JP2015230807A - Method for manufacturing nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a nonaqueous electrolyte secondary battery, by which the initial charging can be completed in a short time while preventing the precipitation of charge carriers.SOLUTION: A method for manufacturing a nonaqueous electrolyte secondary battery according to the invention, which is arranged so as to involve graphite as a negative electrode active material comprises: a step of constructing a battery having a positive electrode and a negative electrode; and an initial charging step of initially charging the battery. The initial charging step includes: a first charging treatment in which the battery is charged with a first charging current density until a structural change of the first stage is caused in the graphite. The first charging current density is set so as to avoid making the potential of the negative electrode 0 V or less; and a second charging treatment in which the battery is charged with a second charging current density smaller than the first charging current density after the first stage structural change is caused in the graphite.

Description

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

  In recent years, lithium ion secondary batteries, nickel metal hydride batteries, and other nonaqueous electrolyte secondary batteries (for example, Patent Document 1) have been used as power sources for mounting on vehicles or personal computers and portable terminals. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is gaining importance as a high-output power source mounted on a vehicle. In a lithium ion secondary battery, charging / discharging is performed by transferring lithium ions between a positive electrode made of a positive electrode active material and a negative electrode made of a negative electrode active material. That is, during charging, lithium (charge carrier) is extracted from the positive electrode active material and released as lithium ions into the electrolytic solution (electrolyte). At the time of charging, the lithium ions enter the structure of a negative electrode active material (for example, layered graphite) provided on the negative electrode side. Here, electrons passing through an external circuit are obtained from the positive electrode active material and occluded.

JP 2012-084322 A

  By the way, since the battery immediately after assembly is in an uncharged state, the battery is first charged (that is, the first charge process performed after assembling battery components such as the positive electrode, the negative electrode, and the electrolyte. ") Is performed. From the viewpoint of production efficiency, it is desirable to complete the initial charging in a short time, but if the current density (charging current value) at the initial charging is increased, the problem is that charge carriers (for example, lithium) precipitate locally at the negative electrode. was there. There is a need to shorten the initial charge while suppressing the deposition of charge carriers. The present invention solves the above problems.

  The method for producing a nonaqueous electrolyte secondary battery proposed here includes graphite as a negative electrode active material and charge carriers that can be held between the graphite layers during charging (for example, lithium in the case of a lithium ion secondary battery). A method for producing a non-aqueous electrolyte secondary battery having a positive electrode active material. This manufacturing method includes a step of constructing a battery including a positive electrode and a negative electrode, and an initial charging step of charging the battery for the first time. Here, in the initial charging step, until the structural change of the first stage occurs in the graphite, a first charging process for charging at a first charging current density set so that the negative electrode potential does not become 0 V or less; And a second charging process in which the graphite is charged at a second charging current density lower than the first charging current density after the first stage structural change occurs in the graphite. According to this configuration, the initial charge can be shortened while suppressing the deposition of charge carriers.

It is a figure which shows typically the lithium ion secondary battery which concerns on one Embodiment. It is a figure which shows typically the wound electrode body used for one Embodiment. It is a graph which shows the voltage characteristic of a lithium / graphite half-cell. It is a figure which shows the presence or absence of Li precipitation of the sample 1. FIG. It is a figure which shows the presence or absence of Li precipitation of the sample 2. FIG. It is a figure which shows the presence or absence of Li precipitation of the sample 3. FIG. It is a graph which shows the relationship between high temperature preservation days and a capacity | capacitance maintenance factor. It is a graph which shows the relationship between the number of cycles and a capacity | capacitance maintenance factor.

  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 the matters specifically mentioned in the present specification and matters necessary for the implementation of the present invention (for example, the configuration and manufacturing method of an electrode body including a positive electrode and a negative electrode, the configuration and manufacturing method of a separator and an electrolyte, General techniques relating to the construction of lithium ion secondary batteries and other batteries, etc.) can be understood as design matters for those skilled in the art based on the prior art in this field.

  Hereinafter, the configuration of the nonaqueous electrolyte secondary battery according to an embodiment of the present invention and the initial charging step will be described in this order. Hereinafter, a case where the lithium ion secondary battery is initially charged will be described, but it is not intended to limit the application target of the present invention.

<Lithium ion secondary battery>
In the lithium ion secondary battery 100 (hereinafter referred to as “battery” as appropriate) of the present embodiment, for example, as shown in FIG. 1, a long positive electrode sheet 10 and a long negative electrode sheet 20 are long. The shape of the electrode body (winding electrode body) 80 wound in a flat shape through the separator 40 is capable of accommodating the winding electrode body 80 together with a non-aqueous electrolyte (not shown) (flat box shape) The case 50 is accommodated in the case 50.

  The case 50 includes a flat rectangular parallelepiped case main body 52 having an open upper end, and a lid 54 that closes the opening. As a material constituting the case 50, a metal material such as aluminum or steel is preferably used (in this embodiment, aluminum). Or the case 50 formed by shape | molding resin materials, such as a polyphenylene sulfide (PPS) and a polyimide resin, may be sufficient. On the upper surface of the 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. Yes. A thin safety valve 56 configured to release the internal pressure of the battery case 50 when the internal pressure of the battery case 50 rises above a predetermined level is formed between both terminals 72 and 74 of the lid 54. In the case 50, a flat wound electrode body 80 is accommodated together with a non-aqueous electrolyte (not shown).

  The wound electrode body 80 according to the present embodiment is the same as the wound electrode body of a normal lithium ion secondary battery, and as shown in FIG. (Strip-shaped) sheet structure.

<Positive electrode sheet>
The positive electrode sheet 10 has a structure in which a positive electrode active material layer 14 containing a positive electrode active material is held on both surfaces of a foil-like positive electrode current collector 12 in the form of a long sheet. However, the positive electrode active material layer 14 is not attached to one side edge (the left side edge portion in the drawing) along the widthwise end of the positive electrode sheet 10, and the positive electrode current collector 12 is exposed with a certain width. The positive electrode active material layer non-formed part 16 is formed. For the positive electrode current collector 12, an aluminum foil or other metal foil suitable for the positive electrode is preferably used.

The positive electrode active material used in the present embodiment is a material that can be used as a positive electrode active material of a lithium ion secondary battery, and is a charge carrier that can be held between layers of a negative electrode active material (graphite described later) during charging (here In this case, one kind or two or more kinds of substances having lithium) can be used. For example, an oxide containing lithium and a transition metal element as a constituent metal element (lithium transition metal oxide) can be given. The oxide may have a layered rock salt structure, a spinel structure, or an olivine structure. Specific examples of such oxides include LiNi _1/3 Mn _1/3 Co _1/3 O _{2 and the} like.

  In addition to the positive electrode active material, the positive electrode active material layer 14 can contain one or two or more materials that can be used as a constituent component of the positive electrode active material layer in a general lithium ion secondary battery as necessary. . An example of such a material is a conductive material. As the conductive material, carbon materials such as carbon powder (for example, acetylene black (AB)) and carbon fiber are preferably used. Alternatively, conductive metal powder such as nickel powder may be used. In addition, examples of a material that can be used as a component of the positive electrode active material layer include various polymer materials (for example, polyvinylidene fluoride (PVDF)) that can function as a binder of the positive electrode active material.

<Negative electrode sheet>
Similarly to the positive electrode sheet 10, the negative electrode sheet 20 has a structure in which a negative electrode active material layer 24 containing a negative electrode active material is held on both surfaces of a long sheet-like foil-shaped negative electrode current collector 22. However, the negative electrode active material layer 24 is not attached to one side edge (the right side edge portion in the drawing) along the widthwise edge of the negative electrode sheet 20, and the negative electrode current collector 22 is exposed with a certain width. The negative electrode active material layer non-forming part 26 is formed. For the negative electrode current collector 22, a copper foil or other metal foil suitable for the negative electrode is preferably used.

The negative electrode active material used in this embodiment contains graphite. As the graphite contained in the negative electrode active material layer disclosed herein, those containing natural graphite or artificial graphite as a main component are preferable, and natural graphite is more preferable. Further, various graphites such as natural graphite and artificial graphite processed into particles (spherical) (pulverization, spherical molding, etc.) can be used. For example, flaky graphite can be used. The average particle diameter of the spheroidized graphite is, for example, approximately the median diameter (average particle diameter D ₅₀ : 50% volume average particle diameter) that can be derived from the particle size distribution measured using a particle size distribution measuring apparatus based on a laser scattering / diffraction method. The thickness is preferably 1 to 30 μm (typically 5 to 20 μm). As a method of processing various types of graphite into particles, a conventionally known method (for example, mechanofusion or hybridization) can be employed without particular limitation.

  In addition to the negative electrode active material, the negative electrode active material layer 24 can contain one or two or more materials that can be used as a constituent component of the negative electrode active material layer in a general lithium ion secondary battery as necessary. . Examples of such materials are polymer materials (eg, PVDF, styrene butadiene rubber (SBR)) that can function as a binder for the negative electrode active material, and function as a thickener for the paste for forming the negative electrode active material layer. Examples thereof include a polymer material to be obtained (for example, carboxymethyl cellulose (CMC)).

<Separator>
As the separator 40 disposed between the positive and negative electrode sheets 10 and 20, various porous sheets similar to those of a general lithium ion secondary battery including a wound electrode body can be used. Preferable examples include porous resin sheets (films, nonwoven fabrics, etc.) made of polyolefin resins such as polyethylene (PE) and polypropylene (PP). Such a porous resin sheet may have a single layer structure, or may have a two or more layers structure (for example, a three-layer structure in which PE layers are laminated on both sides of a PP layer).

<Winded electrode body>
In producing the wound electrode body 80, the positive electrode sheet 10 and the negative electrode sheet 20 are laminated via the separator 40. At this time, the positive electrode sheet 10 and the negative electrode sheet 20 are placed so that the positive electrode active material layer non-formation part of the positive electrode sheet 10 and the negative electrode active material layer non-formation part of the negative electrode sheet 20 protrude from both sides of the separator 40 in the width direction. Laminate slightly shifted in the width direction. The laminated body thus stacked is wound, and then the obtained wound body is crushed from the side surface direction and ablated, whereby a flat wound electrode body 80 can be produced.

  A wound core portion 82 (that is, the positive electrode active material layer 14 of the positive electrode sheet 10, the negative electrode active material layer 24 of the negative electrode sheet 20, and the separator 40) is densely laminated at the center portion in the winding axis direction of the wound electrode body 80. Part) is formed. Further, the electrode active material layer non-formed portions 16 and 26 of the positive electrode sheet 10 and the negative electrode sheet 20 protrude outward from the wound core portion 82 at both ends of the wound electrode body 80 in the winding axis direction. . A positive electrode lead terminal 74 and a negative electrode lead terminal 76 are provided on the protruding portion 16 (that is, the non-formed portion of the positive electrode active material layer 14) 16 and the protruding portion 26 (that is, the non-formed portion of the negative electrode active material layer 24) 26, respectively. Attached and electrically connected to the positive terminal 70 and the negative terminal 72 described above.

<Nonaqueous electrolyte>
Then, the wound electrode body 80 is accommodated in the main body 52 from the upper end opening of the case main body 52, and an appropriate nonaqueous electrolyte is disposed (injected) in the case main body 52. Such a non-aqueous electrolyte typically has a composition in which a supporting salt is contained in a suitable non-aqueous 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, as the supporting salt, for _{example, LiPF 6, LiBF 4, LiAsF} 6, LiCF 3 can be preferably used a lithium salt of SO ₃ and the like.

  Thereafter, the opening is sealed by welding or the like with the lid 54, and the assembly of the lithium ion secondary battery 100 according to the present embodiment is completed. The sealing process of the case 50 and the process of placing (injecting) the electrolyte may be the same as those used in the production of a conventional lithium ion secondary battery, and do not characterize the present invention. In this way, the construction (assembly) of the lithium ion secondary battery 100 according to the present embodiment is completed. In addition, the sealing process of the case main body 52 and the arrangement | positioning (injection) process of electrolyte solution can be performed similarly to the method currently performed by manufacture of the conventional lithium ion secondary battery.

  Thereafter, an initial charging step is performed on the assembled lithium ion secondary battery 100. Here, the initial charging step refers to a charging process performed for the first time after the assembly of the battery (assembly of battery components such as a positive electrode, a negative electrode, and an electrolyte) is completed. In this initial charging step, typically, an external power source is connected between the positive electrode (positive electrode terminal) and the negative electrode (negative electrode terminal) of the battery and charged to a predetermined voltage in a normal temperature range (typically constant current constant). Voltage charging). When initial charging is performed, lithium (charge carrier) is extracted from the positive electrode active material and released as lithium ions into the electrolytic solution (electrolyte). Further, the lithium ions enter the layer of graphite (negative electrode active material) provided on the negative electrode side and are occluded. At that time, as the amount of lithium held between the graphite layers increases (and consequently the negative electrode potential decreases), structural changes in the fourth stage, the third stage, the second stage, and the first stage may occur in the graphite. Here, the third stage is a stage in which lithium is inserted between every three layers of graphite (typically a stage in which the amount of lithium held between graphite layers is one lithium atom per 18 carbon atoms). The second stage is a stage in which lithium is inserted between every two layers of graphite (typically a stage in which the amount of lithium held between graphite layers is one lithium atom per 12 carbon atoms) The first stage is a stage in which lithium is inserted between all the graphite layers (typically a stage in which the amount of lithium held between the graphite layers is one lithium atom per six carbon atoms). is there. This phenomenon can be observed as a flat region showing a stepwise voltage change in the voltage characteristics of the lithium / graphite half-cell (see reference negative electrode potential in FIG. 3). The transition from the second stage to the first stage can occur, for example, when charging to 70% of the total capacity of the negative electrode.

Here, from the viewpoint of production efficiency, it is desirable to increase the charging current density to shorten the initial charging time. On the other hand, if the charging current density is excessively increased, the negative electrode potential is lowered to the lithium deposition potential, so that lithium (charge carrier) may be locally deposited on the negative electrode. As a result of various experiments, the present inventor, when performing initial charging, may or may not depend on whether the slope of the negative electrode potential (the amount of decrease in the negative electrode potential) depends on the magnitude of the charging current density, depending on the stage structure of graphite. I found out. Specifically, a plurality of uncharged lithium / graphite half cells immediately after assembly were prepared, initial charging was performed at various charging current densities, and the transition of the negative electrode potential was measured. Among them, the results of initial charging at each charging current density of 18 mA / ^{m 2} and 90 mA / ^{m 2,} shown in FIG. FIG. 3 shows changes (transitions) in the negative electrode potential during initial charging. Sample 1 shows the transition of the negative electrode potential obtained at 18 mA / m ² , and Sample 2 shows the transition of the negative electrode potential obtained at 90 mA / m ² .

As shown in FIG. 3, in each battery with charging current densities of 18 mA / m ² and 90 mA / m ² , the slope of the negative electrode potential is increased or decreased in current density (charging current value) in the second to fourth stages. It showed almost the same slope regardless. This means that in the second stage to the fourth stage, the slope of the negative electrode potential (and thus the amount of decrease in the negative electrode potential) is substantially the same regardless of the magnitude of the charging current density. That is, in the second stage to the fourth stage, the amount of decrease in the negative electrode potential does not depend on the magnitude of the charging current density. Therefore, the relatively large first voltage set so that the negative electrode potential does not become the lithium deposition potential (0 V) or less. By charging at the charging current density, it is possible to shorten the initial charging time.
On the other hand, in the first stage, a significant difference occurred in the slope of the negative electrode potential due to the magnitude of the charging current density. Specifically, the battery with a charging current density of 90 mA / m ² has an increased negative electrode potential gradient as compared with a battery with 18 mA / m ² . This means that in the first stage, the gradient of the negative electrode potential (and hence the amount of decrease in the negative electrode potential) increases as the charging current density increases. That is, in the first stage, since the amount of decrease in the negative electrode potential depends on the magnitude of the charging current density, the relatively small second charging current density set so that the negative electrode potential does not become the lithium deposition potential (0 V) or less. It becomes possible to suppress precipitation of lithium by charging with.

<Initial charging process>
From the above knowledge, the initial charging step in the present embodiment includes a first charging process and a second charging process.

The first charging process is performed until the first stage structural change occurs in graphite (in other words, before the transition to the first stage, that is, between the fourth stage and the second stage), and the negative electrode potential is 0 V or less. It is the process which charges with the 1st charging current density set so that it may not become. The relatively large first charging current density in the first charging process is preferably set to such a charging current density that the initial charging can be performed at a high speed and the negative electrode potential does not fall below the lithium deposition potential (0 V). For example, the relatively large first charging current density is generally it is desirable to set the 90 mA / ^{m 2} or more 200 mA / ^{m 2} within the following ranges. For example, the relatively high first charging current density is preferably 70 mA / m ² or more is set to (preferably 72 mA / m ² or more) higher current density than the second charging current density to be described later. By performing the initial charging at such a high rate, the initial charging process can be shortened.

The second charging process is a process of charging at a second charging current density smaller than the first charging current density after the first stage structural change occurs in graphite (that is, after shifting to the first stage). The relatively small second charging current density in the second charging process may be set to a charging current density that is smaller than the first charging current density and that the negative electrode potential does not fall below the lithium deposition potential (0 V). preferable. For example, the relatively small second charging current density is generally it is desirable to set the 10 mA / ^{m 2} or more 18 mA / ^{m 2} within the following ranges. By performing the initial charging at such a low rate, precipitation of lithium can be suppressed.

  The determination of whether or not the first stage structural change has occurred in the graphite may be performed based on, for example, monitoring the capacity of the negative electrode. For example, the transition from the second stage to the first stage can occur when charging up to 70% of the total capacity of the negative electrode. In this case, the current charged in the battery is integrated to monitor the capacity of the negative electrode, and when the capacity of the negative electrode is equal to or less than a predetermined reference value, it is determined that the first stage structural change has not occurred in the graphite. What is necessary is just to judge that the structural change of the 1st stage had arisen in graphite when the capacity | capacitance of this exceeded the predetermined reference value. For example, based on the graph of FIG. 3, the reference value for the negative electrode capacity can be set within a range of the negative electrode capacity of approximately 20 Ah to 25 Ah.

  Here, for the sake of convenience, the reference values for the charging current densities and the negative electrode capacities in the initial charging process have been described based on the graph of FIG. 3, but the reference values for the charging current densities and the negative electrode capacities obtained by the graph of FIG. The value does not limit the invention. For example, the reference values for the charging current density and the negative electrode capacity may vary depending on the battery material (particularly, the negative electrode active material), the configuration, and the like. For this reason, the reference values for the charging current density and the negative electrode capacity may be determined based on the results of a preliminary test.

  According to the present embodiment, since the graphite is charged at a relatively high first charging current density until the first stage structural change occurs (first charging process), the charging time is shortened as compared with the conventional case. be able to. Further, after the first stage structural change occurs in graphite, the negative electrode potential is charged at a relatively small second charging current density set so as not to be equal to or lower than the lithium deposition potential (0 V) (second charging). Treatment), lithium precipitation can be suppressed. Therefore, according to the said embodiment, initial charge can be completed quickly, preventing precipitation of lithium.

  Hereinafter, although the test example regarding this invention is demonstrated, it is not intending to limit this invention to what is shown to the following test examples.

LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder as a positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder, the mass ratio of these materials is A paste for a positive electrode active material layer was prepared by mixing in N-methylpyrrolidone (NMP) so as to be 89: 3: 8. The positive electrode active material layer paste is applied to both sides of a long sheet-like positive electrode current collector (aluminum foil having a thickness of about 15 μm) and dried to form a positive electrode active material layer on both surfaces of the positive electrode current collector. A positive electrode sheet provided with was prepared.

  Graphite powder as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener are submerged in water so that the mass ratio of these materials is 98: 1: 1. The mixture was mixed to prepare a negative electrode active material layer paste. The negative electrode active material layer paste is applied to both sides of the negative electrode current collector by applying the negative electrode active material layer paste in a strip shape on both sides of a long sheet of negative electrode current collector (copper foil having a thickness of about 10 μm) and drying it. A negative electrode sheet provided with was prepared.

A wound electrode body was prepared by winding the positive electrode sheet and the negative electrode sheet through two separator sheets. And the winding electrode body was accommodated in the battery case, and the opening part of the battery case was sealed airtightly. After removing moisture by cell drying, a non-aqueous electrolyte was injected from the injection port, and impregnation treatment was performed for 24 hours. As the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3: 3: 4, and about 1 mol of LiPF ₆ as a supporting salt are used. The one contained at a concentration of 1 / liter was used. In this way, a lithium ion secondary battery was assembled. The negative electrode capacity of the lithium ion secondary battery was 28 Ah.

<Initial charging process>
The initial charge process was performed with respect to the lithium ion secondary battery constructed as described above. Here, in samples 1 to 3, the charging current density of the initial charging process is different. In Sample 1, the lithium ion secondary battery was subjected to an operation (charging) in which Li was occluded in graphite until the voltage reached 4.1 V at a current value of 10 A (current density of 18 mA / m ² ). In Sample 2, an operation (charging) was performed in which Li was occluded in graphite until the voltage reached 4.1 V (end voltage) at a current value of 50 A (current density of 90 mA / m ² ). In Sample 3, the charging current value (charging current density) was switched at the timing when the first stage structural change occurred in graphite. Specifically, an operation of occluding Li in graphite (first charging process) at a current value of 50 A (current density of 90 mA / m ² ) until the charge capacity becomes 20 Ah, and then a current value of 10 A ( An operation (second charging process) in which Li was occluded in graphite until the voltage reached 4.1 V at a current density of 18 mA / m ² was performed. Table 1 shows the charging time of each sample 1 to 3.

  In addition, the battery after the initial charging treatment was disassembled, and the presence or absence of Li precipitation in the lower R portion of the wound electrode body was visually confirmed. Here, the presence or absence of Li precipitation was confirmed in the outermost periphery R part of the negative electrode sheet. The results are shown in FIG. 4 (Sample 1), FIG. 5 (Sample 2), and FIG. 6 (Sample 3).

  Moreover, in order to investigate the influence on the battery characteristics when changing the initial charging conditions, a high temperature storage test and a charge / discharge cycle test were performed.

  The high temperature storage test was conducted as follows. The lithium ion secondary battery of each sample was adjusted to SOC 85%, and then housed in a constant temperature bath at 60 ° C. and subjected to high temperature aging for 100 days. The battery capacity was measured when a predetermined number of days had elapsed from the start of the test, and the capacity retention rate after high temperature storage was determined from [(battery capacity after high temperature storage) / (initial capacity)] × 100 (%). The transition of the capacity maintenance rate after high temperature storage is shown in FIG. The horizontal axis of FIG. 7 indicates the square root of the storage days, and the vertical axis indicates the capacity maintenance rate. Table 1 shows the capacity retention ratio after storage at high temperature for 100 days.

  The charge / discharge cycle test was performed as follows. The lithium-ion secondary battery of each sample was repeatedly charged and discharged continuously 600 times under a temperature condition of 25 ° C., after charging to SOC 90% at a current value of 2C and then discharging to SOC 20% at a current value of 2C. It was. At that time, the battery capacity was measured when a predetermined cycle was repeated, and the post-cycle capacity retention rate was determined from [(battery capacity after cycle) / (initial capacity)] × 100 (%). The transition of the capacity retention rate after cycling is shown in FIG. Table 1 shows the capacity retention ratio after 600 cycles.

  The battery capacity and the initial capacity were charged at a current value of 1 C to a voltage of 4.1 V under a temperature condition of 25 ° C., and then charged for 2 hours in a constant voltage manner. The battery was discharged to a voltage of 3.0 V at a current value of 1 C, and the discharge capacity at this time was defined as the battery capacity and the initial capacity.

As shown in FIGS. 5 and 6, in the sample 2 was charged current density 90 mA / ^{m 2,} although Li precipitation was observed in the area enclosed by broken lines, 18 mA / m the charge current density from 90 mA / ^{m 2 In} sample 3 switched to ² , no Li deposition was observed. Moreover, Sample 3 of switching the charging current density from 90 mA / ^{m 2} to 18 mA / ^{m 2} could be achieved time reduction of 1.6 hours compared to the charging current density on the sample 1 was 18 mA / ^{m 2} . From this result, according to the initial charging process of Sample 3, it was confirmed that the initial charging could be completed in a short time while preventing the precipitation of Li. In any of Samples 1 to 3, no significant difference was observed in the capacity retention rate after high-temperature storage and the capacity retention rate after cycling. That is, it was confirmed that even if the charging current density was changed in the middle as in the charging process of Sample 3, the battery characteristics were not affected. From this point, it can be said that the present invention is a significant technique.

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

DESCRIPTION OF SYMBOLS 10 Positive electrode sheet 12 Positive electrode collector 14 Positive electrode active material layer 20 Negative electrode sheet 22 Negative electrode collector 24 Negative electrode active material layer 40 Separator 80 Winding electrode body 100 Lithium ion secondary battery

Claims (1)

A method for producing a non-aqueous electrolyte secondary battery having graphite as a negative electrode active material and a positive electrode active material containing a charge carrier that can be held between the graphite layers during charging,
The following steps:
Building a battery comprising a positive electrode and a negative electrode; and
An initial charging step in which the battery is charged for the first time;
Including
The initial charging step includes a first charging process for charging at a first charging current density set so that a negative electrode potential does not become 0 V or less until a structural change of the first stage occurs in the graphite;
A method of manufacturing a non-aqueous electrolyte secondary battery, comprising: a second charging process in which the graphite is charged at a second charging current density lower than the first charging current density after the first stage structural change occurs in the graphite.