KR101900146B1 - Method of manufacturing lithium ion secondary battery - Google Patents

Abstract

A method of manufacturing a lithium ion secondary battery (1) is provided. The manufacturing method includes a step of charging the battery 1 for the first time and the step of charging the battery 1 to raise the voltage Vt of the battery 1 to the first voltage Vh in the lower decomposition region Ad After the second process (S2, SA2, SA2a) of holding the voltage Vt of the battery 1 at the first voltage Vh and the second process (S2, SA2, SA2a) And a third step (S3, SA3) of performing charging to a second voltage Ve higher than the first voltage Vh.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a lithium ion secondary battery,

The present invention relates to a method for producing a lithium ion secondary battery comprising a positive electrode having a positive electrode active material layer containing positive electrode active material particles, a negative electrode, and a nonaqueous electrolyte solution containing a compound containing fluorine.

In the lithium ion secondary battery (hereinafter simply referred to as battery), it is known that the non-aqueous solvent of the non-aqueous electrolyte is likely to be oxidatively decomposed on the particle surface of the positive electrode active material particle because the positive electrode potential becomes high. When the nonaqueous solvent is oxidatively decomposed to generate hydrogen ions, when the nonaqueous electrolyte contains a fluorine-containing compound, hydrogen ions may react with fluorine to generate hydrofluoric acid (HF). Then, by the action of this hydrofluoric acid, a metal element such as a transition metal in the positive electrode active material particles is eluted and the battery capacity is reduced. Therefore, such a battery has a problem that the battery capacity is largely lowered when a charge-discharge cycle test is conducted.

To solve this problem, there is known a technique of including metal phosphate particles such as lithium phosphate or metal pyrophosphate particles in the positive electrode active material layer. When the metal phosphate particles are contained in the positive electrode active material layer, the above-mentioned hydrofluoric acid reacts with the metal phosphate when the battery is first charged, and a film containing fluorine and phosphorus is formed on the surface of the particles of the positive electrode active material. This coating suppresses direct contact of the non-aqueous electrolyte with the positive electrode active material, so that even after the coating film is formed, oxidative decomposition of the non-aqueous solvent can be suppressed even if the positive electrode potential exceeds the oxidative decomposition potential of the non-aqueous solvent. Therefore, it is possible to suppress the battery capacity from lowering after the battery is subjected to the charge / discharge cycle test. For example, Japanese Patent Application Laid-Open No. 2014-103098 discloses a technique of including metal phosphate particles such as lithium phosphate or sodium phosphate in the positive electrode material mixture layer (positive electrode active material layer).

However, it has been found that when the charging current is increased at the initial charging of the battery, the battery resistance tends to increase. The film containing fluorine and phosphorus is a resistor. However, if the charge current is large when this film is formed, the oxidative decomposition of the nonaqueous electrolyte is excessively caused, and the film is formed thick, which leads to an increase in electrical resistance.

The present invention relates to a method for manufacturing a lithium ion secondary battery capable of lowering battery resistance while forming a coating film containing fluorine and phosphorus on the surface of the particles of the positive electrode active material particles in the first charging step (first charging step) .

According to a first aspect of the present invention, there is provided a positive electrode comprising a positive electrode having a positive electrode active material layer containing positive electrode active material particles, a negative electrode, and a nonaqueous electrolyte solution containing a fluorine-containing compound, Wherein the positive electrode active material layer contains at least one of a metal phosphate and a metal pyrophosphate, and the step of charging the lithium ion secondary battery for the first time A first step of charging the lithium ion secondary battery to raise the voltage of the lithium ion secondary battery to a first voltage in a lower decomposition region of the non-aqueous electrolyte; and a second step of charging the voltage of the lithium ion secondary battery to the first voltage And a third step of performing charging to a second voltage higher than the first voltage after the second step And a method of manufacturing a lithium ion secondary battery.

According to the first aspect of the present invention, in the first charging step, in the second step after the first step, the battery voltage (terminal voltage) is held at the first voltage in the lower decomposition region, (Hereinafter also referred to as " CV charging ") is performed, and then charging is performed up to the second voltage in the third step. Thus, in the second step, oxidative decomposition of the non-aqueous electrolyte occurs while the battery voltage is maintained at the first voltage. However, the first voltage is set to a voltage within a low voltage range called a lower decomposition region, in a range where the non-aqueous electrolyte causes oxidative decomposition. As a result, the oxidative decomposition of the nonaqueous electrolytic solution does not occur only slowly, so that a film containing fluorine and phosphorus can be formed thinly on the surface of the particles of the positive electrode active material, and battery resistance can be suppressed to a low level.

Further, after this coating is appropriately formed on the surface of each positive electrode active material particle, the oxidative decomposition of the non-aqueous electrolyte is suppressed even if the voltage of the battery is within a range that causes the non-aqueous electrolyte to undergo oxidative decomposition. It is considered that the resulting coating hinders contact of the non-aqueous electrolyte with the positive electrode active material particles.

The "lower decomposition region" of the nonaqueous electrolyte means a voltage range from a decomposition lower limit voltage, which is a lower limit voltage at which the nonaqueous electrolytic solution is oxidatively decomposed, to a voltage higher than this by 0.4V. For example, when the decomposition lower limit voltage is 4.0 V, the " lower decomposition area " is 4.0 to 4.4 V. If the voltage is kept within this range, the oxidative decomposition of the non-aqueous electrolyte does not become excessive. The " decomposition lower limit voltage " of the nonaqueous electrolytic solution can be calculated from the decomposition lower limit potential (vs.Li / Li ⁺ ) of the nonaqueous electrolytic solution to the potential of the negative electrode (for example, / Li ^< ⁺ & gt ^; )). The " decomposition lower limit potential (vs. Li / Li ⁺ ) " of the nonaqueous electrolytic solution is a value detected by the following method. A measuring cell having a working electrode including a Pt plate, a counter electrode including metal lithium and a reference electrode, and a non-aqueous electrolyte used for a battery as an electrolyte is prepared. A voltage of 1 mV / sec (vs. Li / Li ^< ^{+ &} gt ^; ) was applied to the cell for measurement using an electrochemical measurement system (for example, The CV measurement is carried out for two cycles. Further, the relationship between the positive electrode potential Ep (V (vs. Li / Li ⁺ )) and the current I (amp / cm2) flowing at that time is obtained when the potential of the working electrode is raised in the third cycle. From this relationship, the relationship (graph) of the positive electrode potential Ep (V (vs. Li / Li ⁺ )) and the derivative value dI / dEp is obtained. The value of the positive electrode potential Ep which draws an approximate straight line overlapping the linearly rising portion of the differential value dI / dEp and the approximated straight line becomes the differential value dI / dEp = 0 is used as the "decomposition lower limit potential (vs. Li / Li ⁺ ) " Epd (see Figs. 6 and 7).

Examples of the composition of the metal phosphate particles contained in the positive electrode active material layer include alkali metal phosphates represented by M ₃ PO ₄ (M: alkali metal) or M ₃ (PO ₄ ) ₂ (M: Group element), or a phosphate containing an alkali metal and a metal of the second group metal. Examples of the alkali metal phosphate include lithium phosphate (Li ₃ PO ₄ ), sodium phosphate (Na ₃ PO ₄ ), potassium phosphate (K ₃ PO ₄ ), sodium di lithium phosphate (Li ₂ NaPO ₄ ) . Examples of the phosphate of the second group element include magnesium phosphate (Mg ₃ (PO ₄ ) ₂ ) and calcium phosphate (Ca ₃ (PO ₄ ) ₂ ). As the phosphate containing both the alkali metal and the Group 2 metal, for example, magnesium sodium phosphate (MgNaPO ₄ ) can be mentioned. In addition, besides a metal phosphate, such as lithium aluminum germanium phosphate _{(LAGP:... Li 1} 5 Al 0 5 Ge 1 5 (PO 4) 3) and the like, containing an element other than the alkali metal and the second group element Metal phosphates which can be used as a metal salt.

As the composition of the particles of the metal pyrophosphate, for example, an alkali metal pyrophosphate represented by M ₄ P ₂ O ₇ (M: alkali metal) or an alkali metal pyrophosphate represented by M ₂ P ₂ O ₇ (M: a Group 2 element) And pyrogen phosphates of the second group of elements. Examples of the alkali metal pyrophosphate include lithium pyrophosphate (Li ₄ P ₂ O ₇ ), sodium pyrophosphate (Na ₄ P ₂ O ₇ ) and potassium pyrophosphate (K ₄ P ₂ O ₇ ). have. Examples of the pyrophosphate of the second group element include magnesium pyrophosphate (Mg ₂ P ₂ O ₇ ) and calcium pyrophosphate (Ca ₂ P ₂ O ₇ ).

The positive electrode active material constituting the " positive electrode active material particle " includes, for example, a lithium-transition metal composite oxide. Examples of the lithium transition metal composite oxide include lithium nickel cobalt manganese composite oxides including nickel (Ni), cobalt (Co) and manganese (Mn) as transition metals, lithium nickel cobalt manganese composite oxides including nickel and manganese as transition metals Manganese composite oxides, lithium nickel oxide (LiNiO ₂ ), lithium cobalt oxide (LiCoO ₂ ), and lithium manganese oxide (LiMn ₂ O ₄ ).

More specifically, as the positive electrode active material, a lithium nickel manganese composite oxide having a spinel type crystal structure represented by the following general formula (1) can be used.

Li (Ni _x M _y Mn _2-xy ) O ₄ ... (One)

Here, x is x> 0, preferably 0.2? X? 1.0.

Y is y? 0, preferably 0? Y <1.0.

X + y < 2.0.

M is at least one element selected from the group consisting of any transition metal element other than Ni and Mn (for example, one or more elements selected from Fe, Co, Cu and Cr) or a typical metal element (for example, Zn, Al Or two or more species selected from the group consisting of:

Whether or not the crystal structure of the positive electrode active material has a spinel structure can be determined by, for example, X-ray structural analysis (preferably single crystal X-ray structural analysis). Concretely, it can be determined by X-ray diffraction measurement using CuK? Ray.

The &quot; coating film containing fluorine and phosphorus &quot; may contain, in addition to fluorine and phosphorus, a decomposition product of components (electrolyte, nonaqueous solvent, additives, etc.) of the nonaqueous electrolyte solution. The "positive electrode active material layer" may contain at least one of positive electrode active material particles, metal phosphate and metal pyrophosphate particles as well as conductive materials such as graphite, carbon black, and acetylene black, polyvinylidene fluoride (PVDF), polytetrafluoro (PTFE), styrene butadiene rubber (SBR), and the like. The &quot; negative electrode &quot; includes a negative electrode active material layer containing negative electrode active material particles formed on the negative electrode current collector foil. Examples of the negative electrode active material particles include particles containing a carbon material capable of inserting and removing lithium such as graphite.

Examples of the non-aqueous solvent of the "nonaqueous electrolyte" include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate , And vinylene carbonate. These solvents may be used alone or in combination of two or more. Fluorine-containing non-water-soluble polymer, fluoroethylene carbonate, 2,2,2-trifluoroethylmethyl carbonate, or the like may be used. Examples of the electrolyte (supporting electrolyte) to be added to the "non-aqueous electrolyte" include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ and LiCF ₃ SO ₃ , which are support electrolytes containing fluorine, Or a combination of two or more species.

The "non-aqueous electrolyte" may contain additives other than the above-described electrolytes. Examples of the additive include fluoride and lithium bisoxalate borate (LiBOB). As the fluoride, for example, AgF, CoF ₂ , CoF ₃ , CuF, CuF ₂ , FeF ₂ , FeF ₃ , LiF, MnF ₂ , MnF ₃ , SnF ₂ , SnF ₄ , TiF ₃ , TiF ₄ , ZrF ₄ , These can be used alone or in combination of two or more. The "fluorine-containing compound" contained in the non-aqueous electrolyte may be an electrolyte containing fluorine such as LiPF ₆ , an additive containing fluorine such as LiF, or fluorine such as fluoroethylene carbonate Or a non-aqueous solvent. The fluorine-containing compound contained in the nonaqueous electrolyte solution may be one kind or two or more kinds. The charging current of 1C indicates the amount of the charging current that can charge the rated capacity of the battery in one hour.

As the charging of the battery in the first step, charging by constant current charging (hereinafter also referred to as CC charging) or charging by constant power charging can be employed. Alternatively, the battery can be charged by the constant voltage charging (CV charging) in which the set voltage is equal to or higher than the first voltage until the battery voltage becomes the first voltage. The charging of the battery in the second step is a constant-voltage charging in which charging is performed while maintaining the first voltage. As the charging of the battery in the third step, charging by constant-current charging or electrostatic charging can be employed. Alternatively, the battery can be charged until the battery voltage becomes the second voltage by the constant voltage charging in which the set voltage is set to a value higher than the second voltage.

In the above-described method of manufacturing a lithium ion secondary battery, the third step may be performed at a charging current higher than 1C. As the charging of the battery in the third step, it is possible to adopt a constant current charging in which the charging current is set to a value larger than 1C, or a charging by electrostatic charging in which the charging current is limited to a value larger than 1C.

In the above-described method of manufacturing a lithium ion secondary battery, in the second step, the voltage of the lithium ion secondary battery may be maintained at the first voltage over a predetermined maintenance period.

In this manufacturing method, in the second step, the voltage of the battery is maintained at the first voltage over a predetermined sustain period. As a result, it is possible to reliably form a coating film on the surface of the positive electrode active material particles in accordance with the sustaining period.

The method for manufacturing a lithium ion secondary battery as described above is characterized in that the holding period is a period during which the second step is performed without extending the holding period and thereafter the battery resistance Rn of the battery produced by performing the third step, When the battery resistance Re of the sustain period extended battery manufactured by performing the third process is compared with the first voltage during the extended sustain period in which the sustain period is extended by 1.5 times instead of the sustain period, Rn = 0.98Re to 1.02Re.

The battery resistance after the first charge decreases as the sustain period becomes longer, that is, as the formation of the film containing fluorine and phosphorus on the particle surface of the positive electrode active material proceeds, but eventually the lowering of the resistance is stopped, The battery resistance does not change even if it is lengthened. In this case, when the battery resistance Rn is Rn = 0.98Re to 1.02Re, the first voltage is maintained for the sustain period (for example, 40 minutes), whereby the surface of the positive electrode active material particles is coated with approximately fluorine and phosphorus , It is shown that even if the holding period is extended again to 1.5 times (for example, 60 minutes), there is hardly any further coating to be formed. That is, if the first voltage is maintained over the sustain period, the film is sufficiently formed such that the cell resistance Rn is no more than 2% at most compared with the cell resistance Re of the sustain period extending battery. Therefore, if the first voltage is maintained over such a sustain period, the formation of the film including fluorine and phosphorus can be shifted to the third step which is followed immediately in a state in which it is almost completed. That is, a battery having a low battery resistance can be produced while a thin film capable of preventing oxidative decomposition of non-aqueous solvent is appropriately formed on the particle surface of the positive electrode active material particle.

The method of manufacturing a lithium ion secondary battery according to any one of claims 1 to 3, wherein the holding period is a period during which the second step is performed without extending the holding period, and thereafter the battery resistance Rn of the battery produced by performing the third step, When the battery resistance Re of the sustain period extended battery manufactured by performing the third process is compared with the first voltage during the extended sustain period in which the sustain period is extended by 1.5 times instead of the sustain period, A period in which Rn = 0.99Re to 1.01Re may be set.

In this manufacturing method, when the first voltage is maintained over the sustain period, the film is sufficiently formed so that the cell resistance Rn is no more than 1% at most compared with the cell resistance Re of the sustain period extending battery. Therefore, if the first voltage is maintained over such a sustain period, the formation of the film including fluorine and phosphorus can be shifted to the third step which is followed immediately in a state in which it is almost completed. That is, it is possible to manufacture a battery in which a film is appropriately formed on the particle surface of the positive electrode active material particles.

And the second step may be maintained at the first voltage until the magnitude of the charge current of the lithium ion secondary battery becomes equal to or lower than a predetermined cutoff current value.

In the second step, the voltage of the battery is maintained at the first voltage. In the case where the period for holding the positive electrode active material particles is the same as that for forming the positive electrode active material particles, the rate of formation of the coating film formed on the surface of the positive electrode active material particles varies. The state is different, and the battery resistance varies in size. For this reason, in order to obtain a film having an appropriate thickness in any cell, it is necessary to set the holding period to be slightly longer in accordance with the battery having a slower speed, and in some cases, the holding period is excessively long. On the other hand, in the above-described manufacturing method, in the second step, not the predetermined sustain period, but the first voltage is maintained until the charge current becomes the cutoff current value or less. Therefore, A film of the same thickness can be formed on the surface of the positive electrode active material particles in a short time.

Further, in the above-described method of manufacturing a lithium ion secondary battery, the cutoff current value may be 2/5 of the off-set current value at the end of the first step.

When the voltage of the battery is set to the first voltage (by charging CC to be charged with a predetermined current) in the first step and then held at the first voltage in the second step, that is, when CV charging is performed, , A curve (initially shaped like a graph of y = 1-e ^x ) which abruptly decreases from the ending current value at the beginning of the first step and then decreases gradually thereafter, . At the beginning of the second step, the battery voltage is set to the first voltage, so that the oxidative decomposition of the electrolytic solution occurs successively, and a large current flows as the decomposition current. However, with the lapse of time, it is considered that the metal phosphate contained in the positive electrode active material layer is consumed to form a coating film and the oxidative decomposition of the electrolytic solution is suppressed, whereby the charging current is gradually reduced.

On the basis of this, as described above, when the cutoff current value in the second step is set to be 2/5 of the end current value, most of the film containing fluorine and phosphorus formed on the particle surface of the positive electrode active material particles Can be formed in the second step, and a good film can be formed on the particle surface of the positive electrode active material particles while the second step is performed for a very short time. Further, the battery resistance can be lowered (specifically, about 7% smaller) than when the second step is not provided.

Further, in the above-described method of manufacturing a lithium ion secondary battery, the cutoff current value may be 1/5 of the off-set current value at the end of the first step.

As described above, when the value of the cutoff current in the second step is 1/5 of the value of the off-set current, most of the coating film containing fluorine and phosphorus formed on the particle surface of the positive electrode active material particles is formed in the second step And a good film can be formed on the particle surface of the positive electrode active material particles while the second step is performed for a short time. In addition, the battery resistance can be lowered (specifically, about 10% smaller) than when the second step is not provided.

Alternatively, in the above-described method of manufacturing a lithium ion secondary battery, the off-set current value at the end of the first step may be 1C or more, and the cut-off current value may be 0.05C.

In the above-described manufacturing method, the second step is performed until the cut-off current value is 0.05C, which is sufficiently small compared to the off-set current value, while the ending current value in the first step is 1C or more. As described above, when the second step is performed until the cutoff current value reaches 0.05C, when the cutoff current value is made smaller (for example, when the cutoff current value is 0.02C) The same. That is, even if the cutoff current value is less than 0.05C, the time of the second step is prolonged, and the decrease of the battery resistance can not be predicted. The formation of the film is considered to be caused by the fact that almost all of the metal phosphate (or metal pyrophosphate) contained in the positive electrode active material layer is consumed at the stage where the charge current becomes 0.05C. Thus, when the cutoff current value is 0.05 C, substantially all of the coating film containing fluorine and phosphorus formed on the particle surface of the positive electrode active material particles can be formed in the second step in a short time. In addition, a good film can be formed, and the battery resistance can be lowered (specifically, about 15% smaller) than in the case where the second step is not provided.

In the method of manufacturing a lithium ion secondary battery according to any one of the above, at least one of the metal phosphate and the metal pyrophosphate included in the positive electrode active material layer may be particles having an average particle diameter of 1.5 탆 or less.

In this production method, the particle diameter of particles of a metal phosphate or the like such as lithium phosphate contained in the positive electrode active material layer is set to 1.5 占 퐉 or less as an average particle diameter. Therefore, if the addition amount is the same, the total amount of the particles and the surface area is increased, so that the reaction with the generated hydrogen fluoride (hydrofluoric acid) tends to occur, so that a film can be formed in a short time, and the time required for the second step, The time required for the charging process can be shortened.

The method of manufacturing a lithium ion secondary battery according to any one of the preceding claims, wherein, in at least a part of the operating range (SOC = 0 to 100%) of the lithium ion secondary battery, the potential of the positive electrode is 4.5 V / Li ^&lt; ^{+ &} gt ^; ) or more.

The lithium ion secondary battery according to this manufacturing method has a potential at which the potential of the positive electrode is 4.5V (vs. Li / Li ⁺ ) or more, at least in a part of SOC = 0 to 100%. As a result, the non-aqueous electrolyte (non-aqueous solvent) is easily oxidized and decomposed on the surface of the particles of the positive electrode active material to generate hydrogen ions. In addition, the non-aqueous electrolyte includes a fluorine-containing compound as described above. Therefore, it is easy to generate hydrofluoric acid from hydrogen ions and fluorine. As described above, in this battery manufacturing method, since the film containing fluorine and phosphorus is formed on the surface of the particles of the positive electrode active material particles in the first charging step (second step), after the first charging step It is possible to suppress the oxidative decomposition of the non-aqueous electrolyte (non-aqueous solvent).

The method for manufacturing a lithium ion secondary battery according to any one of the above-mentioned aspects, wherein the first step and the third step may be charged with a constant current at a predetermined current value of 3C or more.

In this manufacturing method, the first step and the third step are charged with CC at a current value of 3 C or more. Thereby, the time required for the first step can be shortened, and the step of charging the battery for the first time (the first charging step) can be performed in a shorter time.

The technical and industrial significance, features, and advantages of an exemplary embodiment of the present invention are described below with reference to the accompanying drawings. Like numbers refer to like elements in the drawings.
1 is a perspective view of a lithium ion secondary battery according to the first and second embodiments and modifications.
Fig. 2 is a longitudinal sectional view of a lithium ion secondary battery according to the first and second embodiments and its modified form cut in a plane along the battery lateral direction and the battery longitudinal direction. Fig.
3 is a developed view of an electrode body showing a state in which a positive electrode plate and a negative electrode plate are overlapped with each other with a separator interposed therebetween, according to the first and second embodiments and modifications.
Fig. 4 is an explanatory diagram schematically showing the state of the vicinity of the particle surface in the cross-section of the positive electrode active material particles according to the first and second embodiments and modifications. Fig.
5 is a flow chart showing the procedure of each step included in the first filling step according to the first embodiment.
6 is a graph showing the relationship between the positive electrode potential Ep and the current I flowing at that time, measured using a measuring cell, for the non-aqueous electrolyte used for the batteries according to the first, second, and modified embodiments.
7 is a graph showing the relationship between the positive electrode potential Ep and the derivative value dI / dEp obtained from the graph shown in Fig.
FIG. 8 is a graph showing the relationship between the first voltage and the cell resistance ratio in each battery relating to Examples 1 and 2 and Comparative Examples 1 and 2. FIG.
9 is a graph showing the thicknesses of the coating films formed on the positive electrode active material particles of the respective batteries according to Examples 1 and 2 and Comparative Examples 1 to 3.
10 is a graph showing the relationship between the holding period and the cell resistance ratio for each of the batteries of Examples 4 to 13 and Comparative Examples 4 to 7. [
11 is a graph showing the relationship between the average particle diameter of the metal phosphate and the sustain period when the battery resistance ratio is 1.00.
Fig. 12 is a flowchart showing the procedure of each step included in the first charging step according to the second embodiment and its modification; Fig.
Fig. 13 is a flowchart showing a procedure of the second step in the first charging step according to the second embodiment. Fig.
14 is a graph showing the relationship between the charging time t in the first charging step and the terminal-to-terminal voltage Vt of the battery and the charging current Ib in the second embodiment and its modification.
15 is a graph showing the relationship between the cut-off current value Ibc and the cell resistance ratio in the second step in the first charging step according to the second embodiment and the modified embodiment.
Fig. 16 is a flowchart showing the procedure of the second step in the first charging step in the modification mode. Fig.

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described below with reference to the drawings. 1 and 2 show a lithium ion secondary battery (hereinafter simply referred to as &quot; battery &quot;) 1 according to the present embodiment. Fig. 3 shows a developed view of the electrode assembly 20 constituting the battery 1. As shown in Fig. In the following description, the battery thickness direction BH, the battery lateral direction CH, and the battery longitudinal direction DH of the battery 1 will be described with reference to Figs. 1 and 2. This battery 1 is a rectangular and hermetically sealed lithium ion secondary battery mounted on a vehicle such as a hybrid vehicle or an electric vehicle. The battery 1 includes a battery case 10, an electrode body 20 and a non-aqueous electrolyte 40 accommodated in the battery case 10, a positive electrode terminal 50 and a negative electrode terminal 51 supported by the battery case 10 . This battery 1 is a battery in which the voltage Vt between the terminals of the positive electrode terminal 50 and the negative electrode terminal 51 is between 3.5 and 4.9 V (SOC = 0 to 100%). Furthermore, SOC is 0% to 100% in the range of the positive electrode potential is 3.7 to Ep and change the range from 5.0V (vs.Li/Li ^+), the negative electrode potential from 0.2 to 0.1V of En (vs.Li/Li ⁺⁾ Within the range of.

Among them, the battery case 10 has a rectangular parallelepiped shape and includes a metal (aluminum in this embodiment). The battery case 10 includes a case body member 11 in the form of a rectangular parallelepiped box with only an upper side opened and a case cover member 10 in the shape of a rectangular plate welded in such a manner as to close the opening 11h of the case body member 11 13). The case lid member 13 is provided with a safety valve 14 that opens a rupture valve when the internal pressure of the battery case 10 reaches a predetermined pressure. A liquor hole 13h communicating with the inside and the outside of the battery case 10 is formed in the case lid member 13 and is hermetically sealed with a sealing member 15.

The positive electrode terminal 50 and the negative electrode terminal 51 constituted by the inner terminal member 53, the outer terminal member 54 and the bolt 55 are formed in the case lid member 13, Is fixedly provided via an insulating member (57) and an external insulating member (58). Further, the positive electrode terminal 50 includes aluminum, and the negative electrode terminal 51 includes copper. The positive electrode terminal 50 in the battery case 10 is connected to the positive electrode current collecting portion 21m of the positive electrode plate 21 among the electrode bodies 20 to be described later and is conducted. The negative electrode terminal 51 is connected to the negative electrode collector 31m of the negative electrode plate 31 of the electrode assembly 20 and is conductive.

Next, the electrode body 20 will be described (see Figs. 2 and 3). The electrode member 20 has a flat shape and is housed in the battery case 10. The electrode body 20 is formed by winding a strip-shaped positive electrode plate 21 and a strip-shaped negative electrode plate 31 on each other via a pair of band-shaped separators 39 and winding them in a flat shape.

The positive electrode plate 21 is provided with a positive electrode active material layer 23 in the form of a strip on a region extending in both the part of the major sides of the positive electrode current collector foil 22 including the strip- . The positive electrode active material layer 23 includes positive electrode active material particles 24, a conductive material (conductive auxiliary agent) 26, a binder 27 and lithium phosphate particles (metal phosphate particles) 28 described later. In this embodiment, acetylene black (AB) is used as the conductive material 26, polyvinylidene fluoride (PVDF) is used as the binder 27, and lithium phosphate (Li ₃ PO ₄ ) particles Powder) is used.

The mixing ratio of the positive electrode active material particles 24, the conductive material 26, and the binder 27 is 89: 8: 3 by weight. The mixing ratio of the metal phosphate particles 28 is 3 parts by weight based on 100 parts by weight of the positive electrode active material particles 24. One end portion of the positive electrode current collector foil 22 in the width direction is the positive electrode collector portion 21m in which the positive electrode current collector foil 22 is exposed without the positive electrode active material layer 23 in the thickness direction of the positive electrode current collector foil 22 have. The above-described positive electrode terminal 50 is welded to the positive electrode collector 21m.

In the present embodiment, the positive electrode active material particles 24 are lithium-transition metal composite oxides, specifically, LiNi _0.5 Mn _1.5 O ₄ particles, which is one of the lithium nickel manganese composite oxides having a spinel type crystal structure. A film 25 containing fluorine and phosphorus is formed on the particle surface 24n of the positive electrode active material particles 24 (see FIG. 4). The film 25 also contains decomposition products of other components (electrolyte and non-aqueous solvent) of the non-aqueous electrolyte 40, in addition to fluorine and phosphorus.

Next, the negative electrode plate 31 will be described. The negative electrode plate 31 has a negative electrode active material layer 33 in a strip shape on a region extending in a part of the main surface on both sides of the negative electrode current collector foil 32 including the strip- . The negative electrode active material layer 33 includes negative electrode active material particles, a binder, and a thickener. In the present embodiment, graphite particles are used as the negative electrode active material particles, styrene butadiene rubber (SBR) is used as the binder, and carboxymethyl cellulose (CMC) is used as the thickener. One end portion of the negative electrode current collecting foil 32 in the width direction does not have the negative electrode active material layer 33 in the thickness direction of the negative electrode current collecting foil 32 and becomes the negative electrode collector portion 31m in which the negative electrode current collecting foil 32 is exposed have. The above-described negative electrode terminal 51 is welded to this negative electrode collector portion 31m. The separator 39 is a porous film containing a resin and has a strip shape.

Next, the nonaqueous electrolyte solution 40 will be described. The nonaqueous electrolyte solution 40 is contained in the battery case 10 and a part of the nonaqueous electrolyte solution 40 is impregnated in the electrode member 20 and the remainder is stored in the bottom of the battery case 10 as an excess liquid have. The electrolyte of the nonaqueous electrolyte solution 40 is lithium hexafluorophosphate (LiPF ₆ ), and its concentration is 1.0 M. The non-aqueous solvent of the non-aqueous electrolyte (40) is a mixed organic solvent in which fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethyl methyl carbonate are mixed at a volume ratio of 1: 1. As described above, this nonaqueous electrolyte solution 40 contains, as the fluorine-containing compound 41, in addition to LiPF ₆ as a supporting electrolyte, a non-aqueous fluoroethylene carbonate (FEC) and a 2,2,2-trifluoro And ethyl methyl carbonate.

Next, a manufacturing method of the battery 1 will be described. First, the positive electrode plate 21 is formed. Specifically, a positive electrode active material particle 24 comprising LiNi _0.5 Mn _1.5 O ₄ which is a lithium nickel manganese composite oxide having a spinel structure is prepared. The positive electrode active material particles 24, the conductive material 26 (acetylene black), the binder 27 (polyvinylidene fluoride) and the metal phosphate particles 28 (lithium phosphate particles, average particle diameter D50 = 3.0 μm) is kneaded together with a solvent (NMP in this embodiment) to prepare a positive electrode paste. The mixing ratio of the positive electrode active material particles 24 to the conductive material 26 and the binder 27 is 89: 8: 3 by weight as described above. When the positive electrode active material particles 24 are 100 parts by weight, 3 parts by weight of phosphate particles 28 are further added. When metal phosphate particles 28 having an average particle diameter D50 of 1.5 占 퐉 or 0.8 占 퐉 are used as described later, the particle diameter is adjusted to a desired size by using a wet type bead mill.

Thereafter, this positive electrode paste is applied to one main surface of the positive electrode current collector foil 22 including a strip-shaped aluminum foil and dried to form the positive electrode active material layer 23. [ Also, the positive electrode paste is applied to the other main surface of the positive electrode collector foil 22 and dried to form the positive electrode active material layer 23. Thereafter, this is pressed to obtain the positive electrode plate 21. Further, the negative electrode plate 31 is separately formed by a known method.

Subsequently, the positive electrode plate 21 and the negative electrode plate 31 are superimposed on each other with a pair of separators 39 interposed therebetween, and wound using a winding. Further, the electrode body 20 is formed by compressing it into a flat shape. Separately, a case cover member 13, an inner terminal member 53, an outer terminal member 54, a bolt 55, an inner insulating member 57, and an outer insulating member 58 are prepared. The inner surface of the case cover member 13 is covered with the inner terminal member 53, the outer terminal member 54, and the bolt 55 via the inner insulating member 57 and the outer insulating member 58, The terminal 50 and the negative electrode terminal 51 are fixedly installed. Thereafter, the positive electrode terminal 50 and the negative electrode terminal 51 integrated with the case lid member 13 are welded to the positive electrode collector 21m and the negative electrode collector 31m of the electrode assembly 20, respectively. The electrode case 20 is accommodated in the case body member 11 and then the case cover member 13 is welded to the opening of the case body member 11 to form the battery case 10. [

The nonaqueous electrolyte solution 40 is separately prepared. Concretely, LiPF ₆ was dissolved in a mixed organic solvent in which fluoroethylene carbonate and 2,2,2-trifluoroethyl methyl carbonate were mixed at a volume ratio of 1: 1 so as to have a concentration of 1.0M. The non-aqueous electrolyte solution 40 is injected into the battery case 10 from the injection hole 13h, and the non-aqueous electrolyte solution 40 is impregnated into the electrode member 20. Thereafter, the instilling hole 13h is sealed to form the battery 1. [

Then, the battery 1 is first charged (first charging step). In this first charging step, a film 25 containing fluorine and phosphorus is formed on the particle surface 24n of the positive electrode active material particles 24 together with the first charging. Specifically, as a first charging step, the battery 1 is first connected to a CC-CV charging / discharging device (not shown), and the battery 1 is CC-charged at a current of 3.0 C Terminal voltage Vt to 4.1 V (first voltage Vh) (first step S1). Subsequently, the charging is switched to the CV charging of the terminal-to-terminal voltage Vt = 4.1V. That is, the inter-terminal voltage Vt is maintained at the first voltage Vh = 4.1 V over the sustain period Tk = 60 minutes (second step S2). Thereafter, constant current charging (CC charging) is performed until the inter-terminal voltage Vt reaches the second voltage Ve at a constant current of 3.0 C, specifically until the inter-terminal voltage Vt reaches 4.9 V Step S3).

(Vh = 4.1 V, the positive electrode potential Ep of the positive electrode plate 21 = 4.3 V (vs. Li / Li ⁺ Li) in the above-described first charging, specifically in the second step, ) And the coating film containing fluorine and phosphorus (hereinafter referred to as &quot; coating liquid ^& quot ^; ) containing fluorine and phosphorus on the particle surface 24n of the positive electrode active material particle 24 while maintaining the negative electrode potential En of the negative electrode plate 31 at 0.2V 25 are formed. In addition, the positive electrode potential at the time point Ep = 4.3V (vs.Li/Li ^+), there is a higher value than the lower limit voltage by 0.1V decomposition Epd = 4.2V (vs.Li/Li ⁺⁾ as described below . The first voltage Vh = Vt = 4.1 V, which is the inter-terminal voltage maintained, is 0.1 V higher than the decomposition lower limit voltage Vtd = 4.0 V.

The mechanism by which the film 25 is formed is not clear, but the following can be conceived. That is, when the positive electrode potential (redox potential) Ep of the positive electrode plate 21 (positive electrode active material particle 24) becomes equal to or higher than the decomposition lower limit potential Epd described later, the particle surface 24n of the positive electrode active material particle 24 , A nonaqueous solvent (fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethylmethyl carbonate in this embodiment) of the nonaqueous electrolyte solution 40 contacting the surface 24n is oxidized and decomposed And hydrogen ions are generated. This hydrogen ion is dissolved in the fluorine-containing compound 41 (LiPF _{6 in the} supporting electrolyte, fluoroethylene carbonate (FEC) in the solvent, 2,2,2-tri Fluoroethyl methyl carbonate) to produce hydrofluoric acid (HF). This hydrofluoric acid reacts with the metal phosphate (lithium phosphate) particles 28 contained in the positive electrode active material layer 23 to form a film 25 containing fluorine and phosphorus on the particle surface 24n of the positive electrode active material particles 24 . Thereafter, the cell is unsealed, and the cell is sealed again under reduced pressure. In addition, various tests are performed. Thus, the battery 1 is completed.

(Measurement of decomposition lower limit voltage, decomposition lower limit potential)

Next, in the battery 1 having the above-described configuration, the lowest positive electrode (cathode active material particle) 24 in which oxidative decomposition of the nonaqueous electrolyte (nonaqueous solvent) 40 among the positive electrode potential Ep of the positive electrode plate 21 The decomposition lower limit potential Epd, which is the potential Ep, is detected as follows. First, a measuring cell having a working electrode including a Pt plate, a counter electrode including metal lithium, and a reference electrode and using the nonaqueous electrolyte solution 40 used for the battery 1 is prepared. The electrochemical measurement system of AMTEK was used to raise and lower the potential of the working electrode over the range of 3.0 to 5.4 V (vs. Li / Li ⁺ ) at a rate of 1 mV / sec Perform CV measurement for two cycles. Further, the relationship between the positive electrode potential Ep (V (vs. Li / Li ⁺ )) and the current I (㎂ / ㎠) flowing at that time when the potential of the working electrode is raised at the third cycle is obtained ). Further, the current on the charge side is set to a positive value. From this relationship, the relationship between the positive electrode potential Ep (V (vs.Li / Li ⁺ )) and the differential value dI / dEp is obtained (Fig. 7). An approximate straight line L overlapping this change is drawn at a portion where the derivative value dI / dEp linearly increases with the rise of the positive electrode potential Ep, and the approximated straight line L is set to a value of the positive potential Ep at which the differential value dI / Decomposition lower limit potential (vs. Li / Li ⁺ ) &quot; Epd of the non-aqueous electrolyte solution 40. [

The nonaqueous electrolyte solution 40 (fluoroethylene carbonate (FEC) + 2,2,2-trifluoroethylmethyl carbonate (1: 1) and LiPF ₆ The relationship between the positive electrode potential Ep (V (vs. Li / Li ⁺ )) measured with respect to the positive electrode potential Ep (V (vs. Li / Li) and the current I ⁺ )) And the derivative value dI / dEp is shown in Fig.

According to the graph of the positive electrode potential Ep vs. the current I shown in Fig. 6, in the range where the positive electrode potential Ep is 3.3 to 4.1 V (vs. Li / Li ⁺ ), Seems to be increasing. However, in the range in which the positive electrode potential Ep is 4.2 V (vs. Li / Li ⁺ ) or more, the current I seems to be acceleratingly increasing with the increase of the positive electrode potential Ep.

Thus, the derivative value dI / dEp was calculated to obtain a graph of the positive electrode potential Ep versus the derivative value dI / dEp (see Fig. 7). Then, in a range where the positive electrode potential Ep is in the range of 4.4 to 5.0 V (vs. Li / Li ⁺ ), the differential value dI / dEp is linearly increased with increase in the positive electrode potential Ep The current I is increasing in proportion to the square of the potential). Therefore, an approximate straight line L that matches the range in which the differential value dI / dEp linearly increases is drawn. The value of the positive potential Ep (that is, the X-intercept in the graph of Fig. 7) at which the approximate straight line L is such that the differential value dI / dEp is 0 is 4.2 V (vs. Li / Li ⁺ ). Therefore, this positive electrode potential Ep (= 4.2 V (vs. Li / Li ⁺ )) is defined as the decomposition lower limit potential Epd of the nonaqueous electrolyte solution 40 according to this embodiment. The oxidative decomposition of the non-aqueous solvent is considered to be accelerated (quadratic function) as the positive electrode potential Ep increases when the positive electrode potential Ep exceeds the decomposition lower limit potential Epd.

In the battery 1, graphite is used for the negative electrode active material as described above, and the negative electrode potential En is constant at 0.2 V (vs. Li / Li ⁺ ). Therefore, the inter-terminal voltage Vt of the battery 1 in the state where the positive electrode plate 21 is at the decomposition lower potential Epd (= 4.2 V (vs. Li / Li ⁺ )) becomes 4.0 V (Vt = Ep -En = 4.2-0.2 = 4.0V). Therefore, this value is set to the &quot; decomposition lower limit voltage &quot; Vtd (= 4.0 V) in the battery 1. [

In the battery 1, the "lower decomposition region" Ad of the non-aqueous electrolyte is set in the range of Ad = Vtd to Vtd + 0.4 using the decomposition lower limit voltage Vtd. Specifically, the lower decomposition region Ad has a value in the range of 4.0 to 4.4 V (see FIG. 8).

(Examples 1 and 2 and Comparative Examples 1 to 3)

Next, a test conducted to verify the effects of the present invention and the results thereof will be described. A battery using the same positive electrode plate 21, negative electrode plate 31, separator 39 and nonaqueous electrolyte solution 40 as the battery 1 was prepared as shown in the following Table 1, The test was conducted under five kinds of test conditions of Comparative Examples 1 to 3. Therefore, lithium phosphate particles (LPO) having an average particle diameter D50 of 3.0 占 퐉, when the positive electrode active material particle 24 contained in the positive electrode active material layer 23 is 100 parts by weight, are formed in the positive electrode active material layer 23 of each example battery. 3 parts by weight (see Table 1).

In the battery of Comparative Example 1, in the first charging, the lower decomposition region Ad is increased in the inter-terminal voltage Vt up to 3.8 V, which is lower than the lower limit value in the range of 4.0 to 4.4 V The voltage Vt (first voltage Vh) = 3.8 V was maintained for the sustain period Tk = 60 minutes (second process). Thereafter, the constant current charging at the CC charging rate of 3.0 C was performed until the inter-terminal voltage Vt reached the second voltage Ve = 4.9 V (the third step), and the first charging was completed. The total charging time for the first charge of the battery of Comparative Example 1 is 80 minutes.

In the battery of Example 1, after the inter-terminal voltage Vt is raised to the inter-terminal voltage Vt = 4.1 V in the lower decomposition region Ad (the first step) at the first charging, the inter-terminal voltage Vt Voltage Vh) = 4.1 V was maintained for the sustain period Tk = 60 minutes (second step). Thereafter, the constant current charging at the CC charging rate of 3.0 C was performed until the inter-terminal voltage Vt reached the second voltage Ve = 4.9 V (the third step), and the first charging was completed. The total charge time for the first charge is 80 minutes.

In the second embodiment, only the inter-terminal voltage Vt to be held is different from that in the first embodiment. That is, the inter-terminal voltage Vt is raised to Vt = 4.4 V in the lower decomposition area Ad, the inter-terminal voltage Vt (first voltage Vh) = 4.4 V is maintained for the sustaining period Tk = 60 minutes, CC charging rate was 3.0C. The total charge time for the first charge is 80 minutes.

Also in Comparative Example 2, only the inter-terminal voltage Vt to be held is different from that in the first embodiment. However, the inter-terminal voltage Vt is raised to 4.7 V, which is higher than the lower decomposition region Ad, and the inter-terminal voltage Vt (first voltage Vh) = 4.7 V is maintained for the sustaining period Tk = 60 minutes, Charged at a charge rate of 3.0C. The total charge time for the first charge is 80 minutes.

In Comparative Example 3, unlike Comparative Examples 1 and 2 and Examples 1 and 2, the second step of maintaining the voltage is not provided. That is, since the beginning of the first charging, the constant current charging at the CC charging rate of 3.0 C was performed until the inter-terminal voltage Vt reached the second voltage Ve = 4.9 V, and the first charging was terminated. The total charge time for the first charge is 20 minutes shorter than the other.

The battery resistance (IV resistance) was measured for the batteries of Comparative Examples 1 to 3 and Examples 1 and 2 after completion of the first charging. Specifically, each battery was adjusted to SOC of 60% under a temperature environment of 25 캜 and discharged at a constant current of 0.3 C for 10 seconds, and the voltage change before and after discharge was measured. Further, only the discharging current value was increased in the order of 1C, 3C, and 5C, and discharging was performed under the same conditions as those described above to measure voltage changes before and after the discharging for 10 seconds. Thereafter, these data are plotted on the coordinate plane in which the abscissa axis is the discharge current value and the ordinate axis is the voltage change before and after the discharge, and the approximate straight line (linear equation) is calculated by the least squares method. . Then, the battery cell resistance (IV resistance) of Example 2 was used as a standard (= 1.00), and the "battery resistance ratio" of the other batteries was calculated. The results are shown in Table 1 and FIG. 8 is a graph showing the relationship between the first voltage Vh and the cell resistance ratio in each battery. However, the results of Comparative Example 3 are not shown in Fig.

The batteries of Comparative Examples 1 to 3 and Examples 1 and 2 were disassembled to take out the positive electrode active material particles 24 and the particle surface 24n of the positive electrode active material particles 24 was measured using a TEM (transmission electron microscope) (N = 3) of the film 25 containing fluorine and phosphorus formed on the surface of the film. The results are shown in Table 1 and FIG. 9 is a graph showing the thickness of the coating film formed on the positive electrode active material particles of each battery.

It can be seen from Table 1 and Fig. 8 that when the sustain period Tk is 60 minutes in all, and the first voltage Vh is 4.1 V (Example 1), the battery resistance ratio becomes lowest. Also, even when the first voltage Vh is 4.4 V (Example 2), it is understood that the battery resistance ratio is 1.05, and the resistance rises only by about 5%. In Embodiments 1 and 2, the first voltage Vh in the second step is set to Vh = 4.1 V, which is slightly larger than the decomposed lower limit voltage Vtd = 4.0 V, or slightly larger, Vh = 4.4 V, Oxidative decomposition of the nonaqueous electrolyte solution 40 occurs between the two steps. However, the first voltage Vh is set to a voltage within a lower voltage range of the lower decomposition region Ad (= 4.0 to 4.4 V) in the range where the non-aqueous electrolyte causes oxidative decomposition. This prevents the nonaqueous electrolytic solution 40 from being oxidatively decomposed only slowly and prevents the formation of a film 25 containing excessively thick fluorine and phosphorus on the particle surface 24n of the positive electrode active material particles 24, It is considered that the battery resistance can be suppressed to be low. The reason why it was possible to prevent the formation of the coating film 25 including the excessively thick fluorine and phosphorus was that the thickness tt of the coating film 25 shown in Table 1 and Fig. 9 was 10 nm in Example 1, 13 Nm, which is smaller than Comparative Examples 1 to 3.

On the other hand, in Comparative Example 2, the first voltage Vh in the second step was set to 4.7 V which is much larger than the decomposition lower limit voltage Vtd = 4.0 V (exceeding the lower decomposition region Ad). Therefore, a large amount of electric current flows between the second step and the oxidative decomposition of the nonaqueous electrolyte solution 40 occurs at a time, and the particle surface 24n of the positive electrode active material particles 24 contains excessively thick fluorine and phosphorus It is considered that the battery resistance is increased as compared with Examples 1 and 2 because the coating film 25 is formed. The thickness 25 of the film 25 shown in Table 1 and FIG. 9 was 18 nm in Comparative Example 2, which is thicker than those of Examples 1 and 2, .

In Comparative Example 3, since CC charging was performed at a high current of 3.0 C at the charging rate from the beginning without the second step, oxidative decomposition of the nonaqueous electrolyte solution 40 occurred at a time at a large amount, It is considered that the film 25 is formed. The formation of the thick coating 25 is also supported by the fact that the thickness tt of the coating 25 shown in Table 1 and Fig. 9 is the thickest at 20 nm in Comparative Example 3.

In Comparative Example 1, the first voltage Vh in the second step was 3.8 V, which is lower than the decomposition lower limit voltage Vtd = 4.0 V (lower than the lower decomposition region Ad). Therefore, the oxidative decomposition of the nonaqueous electrolyte solution 40 hardly occurs during the second step, and it is considered that almost no film is formed in the second step. However, it is considered that the thick film 25 is formed by the CC charging with a large current such as the charging rate 3.0C in the subsequent third step. Therefore, in Comparative Example 1, the creation pattern is similar to that of Comparative Example 3 in terms of the formation of the film. The formation pattern of this coating is also supported by the fact that the thickness tt of the coating 25 shown in Table 1 and Fig. 9 is 18 nm in Comparative Example 1, which is thicker than those in Examples 1 and 2. Also, the battery resistance is higher than those of Examples 1 and 2.

From the above, the first voltage Vh in the second step is set within the range of the decomposition lower limit voltage Vtd = 4.0 V and the decomposition lower limit voltage Vtd + 0.4 V (= 4.4 V) (Vt = 4.0 to 4.4 V), it is understood that a thin film 25 having a small thickness can be formed, and battery resistance can also be lowered.

(Comparative Examples 3 to 6, Examples 1, 3 to 13)

Subsequently, tests were carried out for each of the batteries of Comparative Examples 3 to 6 and Examples 1 and 3 to 13 in which the mean particle diameters of the metal phosphate (LPO) added to the positive electrode active material layer were different from each other, The battery resistance ratio was obtained (see Table 2). Specifically, a battery in which 3.00 mass% of lithium phosphate particles (LPO) having an average particle diameter D50 of 3.0 占 퐉 was added to the positive electrode active material layer 23 was prepared in the same manner as in Example 1 described above, Terminal voltage Vt until the voltage Vt becomes 4.1 V (the first step). Thereafter, the constant current charging at the CC charging rate of 3.0 C was carried out after the first voltage Vh was set to 4.1 V and the sustain period Tk was set to 0 minute, 20 minutes, 40 minutes, 60 minutes, and 90 minutes (second process) Terminal voltage Vt reached the second voltage Ve = 4.9V (third step). These are referred to as Comparative Example 3, Examples 1 and 3 to 5. The example in which the sustain period Tk is 0 minute corresponds to the above-described Comparative Example 3, and the example in which the sustain period Tk is 60 minutes corresponds to the first embodiment described above.

3 parts by weight of lithium phosphate particles (LPO) having an average particle diameter D50 of 1.5 占 퐉 and a positive electrode active material particle 24 as a reference (100 parts by weight) were used in the positive electrode active material layer 23, The charged battery is prepared and charged for the first charging until the terminal-to-terminal voltage Vt of the battery becomes 4.1 V (the first step). Thereafter, after the terminal voltage Vt was set to the first voltage Vh = 4.1 V and the sustain period Tk was set to 0 minute, 10 minutes, 20 minutes, 30 minutes, and 60 minutes (second step) Was charged until the inter-terminal voltage Vt reached the second voltage Ve = 4.9 V (the third step). These are referred to as Comparative Example 4 and Examples 6 to 9.

3 parts by weight of lithium phosphate particles (LPO) having an average particle diameter D50 of 0.8 占 퐉 and a positive electrode active material particle 24 as a reference (100 parts by weight) were formed in the positive electrode active material layer 23, The charged battery is prepared and charged for the first charging until the terminal-to-terminal voltage Vt of the battery becomes 4.1 V (the first step). Thereafter, after the terminal voltage Vt was set to the first voltage Vh = 4.1 V and the sustain period Tk was set to 0 minute, 10 minutes, 20 minutes, 30 minutes, and 60 minutes (second step) Was charged until the inter-terminal voltage Vt reached the second voltage Ve = 4.9 V (the third step). These are referred to as Comparative Example 5 and Examples 10 to 13.

As Comparative Example 6, the same battery as in Example 1 was charged at the CC charge rate of 0.33 C from the beginning as the initial charge, and at 180 minutes until the inter-terminal voltage Vt reached the second voltage Ve = 4.9 V A constant-current charging was performed. Since the battery of Comparative Example 6 is charged at a low charging rate (charging current) of 0.33C, even if oxidative decomposition of the non-aqueous electrolyte solution 40 (non-aqueous solvent) occurs during the first charging, I never do that. Therefore, it is considered that the coating 25 containing fluorine and phosphorus is gradually formed on the particle surface 24n of the positive electrode active material particles 24, resulting in a thin film 25, and the battery resistance (IV resistance) Is low.

After completion of the first charging, the battery resistance (IV resistance) of the batteries of Comparative Examples 3 to 6, and Examples 1 to 3 to 13 was measured in the same manner as in the battery of Example 1 and the like. Then, the battery cell resistance (IV resistance) of Comparative Example 6 was used as a standard (= 1.00), and the "battery resistance ratio" of each battery was calculated. The results are shown in Table 2 and FIG. 10 is a graph showing the relationship between the sustain period Tk and the cell resistance ratio in each cell. However, the results of Comparative Example 6 are not shown in Fig.

In Table 2 and FIG. 10, first, the batteries of Comparative Examples 3 and Examples 1 and 3 to 5 using Lithium Phosphate Particles (LPO) having an average particle diameter D50 of 3.0 占 퐉 are examined. As can be understood from Table 2 and FIG. 10, in Comparative Example 3 in which the sustain period Tk corresponds to 0 minutes, the cell resistance ratio was 1.18, and the cell resistance was high. However, all of the batteries of Examples 3, 4, and 1 (holding periods Tk of 20, 40, and 60 minutes) had lower battery resistance ratios (battery resistance) than those of Comparative Example 3. In addition, when the batteries of Examples 3, 4, and 1 (holding periods Tk are 20, 40, and 60 minutes, respectively) are compared, battery resistance ratio (battery resistance) becomes lower as the battery has a longer holding period Tk. The reason is thought to be the following. When the sustain period Tk is short, the film 25 is produced, but the thickness thereof is insufficient, and the formation of the film is stopped in a state in which the nonaqueous electrolyte solution 40 (nonaqueous solvent) can be oxidatively decomposed thereafter. As a result, after the second process, the process shifts to the third process, and when the charge is switched to CC charging at a charging rate of 3.0 C, oxidative decomposition of a large amount of non-aqueous solvent occurs at a time due to a large current, And a thick film is formed. As a result, in the batteries in which the sustain period Tk is shorter than that in the first embodiment (Examples 3 and 4), the resistance is higher than that in the battery (the battery in the first embodiment) in which the sustain period Tk is sufficiently secured. However, in Examples 3 and 4, oxidative decomposition of the non-aqueous solvent during CC charging is suppressed as compared with the battery of Comparative Example 3 in which the coating film 25 is formed in advance in the second step. As a result, it is considered that in Examples 3 and 4, the battery resistance becomes smaller than that of the battery having no sustain period Tk (Comparative Example 3). It is considered that the battery resistance in Example 4 is smaller than that in Example 3. [ In the battery of Example 1 (sustain period Tk = 60 minutes) in which the sustain period Tk could be ensured appropriately, the cell resistance ratio (cell resistance) could be lowered to the same level as that of Comparative Example 6. [

On the other hand, when the battery of Example 5 (holding period Tk = 90 minutes) and the battery of Example 1 (holding period Tk = 60 minutes) are compared, the battery resistance ratio does not change even when the holding period Tk is increased Not). When the film 25 is formed, oxidative decomposition of the non-aqueous solvent becomes difficult to occur, and eventually the film is not oxidatively decomposed. Then, since the film 25 is not formed, the increase in the thickness of the film 25 is stopped and the increase in the cell resistance is also lost. Therefore, even if the sustain period Tk is made unnecessarily long, there is no effect of lowering the cell resistance, and it is preferable to terminate the second process in the proper sustain period Tk and proceed to the third process.

Subsequently, the batteries of Comparative Examples 4 and 6 to 9 using lithium phosphate particles (LPO) having an average particle diameter D50 of 1.5 占 퐉 are examined. These batteries can be similarly thought of as the batteries of Comparative Example 3, Examples 1 and 3 to 5 described above. That is, in Comparative Example 4 in which the sustain period Tk corresponds to 0 min, the cell resistance ratio was 1.12 and the cell resistance was high. However, all of the batteries of Examples 6 to 8 (the holding periods Tk of 10, 20, and 30 minutes) had lower battery resistance ratios (battery resistance) than those of Comparative Example 4. In addition, when the batteries of Examples 6 to 8 (holding periods Tk are 10, 20 and 30 minutes, respectively) are compared, the cell resistance ratio (cell resistance) becomes lower as the battery has a longer holding period Tk. In the battery of Example 8 (holding period Tk = 30 minutes), the battery resistance ratio (cell resistance) could be lowered to the same level as that of Comparative Example 6. [ On the other hand, in the battery of Example 9 (holding period Tk = 60 minutes), the battery resistance ratio does not change (does not deteriorate) even when the holding period Tk is increased as compared with Example 8 (holding period Tk = 30 minutes) .

The batteries of Comparative Example 5 and Examples 10 to 13 using lithium phosphate particles (LPO) having an average particle diameter D50 of 0.8 占 퐉 are examined. These batteries can also be considered as the batteries of Comparative Example 3, Examples 1, 3 to 5, Comparative Examples 4 and 6 to 9 described above. That is, in Comparative Example 5 in which the sustain period Tk corresponds to 0 minute, the cell resistance ratio was 1.09, and the cell resistance was high. However, all of the batteries of Examples 10 to 12 (the holding periods Tk of 10, 20 and 30 minutes) lowered the battery resistance ratio (battery resistance) as compared with Comparative Example 5. In addition, when the batteries of Examples 10 to 12 (the holding periods Tk are 10, 20 and 30 minutes, respectively) are compared, the battery resistance ratio (cell resistance) becomes lower as the battery has a longer holding period Tk. In the battery of Example 11 (holding period Tk = 20 minutes), the battery resistance ratio (cell resistance) could be lowered to the same level as that of Comparative Example 6. [ In addition, in the battery of Example 12 (holding period Tk = 30 minutes), the battery resistance ratio (battery resistance) was lower than that of Comparative Example 6 (battery resistance ratio = 0.99). However, in the battery of Example 13 (holding period Tk = 60 minutes), compared with Example 12 (holding period Tk = 30 minutes), the battery resistance ratio does not change (does not deteriorate) even if the holding period Tk is increased. .

From these results, it can be understood that by providing the second step of holding the first voltage Vh over the sustaining period Tk, the cell resistance can be lowered compared to the case where the second step is not provided. In addition, by increasing the sustain period Tk, the battery resistance can be lowered. However, it is preferable that the second step is terminated in the sustain period Tk of an appropriate length and the process proceeds to the third step, because the sustain period Tk has an appropriate length and the sustain period Tk is made unnecessarily long, Able to know.

Thus, as the sustain period Tk, the second process is performed without extending the sustain period Tk, and then the cell resistance Rn of the battery manufactured by performing the third process and the sustain period Tk are changed to 1.5 times The first voltage Vh is maintained for the extended maintenance period and then the battery resistance Re of the maintenance period extended battery manufactured by performing the third process is compared with the range of 0.98Re to 1.02Re Select the period. When the first voltage Vh is maintained over the selected sustain period Tk as described above, the cell resistance Rn of the cell resistance Rn with a difference of at most 2% as compared with the cell resistance Re of the sustain period extended battery having the sustain period extended by 1.5 times 25) can be formed. Therefore, when the first voltage Vh is maintained over the sustain period Tk, the formation of the film 25 can be shifted to the third process which is performed in a substantially completed state. That is, a thin film 25 capable of preventing oxidative decomposition of the nonaqueous solvent is appropriately formed on the particle surface 24n of the positive electrode active material particles 24, and a battery having low battery resistance can be produced in a short time.

Specifically, according to Table 2 and FIG. 10, the relationship between the holding period and the battery resistance is obtained in advance for the battery of a specific type to be manufactured, and the battery resistance Rn in the case where the holding period Tk is a certain value is 1.5 It is preferable to find the range of the sustain period Tk in which the battery resistance Rn is in the range of 0.98Re to 1.02Re. For example, the batteries of Comparative Example 3 and Examples 1 and 3 to 5 (batteries indicated by (1) in Fig. 10) using lithium phosphate particles (LPO) having an average particle diameter D50 of 3.0 占 퐉 are illustrated. The cell resistance Rn of the battery (Example 4) in which the sustain period Tk was set to 40 minutes was 1.02 in terms of the cell resistance ratio. On the other hand, the battery resistance Re of the battery (Example 1) in which the sustain period Tk is extended to 1.5 times is 60 minutes, the battery resistance ratio is 1.00. Therefore, the battery resistance Rn of the battery of Example 4 falls within the range of 0.98Re to 1.02Re. In this respect, with respect to the battery (Comparative Example 3, Examples 1, 3 to 5) using lithium phosphate particles (LPO) having an average particle diameter D50 of 3.0 占 퐉, it is preferable that the storage period Tk is 40 minutes or more Able to know.

As the sustain period Tk, the second step is performed without extending the sustain period Tk. Thereafter, in place of the cell resistance Rn of the battery manufactured by performing the third step and the sustain period Tk, an extension The first voltage Vh is maintained during the sustain period, and then the battery resistance Re of the sustain period extended battery manufactured by performing the third process is compared, a period in which Rn is included in the range of 0.99Re to 1.01Re is selected . When the first voltage Vh is maintained over the selected sustain period Tk as described above, the cell resistance Rn which is no more than 1% at most compared to the cell resistance Re of the sustain period extension battery in which the sustain period is extended by 1.5 times (25) can be formed. Therefore, if the first voltage Vh is maintained over the sustain period Tk, the formation of the film 25 can be shifted from the substantially completed state to the subsequent third step. That is, a thin film 25 capable of preventing oxidative decomposition of the non-aqueous solvent is more suitably formed on the particle surface 24n of the positive electrode active material particles 24, and a battery having a low battery resistance can be manufactured in a short time .

In this case, with respect to a battery (Comparative Example 3, Examples 1, 3 to 5) using lithium phosphate particles (LPO) having an average particle diameter D50 of 3.0 占 퐉, for example, It can be seen that

Next, the relationship between the size of the average particle diameter D50 of the lithium phosphate particles 28 added to the positive electrode active material layer 23 and the sustain period Tk is examined (see Table 2 and FIG. 11). First, in a battery (Comparative Example 3, Examples 1 to 3 to 5) using lithium phosphate particles 28 having an average particle diameter D50 of 3.0 占 퐉, a battery having a battery resistance ratio of 1.00 (battery resistance equivalent to that of the battery of Comparative Example 6) The sustain period Tk of the first embodiment is 60 minutes. In the battery (Comparative Example 4, Examples 6 to 9) using particles 28 having an average particle diameter D50 of 1.5 占 퐉, the holding period Tk of Example 8 is 30 minutes. Further, in the battery (Comparative Example 5, Examples 10 to 13) using the particles 28 having an average particle diameter D50 of 0.8 占 퐉, the holding period Tk of Example 11 is 20 minutes. The relationship between the average particle size D50 of the particles 28 in these cells and the sustain period Tk at which the battery resistance ratio becomes 1.00 is shown in Fig. That is, the size of the storage period Tk required for obtaining the battery resistance (battery resistance ratio of 1.00) of the battery of Comparative Example 6 in which the initial charging was performed at a small charging rate of 0.33 C was larger than that of the lithium phosphate particles 28, Specifically, a linear relationship with the average particle diameter D50 of the particles 28. The smaller the average particle diameter D50 of the particles 28 is, the shorter the maintenance period Tk can be. Particularly, when the average particle diameter D50 of the lithium phosphate particles 28 is 1.5 占 퐉 or less, the holding period Tk can be made 30 minutes or less, which can contribute to shortening the time required for the first charging. When the addition amount is the same, the smaller the average particle diameter D50 is, the more the number of particles and the surface area of the lithium phosphate particles 28 are increased. Therefore, the reaction with the generated hydrogen fluoride (HF) tends to occur, It is thought that it was possible to form.

As described above, in the method of manufacturing the battery 1, the inter-terminal voltage Vt is applied to the first voltage Vh in the lower decomposition region Ad during the first sustain period Tk, And thereafter, charging is performed until the voltage Ve reaches the second voltage Ve in the third step. Thus, in this second step, the oxidative decomposition of the nonaqueous electrolyte solution 40 occurs while the terminal voltage Vt is maintained at the first voltage Vh (Vt = Vh). However, the first voltage Vh is set to a voltage within a low voltage range called the lower decomposition area Ad, even in the range where the non-aqueous electrolyte solution 40 causes oxidative decomposition. As a result, the oxidative decomposition of the nonaqueous electrolyte solution 40 is only gradually generated, and the film 25 containing fluorine and phosphorus can be thinly formed on the particle surface 24n of the positive electrode active material particles 24, Can be suppressed to a low level.

(Second Embodiment)

Next, a second embodiment of the present invention will be described. In the first embodiment described above, CC charging at a charging rate of 3.0 C in the first step S1 of the first charging process of the battery 1 is repeated until the inter-terminal voltage Vt reaches the first voltage Vh (Vt = Vh = 4.1 V). Thereafter, in the second step S2, the CV charging is performed over the predetermined maintenance period Tk. Thereafter, in the third step S3, CC charging at the charging rate 3.0C is performed until the inter-terminal voltage Vt reaches the second voltage Ve (Vt = Ve = 4.9V).

On the other hand, in the second embodiment (and the same applies to the modified embodiment), in the first step SA1 of the first charging step of the battery 1, as in the first embodiment, (Vt = Vh = 4.1 V) until reaching Vh (see Fig. 12). However, the second embodiment is different from the first embodiment in that the charging rate is 5.0 C (charge current Ib = 5.0 C). Also, in the third step SA3, as in the first embodiment, CC charging is performed until the inter-terminal voltage Vt reaches the second voltage Ve (Vt = Ve = 4.75 V). However, the second embodiment is different from the first embodiment in that the charging rate is 5.0 C (charge current Ib = 5.0 C). Further, the second embodiment is different from the first embodiment in that CC charging is performed until the second voltage Ve = 4.75V, that is, the second embodiment, until the inter-terminal voltage Vt reaches the second voltage Ve = 4.75V. In the second embodiment, unlike the first embodiment in which the sustain period Tk is determined in the second step SA2, the CV charging in which the inter-terminal voltage Vt is maintained at the first voltage Vh (= 4.1 V) Until the charge current Ib flowing through the capacitor 1 reaches a predetermined cutoff current value Ibc. In the second embodiment, the cut-off current value Ibc is 0.05C. Therefore, the following description will be focused on the parts different from the first embodiment, and the same parts are omitted or simplified.

In the second embodiment, a battery 1 similar to that of the first embodiment is used. The manufacturing method of the battery 1 is also the same as that of the first embodiment except for the first charging step to be described below. In the first embodiment, particles having an average particle diameter D50 of 3.0 mu m (or 1.5 mu m or 0.8 mu m) are used as the lithium phosphate particles 28 added to the positive electrode active material layer 23. In the second embodiment, And differs from the first embodiment in that particles having an average particle diameter D50 of 1.0 mu m are used.

Next, the first charging step among the manufacturing methods of the battery 1 according to the second embodiment will be described with reference to Figs. 12 to 15. Fig. In the first charging step, first, the battery 1 is connected to a not-shown CC-CV charging / discharging device, and after the starting time t0, the battery 1 is charged at a charging rate 5.0 C (charge current Ib1 = 5.0 C) to raise the inter-terminal voltage Vt to 4.1 V (first voltage Vh) (first step SA1). The charging current Ib1 (= 5.0 C) at the end of the first step (1-2 switching time t12 when the terminal voltage Vt = Vh (= 4.1 V) is reached) is set as the closing current value. However, since the first step in the second embodiment is the constant current charging, the closing current value is equal to the charging current Ib1 in the first step as described above. As shown in Fig. 14, in the second embodiment, the period (t0 to t12) of the first step SA1 is about one minute, and the short period of time immediately after the CC charging start time t0 in the first step SA1 Terminal voltage Vt increases to about 3 V, and after that, the inter-terminal voltage Vt reaches the first voltage Vh (= 4.1 V) in about one minute.

Subsequently, in the second step (SA2), CV charging is carried out while maintaining the inter-terminal voltage Vt (= Vh = 4.1 V). More specifically, as shown in Fig. 13, after the 1-2 switching time t12, the charging current Ib2 is detected at step SA21, and at step SA22, whether or not the charging current Ib2 becomes 0.05C or less . If " NO ", i.e., the charge current Ib2 is greater than 0.05C (Ib2 > 0.05C), the process returns to step SA21. On the other hand, if YES in step SA22, that is, when the charging current Ib2 becomes 0.05C or less (Ib2? 0.05C) (this timing is referred to as 2-3 switching time t23) Go ahead.

In the second embodiment, the period (t12 to t23) of the second step SA2 is about 21 minutes. Immediately after the start of the CV charging in the second process SA2, the charging current Ib2 abruptly decreases from the abstraction current value Ib1, then gradually decreases, and then to zero. The shape of this curve resembles a graph of y = 1-e ^x as shown in Fig. This is considered to be due to the following reasons. Initially, in the second step SA2, the oxidative decomposition of the nonaqueous electrolyte solution 40 is sequentially performed by setting the terminal voltage Vt to the first voltage Vh (= 4.1 V) in the lower decomposition region Ad (4.0 to 4.4 V) , A large current flows as the decomposition current. However, with the lapse of time, the lithium phosphate particles 28 contained in the positive electrode active material layer 23 are consumed to form the coating film 25 and the oxidative decomposition of the non-aqueous electrolyte solution 40 is suppressed, Is gradually reduced.

12, the battery 1 is charged with CC at a charging rate of 5.0 C (charge current Ib3 = 5.0 C), and the inter-terminal voltage Vt is 4.75 V (the second voltage Ve), the first charging process is terminated. This timing is set as the end time t3e. In the second embodiment, the period (t23 to t3e) of the third step SA3 is about 10 minutes. Therefore, the first filling step in the second embodiment is a total of about 32 minutes from the first step to the third step (the first step is 1 minute, the second step is 21 minutes, the third step is 10 minutes) Lt; / RTI &gt;

In the second step SA2 of the second embodiment, the inter-terminal voltage Vt of the battery 1 is maintained at the first voltage Vh (= 4.1 V). However, a variation in the rate of film formation formed on the surface 24n of the positive electrode active material particles 24 occurs due to the variation of the individual cells 1 (see FIG. 4). Therefore, when the periods t12 to t23 for holding the first voltage Vh are made the same, that is, when the sustain period Tk is set as in the first embodiment, the positive electrode active material particles 24 are formed on the surface 24n The thickness of the coating film 25, and the like are different from each other, resulting in a variation in the size of the battery resistance. Thus, in order to obtain a film 25 having an appropriate thickness for any cell 1, it is necessary to set the holding period Tk to be slightly longer in accordance with the battery with a slow film formation speed. When the holding period Tk is set to be slightly longer in accordance with the battery with a slow film formation rate, the holding period Tk may be excessively long with respect to the individual batteries 1. On the other hand, in the manufacturing method of the second embodiment, since the first voltage Vh is maintained until the charge current Ib2 becomes equal to or less than the cutoff current value Ibc (Ib2 &lt; = Ibc) in the second step SA2, The same effect as that in the case where the sustain period Tk is determined for the battery with a slow film formation rate on the surface 24n of the positive electrode active material particles 24 in the shortest time A thick film 25 can be formed. Thus, in the case where the first charging process is performed for a large number of cells 1 in order, the process can be shortened as a whole, and the fluctuation of the thickness of the film 25 in each battery, .

Subsequently, for each cell 1, the cut-off current value Ibc in the first charging step was changed to five levels of 2.0 C, 0.5 C, 0.1 C, 0.05 C, and 0.02 C, 1), the battery resistance (IV resistance) was measured in the same manner as in the first embodiment. Further, assuming that the battery resistance in the battery in the case where the second step SA2 is not provided (that is, when the battery 1 is charged with CC charging at a charging rate of 5.0 C) is set as a reference (= 1.00) The battery resistance ratio Rr was obtained (see Fig. 15).

According to the graph of FIG. 15, the second step is provided in comparison with the reference battery (Rr = 1.00) in which the first charging step was performed with CC charging at a charging rate of 5.0 C, and as the cut- Rr becomes smaller. For example, assuming that Ibc is 2.0C, the battery resistance ratio Rr is 93%, and the battery resistance can be lowered by about 7%. When Ibc is 1.0C, the battery resistance ratio Rr is 90%, which means that the battery resistance can be lowered by about 10%. Further, when Ibc is 0.5C, the battery resistance ratio Rr is 88%, which means that the battery resistance can be lowered by about 12%. When Ibc is 0.05C, the battery resistance ratio Rr is 84.5%, which means that the battery resistance can be lowered by about 15%.

However, even if the cut-off current value Ibc is smaller than 0.05C (for example, Ibc = 0.02C), the battery resistance ratio Rr does not decrease as compared with the case where Ibc is 0.05C. That is, even if the cut-off current value Ibc is made smaller than 0.05C, it can be understood that the battery resistance can not be further reduced. This is considered to be because almost all of the lithium phosphate particles 28 contained in the positive electrode active material layer 23 are consumed in the step of forming the film 25 at the stage where the charging current Ib is 0.05C.

As described above, in the manufacturing method of the second embodiment, the cut-off current value Ibc is sufficiently small (1/100 of the initial current value Ib1) The second step SA2 is carried out until the temperature becomes 0.05C. When the second step is performed until the cutoff current value reaches 0.05C, the battery resistance becomes almost equal to the case where the cutoff current value is made smaller (for example, when the cutoff current value is 0.02C). Therefore, when the cut-off current value Ibc is 0.05C, almost all of the film 25 including fluorine and phosphorus formed on the particle surface 24n of the positive electrode active material particles 24 in the shortest time is subjected to the second process SA2. &Lt; / RTI &gt; In addition, in the second embodiment, a good film 25 can be formed, and the battery resistance can be lowered (specifically, about 15% smaller) than in the case where the second step SA2 is not provided.

(Modified form)

In the second embodiment described above, the cutoff current value Ibc in the second step SA2 (step SA22) is set to 0.05C. However, although the effect of lowering the cell resistance is suppressed, the value of the cut-off current value Ibc may be made larger than 0.05C in order to shorten the period of the second step SA2. That is, this modification is different from the second embodiment only in that the cut-off current value Ibc is set to 2.0C, and the other is the same.

The first charging process among the manufacturing methods of the battery 1 according to this modification will be described with reference to Figs. 12 and 14 to 16. Fig. First, in the first step (SA1), as in the first embodiment, the battery 1 is charged at a charge rate of 5.0 C (charge current Ib1 = 5.0 C) until the start time t0, To increase the terminal voltage Vt to 4.1 V (the first voltage Vh). The closing current value is equivalent to the charging current Ib1 = 5.0C.

In the subsequent second step (SA2a), as in the first and second embodiments, CV charging is carried out while maintaining the inter-terminal voltage Vt = Vh (= 4.1 V). More specifically, as shown in Fig. 16, after the 1-2 switching time t12, the charging current Ib2 is detected at step SA21. Subsequently, in step SA22a, it is determined whether or not the charge current Ib2 becomes Ibc = 2.0C or less by using a cutoff current value Ibc = 2.0C larger than the second embodiment (Ibc = 0.05C). If " NO ", i.e., if the charging current Ib2 is larger than 2.0C (Ib2 > 2.0C), the process returns to step SA21. On the other hand, if YES in step SA22a, that is, when the charging current Ib2 becomes 2.0C or less (Ib2? 2.0C) (this timing is referred to as 2-3 switching time t23a. 3 Proceed to SA3. The period (t12 to t23a) of the second step SA2a in this modification is about one minute. In the case of this modification, there is no period from t23a to t23 in Fig.

In the subsequent third step SA3, as shown in Fig. 12, the battery 1 is charged with a current of CC of 5.0 C at the charging rate, and the inter-terminal voltage Vt becomes Vt = Ve = When the voltage rises to 4.75 V (second voltage Ve), the first charging step is terminated. In this modification, the period (t23a to t3e) of the third step SA3 is also about 10 minutes.

As a result, the first filling step of the present modification mode is substantially shorter than the second embodiment, and the total time from the first step to the third step is about 12 minutes (the first step is 1 minute, the second step is 1 minute, 10 minutes). Further, as shown in Fig. 15, in the battery 1 of the present modification in which the cut-off current value Ibc is 2.0 C, the battery resistance can be lowered by about 7% as compared with the case where the second step is not provided.

Further, in this modification, the cutoff current value Ibc is set to 2.0 C in step SA22a, but the second step may be performed with Ibc set to 1.0 C as the cutoff current value, for example. In this case, the period (t12 to t23b) of the second process is about two minutes in length. The 2-3 switching time t23b is the timing at which the charging current Ib2 becomes 1.0 C or less (Ib2? 1.0 C) (refer to Fig. 14). In this case as well, the period from t23b to t23 in Fig. 14 does not exist. When the cut-off current value Ibc is set to 1.0 C, the first filling step (the first step to the third step) is performed for about 13 minutes (the first step is 1 minute, the second step is 2 minutes, Minutes). On the other hand, by setting the cut-off current value Ibc to 1.0C, the battery resistance can be lowered by about 10% as compared with the case where the second step is not provided.

The lithium phosphate particles 28 contained in the positive electrode active material layer 23 also had particles having an average particle diameter D50 of 1.5 m or less in the method of manufacturing the battery 1 described in the second embodiment and the modified embodiments. Therefore, when particles having an average particle diameter D50 of 1.5 m or less are used, the total amount of particles and surface area increases when the addition amount is the same as in the case of using particles having an average particle diameter D50 larger than 1.5 m, The film 25 can be formed in a short time, which contributes to the time required for the second process steps SA2 and SA2a, and hence the time required for the first filling step.

The battery 1 according to the manufacturing method described in the first, second, and modified embodiments described above has a positive electrode potential Ep of at least 4.5 V (vs. Li / Li ⁺ ) Or more. Therefore, when the SOC of the battery 1 is high, the nonaqueous electrolyte solution 40 is easily oxidized and decomposed at the particle surface 24n of the positive electrode active material particles 24 to generate hydrogen ions. Moreover, since the nonaqueous electrolyte solution 40 contains the fluorine-containing compound 41, it is easy to generate hydrofluoric acid from hydrogen ions and fluorine. In the manufacturing method of the battery 1 according to the first and second embodiments and the modified embodiment, the particle surface 24n of the positive electrode active material particles 24 in the second step S2, SA2, Since the film 25 containing fluorine and phosphorus is formed in the non-aqueous electrolyte solution 40, it is possible to appropriately suppress the oxidative decomposition of the nonaqueous electrolyte solution 40 after the first charging step.

In the manufacturing method according to the first, second and third embodiments, the first steps S1, SA1 and the third steps S3, SA3 are CC-charged with current values Ib1, Ib3 of 3.0C or 5.0C. As a result, the time required for the first step and the third step can be shortened, and the first filling step can be performed in a shorter time. In any of the first and second embodiments and modifications, the charging current Ib1 in the first step and the charging current Ib3 in the third step are made equal. However, the charge currents Ib1 and Ib3 may be set to be different from each other, for example, Ib1 is set to 3.0C and Ib3 is set to 5.0C. In particular, Ib1 is preferably Ib3 or less. As can be easily understood from FIG. 14, contribution to the shortening of the charging time t by increasing the charging current is larger than Ib1 because Ib3 is larger. The smaller Ib1 also has an advantage that the time of the first step is increased but the amount of the film 25 formed in the first step can be suppressed before proceeding to the second step.

Although the present invention has been described based on the first and second embodiments and modifications, the present invention is not limited to the above-described embodiments and the like, and may be appropriately changed and applied without departing from the gist of the invention Of course you can. For example, in the battery 1 or the like described above, the lithium phosphate particles 28 are used as the metal phosphate particles, but the present invention is not limited thereto. For example, other metal phosphate particles such as sodium phosphate, potassium phosphate, magnesium phosphate, and calcium phosphate may be added to the positive electrode active material layer. In place of or in addition to the metal phosphate particles such as lithium phosphate particles 28, metal pyrophosphate particles such as lithium pyrophosphate particles, sodium pyrophosphate particles, magnesium pyrophosphate particles and calcium pyrophosphate particles may be used as the positive electrode active material Layer.

Claims (11)

A nonaqueous electrolytic solution (40) comprising a positive electrode (21) having a positive electrode active material layer (23) containing positive electrode active material particles (24), a negative electrode (31) and a fluorine - containing compound The positive electrode active material particle (24) has a coating film (25) containing fluorine and phosphorus on the surface of the particle, characterized in that in the production method of the lithium ion secondary battery (1)
Wherein the positive electrode active material layer (23) comprises at least one of particles (28) of a metal phosphate and a metal pyrophosphate, and the step of first charging the lithium ion secondary battery comprises charging the lithium ion secondary battery A first step (S1) of raising the voltage of the lithium ion secondary battery to a first voltage in a lower decomposition region of the non-aqueous electrolyte,
A second step (S2) of maintaining the voltage of the lithium ion secondary battery at the first voltage,
And a third step (S3) of performing charging to a second voltage higher than the first voltage after the second step. The method of manufacturing a lithium ion secondary battery according to claim 1, wherein the third step (S3) is performed at a charging current higher than 1C. The method according to claim 1 or 2, wherein the second step (S2) holds the voltage of the lithium ion secondary battery at the first voltage over a predetermined maintenance period. The method according to claim 3, characterized in that the sustain period is a period during which the second step (S2) is performed in the predetermined sustain period, and thereafter the cell resistance Rn of the battery manufactured by performing the third step (S3) Wherein the first voltage is maintained for an extended sustain period in which the predetermined sustain period is extended by 1.5 times and then the battery resistance of the sustain period extended battery manufactured by performing the third step (S3) Re is in a range of Rn = 0.98Re to 1.02Re when Re is compared. The method according to claim 3, characterized in that the sustain period is a period during which the second step (S2) is performed in the predetermined sustain period, and thereafter the cell resistance Rn of the battery manufactured by performing the third step (S3) Wherein the first voltage is maintained for an extended sustain period in which the predetermined sustain period is extended by 1.5 times and then the battery resistance of the sustain period extended battery manufactured by performing the third step (S3) Wherein Re is a period in which Rn = 0.99Re to 1.01Re when Re is compared. 3. The method according to claim 1 or 2, wherein the second step (S2) is repeated until the magnitude of the charge current of the lithium ion secondary battery (1) becomes equal to or lower than a predetermined cut- Wherein the lithium ion secondary battery is a lithium ion secondary battery. The method of manufacturing a lithium ion secondary battery according to claim 6, wherein the cut-off current value is 2/5 of the off-set current value in the end of the first step (S1). 7. The method of manufacturing a lithium ion secondary battery according to claim 6, wherein the off-set current value at the end of the first step (S1) is 1C or more and the cut-off current value is 0.05C. 3. The lithium ion secondary battery according to claim 1 or 2, wherein at least one of the metal phosphate and the metal pyrophosphate included in the positive electrode active material layer (23) is a particle having an average particle diameter of 1.5 m or less Gt; The method for manufacturing a lithium ion secondary battery according to claim 1 or 2, wherein the first step (S1) and the third step (S3) are constant current charging at a predetermined current value of 3C or more. 3. The method according to claim 1 or 2, wherein the first step (S1) comprises a constant current charging at a predetermined first current value,
The third step (S3) includes a constant current charging with a predetermined second current value,
Wherein the first current value is equal to or less than the second current value.

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