discharge Pretreatment Charging performance depends on the size of the active material particles and the electrode structure in addition to the basic characteristics of the active material. It can be confirmed that there is no problem though it takes time for the charging speed to be slow. On the other hand, if the charging speed is too high, the charge / discharge pretreatment of the present invention may not be sufficiently performed to the inside of the crystal. Moreover, it deviates from the idea of the present invention to process mildly. From the above viewpoint, the charging conditions for the charge / discharge pretreatment may be performed within a range that does not impair the effects of the present invention, and need not be particularly specified. It can be said that it is desirable to use. However, since the charging performance described above varies depending on the active material particle size and the electrode structure, in addition to the basic characteristics of the active material, it is a case where the current rate is exceeded. The case where it can be sufficiently performed to the inside is included in the technical scope of the present invention. The discharge conditions of the charge / discharge pretreatment are the same as the above-described charge conditions. That is, it can be said that it is desirable to use a current rate of 0.5 C or less, but the current rate is not necessarily limited.

  Moreover, the temperature at the time of performing the pre-charging / discharging treatment of the present invention can be arbitrarily set as long as it is within a range that does not impair the effects of the present invention. Specifically, it may be performed at room temperature, may be performed at a temperature higher than room temperature, or may be performed at a temperature lower than room temperature. From the economical point of view, it is desirable to carry out at room temperature that does not require special heating and cooling.

  Moreover, it is desirable to carry out at a temperature higher than room temperature from the viewpoint that a larger capacity can be expressed and the cycle durability can be improved by a short charge / discharge pretreatment. The temperature at the time of performing the charge / discharge pretreatment may be higher than room temperature, but is preferably 35 ° C. or higher and 80 ° C. or lower, and more preferably in the range of 40 to 60 ° C. The room temperature here means a temperature in a state where no special heating / cooling is performed, and it is in a range that can be said to be approximately 15 ° C. or more and less than 35 ° C. However, even if the temperature is out of the above range, it can be said that the temperature is at room temperature as long as the temperature is not in the state of special heating and cooling.

  It does not restrict | limit especially as a process (time) which performs the charging / discharging pretreatment of this invention. For example, the charge / discharge pretreatment can be performed in a state in which a battery is configured, or an electrode or a configuration corresponding to an electrode, as described above. That is, in addition to the application in which the electrode is configured, the application after assembling the battery together with the negative electrode, the application in the state of the positive electrode active material powder may be used. Application to a battery can be carried out by considering the potential profile of the capacitance of the negative electrode to be combined and determining the application conditions of the present invention (conditions for pre-charge / discharge pretreatment; particularly a predetermined maximum potential Ec (max), etc.). In the present invention, once the charge / discharge pretreatment pattern in which the amount of electricity is regulated is determined for one positive electrode material, the positive electrode can appropriately perform precharge / discharge pretreatment without using a potential reference such as lithium. Therefore, high-energy-density lithium ion batteries with good cycle durability can be implemented without using an appropriate potential reference for mass processing of positive electrodes and positive electrode materials, and further, charging and discharging pretreatment of the positive electrodes in a battery assembly. Can be efficiently manufactured in large quantities.

  Here, in the case where the battery is configured, it is superior in that pre-charge / discharge pretreatment of a large number of electrodes can be performed at a time, rather than performing each of the individual electrodes or configurations corresponding to the electrodes. On the other hand, when the process is performed for each individual electrode or each electrode-corresponding configuration, it is superior to the state in which the battery is configured in that the degree of pre-charge / discharge pretreatment on each electrode is less likely to occur.

In addition, the method for producing a solid solution represented by the above general formula: xLiMO ₂ · (1-x) Li ₂ NO ₃ before performing the charge / discharge pretreatment is not particularly limited, and a conventionally known production method. Can be used as appropriate. For example, as shown in the Examples, the composite carbonate method can be used as follows. That is, a predetermined amount of, for example, nickel sulfate, cobalt sulfate, and manganese sulfate, such as metal sulfate salts and metal nitrate salts of metal elements corresponding to M and N in the above formula, is prepared to prepare a mixed solution thereof. Ammonia water was added dropwise to this until pH 7 was reached, and a Na ₂ CO ₃ solution was further added dropwise to form a composite carbonate of Ni—Co—Mn (however, the M—N by the combination of M and N in the above formula). Different types of metal complex carbonates). Then, after suction filtration, it is washed with water and dried at a predetermined temperature and time (for example, at 120 ° C. for 5 hours). This is calcined at a predetermined temperature and time (for example, at 500 ° C. for 5 hours). A small excess of LiOH.H ₂ O was added thereto and mixed for a predetermined time (for example, 30 minutes) in an automatic mortar. Thereafter, the main calcination is performed at a predetermined temperature and time (for example, at 900 ° C. for 12 hours), followed by rapid cooling using liquid nitrogen, whereby the above-described general formula: xLiMO ₂ · (1-x ) A solid solution represented by Li ₂ NO ₃ can be produced. The last rapid cooling using liquid nitrogen is not particularly necessary, but can be said to be a useful processing operation in that a solid solution can be produced with a very beautiful state by performing such processing. .

In addition, the identification of the solid solution represented by the above general formula: xLiMO ₂ · (1-x) Li ₂ NO ₃ before performing the charge / discharge pretreatment is performed by X-ray diffraction (XRD) as performed in Examples described later. ), And can be analyzed using inductively coupled plasma (ICP) elemental analysis.

  The charge / discharge pretreatment (method) of the positive electrode for a lithium ion battery is as described above. That is, as an effective charge / discharge pretreatment (method) of the solid solution system positive electrode according to the present invention, the above-described charge / discharge pretreatment in which the amount of charge electricity is regulated in the state in which the battery is configured or the electrode or an electrode-corresponding configuration. It is effective to apply. Thereby, a positive electrode for lithium ion batteries with high capacity and good cycle durability and batteries with high energy density can be produced in large quantities.

  The above is the description regarding the characteristic structural requirements of the lithium ion battery of the present invention, and the other structural requirements are not particularly limited. Therefore, in the following, regarding the other constituent elements other than the characteristic constituent elements of the lithium ion battery of the present invention, the non-bipolar lithium ion secondary battery shown in FIG. 1 and FIG. A description will be given focusing on the secondary battery. However, the present invention is not limited to these.

[Current collector]
The current collector is not particularly limited with respect to any of the non-bipolar type and the bipolar type lithium ion secondary battery. Specifically, the current collector is at least one type of current selected from the group consisting of iron, chromium, nickel, manganese, titanium, molybdenum, vanadium, niobium, aluminum, copper, silver, gold, platinum, and carbon. A current collector made of a current material can be used. In the present invention, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these current collector materials can be preferably used. Further, a current collector in which the surface of a metal (excluding aluminum) as the current collector material is coated with aluminum as another current collector material may be used. Moreover, you may use the electrical power collector which bonded together the metal foil which is two or more said electrical power collector materials depending on the case. Although the thickness of a collector is not specifically limited, Usually, it is about 1-100 micrometers.

[Electrodes (positive electrode and negative electrode)]
The configurations of the positive electrode (positive electrode active material layer) and the negative electrode (negative electrode active material layer) are not particularly limited for both non-bipolar and bipolar lithium ion secondary batteries, and known positive electrodes and negative electrodes are applicable. . The electrode includes a positive electrode active material if the electrode is a positive electrode and a negative electrode active material if the electrode is a negative electrode.

  The material (material) of the positive electrode active material and the negative electrode active material is not particularly limited as long as it has the characteristic constituent requirements of the lithium ion battery of the present invention, and depends on the type of battery. What is necessary is just to select suitably.

Specifically, as the positive electrode active material, the positive electrode material for a lithium ion battery of the present invention represented by the above general formula; xLiMO ₂ · (1-x) Li ₂ NO ₃ is used as the main active material of the positive electrode. is there.

As the positive electrode active material, the positive electrode material for a lithium ion battery of the present invention represented by the above general formula; xLiMO ₂ · (1-x) Li ₂ NO ₃ may be used alone, and further as necessary. Other conventionally known positive electrode active materials may be used in combination. Other positive electrode active materials include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Co—Mn) O _2, and lithium—such as those in which some of these transition metals are substituted with other elements A transition metal complex oxide is mentioned. In addition, for example, a lithium-transition metal phosphate compound, a lithium-transition metal sulfate compound, and the like can be given. In some cases, two or more other positive electrode active materials may be used in combination. Preferably, it is a lithium-transition metal composite oxide from the viewpoint of capacity and output characteristics, but it is needless to say that other positive electrode active materials may be used.

Here, in the positive electrode active material, the content of the main active material represented by the above general formula; xLiMO ₂ · (1-x) Li ₂ NO ₃ is 50% by mass or more, preferably 70% by mass or more. Preferably it is 85 mass% or more, More preferably, it is 95 mass% or more. Among them, it is particularly desirable to use a solid solution system material represented by the above general formula that can exhibit a large electric capacity exceeding 200 mAh / g in the total amount (100 mass%).

As the negative electrode active material, any negative electrode active material usually used in a lithium ion secondary battery may be used. Specifically, carbon or a lithium-transition metal composite oxide can be suitably used. Examples of the carbon include crystalline carbon materials such as natural graphite, artificial graphite, carbon black, acetylene black, activated carbon, carbon fiber, coke, soft carbon, and hard carbon (non-graphitizable carbon material), and amorphous carbon materials. For example, carbon. Examples of the lithium-transition metal composite oxide include a lithium-tin alloy, a lithium-silicon alloy, and a lithium alloy obtained by adding other elements thereto; lithium-titanium composite oxide (lithium titanate: Li ₄ Ti ₅ O ₁₂ ) And lithium-transfer metal composite oxide. However, it is not limited to these. These may be used alone or in combination of two or more.

  The average particle diameter of each active material contained in each positive electrode active material layer and negative electrode active material layer is not particularly limited, but is preferably 1 to 20 μm from the viewpoint of increasing the output. In the present specification, the “particle diameter” means the maximum distance L among the distances between any two points on the contour line of the active material. As the value of “average particle diameter”, the average particle diameter of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The calculated value shall be adopted. The particle diameters and average particle diameters of other components can be defined in the same manner.

  When the optimum particle size for expressing the unique effect of each active material is different, the optimum particle size for expressing each unique effect may be blended and used. It is not always necessary to make the particle size uniform.

  The thickness of the positive electrode (positive electrode active material layer: one side) and the negative electrode (negative electrode active material layer: one side) may be determined as appropriate in consideration of the intended use of the battery (emphasis on output, energy, etc.) and ion conductivity. Both are usually about 1 to 500 μm.

For the positive electrode (positive electrode active material layer: one side) and the negative electrode (negative electrode active material layer), any of kneading methods, sputtering, vapor deposition, CVD, PVD, ion plating and thermal spraying can be used in addition to the usual method of applying (coating) slurry. It can also be formed by this method. As the negative electrode active material suitable for such a forming method, carbon, lithium metal, lithium aluminum alloy, lithium tin alloy, lithium silicon alloy and the like can be suitably used in addition to lithium titanate. About the positive electrode active material, what is necessary is just to include the positive electrode material for lithium ion batteries of the present invention represented by the above general formula; xLiMO ₂ · (1-x) Li ₂ NO ₃ .

  Electrode (positive electrode and negative electrode) is a conductive material (hereinafter also referred to as a conductive additive), binder, electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.) for enhancing electronic conductivity, and ion conductivity. For example, an electrolyte supporting salt (lithium salt) may be included.

  Examples of the conductive material include acetylene black, carbon black, graphite, and carbon fiber. By including a conductive additive, the conductivity of electrons generated at the electrode can be increased, and the battery performance can be improved.

  Examples of the binder include polyvinylidene fluoride (PVdF), styrene butadiene rubber, and polyimide. However, it is not necessarily limited to these.

  The conductive binder having the functions of the conductive material and the binder may be used in place of the conductive material and the binder, or may be used in combination with one or both of the conductive material and the binder. Commercially available TAB-2 (manufactured by Hosen Co., Ltd.) or the like can be used as the conductive binder.

  Examples of the electrolyte include ion conductive polymers (solid polymer electrolytes) including lithium salts such as polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof.

What is necessary is just to select the electrolyte support salt (lithium salt) used according to the kind of battery. For example, inorganic acid anion salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiTaF ₆ , LiAlCl ₄ , Li ₂ B ₁₀ Cl ₁₀ ; LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li Organic acid anion salts such as (C ₂ F ₅ SO ₂ ) ₂ N; mixtures thereof and the like can be used. However, it is not necessarily limited to these.

  Active material, conductive material, binder, electrolyte (polymer matrix, ion-conducting polymer, electrolyte, etc.), the amount of electrode constituent materials such as electrolyte support salt (lithium salt), etc. It is preferable to determine in consideration of ionic conductivity.

[Electrolyte layer]
The electrolyte layer may be in a liquid, gel, or solid phase for any of the non-bipolar and bipolar lithium ion secondary batteries. In consideration of safety when the battery is damaged and prevention of liquid junction, the electrolyte layer is preferably a solid electrolyte such as a gel polymer electrolyte layer or an all-solid electrolyte layer. By using a solid electrolyte (which will be described later in detail, including a polymer gel electrolyte, a solid polymer electrolyte, and an inorganic solid electrolyte) as the electrolyte layer, it becomes possible to prevent liquid leakage. This is because it is possible to construct a lithium ion battery with high reliability that prevents entanglement.

  By using a gel polymer electrolyte layer (polymer gel electrolyte) as the electrolyte layer, the fluidity of the electrolyte is lost, the electrolyte is prevented from flowing out to the current collector, and the ionic conductivity between the layers can be blocked. . Examples of the gel electrolyte host polymer include PEO, PPO, PVdF, polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), PAN, PMA, and PMMA. Moreover, as a plasticizer, it is possible to use the electrolyte solution normally used for a lithium ion battery.

  The gel polymer electrolyte (polymer gel electrolyte) is produced by including an electrolyte solution usually used in a lithium ion battery in an all solid polymer electrolyte such as PEO or PPO. PVdF, PAN, PMMA, and the like, in which the electrolyte solution is held in a polymer skeleton having no lithium ion conductivity, also corresponds to the gel polymer electrolyte (polymer gel electrolyte). The ratio of the polymer constituting the gel polymer electrolyte (polymer gel electrolyte) and the electrolytic solution is not particularly limited. When 100% of the polymer is an all solid polymer electrolyte and 100% of the electrolytic solution is a liquid electrolyte, the intermediate is All are included in the concept of gel polymer electrolyte (polymer gel electrolyte). An inorganic solid electrolyte having ion conductivity such as an inorganic solid such as ceramic corresponds to the all solid electrolyte. Therefore, the polymer gel electrolyte, the solid polymer electrolyte, and the inorganic solid electrolyte are all included in the solid electrolyte.

  As the electrolyte layer, a conventionally known material can be used. Specifically, (a) polymer gel electrolyte (gel polymer electrolyte), (b) all solid polymer electrolyte (polymer solid electrolyte, inorganic solid electrolyte), (c) liquid electrolyte (electrolyte) or (d ) Separators (including non-woven fabric separators) impregnated with these electrolytes can be used.

(A) Gel polymer electrolyte (polymer gel electrolyte)
The gel polymer electrolyte (polymer gel electrolyte) refers to an electrolyte solution held in a polymer matrix. By using a gel polymer electrolyte as the electrolyte, the fluidity of the electrolyte is lost, and it is easy to cut off the ionic conductivity between each layer by suppressing the outflow of the electrolyte to the current collector layer such as a conductive polymer film. Is excellent.

Examples of the polymer matrix (polymer) or the gel electrolyte host polymer used as the polymer gel electrolyte include polymers having polyethylene oxide in the main chain or side chain (PEO), polymers having polypropylene oxide in the main chain or side chain ( PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polymethacrylic acid ester, polyvinylidene fluoride (PVdF), a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVdF-HFP), poly (methyl methacrylate) ( PMMA) and copolymers thereof are desirable. Among these, it is desirable to use PEO, PPO and their copolymers, or PVdF-HFP. Moreover, as a plasticizer, it is possible to use the electrolyte solution normally used for a lithium ion battery. Such an electrolytic solution is obtained by dissolving an electrolyte salt in a solvent. As the electrolyte _{(salt), LiPF 6, LiBF 4,} LiClO 4, LiAsF 6, LiTaF 6, LiAlCl 4, Li 2 B 10 Cl 10 inorganic acid anion salts such _{as, LiCF 3 SO 3, Li (} CF 3 SO 2 ) At least one selected from organic acid anion salts such as ₂ N and Li (C ₂ F ₅ SO ₂ ) ₂ N is desirable. As the solvent, ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), dimethyl carbonate (DMC), diethyl carbonate (DEC) and mixtures thereof are desirable.

  The ratio of the electrolytic solution in the gel electrolyte in the present invention is not particularly limited, but is preferably about several mass% to 98 mass% from the viewpoint of ionic conductivity. The present invention is particularly effective for a gel electrolyte having a large amount of electrolytic solution in which the proportion of the electrolytic solution is 70% by mass or more.

(B) All solid electrolyte (all solid polymer electrolyte, polymer solid electrolyte, inorganic solid electrolyte)
The use of an all solid electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost, the electrolyte does not flow out to the current collector layer, and the ion conductivity between the layers can be blocked.

Examples of the all solid polymer electrolyte include known solid polymer electrolytes such as PEO, PPO, and copolymers thereof, and inorganic solid electrolytes having ion conductivity such as ceramics. The solid polymer electrolyte contains a lithium salt in order to ensure ionic conductivity. As the lithium salt, LiBF ₄ , LiPF ₆ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , or a mixture thereof can be used.

(C) Liquid electrolyte (electrolyte)
Examples of the electrolytic solution include those obtained by dissolving an electrolyte salt in a solvent. As the electrolyte _{(salt), LiPF 6, LiBF 4,} LiClO 4, LiAsF 6, LiTaF 6, LiAlCl 4, Li 2 B 10 Cl 10 inorganic acid anion salts such _{as, LiCF 3 SO 3, Li (} CF 3 SO 2 ) At least one selected from organic acid anion salts such as ₂ N and Li (C ₂ F ₅ SO ₂ ) ₂ N is desirable. As the solvent, EC, PC, GBL, DMC, DEC and a mixture thereof are desirable.

(D) Separator impregnated with the electrolyte (including non-woven separator)
As the electrolyte that can be impregnated in the separator, the same electrolytes as those already described (a) to (c) can be used.

  Examples of the separator include a porous sheet and a nonwoven fabric made of a polymer that absorbs and holds the electrolyte.

  As the porous sheet, for example, a microporous separator can be used. Examples of the polymer include polyolefins such as polyethylene (PE) and polypropylene (PP); laminates having a three-layer structure of PP / PE / PP, polyimide, and aramid. The thickness of the separator cannot be uniquely defined because it varies depending on the intended use. However, in applications such as a secondary battery for driving a motor such as an electric vehicle (EV), a hybrid electric vehicle (HEV), and a fuel cell vehicle (FCV), the thickness is preferably 4 to 60 μm in a single layer or multiple layers. The separator preferably has a fine pore size of 1 μm or less (usually a pore size of about several tens of nm) and a porosity of 20 to 80%.

  As the nonwoven fabric, cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; conventionally known materials such as polyimide and aramid are used alone or in combination. The bulk density of the nonwoven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated polymer gel electrolyte. The porosity of the nonwoven fabric separator is preferably 50 to 90%. Furthermore, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, particularly preferably 10 to 100 μm. When the thickness is less than 5 μm, the electrolyte retention deteriorates, and when it exceeds 200 μm, the resistance increases.

[Seal (also called sealant or peripheral insulating layer)]
For the bipolar lithium ion secondary battery, the seal part is used to prevent adjacent collectors in the battery from contacting each other and short-circuiting due to slight unevenness of the end of the laminated electrode. It arrange | positions at the peripheral part of a battery layer. Bipolar lithium ion secondary batteries are effectively used to prevent liquid junction due to leakage of the electrolyte layer. As the seal portion, for example, polyolefin resin such as PE and PP, epoxy resin, rubber, polyimide and the like can be used, and polyolefin resin is preferable from the viewpoint of corrosion resistance, chemical resistance, film-forming property, economy and the like. . However, it is not limited to these.

[Positive electrode and negative electrode tab]
In the non-bipolar and bipolar lithium ion batteries of the present invention, a tab (positive electrode tab and negative electrode) that is electrically connected to each current collector or to the outermost layer current collector for the purpose of taking out current outside the battery. Tab) is taken out of the battery case. Specifically, as shown in FIG. 1, a laminate sheet in which a positive electrode tab electrically connected to each positive electrode current collector and a positive electrode tab electrically connected to each negative electrode current collector are battery exterior materials. It is taken out outside. Alternatively, as shown in FIG. 2, a laminate in which a positive electrode tab electrically connected to the positive electrode outermost layer current collector and a negative electrode tab electrically connected to the negative electrode outermost layer current collector are battery outer packaging materials. It is taken out of the sheet.

  The material which comprises a tab (a positive electrode tab and a negative electrode tab) in particular is not restrict | limited, The well-known highly electroconductive material conventionally used as a tab for lithium ion secondary batteries can be used. As a constituent material of the tab, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable, and aluminum, copper, and the like are more preferable from the viewpoint of light weight, corrosion resistance, and high conductivity. Is preferable, and aluminum is particularly preferable. Note that the same material may be used for the positive electrode tab and the negative electrode tab, or different materials may be used. Moreover, it is good also as a positive electrode and a negative electrode tab by extending each electrical power collector or outermost layer electrical power collector, and you may connect the positive electrode and negative electrode tab which were prepared separately to each electrical power collector or outermost layer electrical power collector. .

[Positive electrode and negative electrode lead]
The positive electrode and the negative electrode lead are also used as necessary. For example, when directly taking out the positive electrode tab and the negative electrode tab to be output electrode terminals from each current collector or the outermost current collector, the positive electrode and the negative electrode lead may not be used.

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

[Battery exterior materials]
As a battery exterior material, a conventionally known metal can case can be used, and a bag-like case that can cover a power generation element (battery element) using a laminate film containing aluminum can be used. For example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used as the laminate film, but the laminate film is not limited thereto.

[Appearance structure of lithium ion secondary battery]
FIG. 3 is a perspective view showing an appearance of a stacked flat non-bipolar or bipolar lithium ion secondary battery which is a typical embodiment of the lithium ion battery according to the present invention.

  As shown in FIG. 3, the stacked flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive electrode tab 58 and a negative electrode tab 59 for taking out electric power from both sides thereof. Has been pulled out. The power generation element (battery element) 57 is wrapped by the battery outer packaging material 52 of the lithium ion secondary battery 50, and the periphery thereof is heat-sealed. The power generation element (battery element) 57 includes a positive electrode tab 58 and a negative electrode tab 59. It is sealed in a state where it is pulled out to the outside. Here, the power generation element (battery element) 57 corresponds to the power generation elements (battery elements) 17 and 37 of the non-bipolar or bipolar lithium ion secondary batteries 10 and 30 shown in FIG. 1 or FIG. To do. Specifically, a plurality of single battery layers (single cells) 16 and 36 composed of positive electrodes (positive electrode active material layers) 12 and 32, electrolyte layers 13 and 35, and negative electrodes (negative electrode active material layers) 15 and 33 are laminated. It is a thing.

  The lithium ion battery of the present invention is not limited to the stacked flat shape as shown in FIGS. For example, the wound type lithium ion battery may have a cylindrical shape, or may have a shape that is a flattened rectangular shape by deforming such a cylindrical shape. There is no particular limitation. In the said cylindrical shape thing, a laminate film may be used for the exterior material, and the conventional cylindrical can (metal can) may be used, for example, It does not restrict | limit.

  Also, the removal of the tabs 58 and 59 shown in FIG. 3 is not particularly limited. For example, the positive electrode tab 58 and the negative electrode tab 59 may be drawn out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of parts and taken out from each side. It is not limited to what is shown. Further, in a wound type lithium ion battery, instead of a tab, for example, a terminal may be formed using a cylindrical can (metal can).

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

[Battery]
The assembled battery of the present invention is formed by connecting a plurality of lithium ion secondary batteries of the present invention. Specifically, at least two or more are used, and are configured by serialization, parallelization, or both. Capacitance and voltage can be freely adjusted by paralleling in series. In the assembled battery of the present invention, the non-bipolar lithium ion secondary battery and the bipolar lithium ion secondary battery of the present invention are used, and these are combined in series, in parallel, or in series and in parallel. Thus, an assembled battery can also be configured.

  4 is an external view of a typical embodiment of the assembled battery according to the present invention, FIG. 4A is a plan view of the assembled battery, FIG. 4B is a front view of the assembled battery, and FIG. It is a side view of an assembled battery.

  As shown in FIG. 4, an assembled battery 300 according to the present invention forms a small assembled battery 250 in which a plurality of lithium ion secondary batteries of the present invention are connected in series or in parallel to be detachable. It is also possible to form a plurality of possible small battery packs 250 connected in series or in parallel. As a result, it is possible to form the assembled battery 300 having a large capacity and a large output suitable for a vehicle driving power source and an auxiliary power source that require a high volume energy density and a high volume output density. 4A is a plan view of the assembled battery, FIG. 4A is a front view, and FIG. 4C is a side view. The small assembled battery 250 that can be attached / detached has an electrical connection means such as a bus bar. The assembled battery 250 is stacked in a plurality of stages using the connection jig 310. How many non-bipolar or bipolar lithium ion secondary batteries are connected to create the assembled battery 250 and how many assembled batteries 250 are stacked to produce the assembled battery 300 are mounted. What is necessary is just to determine according to the battery capacity and output of the vehicle (electric vehicle) to be.

[vehicle]
The vehicle of the present invention is characterized in that the lithium ion battery of the present invention or an assembled battery formed by combining a plurality of these is mounted. When the high-capacity positive electrode of the present invention is used, a battery having a high energy density can be configured. Therefore, when such a battery is mounted, a plug-in hybrid electric vehicle having a long EV travel distance or an electric vehicle having a long charge travel distance can be configured. In other words, the lithium ion battery of the present invention or an assembled battery formed by combining a plurality of these can be used as a power source for driving a vehicle. This is because the use of the lithium ion battery of the present invention or a combination battery composed of a plurality of these in a vehicle results in a long-life and highly reliable automobile. Examples of such vehicles include hybrid vehicles, fuel cell vehicles, and electric vehicles (including automobiles such as passenger cars, trucks, and buses, four-wheeled vehicles such as light vehicles, and motorcycles and three-wheeled vehicles). Etc. However, the application is not limited to automobiles. For example, it can be applied to various power sources for moving vehicles such as other vehicles, for example, trains, and power sources for mounting such as uninterruptible power supplies. It is also possible to use as.

  FIG. 5 is a conceptual diagram of a vehicle equipped with the assembled battery of the present invention.

  As shown in FIG. 5, in order to mount the assembled battery 300 on a vehicle such as the electric vehicle 400, the battery pack 300 is mounted under the seat at the center of the vehicle body of the electric vehicle 400. This is because if it is installed under the seat, the interior space and the trunk room can be widened. The place where the assembled battery 300 is mounted is not limited to the position under the seat, but may be a lower part of the rear trunk room or an engine room in front of the vehicle. The electric vehicle 400 using the assembled battery 300 as described above has high durability and can provide sufficient output even when used for a long period of time. Furthermore, it is possible to provide electric vehicles and hybrid vehicles that are excellent in fuel efficiency and running performance. A vehicle equipped with the assembled battery of the present invention can be widely applied to a hybrid vehicle, a fuel cell vehicle and the like in addition to an electric vehicle as shown in FIG.

[Method of manufacturing lithium ion battery]
Next, the method for producing the lithium ion battery of the present invention is not particularly limited except that the above-described pretreatment for charging and discharging the positive electrode of the present invention is performed in an appropriate step, and is conventionally known. This method can be applied.

  Therefore, below, it demonstrates about the manufacturing method of the lithium ion secondary battery of this invention other than the charging / discharging pretreatment of the positive electrode of this invention demonstrated above. However, the production method of the present invention is not limited to these.

  Production of a battery having an electrolyte as an electrolyte is performed by cutting the negative electrode slightly larger from the positive electrode and the negative electrode that have been subjected to the charge / discharge pretreatment as described above, and vacuum-drying each at a predetermined temperature (for example, 90 ° C.). And dried for 1 day. Between the positive electrode and the negative electrode, the positive electrode and the negative electrode are alternately laminated so that the outermost side becomes a negative electrode through a porous film of polypropylene having a predetermined thickness (for example, 25 μm), and each positive electrode and the negative electrode are bundled. Then, the leads are welded to form this laminate. In this laminate, positive and negative leads are taken out and placed in an aluminum laminate film back, and an electrolytic solution is injected with a liquid injector, and sealed under reduced pressure to obtain a battery. In addition, after using it as the battery using the positive electrode which has not performed the charge / discharge pretreatment, you may perform the charge / discharge pretreatment as mentioned above. In this case, a part of the seal is sealed with an appropriate clip or the like without sealing, and the gas generated in the pre-charge / discharge pretreatment is removed from the unsealed portion by removing the clip and then unsealed. The part may be sealed under reduced pressure.

  In addition to electrolyte batteries, electrolyte batteries, gel batteries, all-solid polymer batteries, and bipolar batteries using the electrolytes listed here can be produced by our well-known technology, so they are omitted here. To do.

  Next, a description will be given of criteria for determining whether or not the constituent requirements (technical scope) of the present invention are satisfied regardless of the manufacturing history.

(1) Constituent Requirements of the Present Invention: In the positive electrode represented by the general formula: xLiMO ₂ · (1-x) Li ₂ NO ₃ , the main active material is subjected to charge / discharge pretreatment that regulates the amount of charge. A positive electrode material for a lithium ion battery. Here, x in the formula is a number satisfying 0 <x <1, M is one or more transition metals whose average oxidation state is 3+, and N is 1 whose average oxidation state is 4+ One or more transition metals. The charge / discharge pre-treatment that regulates the amount of charge is the first charge after charging to the predetermined amount of electricity at the first time, then discharging to a predetermined potential and adding the predetermined amount of electricity to the initial amount of discharged electricity. The charge / discharge pretreatment is repeated until the charge potential reaches a predetermined maximum potential.

(2) Judgment criteria as to whether or not the constituent requirements (technical scope) of the present invention are satisfied (see comparison between Example 5 and Comparative Example 4 described later)
(I) A battery that is considered to satisfy the constituent requirements (technical scope) of the present invention is prepared (obtained), disassembled in a discharged state, the positive electrode is taken out, and a battery using lithium as a counter electrode is configured. In addition, the battery mounted on the device is configured as an initial charge / discharge several times at the single cell stage after the battery configuration, a module battery (small assembled battery 250 in FIG. 4), and an assembled battery, and further mounted on the device. After the initial charge / discharge inspection, it may be put on the market. Therefore, a battery that can be prepared (obtained) is considered to have undergone a charge / discharge test about 5 to 50 times after the battery configuration.

    (Ii) Therefore, a battery constituted by using the positive electrode taken out from the disassembled battery is subjected to a constant current charge / discharge test at room temperature in a voltage range of 2.0 V to 4.8 V.

    (Iii) A potential differentiation (dQ / dE) of the electric quantity (Q) is calculated from the obtained data and plotted against the potential (E).

  FIG. 9 (after 50 cycles) shows a comparison between the case where the pre-charge / discharge pretreatment in which the amount of charged electricity is regulated according to the present invention is applied and the case where it is not applied. In FIG. 9, the dQ / dE curve in which the data when the charge / discharge pretreatment restricting the amount of charged electricity according to the present invention is performed is plotted and expressed is “with pretreatment”. On the other hand, a dQ / dE curve obtained by plotting data in the case where the charge / discharge pretreatment with the charged electric quantity regulated according to the present invention is not performed is indicated as “no pretreatment”.

  From comparison of waveforms in the region of 3.0V to 3.3V as shown in FIG. 9, the positive electrode subjected to the pre-charging / discharging pretreatment that regulates the amount of charge of the present invention shows a characteristic peak at 3.2V. On the other hand, those not subjected to the charge / discharge pretreatment that regulates the charge electricity amount of the present invention do not have this peak.

  It can be determined whether or not the constituent requirements (technical scope) of the present invention are satisfied by the presence or absence of this peak. Also, even if the batteries are shipped in a charge / discharge cycle that does not reach 50 cycles, several batteries are taken out and charged / discharged for 10 cycles, 20 cycles, 30 cycles, and 40 cycles, respectively. If the disassembly inspection is performed, it can be determined whether or not the configuration requirement (technical scope) of the present invention is satisfied by the same determination standard (the presence or absence of a characteristic peak of 3.2 V).

(3) Physical meaning of pre-charging / discharging pretreatment with regulated charge electricity according to the present invention By pre-charging / discharging pre-treatment with regulated charge electricity according to the present invention, the main active material of the positive electrode (xLiMO ₂ · (1-x) Although the charge / discharge cycle characteristics in the high potential region of Li ₂ NO ₃ ) are remarkably improved, this mechanism is considered as follows. This main active material has a layered structure such as LiCoO ₂ , but the transition metal layer also contains Li ⁺ . When charged to the high potential region for expressing a high capacity, Li ⁺ not a layer of Li ⁺ only of the transition metal layer Li ⁺ and oxygen in the crystalline framework is released, the movement of large ions inside the crystal (rearrangements) are It is thought to happen. If the pre-charge / discharge pretreatment with the charged electric quantity regulated according to the present invention is not performed, it is considered that the deterioration proceeds during the rapid rearrangement of ions. The deterioration mechanism is considered to be deteriorated by changing from a layered structure to a spinel structure by charge / discharge in a small region in the crystal, as was the case with conventional layered LiMnO ₂ .

Li ⁺ ion exchange with H ⁺ , which can occur by oxidative decomposition of the solvent at high potential, is more likely to occur due to the crystal surface opening or defects during this rapid ion rearrangement. This can accelerate the degradation.

On the other hand, since the rearrangement of ions in the crystal gradually proceeds by the pre-charging / discharging pretreatment in which the amount of charge electricity of the present invention is regulated, a stable layered state is obtained without greatly disturbing the initial layer structure. It is considered that the cycle durability is improved because the structure is reached. Candidates for a stable layered structure include a crystal structure with relatively fewer defects, a very small amount of Ni ²⁺ entering the lithium layer in the crystal as a pillar, and a very small number of nanocrystals. The thing which has the role of can be considered.

  Moreover, as shown in the Example part, the generation of cracks on the surface of the active material particles due to the pre-charge / discharge treatment is suppressed. For this reason, it is likely that subsequent cycle deterioration is greatly suppressed.

  Hereinafter, the present invention will be described in detail using examples.

1. Synthesis of Solid Solution Cathode Material A sample (solid solution cathode material) was synthesized using a composite carbonate method as follows. Nickel sulfate, cobalt sulfate, and manganese sulfate are weighed in predetermined amounts to prepare a mixed solution thereof. Ammonia water is added dropwise until pH 7 is reached, and a Na ₂ CO ₃ solution is further added dropwise to add Ni—Co—. A complex carbonate of Mn was precipitated. While the Na ₂ CO ₃ solution was dropped, pH 7 was maintained with aqueous ammonia. Then, it filtered by suction, washed with water, and dried at 120 degreeC for 5 hours. This was calcined at 500 ° C. for 5 hours. A small excess of LiOH.H ₂ O was added thereto and mixed for 30 minutes in an automatic mortar. Thereafter, the main calcination was performed at 900 ° C. for 12 hours, followed by rapid cooling using liquid nitrogen.

  The three types of samples obtained were identified not only by XRD results but also by elemental analysis by ICP. The three synthesized samples are all space groups.

A diffraction line showing a superlattice structure appeared at 20 to 23 °. The composition was as shown in Table 1. For example, in Example 3: Li [Ni _0.084 Li _0.267 Co _0.032 Mn _0.617 ] O ₂ → Li [Ni _0.08 Li _0.27 Co _0.03 Mn _0.62 ] O ₂ there were. Example _{4: Li [Ni 0.21 Li 0.167} Co 0.08 Mn 0.543] O 2 → Li [Ni 0.2 1Li 0.17 Co 0.08 Mn 0.54] was _{O 2} . Thus, not only the XRD results (composition on the left side of the arrow) but also the results identified by elemental analysis by XRD and ICP (composition on the right side of the arrow) are shown in Table 1. When the coefficient of the lower composition formula of each sample in Table 1 (the above general formula: xLiMO ₂ · (1-x) Li ₂ NO ₃ ) is multiplied by the conversion factor, the upper composition of each sample in Table 1 It becomes the expression notation. That is, the notation of the composition formula in the upper part of each sample in Table 1 is a notation when all are regarded as layered LiMO ₂ (M: one or more transition metals having an average oxidation state of 3+). In the following description, the notation of the sample may use the notation of the composition formula in the upper part of the sample in Table 1.
2. Evaluation of electrode (1) Preparation of electrode and evaluation cell The electrode was made of an active material (using the above sample): conductive binder (TAB-2) = 20: 12 (mass ratio), and kneading was performed. The sample electrode was formed into a pellet having a diameter of 16 mm, pressed onto a stainless mesh having the same diameter, and heated and dried at 120 ° C. for 4 hours under vacuum to obtain a sample electrode. Here, a cell is assembled by using lithium foil as a counter electrode and glass filter paper as a separator, and adding an electrolytic solution of 1M LiPF ₆ EC: DMC = 1: 2 (volume ratio) as an electrolytic cell. The charge / discharge characteristics were evaluated as follows.

(2) Charging / discharging test of electrode The charging / discharging of the cell of the Example performed the charging / discharging pretreatment as typically shown in FIG. In the example given here, the amount of increase in the charge capacity at each time is made the same, but these may be changed appropriately. First, the contribution (II → III → IV) of Ni in the theoretical capacity as seen from the composition formula and the capacity (mAh / g) of contribution (III → IV) of Co (the first charge shown in Table 1 were obtained. "Capacitance"), and charging is performed at a constant current for the first time by the amount of electricity corresponding to these electrodes. Next, it discharges to 2.0V with respect to a lithium counter electrode with a constant current. The constant current charge / discharge was performed using 20 mA / g as the current value. The amount of increase in charge capacity shown in Table 1 is added to the discharge electricity amount at this time in terms of per electrode, and the value is used as the second charge electricity amount. As the second charge, the amount of electricity is charged at a constant current. This operation was continued until the maximum potential during charging was 5.0 V with respect to lithium, and then the battery was discharged at a constant current to 2.0 V to complete the pre-charging / discharging pretreatment. With this state as the initial state, charging and discharging between 2.0 V and 4.8 V with respect to lithium at a constant current and measuring the change in charge and discharge capacity at that time, the fifth time from the initial state The discharge capacity is shown in Table 1 as “discharge capacity after 5 cycles”. On the other hand, in the cell of the comparative example, the change in the charge / discharge capacity at that time was measured by charging / discharging between 2.0 V and 4.8 V with respect to lithium at a constant current without the above-described pre-charge / discharge pretreatment. The discharge capacity at the fifth time is shown in Table 1 as “discharge capacity after 5 cycles”. FIG. 8 is a diagram illustrating a first charge / discharge curve of the pre-charge / discharge treatment of the cell of Example 1 and a fifth charge / discharge curve from the initial state after the pre-charge / discharge treatment.

  As can be seen from Table 1, by performing the charge / discharge pretreatment of the present invention, it can be seen that the charge / discharge cycle characteristics up to 4.8 V, which expresses a high capacity, are greatly improved.

Example 5 and Comparative Example 4
For both Example 5 and Comparative Example 4, the electrode of Example 1: Li [Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ] O ₂ was used as the positive electrode active material, and the negative electrode was lithium. A cell was constructed using metal, and a constant current charge / discharge test was conducted. In addition, the charge / discharge pretreatment in Example 5 and the charge / discharge as a battery use for the precharge / discharge pretreatment were performed at room temperature. In Comparative Example 4, charging / discharging as battery use was performed at room temperature without performing pre-charging / discharging pretreatment. The cell was manufactured as follows.

Using 20 mg of the active material (sample of Example 1) and 12 mg of TAB-2 as the conductive binder, a pellet was prepared, and then pressure-bonded to a stainless mesh current collector to form a positive electrode. The electrochemical test used a 2032 type coin cell. At this time, the negative electrode was prepared using an organic solvent of EC / DMC (EC: DMC = 1: 2 (volume ratio)) containing lithium metal as the negative electrode and 1M LiPF ₆ as the electrolyte. The cell was produced in a glove box under an argon atmosphere.

The constant current charge / discharge test was performed at room temperature, a voltage range of 2.0 V to 4.8 V, and a current density of 0.2 mA / cm ² . In Example 5, the pre-charge / discharge pretreatment was performed under the same conditions as in Example 1 as the pre-charge / discharge pretreatment of the present invention. The constant current charging / discharging at this time was performed using 20 mA / g as a current value. In the charge / discharge test of 50 cycles of the treatment cell, the charge / discharge cycle of the pre-charge / discharge treatment was not counted. From the obtained charge / discharge data, the potential differentiation of the capacity was calculated using PC 6.0: Origin 6.0 professional, and the data of the cell (Example 5) subjected to the charge / discharge pretreatment and the cell not subjected to the comparison (Comparative Example) The results of 4) are shown together in FIG.

  From the dQ / dE curve after 50 cycles shown in FIG. 9, a peak of about 3.1 V appears clearly in the electrode not subjected to the pre-charge / discharge treatment of Comparative Example 4 (no treatment), and the charge / discharge of Example 5 was observed. The pretreated electrode (with pretreatment) showed a tendency for a peak of 3.2 V to appear strongly. This result suggests that the structural change between the electrode not subjected to the charge / discharge pretreatment and the electrode subjected to the charge / discharge pretreatment is different (in the specification, “the charge / discharge pretreatment of the present invention”). See the section on physical meaning).

Example 6 and Comparative Example 5
In both Example 6 and Comparative Example 5, the sample of Example 1: Li [Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ] O ₂ was used as the positive electrode, and the negative electrode was lithium. A cell was constructed using metal, and a constant current charge / discharge test was conducted. In addition, the charge / discharge pretreatment in Example 6 and the charge / discharge as the battery specifications of the precharge / discharge pretreatment were performed at room temperature. In Comparative Example 5, the battery was charged to 4.8 V at a time and then discharged to 2.0 V without performing the charge / discharge pretreatment. Both batteries were disassembled in a cocoon lobe box, washed with dry dimethyl carbonate, and after drying, the active material was separated to obtain a sample for TEM observation. The characteristic differences between the two samples are shown in FIG. (A) is a pre-charge / discharge pretreatment, and (b) is an active material that is charged to 4.8 V at a time without performing pre-charge / discharge pretreatment and then discharged to 2.0 V. As is clear from the figure, the sample that was not pre-charged / discharged was compared with the sample that was pre-charged / discharged compared to the sample that was clearly cracked near the active material particle surface. There are almost no cracks. Since the cracks near the generated surface may cause the subsequent cycle deterioration, the effect of pre-charge / discharge pretreatment improves the cycle durability by suppressing the occurrence of such cracks. Is also considered a mechanism.

DESCRIPTION OF SYMBOLS 10 Non-bipolar type lithium ion secondary battery 11 Positive electrode collector 11a Outermost layer positive electrode collector 12, 32 Positive electrode (positive electrode active material layer)
13, 35 Electrolyte layer 14 Negative electrode current collector 15, 33 Negative electrode (negative electrode active material layer)
16, 36 single battery layer (= battery unit or single cell)
17, 37, 57 Power generation element (battery element; laminate)
18, 38, 58 Positive electrode tab 19, 39, 59 Negative electrode tab 20, 40 Positive electrode terminal lead 21, 41 Negative electrode terminal lead 22, 42, 52 Battery exterior material (for example, laminate film)
30 Bipolar lithium ion secondary battery 31 Current collector 31a Outermost layer current collector 31b on the positive electrode side Outermost layer current collector 34 on the negative electrode side Bipolar electrodes 34a and 34b Electrode 43 positioned on outermost layer Seal portion (insulating layer)
50 Lithium ion secondary battery 250 Small battery pack (module battery)
300 assembled battery 310 connecting jig 400 electric vehicle

Claims (7)

The main active material is the general formula
(Where x is a number satisfying 0 <x <1, M is one or more metal elements having an average oxidation state of 3+, and N is one or more types having an average oxidation state of 4+. In the positive electrode for a lithium ion battery represented by:
After charging a predetermined positive electric quantity Qc (1) of 80% or more and 130% or less of the contribution to the theoretical capacity when M is a one-electron reaction with LiMO ₂ for the first time, it is converted to lithium metal or lithium metal. Discharging the electric quantity Qd (1) (where 0 <Qd (1) <Qc (1)) to a predetermined positive potential Ed (1) between 1.5V and 4.0V in potential,
Thereafter , the amount of electricity Qc (n) (where Qc (n) = Qd (n−1) + ΔQ (n), ΔQ (n)> 0, n is an integer of 2 or more) is charged for the nth time, and lithium Electric quantity Qd (n) up to a predetermined positive potential Ed (n) between 1.5 V and 4.0 V in terms of metal or lithium metal (where 0 <Qd (n) <Qc (n)) The charging / discharging operation is performed at a predetermined maximum potential that is set to a potential higher than the potential of the plateau part in the initial charging curve with respect to the potential converted to lithium metal or lithium metal. A positive electrode for a lithium ion battery, which is subjected to charge / discharge pretreatment that is repeated until the lithium ion battery is reached. 2. The positive electrode for a lithium ion battery according to claim 1, wherein the predetermined maximum potential is set to 4.6 V or more as a potential converted to lithium metal or lithium metal. The predetermined amount of electricity ΔQ (n) to be added to the n−1th discharge amount of electricity Qd (n−1 ) is:
In the case of adding a constant amount of electricity sequentially each time in the n-th charge, the range is from 10 to 70 mAh / g,
The amount of electricity added in charge of n-th time, if not constant in each time, the positive electrode for a lithium ion battery according to claim 1 or 2, characterized in that in the range of 0~100mAh / g. The positive electrode for a lithium ion battery according to any one of claims 1 to 3 , wherein the predetermined maximum potential is in a range of 4.6 V to 5.5 V in terms of lithium metal or a potential converted to lithium metal. . Wherein M is, Mn, Ni, a positive electrode for a lithium ion battery according to any one of claims 1 to 4, characterized in that one or more transition metal elements comprising selected from Co and Fe. Wherein N is, Mn, a positive electrode for a lithium ion battery according to any one of claims 1 to 5, characterized in that one or more kinds of elements consisting chosen from Zr and Ti. A lithium ion battery comprising the positive electrode for a lithium ion battery according to any one of claims 1 to 6 .