JP2011044333A - Method of manufacturing lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a lithium secondary battery with better battery performance (for instance, capable of obtaining higher capacity). <P>SOLUTION: The method is for manufacturing a lithium secondary battery equipped with a positive electrode containing an olivine type phosphate compound as a positive electrode active material, a negative electrode, and nonaqueous electrolyte solution. The method includes a step of assembling a lithium secondary battery consisting of the positive electrode, the negative electrode and the nonaqueous electrolyte solution, and a step of applying initial charging to the lithium secondary battery thus assembled. At the initial charging step, a preliminary charge and discharge is carried out by one cycle including a charging process so that a desorption rate of lithium in the positive electrode active material becomes 10-85%, and then, full charging is carried out. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a lithium secondary battery.

  In recent years, lithium secondary batteries that are lightweight and have a high energy density are expected to be preferably used as high-output power supplies for vehicles. Such a lithium secondary battery includes an electrode body configured with a separator interposed between a positive electrode and a negative electrode, and is charged and discharged by movement of lithium (Li) ions between the positive and negative electrodes. Patent documents 1-3 are mentioned as conventional technology about this kind of lithium secondary battery.

This type of lithium secondary battery includes a positive electrode having a configuration in which a positive electrode active material capable of reversibly occluding and releasing Li ions is held on a positive electrode current collector. For example, as one of the positive electrode active materials used for the positive electrode, a phosphate compound containing lithium and a transition metal element and having a so-called olivine structure (for example, an olivine phosphate such as LiFePO ₄ or LiMnPO ₄ ) is used. Can be mentioned. Such an olivine-type phosphate compound has been attracting attention as a promising positive electrode active material because it has a high theoretical capacity (for example, 170 mAh / g for LiFePO ₄ ) and is excellent in thermal stability at low cost.

JP 2001-325988 A JP 2008-504662 A JP 2003-109662 A

  By the way, in such a lithium secondary battery, after being assembled as a battery, an initial charging process (that is, a charging process that is performed only after assembling battery components such as a positive electrode, a negative electrode, and an electrolytic solution. (Patent Documents 1 to 3). In a battery using the olivine-type phosphate compound as described above as the positive electrode active material, it is desirable to set the upper limit of the positive electrode potential in the initial charging to a relatively high potential because the redox potential of the phosphate compound is high. However, when the upper limit potential of the positive electrode is set to a high potential, a large amount of lithium is desorbed from the positive electrode active material, so that the crystal structure of the positive electrode active material becomes unstable, and the reactivity between the positive electrode active material and the non-aqueous electrolyte is reduced. Increase. As a result, there is a problem that an irreversible reaction with the non-aqueous electrolyte easily occurs on the surface of the positive electrode active material, irreversible capacity is generated, and the capacity of the battery is greatly reduced.

  This invention is made | formed in view of this point, The main objective is to provide the manufacturing method of a lithium secondary battery with better battery performance (for example, higher capacity is obtained).

  The method provided by the present invention is a method for producing a lithium secondary battery comprising a positive electrode containing an olivine-type phosphate compound as a positive electrode active material, a negative electrode, and a non-aqueous electrolyte. This manufacturing method includes a step of assembling a lithium secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, and a step of performing initial charging on the assembled lithium secondary battery. In the initial charging step, at least one cycle of preliminary charging / discharging including a process of charging so that a lithium desorption rate in the positive electrode active material is 10% to 85% is performed, and then the battery is fully charged. And

  According to the method of the present invention, at least one cycle of pre-charging / discharging including a process of charging so that 10% to 85% of lithium contained in the positive electrode active material is desorbed is performed. Therefore, the irreversible capacity is less likely to occur compared to the conventional mode in which the lithium is fully charged from the beginning. Therefore, a discharge capacity closer to the theoretical capacity can be obtained.

The lithium desorption rate in the preliminary discharge may be about 10% to 85%, preferably about 30% to 80%, for example, preferably in the range of 50% to 80%. If it is out of this range, the amount of lithium desorbed at the time of preliminary charging may be too much or too little, so that the effect of performing the preliminary charging may not be sufficiently obtained. The lithium desorption rate is determined, for example, by performing inductively coupled plasma atomic emission spectrometry (ICP-AES) composition analysis of the phosphoric acid compound (positive electrode active material) after preliminary charging, It is preferable to determine the composition ratio with other metal elements and estimate the lithium desorption rate from this composition ratio. For example, the phosphoric acid compound used for the assembly of the lithium secondary battery is LiMnPO ₄ (composition ratio of Li and Mn is 1: 1), and the composition ratio (atomic ratio) of Li and Mn obtained after charging Is 0.3: 1, the lithium desorption rate can be estimated to be about 70%.

  In the preferable one aspect | mode of the lithium secondary battery manufacturing method disclosed here, the said preliminary charging / discharging is repeated 2 cycles or more. By repeating the pre-charging / discharging for 2 cycles or more, generation of irreversible capacity is suppressed, and higher discharge capacity can be obtained. The number of pre-charging / discharging cycles is not particularly limited, but usually 2 to 10 cycles is appropriate, and approximately 3 to 5 cycles is preferable. As the number of cycles is increased within this range, more favorable results can be achieved.

  In a preferred embodiment of the method for producing a lithium secondary battery disclosed herein, the preliminary charging / discharging is repeated while changing the lithium desorption rate for each cycle. By changing the lithium desorption rate (that is, the state of charge of the battery) stepwise in each cycle, the generation of irreversible capacity is effectively suppressed, and a higher discharge capacity can be obtained.

  In a preferred embodiment of the method for producing a lithium secondary battery disclosed herein, the preliminary charge / discharge is repeated while increasing the lithium desorption rate in the order of cycles. In this case, it is possible to charge from 10% to 60% in the first preliminary charge / discharge, to charge from 60% to 85% in the final round, and to gradually increase the lithium desorption rate from the first round to the final round. preferable. For example, when 3 cycles of pre-charging / discharging are performed, 30% to 50% is charged in the first cycle (first time) of pre-charging / discharging, 50% to 70% is charged in the second cycle, and the third cycle ( In the last round, it is better to charge up to 70% to 85%. In this way, by gradually increasing the lithium desorption rate from the first time to the last time while approaching full charge, generation of irreversible capacity is more effectively suppressed, and high discharge capacity can be obtained.

The technique disclosed here can be preferably applied when the olivine-type phosphate compound is LiMnPO ₄ . LiMnPO ₄ has a high theoretical capacity and excellent thermal stability, so that it has preferable properties as a positive electrode active material. On the other hand, it is necessary to set the upper limit of the positive electrode potential in the initial charge to a high potential, so that an irreversible capacity is generated. Cheap. Therefore, when the olivine-type phosphate compound is LiMnPO _4, it is particularly significant to apply the technique disclosed herein.

  The present invention also provides a lithium secondary battery manufactured by the manufacturing method disclosed herein. Since this lithium secondary battery is manufactured through the initial charging step disclosed herein, the battery performance (for example, charge / discharge characteristics) after the initial charging is improved.

  Since such a lithium secondary battery exhibits good battery performance as described above, it is suitable as a battery mounted on a vehicle such as an automobile. Therefore, according to the present invention, there is provided a vehicle including any of the lithium secondary batteries disclosed herein (which may be in the form of an assembled battery in which a plurality of batteries are connected). In particular, since good load characteristics can be obtained, a vehicle (for example, an automobile) including the lithium ion secondary battery as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is provided.

It is a schematic diagram which shows the structure of the lithium secondary battery which concerns on one Embodiment of this invention. It is a schematic diagram which shows the structure of the wound electrode body which concerns on one Embodiment of this invention. It is a figure which shows the manufacturing process flow which concerns on one Embodiment of this invention. It is a figure which shows the preliminary charging / discharging process flow which concerns on one Embodiment of this invention. It is a fragmentary sectional view which shows typically the coin cell produced for performance evaluation. It is a graph which shows the lithium desorption rate of each cycle of an Example and a comparative example. It is a graph which shows the measurement result of the discharge capacity of an Example and a comparative example. It is a side view of a vehicle provided with the lithium secondary battery which concerns on one Embodiment of this invention.

  Embodiments according to the present invention will be described below with reference to the drawings. In the following drawings, members / parts having the same action are described with the same reference numerals. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than those particularly mentioned in the present specification, and matters necessary for the implementation of the present invention (for example, general configurations and manufacturing methods of separators and electrolytes, lithium secondary batteries and other batteries related to construction) Technology, etc.) can be understood as a design matter of those skilled in the art based on the prior art in the field.

  Although not specifically intended to be limited, in the following, a flatly wound electrode body (winding electrode body) and a non-aqueous electrolyte are accommodated in a flat box-shaped (cuboid shape) battery case. This embodiment will be further described by taking a lithium ion secondary battery as an example.

  A schematic configuration of a lithium secondary battery according to an embodiment of the present invention is shown in FIGS. The lithium secondary battery 100 includes an electrode body (winding electrode body) 80 in which a long positive electrode sheet 10 and a long negative electrode sheet 20 are wound flatly via a long separator 40. However, it has the structure accommodated in the battery case 50 of the shape (flat box shape) which can accommodate this winding electrode body 80 with the nonaqueous electrolyte solution which is not shown in figure.

  The battery case 50 includes a flat cuboid case main body 52 having an open upper end, and a lid 54 that closes the opening. As a material constituting the battery case 50, a metal material such as aluminum or steel is preferably used (in this embodiment, aluminum). Or the battery case 50 formed by shape | molding resin materials, such as a polyphenylene sulfide (PPS) resin and a polyimide resin, may be sufficient. On the upper surface of the battery case 50 (that is, the lid body 54), a positive electrode terminal 70 that is electrically connected to the positive electrode of the wound electrode body 80 and a negative electrode terminal 72 that is electrically connected to the negative electrode 20 of the electrode body 80 are provided. It has been. Inside the battery case 50, a flat wound electrode body 80 is accommodated together with a non-aqueous electrolyte (not shown).

  The constituent elements constituting the wound electrode body 80 may be the same as those of the wound electrode body of the conventional lithium ion secondary battery, and are not particularly limited.

  As shown in FIG. 2, the positive electrode sheet 10 is formed by providing a positive electrode mixture layer 14 containing the above-described positive electrode active material as a main component on a long positive electrode current collector 12. For the positive electrode current collector 12, an aluminum foil or other metal foil suitable for the positive electrode is preferably used.

Examples of the positive electrode active material used for the positive electrode include phosphoric acid compounds containing lithium and a transition metal element and having a so-called olivine structure (for example, olivine-type phosphates such as LiFePO ₄ and LiMnPO ₄ ). The olivine-type phosphate compound is represented by the general formula LiMPO ₄ . M in the formula is composed of at least one transition metal element, and includes, for example, one or more elements selected from Mn, Fe, Co, Ni, Mg, Zn, Cr, Ti, and V. As such a lithium-containing phosphate compound (typically in particulate form), for example, a phosphate compound powder prepared by a conventionally known method can be used as it is.

  The positive electrode mixture layer 14 can contain one or more materials that can be used as components of the positive electrode mixture layer in a general lithium secondary battery, if necessary. An example of such a material is a conductive material. As the conductive material, a carbon material such as carbon powder or carbon fiber is preferably used. Alternatively, conductive metal powder such as nickel powder may be used. In addition, examples of the material that can be used as a component of the positive electrode mixture layer include various polymer materials that can function as a binder for the above constituent materials.

  The negative electrode sheet 20 is formed by applying a negative electrode mixture layer 24 mainly composed of a negative electrode active material for a lithium ion battery on a long negative electrode current collector 22. For the negative electrode current collector 22, a copper foil or other metal foil suitable for the negative electrode is preferably used. As the negative electrode active material, one or more of materials conventionally used in lithium secondary batteries can be used without any particular limitation. Preferable examples include carbon-based materials such as graphite carbon and amorphous carbon, lithium-containing transition metal oxides and transition metal nitrides.

  Suitable separator sheets 40 used between the positive and negative electrode sheets 10 and 20 include those made of a porous polyolefin resin. For example, a synthetic resin (for example, polyolefin such as polyethylene) porous separator sheet having a thickness of about 5 to 30 μm (for example, 25 μm) can be suitably used.

As the non-aqueous electrolyte accommodated in the case main body 52 together with the wound electrode body 80, the same non-aqueous electrolyte used in conventional lithium secondary batteries can be used without any particular limitation. Such a nonaqueous electrolytic solution typically has a composition in which an electrolyte (supporting salt) is contained in a suitable nonaqueous solvent. As said non-aqueous solvent, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC) etc. can be used, for example. Further, Examples of the electrolyte (supporting salt), for _{example, LiPF 6, LiBF 4, LiAsF} 6, LiCF can ₃ be preferably used a lithium salt of SO ₃ and the like. The electrolyte concentration in the non-aqueous electrolyte is, for example, about 0.05 mol / L to 10 mol / L, preferably about 0.1 mol / L to 5 mol / L, and usually about 1 mol / L.

  Next, a method for manufacturing a lithium secondary battery according to this embodiment will be described using the lithium secondary battery 100 having the above structure as an example. The method of this embodiment is a method of manufacturing a lithium secondary battery including a positive electrode containing an olivine-type phosphate compound as a positive electrode active material, a negative electrode, and a nonaqueous electrolytic solution. In this manufacturing method, as shown in FIG. 3, a process of assembling a lithium secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte (battery assembly process), and initial charging of the assembled lithium secondary battery are performed. Process (initial charging process). Hereinafter, the battery assembly process and the initial charging process will be described in this order.

  The battery assembling step is a step of assembling the lithium secondary battery 100 including the positive electrode 10, the negative electrode 20, and the non-aqueous electrolyte. In this embodiment, first, the wound electrode body 80 is constructed. When constructing the wound electrode body 80, as shown in FIG. 2, a sheet-like electrode body in which the positive electrode sheet 10 and the negative electrode sheet 20 are laminated via the separator sheet 40 is prepared. At this time, the separator sheet 40 faces the positive electrode mixture layer 14 and the separator sheet 40 so that the positive electrode mixture layer non-forming portion (exposed portion of the positive electrode current collector 12) of the positive electrode sheet 10 protrudes outward. As superimposed). The negative electrode sheet 20 is also laminated in the same manner as the positive electrode sheet 10 so that the negative electrode mixture layer non-formed portion (exposed portion of the negative electrode current collector 22) protrudes outward from the separator sheet 40 (that is, the negative electrode mixture layer 24 and the separator). The sheet 40 is superposed so that it faces the sheet 40. A flat wound electrode body 80 is obtained by winding such a sheet-like electrode body and then crushing the obtained wound body from the side surface direction so as to be ablated.

  The wound electrode body 80 having such a configuration is accommodated in the case main body 52, an appropriate nonaqueous electrolytic solution is disposed (injected) into the case main body 52, and the opening of the case main body 52 is connected to the lid 54. By sealing by welding or the like, the assembly process of the lithium secondary battery 100 according to this embodiment is completed. Note that the welding process between the case body 52 and the lid body 54 and the placement (injection) process of the electrolytic solution can be performed in the same manner as that used in the manufacture of conventional lithium secondary batteries.

  In the initial charging step, initial charging is performed on the assembled lithium secondary battery 100. In this initial charging step, as shown in FIG. 3, at least one cycle of preliminary charging and discharging including a process of charging so that the lithium desorption rate in the positive electrode active material is 10% to 85% is performed, and then the full charging is performed. To do. That is, after pre-charging / discharging including a process of charging so that 10% to 85% of lithium contained in the positive electrode active material is desorbed, full charge is performed until the lithium desorption rate reaches 100%. To do.

  According to the method of the present embodiment, at least one cycle of preliminary charge / discharge including a process of charging so that 10% to 85% of lithium contained in the positive electrode active material is desorbed, and then the fully charged state (that is, the positive electrode) Therefore, the irreversible capacity is less likely to occur compared to the conventional mode in which the lithium is fully charged from the beginning. Therefore, a discharge capacity closer to the theoretical capacity can be obtained.

  The lithium desorption rate in the preliminary discharge may be about 10% to 85%, preferably about 30% to 80%, for example, preferably in the range of 50% to 80%. If it is out of this range, the amount of lithium desorbed at the time of preliminary charging may be too much or too little, so that the effect of performing the preliminary charging may not be sufficiently obtained.

  In one aspect disclosed herein, as shown in FIG. 4, it is preferable to repeat the pre-charging / discharging two or more cycles. By repeating the pre-charging / discharging for 2 cycles or more, generation of irreversible capacity is suppressed, and higher discharge capacity can be obtained. The number of pre-charging / discharging cycles is not particularly limited, but usually 2 to 10 cycles is appropriate, and approximately 3 to 5 cycles is preferable. As the number of cycles is increased within this range, more favorable results can be achieved (3 cycles in FIG. 4).

  In the technique disclosed herein, it is preferable to repeat the preliminary charge / discharge while changing the lithium desorption rate for each cycle. By changing the lithium desorption rate (that is, the state of charge of the battery) stepwise in each cycle, the generation of irreversible capacity can be effectively suppressed and a higher discharge capacity can be realized.

  In a preferred embodiment disclosed herein, the preliminary charge / discharge is repeated while increasing the lithium desorption rate in the order of cycles. In this case, it is possible to charge from 10% to 60% in the first preliminary charge / discharge, to charge from 60% to 85% in the final round, and to gradually increase the lithium desorption rate from the first round to the final round. preferable. For example, as shown in FIG. 4, when 3 cycles of pre-charging / discharging are performed, charging is performed up to 50% in the first cycle (first time) of pre-charging / discharging, and is charged up to 70% in the second cycle. In the (last round), it is good to charge up to 80%. In this manner, by gradually increasing the lithium desorption rate from the first time to the last time while approaching a fully charged state, generation of irreversible capacity is more effectively suppressed, and a high discharge capacity is obtained.

  In implementing the technique disclosed herein, it is not necessary to clarify the reason why a high discharge capacity can be obtained by performing pre-charging / discharging so that the lithium desorption rate is 10% to 85%. For example, it is considered as follows.

  That is, in the conventional mode in which the battery is fully charged from the beginning, nearly 100% of lithium is desorbed from the positive electrode active material at the first charge, so that the crystal structure of the positive electrode active material becomes unstable, and the positive electrode active material and the nonaqueous electrolytic solution And the reactivity increases. As a result, an irreversible reaction (decomposition of the electrolytic solution) with the nonaqueous electrolytic solution is likely to occur on the surface of the positive electrode active material, irreversible capacity is generated, and the battery capacity is greatly reduced. On the other hand, in this embodiment, since the lithium desorption rate is changed stepwise, the crystal structure of the positive electrode active material is kept stable, and the irreversible reaction with the nonaqueous electrolytic solution hardly occurs. Thereby, generation | occurrence | production of an irreversible capacity | capacitance was suppressed and it is thought that high discharge capacity was obtained. Moreover, it is considered that a film useful for diffusion of lithium is formed on the surface of the positive electrode active material by performing stepwise preliminary charge / discharge, and a high discharge capacity is obtained by this film.

  In addition, it is considered that the lithium diffusion path in the positive electrode active material is formed at the time of the first charge. However, in the conventional mode in which the charge is fully charged from the beginning, all the lithium is released from the positive electrode active material in the first charge. For this reason, the structure of the positive electrode active material collapses and a proper diffusion path cannot be formed in the positive electrode active material. On the other hand, in this embodiment, since only 10% to 85% of lithium is desorbed at the time of initial charge, a diffusion path can be formed while keeping the crystal structure of the positive electrode active material stable. It is considered that the lithium diffusion path generated here enables smooth discharge, and a high discharge capacity was obtained even after full charge.

  After performing the initial charging process in this way, the gas generated inside the battery case 50 is discharged out of the case by an appropriate degassing process, and the battery case 50 is hermetically sealed. The manufacture of the lithium secondary battery 100 is completed. In addition, the degassing process in the battery case 50 and the sealing process of the battery case 50 can be performed in the same manner as that used in the manufacture of a conventional lithium secondary battery.

  Examples 1 to 4 relating to the present invention will be described below, but the present invention is not intended to be limited to the specific examples.

<Assembly of lithium secondary battery>
LiMnPO ₄ powder as a positive electrode active material, carbon black (conductive material) and polyvinylidene fluoride (PVdF) in N-methylpyrrolidone (NMP) so that the mass ratio of these materials is 75: 20: 5. By mixing, a paste-like composition for the positive electrode mixture layer was prepared. The positive electrode sheet in which the positive electrode mixture layer is provided on one side of the positive electrode current collector by applying the paste-like composition for the positive electrode mixture layer in layers on one side of the aluminum foil (positive electrode current collector) and drying it. Got.

The positive electrode sheet was punched into a circle having a diameter of 16 mm to produce a positive electrode. This positive electrode (working electrode), metallic lithium as a negative electrode (counter electrode) (a metal Li foil having a diameter of 19 mm and a thickness of 0.02 mm), and a separator (a porous polyolefin having a diameter of 22 mm and a thickness of 0.02 mm) And a coin cell 60 (half cell for charge / discharge performance evaluation) shown in FIG. 5 having a diameter of 20 mm and a thickness of 3.2 mm (2032 type). It was constructed. In FIG. 5, reference numeral 61 is a positive electrode (working electrode), reference numeral 62 is a negative electrode (counter electrode), reference numeral 63 is a separator impregnated with an electrolyte, reference numeral 64 is a gasket, reference numeral 65 is a container (negative electrode terminal), Reference numeral 66 denotes a lid (positive electrode terminal). In addition, as a non-aqueous electrolyte solution, LiPF ₆ as a supporting salt is approximately mixed in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3: 3: 4. The one contained at a concentration of 1 mol / liter was used.

<Initial charging and performance evaluation>
The coin cell manufactured as described above was initially charged under the conditions shown in Table 1 below. Here, the “initial charging process” includes the process up to full charge after preliminary charge / discharge. Example 1 will be described. The assembled cell is placed in a temperature environment of 20 ° C., and pre-charging / discharging is performed for 3 cycles under the following conditions (1) to (3). Thereafter, the following condition (4) is satisfied. Was fully charged and the initial charging process was completed. Then, the discharge capacity after full charge (that is, the discharge capacity at the fourth cycle) was measured and evaluated. The lithium desorption rate is determined by performing inductively coupled plasma atomic emission spectrometry (ICP-AES) composition analysis of LiMnPO ₄ after the charging operation, and determining the composition ratio of Li and Mn contained in LiMnPO ₄ . The lithium desorption rate was estimated from this composition ratio. For example, when the composition ratio of Li and Mn obtained after charging was 0.3: 1, the lithium desorption rate was estimated to be 70%.

(1) Charging is performed at a constant current of 0.05 C until the lithium desorption rate reaches 50% (interelectrode voltage is 4.18 V), and then the interelectrode voltage is 2 at a constant current of 0.05. Discharge was performed until the voltage reached 0.0 V (lower limit voltage).
(2) Charging is performed at a constant current of 0.05 C until the lithium desorption rate reaches 70% (interelectrode voltage is 4.22 V), and then the interelectrode voltage is 2 at a constant current of 0.05. Discharge was performed until the voltage reached 0.0 V (lower limit voltage).
(3) Charging is performed at a constant current of 0.05 C until the lithium desorption rate is 80% (interelectrode voltage is 4.33 V), and then the interelectrode voltage is 2 at a constant current of 0.05. Discharge was performed until the voltage reached 0.0 V (lower limit voltage).
(4) Charging is performed at a constant current of 0.05 C until the lithium desorption rate reaches 100% (interelectrode voltage is 4.80 V), and then the interelectrode voltage is 2 at a constant current of 0.05. Discharge was performed until the voltage reached 0.0 V (lower limit voltage).

  For other Examples 2 to 4, initial charge was performed in the same manner as in Example 1 except that the lithium desorption rates of the above (1) to (4) were changed as shown in Table 1. Example 4 will be described. The assembled cell is subjected to a pre-charge / discharge cycle so that the lithium desorption rate is 80%, and then fully charged so that the lithium desorption rate is 100%. To complete the initial charging process. After the discharge, two full charge / discharge cycles were performed, and the discharge capacity at the fourth cycle was measured as a whole. For comparison, the assembled cell was charged and discharged for 4 cycles so that the lithium desorption rate was 100%, and the discharge capacity at the 4th cycle was measured. FIG. 6 shows the lithium desorption rate in each cycle of Examples 1 to 4 and the comparative example. Moreover, the measurement result of the discharge capacity of the 4th cycle is shown in FIG.

  As can be seen from FIG. 7, the discharge capacities of the cells of Examples 1 to 4 that were subjected to the preliminary charge / discharge were clearly improved compared to the cells of the comparative example that were not subjected to the preliminary charge / discharge. From this, it was confirmed that a high capacity can be obtained by performing preliminary charge / discharge. In addition, the cells of Examples 1 to 3 in which the pre-charging / discharging was performed for two cycles or more further improved the discharge capacity as compared with the cell of Example 4 of one cycle. From this, it was confirmed that a higher capacity can be obtained by repeating the pre-charging / discharging for 2 cycles or more (preferably 3 cycles). Furthermore, it was confirmed from the comparison of Examples 1 and 2 and Example 3 that a higher discharge capacity can be obtained by charging 30 to 50% of the first preliminary charge / discharge. In particular, the cell of Example 1 that was charged to 50% in the first preliminary charge / discharge had a discharge capacity of 145 mAh / g, and a capacity close to the theoretical capacity was realized.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible.

  Since the lithium secondary battery according to the present invention has a high discharge capacity as described above and exhibits better battery performance, it is preferably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. obtain. Therefore, the present invention, as schematically shown in FIG. 8, is a vehicle (typically an automobile, particularly a hybrid automobile) provided with such a lithium secondary battery 100 (typically, a battery pack formed by connecting a plurality of series batteries) as a power source. , An automobile equipped with an electric motor such as an electric vehicle and a fuel cell vehicle.

DESCRIPTION OF SYMBOLS 10 Positive electrode sheet 12 Positive electrode collector 14 Positive electrode mixture layer 20 Negative electrode sheet 22 Negative electrode collector 24 Negative electrode mixture layer 40 Separator sheet 50 Battery case 52 Case main body 54 Lid body 70 Positive electrode terminal 72 Negative electrode terminal 80 Winding electrode body 100 Lithium secondary battery

Claims (7)

A method for producing a lithium secondary battery comprising a positive electrode containing an olivine-type phosphate compound as a positive electrode active material, a negative electrode, and a non-aqueous electrolyte,
The following steps:
Assembling a lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte; and
Performing an initial charge on the assembled lithium secondary battery;
Including
In the initial charging step, at least one cycle of pre-charging / discharging including a process of charging so that a lithium desorption rate in the positive electrode active material is 10% to 85% is performed, and then full charging is performed. And a method for producing a lithium secondary battery.   The manufacturing method of Claim 1 which repeats the said preliminary charging / discharging 2 cycles or more.   The manufacturing method according to claim 2, wherein the preliminary charge / discharge is repeated while changing the lithium desorption rate for each cycle.   The manufacturing method according to claim 2, wherein the preliminary charging / discharging is repeated while increasing the lithium desorption rate in order of cycles.   The initial charge of the preliminary charge / discharge is charged to 10% to 60%, charged to 60% to 85% at the final time, and the lithium desorption rate from the first time to the final time is sequentially increased. To 4. The production method according to any one of 4 to 4. The production method according to claim 1, wherein the olivine-type phosphate compound is LiMnPO ₄ .   A vehicle comprising a lithium secondary battery manufactured by the method according to any one of claims 1 to 6.

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