JP2018098012A - Method for manufacturing nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery including a positive electrode mixture layer with a trilithium phosphate powder added thereto, which allows such a nonaqueous electrolyte secondary battery to appropriately exhibit the effect of addition of the trilithium phosphate powder and which can suitably decrease various problems that will be caused in the state of being overcharged.SOLUTION: A method for manufacturing a nonaqueous electrolyte secondary battery disclosed therein comprises: a positive electrode; a negative electrode; a nonaqueous electrolyte solution; and a battery case. The manufacturing method comprises the steps of: putting a positive electrode mixture containing a positive electrode active material, trilithium phosphate powder and a solvent on a positive electrode current collector, thereby forming a positive electrode mixture layer; and encasing the positive and negative electrodes in the battery case to construct a cell assembly and then, heating the constructed cell assembly to a temperature region of 110°C or above and 140°C or below to perform a dry process in a stage before supplying the nonaqueous electrolyte solution into the battery case.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery.

  Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are lighter and have higher energy density than existing batteries, and have recently been used as so-called portable power sources for vehicles and personal computers and power sources for driving vehicles. ing. Such a lithium ion secondary battery is manufactured by housing an electrode body, which is a power generation element, in a battery case, and supplying (injecting) a nonaqueous electrolytic solution into the case and then sealing the case. Patent Document 1 discloses a technique for performing a drying process at a predetermined temperature (maximum temperature: 100 ° C.) in such a manufacturing process.

By the way, in recent lithium ion secondary batteries, a technique of adding an inorganic phosphate compound such as trilithium phosphate (Li ₃ PO ₄ ) to the positive electrode mixture layer of the positive electrode has been proposed. Such an inorganic phosphate compound adsorbs an acid (for example, hydrogen fluoride (HF)) generated by the decomposition of the non-aqueous electrolyte when the battery is overcharged (high voltage state), and generates heat or a metal element. Various problems due to overcharging such as elution of selenium can be suppressed (for example, Patent Documents 2 and 3).

JP 2013-1887086 A JP-A-2015-103332 Japanese Patent No. 3358478

  In the techniques described in Patent Documents 2 and 3 described above, the content of the inorganic phosphate compound with respect to the positive electrode mixture layer is specified in order to appropriately exert the effect of the inorganic phosphate compound such as trilithium phosphate. . However, when trilithium phosphate is actually included in the positive electrode mixture layer, the function of trilithium phosphate is limited despite the fact that the content of trilithium phosphate is regulated as in the prior art described above. In some cases, variation may occur and a suitable effect may not be obtained.

  The present invention has been made in view of the above points, and its main object is to add the trilithium phosphate in a non-aqueous electrolyte secondary battery in which trilithium phosphate is added to the positive electrode mixture layer. It is to provide a non-aqueous electrolyte secondary battery in which various effects caused by an overcharged state can be suitably suppressed by appropriately exhibiting the effect of the above.

  In order to achieve the above object, the present invention provides a method for manufacturing a non-aqueous electrolyte secondary battery having the following configuration (hereinafter also simply referred to as “manufacturing method”).

The non-aqueous electrolyte secondary battery manufacturing method disclosed herein includes a positive electrode in which a positive electrode mixture layer including a positive electrode active material is formed on a positive electrode current collector, and a negative electrode active material on the negative electrode current collector. This is a method for producing a non-aqueous electrolyte secondary battery comprising a negative electrode on which a negative electrode mixture layer is formed, a non-aqueous electrolyte, and a battery case containing the positive and negative electrodes and the non-aqueous electrolyte.
Such a production method includes forming a positive electrode mixture layer by applying a positive electrode mixture containing a trilithium phosphate powder and a solvent together with a positive electrode active material onto a positive electrode current collector, and forming the positive electrode and the negative electrode into a battery case. After constructing the cell assembly by housing the cell assembly, the constructed cell assembly is heated to a temperature range of 110 ° C. or more and 140 ° C. or less before supplying the non-aqueous electrolyte to the battery case. A drying process is performed.

The present inventor has conducted experiments and studies on the cause of variation in the function of trilithium phosphate despite the fact that the content of trilithium phosphate is the same, and as a result, phosphorus added to the positive electrode mixture It has been found that the trilithium acid powder may contain moisture, and that the moisture causes the function of the trilithium phosphate to vary.
Specifically, as a result of analyzing the trilithium phosphate powder added to the positive electrode mixture, the trilithium phosphate powder may contain moisture, and the moisture may be trilithium phosphate particles. It has been found that the function of trilithium phosphate that adsorbs an acid such as hydrogen fluoride (HF) decreases when adhering to the surface.
As a result of further experiments and examinations, the conventional drying treatment (maximum temperature: 100 ° C.) may not be able to properly remove the water contained in the trilithium phosphate powder. It was found that a drying process was necessary.

  The manufacturing method of the non-aqueous electrolyte secondary battery disclosed here is based on the above-described knowledge, and the cell assembly is 110 at a stage before supplying the non-aqueous electrolyte to the battery case. The drying process is performed by heating to a temperature range of not lower than 140 ° C. and lower than 140 ° C. As a result, even if the trilithium phosphate powder contains moisture, the moisture can be appropriately removed. It is possible to reliably prevent the lithium function from deteriorating.

It is a perspective view which shows typically the external shape of a lithium ion secondary battery. It is a perspective view which shows typically the electrode body of a lithium ion secondary battery. 6 is a graph showing the results of an evaluation test in Experiment A. A D ₅₀ particle size of tricalcium phosphate lithium powder in Experiment B, a viscosity of positive electrode immediately after the preparation is a graph showing the relationship between the capacity retention rate at the continuous input cycle. A D ₅₀ particle size of tricalcium phosphate lithium powder in Experiment B, a viscosity of positive electrode after 3 days from the preparation is a graph showing the relationship between the capacity retention rate in high-rate cycle. A D ₅₀ particle size of tricalcium phosphate lithium powder in Experiment B, a viscosity of positive electrode after one week from the preparation is a graph showing a relation between the DC resistance at 25 ° C.. A D ₅₀ particle size of tricalcium phosphate lithium powder in Experiment B, a viscosity of positive electrode after 2 weeks from the preparation is a graph showing the relationship between the reaction resistance at -30 ° C..

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following drawings, members / parts having the same action are denoted by the same reference numerals. In addition, the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, the composition of the negative electrode, general techniques related to the construction of the nonaqueous electrolyte secondary battery, etc.) Therefore, it can be grasped as a design matter of a person skilled in the art based on the prior art in the field.

1. First, a lithium ion secondary battery will be described as an example of a non-aqueous electrolyte secondary battery obtained by the manufacturing method according to the present embodiment.
FIG. 1 is a perspective view schematically showing an outer shape of a lithium ion secondary battery, and FIG. 2 is a perspective view schematically showing an electrode body of the lithium ion secondary battery. The lithium ion secondary battery 100 accommodates an electrode body 80 (see FIG. 2) including the positive electrode 10 and the negative electrode 20 and a non-aqueous electrolyte (not shown) in the rectangular battery case 50 shown in FIG. It is produced by.

(1) Battery Case The battery case 50 includes a flat case body 52 having an open upper end, and a lid 54 that closes an opening at the upper end. The lid 54 is provided with a positive terminal 70 and a negative terminal 72. Although not shown, the positive electrode terminal 70 is electrically connected to the positive electrode 10 of the electrode body 80 in the battery case 50, and the negative electrode terminal 72 is electrically connected to the negative electrode 20. In addition, the lid 54 of the lithium ion secondary battery 100 according to the present embodiment is provided with a liquid injection port 56 for supplying a nonaqueous electrolytic solution into the battery case 50. A sealing cap is fitted into the liquid injection port 56, and the sealing cap and the lid body 54 are joined.

(2) Electrode body Next, the electrode body 80 accommodated in the battery case 50 described above will be described. As shown in FIG. 2, the electrode body 80 in this embodiment is a wound electrode body produced by laminating and winding a long sheet-like positive electrode 10 and a negative electrode 20 together with a long sheet-like separator 40. It is. In addition, the electrode body used for the non-aqueous electrolyte secondary battery disclosed here is not limited to the wound electrode body as shown in FIG. 2, for example, a plurality of positive electrodes and negative electrodes are interposed via a separator. It may be a laminated electrode body laminated alternately.

(A) Positive Electrode In the positive electrode 10 in FIG. 2, a positive electrode mixture layer 14 mainly composed of a positive electrode active material is formed on both surfaces of a long sheet-like positive electrode current collector 12. A positive electrode mixture layer non-formation portion 16 that is not coated with the positive electrode mixture layer 14 is formed on one side edge in the width direction of the positive electrode 10, and the positive electrode mixture layer non-formation portion 16 is formed. Is electrically connected to the positive electrode terminal 70 (see FIG. 1) described above.

  The positive electrode active material that is the main component of the positive electrode mixture layer 14 is a compound capable of reversibly occluding and releasing lithium ions, and is composed of an oxide containing at least lithium (lithium composite oxide). In the present embodiment, the type of the positive electrode active material is not particularly limited, and the same positive electrode active material as that of a general lithium ion secondary battery can be used. Specific examples of such a positive electrode active material include lithium nickel composite oxide, lithium nickel cobalt composite oxide, lithium nickel cobalt manganese composite oxide, and the like.

Further, the positive electrode mixture layer 14 in the present embodiment contains trilithium phosphate (Li ₃ PO ₄ ) powder. Such trilithium phosphate is overcharged by adsorbing an acid (for example, hydrogen fluoride (HF)) generated by the decomposition of the non-aqueous electrolyte when the lithium ion secondary battery 100 is overcharged. Heat generation at the time and elution of metal elements can be suppressed.

Incidentally, D ₅₀ particle size of the tricalcium phosphate lithium particles (in volume-based particle size distribution based on the laser diffraction light scattering method, the particle diameter corresponding the smaller in particle diameter cumulative 50% (average particle diameter, median diameter) ) Is preferably 0.3 μm to 27.4 μm, more preferably 1.3 μm to 24.8 μm, further preferably 1.8 μm to 8.3 μm, and particularly preferably 2.1 μm to 5.6 μm.
When the particle size of the trilithium phosphate particles is reduced, it is possible to obtain the effect of improving the battery performance such as improvement of the capacity retention rate and reduction of the battery resistance. On the other hand, when the particle size is too small, the positive electrode mixture There is a possibility that it becomes difficult to produce a positive electrode due to an increase in the viscosity. The range of the D ₅₀ particle diameter of the above-described trilithium phosphate particles is defined in consideration of this relationship, and by using trilithium phosphate powder having a particle diameter within the above range, a high battery can be obtained. A lithium ion secondary battery having performance can be manufactured with high productivity.

  The positive electrode mixture layer 14 may contain various additives such as a conductive agent and a binder in addition to the above-described positive electrode active material and trilithium phosphate powder. As the conductive agent, for example, a carbon material such as carbon black can be used, and as the binder, for example, polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyethylene oxide (PEO), or the like can be used. .

(B) Negative Electrode Similarly to the positive electrode 10, the negative electrode 20 has a negative electrode mixture layer 24 mainly composed of a negative electrode active material on both surfaces of a long sheet-like negative electrode current collector 22. A negative electrode mixture layer non-formed portion 26 is formed at one side edge in the width direction of the negative electrode 20, and the negative electrode mixture layer non-formed portion 26 is electrically connected to the negative electrode terminal 72 (see FIG. 1). It is connected.

  In the present embodiment, the composition of the negative electrode mixture layer 24 is not particularly limited, and can be the same composition as the negative electrode mixture layer of a general lithium ion secondary battery. For example, as the negative electrode active material, a carbon material such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), carbon nanotube, or a combination of these is used. Can do. From the viewpoint of energy density, it is preferable to use graphite-based materials (natural graphite (graphite), artificial graphite, etc.) among these carbon materials. Further, the negative electrode mixture layer 24 may contain other additives (for example, a binder, a thickener, and the like). Examples of the binder include styrene butadiene rubber (SBR), and examples of the thickener include carboxymethyl cellulose (CMC).

(C) Separator A strip-shaped sheet material having a predetermined width and having a plurality of minute holes is used for the separator 40. As the separator 40, the same separator as that used in a general lithium ion secondary battery can be used.
However, in the manufacturing method according to the present embodiment, the heating temperature in the drying process is set to 110 ° C. to 140 ° C., which is higher than the conventional temperature, as will be described later, and therefore the separator 40 is damaged by the heat in the drying process. From the viewpoint of reliably preventing this, it is preferable to use a heat-resistant separator made of wholly aromatic polyamide (aramid) or the like.

(3) Nonaqueous Electrolyte As described above, the nonaqueous electrolyte is housed in the battery case 50 of the lithium ion secondary battery 100 shown in FIG. As such a non-aqueous electrolyte, a non-aqueous electrolyte used in a general lithium ion secondary battery can be used. As such a non-aqueous electrolyte, for example, a mixed salt of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (for example, volume ratio 3: 4: 3) is used with a supporting salt at a predetermined concentration. (For example, about 1 mol / L). As the supporting salt, it is preferable to use a lithium compound containing fluorine, for example, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ or the like.

2. Next, a method for manufacturing a lithium ion secondary battery for manufacturing the above-described lithium ion secondary battery will be described.

(1) Formation of Positive Electrode Mixture Layer In this embodiment, first, a positive electrode composite containing a trilithium phosphate powder and a solvent together with a positive electrode active material is prepared, and the positive electrode mixture is applied onto the positive electrode current collector 12. By doing so, the positive electrode mixture layer 14 is formed.
Specifically, first, a paste-like positive electrode mixture is prepared by dispersing a positive electrode active material, trilithium phosphate powder, and other additives in a solvent. As the solvent at this time, for example, an organic solvent such as NMP (N methylpyrrolidone) is preferably used.
Next, in this step, the prepared positive electrode mixture is applied to the surface of the positive electrode current collector 12, and after the positive electrode mixture is dried, press working is performed, so that the positive electrode mixture is formed on the positive electrode current collector 12. The sheet-like positive electrode 10 provided with the layer 14 is produced.

(2) Construction of cell assembly As the next step, the above-described electrode body 80 is manufactured from the above-described positive electrode 10 and the separately-prepared negative electrode 20, and the electrode body 80 is accommodated in the battery case 50 to form a cell. Build an assembly. In addition, since the process of manufacturing the negative electrode 20 and the process of manufacturing the electrode body 80 can be implemented in the same procedure as the manufacturing method of a general lithium ion secondary battery, since it does not characterize this invention, it demonstrates. Omitted.

When the electrode body 80 is accommodated in the battery case 50 in this step, first, the positive electrode terminal 70 of the lid body 54 is connected to the positive electrode mixture layer non-forming portion 16 of the positive electrode 10 and the negative electrode terminal 72 is connected to the negative electrode. After connecting to the negative electrode composite material layer non-forming portion 26, the electrode body 80 is accommodated in the case main body 52.
When constructing the cell assembly, the lid 54 is fitted into the opening at the top of the case main body 52, and the contact portion between the case main body 52 and the lid 54 is irradiated with laser. As a result, the case body 52 and the lid body 54 are welded to construct a cell assembly.

(3) Drying process In the manufacturing method according to the present embodiment, the cell assembly is heated to dry the positive electrode mixture layer 14 before the non-aqueous electrolyte is supplied to the battery case. I do. In the manufacturing method according to the present embodiment, the heating temperature in the drying process is a temperature at which moisture contained in the trilithium phosphate powder can be appropriately removed from the positive electrode mixture layer 14, that is, 110 ° C. or higher. The temperature is raised to 140 ° C or lower.
Specifically, as described above, the trilithium phosphate powder contained in the positive electrode mixture may contain moisture, and when such moisture is adsorbed on the surface of the trilithium phosphate particles, There is a possibility that the function of trilithium will be reduced and the temperature rise at the time of overcharging in the manufactured battery cannot be suppressed appropriately.
On the other hand, in the manufacturing method according to this embodiment, before supplying the non-aqueous electrolyte into the battery case of the cell assembly, by heating the cell assembly to a high temperature range of 110 ° C. or higher, Water contained in the powder of trilithium phosphate powder is evaporated. As a result, it is possible to prevent moisture from adsorbing to the surface of the trilithium phosphate particles, so that the function of the trilithium phosphate can be appropriately exerted, and the manufactured battery is overcharged. In this case, it is possible to appropriately suppress a sudden temperature rise.
If the heating temperature in the drying step exceeds 140 ° C., the negative electrode current collector (such as copper foil) may be oxidized and the battery resistance may be greatly increased. In this embodiment, the upper limit of the heating temperature in the drying step Is 140 ° C.

  Moreover, in the above-described drying process, from the viewpoint of more reliably evaporating the water contained in the trilithium phosphate, the pressure during the drying process (drying pressure) and the duration of the drying process (drying time) are set. It is preferable to adjust appropriately. For example, the drying pressure is preferably set in the range of 10 kPa to 50 kPa (for example, 30 kPa), and the drying time is preferably set in the range of 20 min to 60 min (40 min).

(4) Sealing of cell Next, in the present embodiment, after the drying process is performed to evaporate the moisture of the positive electrode mixture layer 14, a nonaqueous electrolyte is supplied into the battery case 50, and the battery case 50 is sealed to manufacture a lithium ion secondary battery 100. Specifically, after the drying process is completed, a nonaqueous electrolytic solution is supplied (injected) into the battery case 50 from the injection port 56 of the lid 54.
Then, a sealing cap is fitted into the liquid injection port 56, and a contact portion between the lid 54 and the sealing cap is joined by laser welding or the like. Thereby, the battery case 50 is sealed and the lithium ion secondary battery 100 is produced.

  As described above, the lithium ion secondary battery 100 obtained by such a manufacturing method has been subjected to a drying process of heating the cell assembly to a temperature range of 110 ° C. or higher and 140 ° C. or lower. The water is appropriately removed from the trilithium phosphate powder contained in 14. For this reason, it is possible to prevent moisture from adhering to the surface of the trilithium phosphate particles and lowering the function of the trilithium phosphate, and to prevent various problems caused by overcharge such as heat generation and elution of metal elements. Can be suppressed.

[Test example]
Hereinafter, although the test example regarding this invention is demonstrated, description of a test example is not intending limiting this invention.

1. Experiment A
(1) Production of Test Example 1 to Test Example 9 In Experiment A, a 4V class lithium ion secondary battery was produced by varying the heating temperature in the drying process in each of Test Example 1 to Test Example 9, and the production was performed. The performance of the battery was evaluated.

Specifically, for each of Test Examples 1 to 9, LNCM composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) that is a positive electrode active material and trilithium phosphate (Li ₃₎ PO ₄ ), a binder (PVDF), and a solvent (NMP: N-methylpyrrolidone) were mixed to prepare a paste-like positive electrode mixture. And after apply | coating the prepared positive mix to both surfaces of a positive electrode electrical power collector (aluminum foil) and making it dry, the sheet-like positive electrode was produced by pressing with a predetermined pressure.

Further, a negative electrode active material (graphite), a binder (SBR: styrene-butadiene copolymer), a thickener (CMC) and a dispersion medium (water) are mixed to prepare a paste-like negative electrode mixture, The negative electrode mixture was applied to both sides of a sheet-like negative electrode current collector (copper foil), dried, and then pressed to prepare a sheet-like negative electrode.
Next, a heat resistant separator (aramid separator) is used as a separator, positive and negative electrodes are laminated through the heat resistant separator, and then the laminated body is wound to produce a wound electrode body. The rotating electrode body was accommodated in a battery case to produce a cell assembly.

And the produced cell assembly was arrange | positioned inside a drying furnace (furnace pressure: 30 kPa), and the drying process of the cell assembly of each test example was performed by heating for 40 minutes. In Experiment A, as shown in Table 1, the heating temperature at this time was varied for each of Test Example 1 to Test Example 9.
Next, after supplying the non-aqueous electrolyte from the liquid injection port to the inside of the cell assembly, the liquid injection port is sealed with a sealing cap, and the battery case is sealed, so that the battery case is sealed. An ion secondary battery was produced. In addition, the non-aqueous electrolyte solution contains a supporting salt (LiPF ₆ ) at a concentration of about 1 mol / L in a mixed solvent containing EC, DMC, and EMC in a volume ratio of 3: 4: 3. It was used.

(2) Evaluation test In Experiment A, the battery temperature and the IV resistance at the time of overcharging were measured with respect to Test Example 1 to Test Example 9 described above. Specific measurement conditions will be described below.

(A) Measurement of battery temperature during overcharge Each battery is overcharged by charging up to 5.1 V at a constant current of 20 C with respect to the 4 V class lithium ion secondary battery produced in each test example. And the battery temperature at the time of overcharge was measured by measuring the temperature of the center part outside the battery case of each battery. The measurement results are shown in Table 1 and FIG. In addition, about the measurement result, in Table 1, it shows by the relative evaluation when Test Example 1 is set to 100. In addition, among the two types of plots shown in FIG. 3, the rhombus plot indicates the battery temperature during overcharge.

(B) Measurement of IV resistance For the batteries of each of the test examples after fabrication, the initial capacity was measured, and then a constant current (CC) current charge was performed at a charge rate of 1 C under a temperature condition of 25 ° C. to charge 20% SOC. The battery is adjusted to a state, discharged at 10C for 10 seconds, and the initial battery resistance (IV resistance) (mΩ) is obtained from the slope of the first-order approximation line of the current (I) -voltage (V) plot value. It was. And IV resistance (IV resistance ratio) of each test example when the IV resistance of test example 1 was set to 100 was calculated. The results are shown in Table 1 and FIG. Of the two types of plots shown in FIG. 3, a square plot indicates the measurement result of the IV resistance ratio.

(3) Test results As shown in Table 1 and FIG. 3, as the heating temperature (drying temperature) in the drying process is increased, the battery temperature at the time of overcharging decreases, but when the drying temperature is excessively increased, the IV resistance We were able to confirm the tendency of the ratio to increase.
And when each test example is compared in detail, while the battery temperature is greatly reduced in Test Examples 3 to 9 where the drying temperature is 110 ° C. or higher, the test example in which the drying temperature exceeds 140 ° C. In Test Example 9 to Test Example 9, the IV resistance ratio was significantly increased even though the battery temperature at the time of overcharge was similar to Test Example 3 to Test Example 6.
Therefore, as in Test Example 3 to Test Example 6, by defining the drying temperature in the drying process within the range of 110 ° C. to 140 ° C., the function of trilithium phosphate can be appropriately exerted and overcharged It was found that the battery temperature of the battery can be lowered appropriately, and that the battery performance can be prevented from being lowered due to a large increase in resistance.

2. Experiment B
Next, the present inventor conducted Experiment B in order to investigate an appropriate particle size of the trilithium phosphate powder.

(1) Preparation of Test Example 10 to Test Example 26 In Experiment B, as shown in Table 2 and Table 3 below, the D ₅₀ particle size of the trilithium phosphate powder in each of Test Example 10 to Test Example 26 was set as follows. A 4V-class lithium ion secondary battery was manufactured by making different.
In addition, as for the production conditions of the batteries in Test Examples 10 to 26, the D ₅₀ particle diameter of trilithium phosphate was changed in each test example as described above, and the temperature of the drying treatment was set to 115 ° C. The same conditions as in Experiment A described above were used except for the three points that a separator having a three-layer structure of PP / PE / PP was used as the separator.

(2) Evaluation test In the evaluation test of Experiment B, the viscosity, capacity retention ratio, and battery resistance of the positive electrode mixture were measured.

(A) Measurement of Viscosity For each of Test Example 10 to Test Example 26, a portion of the paste-like positive electrode mixture used to produce the positive electrode mixture layer was collected and an E-type viscometer (measuring environment: room temperature) , Rotation speed: 20 rpm), and the viscosity was measured. In this test, the viscosity was measured four times immediately after preparation, 3 days later, 1 week later, and 2 weeks later. Each measurement result is shown in Table 2, Table 3, and FIGS. The measurement results in Tables 2 and 3 are shown as relative evaluations when the measurement result of Test Example 26 is 100. Moreover, in FIGS. 4-7, the rhombus plot has shown the measurement result of the viscosity.

(B) Measurement of capacity maintenance rate In this test, for each of the batteries of Test Example 10 to Test Example 26 produced, two types of capacity maintenance rates, a capacity maintenance rate in a continuous input cycle and a capacity maintenance rate in a high rate cycle, were used. Was measured.

(B-1) Capacity maintenance rate in continuous input cycle First, under the temperature condition of 25 ° C., the battery of each example was charged with a constant current (CC) to 4.1 V at a rate of 1 C, and then rested for 5 minutes. The battery was rested for 5 minutes after being discharged at a rate of 3.0V to a constant current (CC). Subsequently, after performing CCCV charge (4.1V, rate 1C, 0.1C cut) and resting for 10 minutes, initial charge / discharge which performs CCCV discharge (3.0V, rate 1C, 0.1C cut) was performed. The discharge capacity at this time was measured and used as the initial capacity.

  Then, the SOC of each battery is adjusted to 80%, and (1) charging at 150A for 0.1 second, (2) resting for 5 seconds, (3) discharging at 150A for 0.1 second in an environment of −30 ° C. ( 4) 4000 continuous input cycles with a 5-second pause as one cycle were performed, and the capacity retention rate (%) after 4000 cycles was measured. The results are shown in Table 2, Table 3 and FIG. The measurement results in Tables 2 and 3 are shown as relative evaluations when the initial capacity is 100. In FIG. 4, a square plot indicates the measurement result of the capacity retention rate in the continuous input cycle.

(B-2) Capacity Maintenance Rate in High Rate Cycle In measurement of capacity maintenance rate in high rate cycle, first, initial charge is measured by performing the same procedure as in the continuous input cycle described above, and then high rate charge / discharge is performed. After 1000 cycles, the capacity retention rate (%) after 1000 cycles was measured.
Specifically, the SOC of each battery was adjusted to 50%, (1) charged at 100 A for 10 seconds, (2) paused for 5 seconds, (3) discharged at 100 A for 10 seconds in an environment of −15 ° C., (4 ) 1000 cycles of high-rate charge / discharge with a 5-second pause as one cycle, and the capacity retention rate (%) after 1000 cycles was measured. The results are shown in Table 2, Table 3 and FIG. The measurement results in Tables 2 and 3 are shown as relative evaluations when the initial capacity is 100. Further, in FIG. 5, a square plot shows the measurement result of the capacity retention rate in the high rate cycle.

(C) Measurement of battery resistance In this test, two types of battery resistance were measured: DC resistance at 25 ° C. and reaction resistance at −30 ° C.

(C-1) Measurement of DC resistance The lithium ion secondary battery produced in each test example was placed in an environment of 25 ° C., and AC impedance was measured under the conditions of amplitude: 5 mV and measurement frequency range: 10,000 to 0.1 Hz. went. And DC resistance (m (ohm)) in 25 degreeC was calculated | required based on the intersection of the circular arc shape of the obtained Cole-Cole plot, and an x-axis. The measurement results are shown in Table 2, Table 3, and FIG. The measurement results in Tables 2 and 3 are shown by relative evaluation (DC resistance ratio) when Test Example 10 is 100. In FIG. 6, a square plot shows the measurement result of the DC resistance.

(C-2) Measurement of reaction resistance The lithium ion secondary battery produced in each test example was placed in an environment of −30 ° C., and the AC impedance was measured under the conditions of amplitude: 5 mV, measurement frequency range: 10,000 to 0.001 Hz. Measurement was performed, and the reaction resistance (mΩ) was determined based on the arc-shaped diameter of the obtained Cole-Cole plot. The measurement results are shown in Table 2, Table 3, and FIG. In addition, the measurement results in Tables 2 and 3 are shown by relative evaluation (reaction resistance ratio) when Test Example 10 is 100. In FIG. 7, a square plot indicates the measurement result of reaction resistance.

(3) From the test results above test results, according to D ₅₀ particle size of the tricalcium phosphate lithium powder is small, since there is a tendency that viscosity of the paste-like positive electrode is likely to increase, in terms of improving productivity It was found that it is preferable to use trilithium phosphate powder having a large D ₅₀ particle size.
On the other hand, as the D ₅₀ particle size of the trilithium phosphate powder increases, the capacity retention rate tends to decrease and the battery resistance increases, etc., so from the viewpoint of battery performance, the D ₅₀ particle size is small. It has been found that it is preferable to use trilithium phosphate powder.

As a result of examining each of the test examples in detail with reference to FIG. 4, the viscosity of the positive electrode just after the preparation D ₅₀ particle size of the tricalcium phosphate lithium powder is less than 0.3μm as in Test Example 10 Significantly increased, and when it exceeded 27.4 μm as in Test Example 24 to Test Example 26, the result was that the capacity retention rate in the continuous input cycle was significantly reduced. From this, it was found that the D ₅₀ particle diameter of the trilithium phosphate powder is preferably 0.3 μm to 27.4 μm.

Further, as a result of examination with reference to FIG. 5, from the viewpoint of maintaining the viscosity of the positive electrode mixture in a low state even after 3 days from the preparation and further increasing the capacity retention rate in the high rate cycle, Test Example 13 to Test Example It was found that it is more preferable that the D ₅₀ particle diameter of the trilithium phosphate powder is set in the range of 1.3 μm to 24.8 μm, as shown in FIG.
In addition, as a result of investigation with reference to FIG. 6, from the viewpoint of maintaining the viscosity of the positive electrode mixture at a low level even after one week from the preparation and reducing the DC resistance at 25 ° C., Test Example 15 to Test Example As shown in FIG. 20, it was found that it is more preferable to set the D ₅₀ particle diameter of the trilithium phosphate powder within the range of 1.8 μm to 8.3 μm.
Further, as a result of investigation with reference to FIG. 7, from the viewpoint of maintaining the viscosity of the positive electrode mixture at a low level even after 2 weeks from the preparation and lowering the reaction resistance at −30 ° C., Test Example 16 to Test As in Example 19, it was found that it is more preferable to set the D ₅₀ particle diameter of the trilithium phosphate powder within the range of 2.1 μm to 5.6 μm.

  As mentioned above, although this invention was demonstrated in detail, above-described embodiment is only an illustration and what changed and modified the above-mentioned specific example is contained in the invention disclosed here.

DESCRIPTION OF SYMBOLS 10 Positive electrode 12 Positive electrode collector 14 Positive electrode mixture layer 16 Positive electrode mixture layer non-formation part 20 Negative electrode 22 Negative electrode collector 24 Negative electrode mixture layer 26 Negative electrode mixture layer non-formation part 40 Separator 50 Battery case 52 Case main body 54 Cover Body 56 Injection port 70 Positive electrode terminal 72 Negative electrode terminal 80 Winding electrode body 100 Lithium ion secondary battery

Claims (1)

A positive electrode in which a positive electrode mixture layer containing a positive electrode active material is formed on a positive electrode current collector, a negative electrode in which a negative electrode mixture layer containing a negative electrode active material is formed on a negative electrode current collector, a non-aqueous electrolyte, A method for producing a non-aqueous electrolyte secondary battery comprising the positive and negative electrodes and a battery case containing the non-aqueous electrolyte,
Forming the positive electrode mixture layer by applying a positive electrode mixture containing a trilithium phosphate powder and a solvent together with the positive electrode active material on the positive electrode current collector; and
After the positive electrode and the negative electrode are accommodated in a battery case to construct a cell assembly, before the non-aqueous electrolyte is supplied to the battery case, the constructed cell assembly is 110 ° C. or higher and 140 ° C. Heating to the following temperature range for drying treatment,
A method for producing a non-aqueous electrolyte secondary battery.

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