JP2011216428A - Li DEPOSITION-RESISTANCE IMPROVEMENT METHOD, METHOD FOR MANUFACTURING LITHIUM SECONDARY BATTERY, AND LITHIUM SECONDARY BATTERY - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Li deposition-resistance improvement method capable of improving resistance for Li-deposition concerning a lithium secondary battery having a negative electrode body containing a carbon-system anode active material.SOLUTION: In the Li deposition-resistance improvement method, for improving resistance concerning Li-deposition in the lithium secondary battery 100 having a negative electrode plate 131 containing the carbon-system anode active material, alternately makes both of a charging step of charging the lithium secondary battery 100 and a discharging step of discharging the lithium secondary battery 100 repeated 500 times or more under an environment of -15 to +65°C while at least the magnitude of either charging current or discharging current is set at 8C or more.

Description

  The present invention relates to a Li deposition resistance improving method for improving resistance related to Li deposition in which Li metal is deposited on a negative electrode body of a lithium secondary battery. Moreover, it is related with the manufacturing method of a lithium secondary battery provided with the Li tolerance improvement process which performs the Li precipitation tolerance improvement method. Moreover, it is related with the lithium secondary battery which gave the Li precipitation tolerance improvement method.

  Conventionally, in lithium secondary batteries, it is known that Li deposition (dendrites) in which Li metal is deposited on the negative electrode body occurs. When the dendrite grows and reaches the positive electrode body, the negative electrode body and the positive electrode body are short-circuited, and even if the short-circuit is not reached, the battery capacity is reduced. Therefore, in the lithium secondary battery, it is desired to suppress the generation of dendrite so that it can be used safely for a long period of time.

  In order to suppress the generation of dendrite, methods such as (1) developing a negative electrode body that hardly generates dendrite, and (2) controlling a charging current so that dendrite is hardly generated during charging are usually taken. However, when the negative electrode body is improved so that dendrite is difficult to be generated, on the other hand, another deterioration is easily promoted, and technical difficulties are involved. In addition, regarding the control of the charging current, for example, in a vehicle such as a hybrid vehicle or an electric vehicle equipped with a lithium secondary battery, it is difficult to efficiently perform charging by the regenerative brake, which is a factor in improving fuel consumption.

As methods for solving such problems, for example, methods disclosed in Patent Documents 1 to 3 have been proposed. That is, in Patent Document 1, in a lithium secondary battery using Li metal as a negative electrode active material, discharge is performed for 30 seconds at a current density of 5 mA / cm ² or more at the end of charge or at the start of discharge. Generation is suppressed.
In Patent Document 2, the amount of dendrite deposited on the negative electrode body is calculated, and when this amount exceeds a predetermined value, a reverse voltage is applied to the lithium secondary battery. Thereby, the dendrite is dissolved and removed.
Moreover, in patent document 3, in the lithium secondary battery which uses Li metal as a negative electrode active material, ethylene carbonate is used for the nonaqueous solvent of a nonaqueous electrolyte. And the production | generation of a dendrite is suppressed by performing pulse charge.

JP-A-7-65867 JP 2009-199936 A Japanese Patent Laid-Open No. 7-263031

  The methods of Patent Documents 1 to 3 described above are considered to have an effect of suppressing the formation of dendrites for lithium secondary batteries using Li metal as a negative electrode active material. However, these methods cannot suppress the formation of dendrites for lithium secondary batteries having a carbon-based negative electrode active material.

  The present invention has been made in view of the current situation, and for lithium secondary batteries having a negative electrode body containing a carbon-based negative electrode active material, improved resistance to Li deposition in which Li metal is deposited on the negative electrode body. To provide a method for improving Li precipitation resistance, a method for producing a lithium secondary battery including a Li resistance improvement step for applying this method for improving Li precipitation resistance, and a lithium secondary battery subjected to this method for improving Li precipitation resistance With the goal.

  One aspect of the present invention for solving the above-described problems is that a lithium secondary battery having a negative electrode body containing a carbon-based negative electrode active material is improved in resistance to Li deposition in which Li metal is deposited on the negative electrode body. A method for improving Li precipitation resistance, wherein a charging step for charging the lithium secondary battery and a discharging step for discharging the lithium secondary battery are performed under a charging current and a discharging current in an environment of -15 to 65 ° C. This is a Li precipitation resistance improving method in which at least one size is set to 8C or more and alternately 500 times or more.

In this method for improving Li precipitation resistance, as described above, charging and discharging are alternately performed 500 times or more alternately in an environment of −15 to 65 ° C. with at least one of the charging current and the discharging current being 8 C or more. . By performing such a charge / discharge cycle, the resistance with respect to Li precipitation (dendrites) can be improved for a lithium secondary battery having a negative electrode body containing a carbon-based negative electrode active material.
Furthermore, in order to improve the tolerance regarding Li precipitation (dendrites), it is preferable that the magnitude of at least one of the charging current and the discharging current is 15 C or more. Moreover, it is preferable that the charging step and the discharging step are each performed 15000 times or more.

This method for improving Li precipitation resistance may be performed in the course of manufacturing a lithium secondary battery, or the lithium secondary battery may be used in a vehicle such as a hybrid vehicle or an electric vehicle, a personal computer, or a mobile phone. It may be performed after being mounted on the device. Further, this Li precipitation resistance improving method may be performed before the first use of these vehicles or battery-powered devices, or may be performed during maintenance of the vehicle or battery-powered devices.
Examples of the “carbon-based negative electrode active material” include amorphous carbonaceous materials such as soft carbon and hard carbon, and highly graphitized carbon materials such as artificial graphite and natural graphite.

  Furthermore, it is preferable to use the above Li deposition resistance improvement method, wherein the charge current and the discharge current are different from each other. By doing in this way, Li precipitation tolerance can further be improved compared with the case where charging current and discharge current are made the same magnitude.

  Furthermore, it is preferable to use the above Li precipitation resistance improvement method, wherein the difference between the charging current and the discharge current is 5C or more. By doing in this way, Li precipitation tolerance can further be improved.

  Furthermore, it is good to set it as the Li precipitation tolerance improvement method in any one of said, Comprising: The Li precipitation tolerance improvement method which makes the said discharge current larger than the said charging current. By doing in this way, Li precipitation tolerance can further be improved.

  Furthermore, it is good to set it as the Li precipitation tolerance improvement method in any one of said, Comprising: The discharge time in the said discharge process is 2-50 second. By doing in this way, Li precipitation tolerance can further be improved.

  Furthermore, in the Li precipitation resistance improvement method according to any one of the above, the Li precipitation resistance improvement is performed in which the charging step and the discharging step are performed in an environment of 45 ° C. or less, more preferably in an environment of 25 ° C. or less. It would be better to do it. By doing in this way, Li precipitation tolerance can further be improved.

  Furthermore, it is the Li deposition resistance improving method according to any one of the above, wherein the amount of charge to charge the lithium secondary battery in the charging step and the amount of discharge to discharge the lithium secondary battery in the discharging step It is preferable to use a method for improving Li precipitation resistance so that the

  In this method for improving Li precipitation resistance, the charging electric quantity for charging the lithium secondary battery in the charging process is equal to the discharging electric quantity for discharging the lithium secondary battery in the discharging process. If performed once, the state of charge of the lithium secondary battery can be returned to the original state before performing these steps. Therefore, it is easy to repeat the charging process and the discharging process repeatedly as described above.

  Moreover, another aspect is a method for producing a lithium secondary battery having a negative electrode body containing a carbon-based negative electrode active material, wherein the Li resistance improvement step for applying the Li precipitation resistance improvement method according to any one of the above is performed. It is a manufacturing method of the lithium secondary battery provided.

  Since this method for producing a lithium secondary battery includes the Li tolerance improving step for applying the aforementioned Li deposition tolerance improving method, a lithium secondary battery with improved tolerance for Li deposition can be easily produced.

  Another aspect is a lithium secondary battery having a negative electrode body containing a carbon-based negative electrode active material, wherein the lithium secondary battery is formed by performing the Li precipitation resistance improving method according to any one of the above. .

  Since this lithium secondary battery has been subjected to the above-described method for improving Li precipitation resistance, the lithium secondary battery has good resistance to Li precipitation.

It is a longitudinal cross-sectional view of the lithium secondary battery which concerns on embodiment. 1 is a perspective view showing a wound electrode body according to an embodiment. It is a top view which concerns on embodiment and shows a positive electrode plate. It is a top view which concerns on embodiment and shows a negative electrode plate. It is a top view which concerns on embodiment and shows a separator. It is an exploded perspective view showing a case lid member, a positive electrode terminal member, a negative electrode terminal member, etc. concerning an embodiment. It is a graph which shows the relationship between the implementation days of Li tolerance improvement process, and the capacity | capacitance reduction rate At of a lithium secondary battery about Examples 1-5 and Comparative Examples 1 and 2. FIG. It is a graph which shows the relationship between the discharge time in one discharge process, and the capacity | capacitance fall rate At of a lithium secondary battery about Examples 6-11. It is a graph which shows the relationship between the implementation days of a Li tolerance improvement process, and the capacity | capacitance reduction rate At of a lithium secondary battery about Examples 12-15. It is a graph which shows the relationship between the storage days after performing a Li tolerance improvement process, and the capacity | capacitance reduction rate At of a lithium secondary battery about Examples 16-18.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a lithium secondary battery 100 according to this embodiment. FIG. 2 shows a wound electrode body 120 constituting the lithium secondary battery 100. Furthermore, the positive electrode plate 121 constituting the wound electrode body 120 is shown in FIG. 3, the negative electrode plate 131 is shown in FIG. 4, and the separator 141 is shown in FIG. FIG. 6 shows details of the case lid member 113, the positive electrode terminal member 150, the negative electrode terminal member 160, and the like.

  The lithium secondary battery 100 is a prismatic battery that is mounted on a vehicle such as a hybrid vehicle or an electric vehicle, or on a battery using device such as a hammer drill. The battery capacity is 5 Ah. The lithium secondary battery 100 includes a rectangular battery case 110, a wound electrode body 120 accommodated in the battery case 110, a positive electrode terminal member 150 and a negative electrode terminal member 160 supported by the battery case 110, and the like. (See FIG. 1). In addition, an electrolyte solution (not shown) is injected into the battery case 110.

  Among these, the battery case 110 is made of metal and formed in a rectangular parallelepiped shape. The battery case 110 has a box shape in which only the upper side is opened, and a rectangular shape welded in a form that closes an opening 111h of the case body member 111 and a case body member 111 that accommodates a wound electrode body 120 described later. It is comprised from the plate-shaped case cover member 113. FIG.

A positive electrode terminal member 150 and a negative electrode terminal member 160 are fixed at predetermined positions of the case lid member 113 via three insulating members 181, 183, and 185, respectively (see FIGS. 1 and 6). . The positive electrode terminal member 150 and the negative electrode terminal member 160 are constituted by three terminal fittings 151, 153, and 155, respectively. In the battery case 110, the positive electrode terminal member 150 is connected to the positive electrode plate 121 (the positive electrode current collector 121 m) of the wound electrode body 120, and the negative electrode terminal member 160 is the negative electrode of the wound electrode body 120. It is connected to the electrode plate 131 (negative electrode current collector 131m).
In addition, a safety valve portion 113j that breaks when the internal pressure of the battery case 110 reaches a predetermined pressure is provided at the center in the longitudinal direction of the case lid member 113. In addition, an electrolytic solution injection port 113 d for injecting the electrolytic solution into the battery case 110 is provided at a predetermined position on the negative electrode terminal member 160 side from the longitudinal center of the case lid member 113.

Next, the wound electrode body 120 will be described. The wound electrode body 120 is housed in an insulating film enclosure 170 formed in a bag shape with only the upper opening of the insulating film, and is housed in the battery case 110 in a laid state (FIG. 1). reference).
This wound electrode body 120 allows a long positive electrode plate (positive electrode body) 121 (see FIG. 3) and a long negative electrode plate (negative electrode body) 131 (see FIG. 4) to ventilate. These are overlapped with each other through a long separator 141 (see FIG. 5) and wound around an axis AX and compressed into a flat shape (see FIG. 2).

  On one side of the wound electrode body 120 in the axis AX direction (left side in FIG. 1, left side in FIG. 2), a positive electrode current collector 121m, which will be described later, of the positive electrode plate 121 forms a spiral. 141 protrudes. On the other hand, on the other side of the wound electrode body 120 in the axis AX direction (right side in FIG. 1, right side in FIG. 2), a negative electrode current collector 131m described later of the negative electrode plate 131 has a spiral shape. , Protruding from the separator 141.

Among these, the positive electrode plate 121 has a positive electrode current collector foil 122 made of a long aluminum foil as a core material, as shown in FIG. A positive electrode active material layer 123 including a positive electrode active material, a conductive agent, and a binder is provided on both surfaces of the positive electrode current collector foil 122 in a strip shape in the longitudinal direction (left and right direction in FIG. 3). A portion of the positive electrode plate 121 where the positive electrode active material layer 123 is formed is a positive electrode portion 121w. In this embodiment, LiNoCoO ₂ is used as the positive electrode active material, acetylene black is used as the conductive agent, and CMC is used as the binder.

  Further, with the formation of the positive electrode part 121w on the positive electrode plate 121, one end in the width direction (upward in FIG. 3) of the positive electrode current collector foil 122 has the positive electrode active material layer 123 in its thickness direction. However, the positive electrode current collector 121m extends in a strip shape in the longitudinal direction (left and right direction in FIG. 3). As described above, the positive electrode current collector 121m protrudes from the separator 141 to one side in the axis AX direction in a state where the wound electrode body 120 is formed (see FIGS. 1 and 2).

  As shown in FIG. 4, the negative electrode plate 131 has a negative electrode current collector foil 132 made of a long copper foil as a core material. A negative electrode active material layer 133 containing a carbon-based negative electrode active material, a binder, and a thickener is provided on both surfaces of the negative electrode current collector foil 132 in a strip shape in the longitudinal direction (left and right direction in FIG. 4). It has been. A portion of the negative electrode plate 131 where the negative electrode active material layer 133 is formed is a negative electrode portion 131w. In this embodiment, graphite is used as the carbon-based negative electrode active material, SBR is used as the binder, and CMC is used as the thickener.

In addition, as the negative electrode portion 131w is formed on the negative electrode plate 131, the other end (downward in FIG. 4) in the width direction of the negative electrode current collector foil 132 has the negative electrode active material layer 133 in its thickness direction. The negative electrode current collector 131m does not exist and extends in a strip shape in the longitudinal direction (left and right direction in FIG. 4). As described above, the negative electrode current collector 131m protrudes from the separator 141 to the other side in the axis AX direction in a state where the wound electrode body 120 is formed (see FIGS. 1 and 2).
The separator 141 is made of PP / PE / PP, and has a long shape as shown in FIG.

  The lithium secondary battery 100 of the present embodiment is obtained by performing a Li resistance improving step (Li precipitation resistance improving method) described later in the manufacturing process. For this reason, although the negative electrode active material layer 133 of the negative electrode plate 131 contains a carbon-type negative electrode active material, the tolerance regarding Li precipitation (dendrites) is greatly improved.

Next, a method for manufacturing the lithium secondary battery 100 will be described.
First, a positive electrode current collector foil 122 made of a long aluminum foil is prepared, and a positive electrode active material paste containing a positive electrode active material, a conductive material, and a binder is applied to predetermined positions on both surfaces thereof. Thereafter, hot air is blown to dry the applied positive electrode active material paste to form the positive electrode active material layer 123. Further, the positive electrode active material layer 123 is compressed by a pressure roll to form the positive electrode plate 121 shown in FIG.

  Moreover, the negative electrode current collection foil 132 which consists of elongate copper foil is prepared, and the negative electrode active material paste containing a carbon-type negative electrode active material, a binder, and a thickener is apply | coated to the predetermined position of both surfaces. Thereafter, hot air is blown to dry the applied negative electrode active material paste to form the negative electrode active material layer 133. Further, the negative electrode active material layer 133 is compressed by a pressure roll to form the negative electrode plate 131 shown in FIG.

Next, a long separator body 141 is prepared, and the positive electrode plate 121 and the negative electrode plate 131 are overlapped with each other via the separator 141 and wound around the axis line AX. Form (see FIG. 2).
Next, the case body member 111, the case lid member 113, the terminal fittings 151, 153, 155, the insulating film enclosure 170, and the insulating members 181, 183, 185 are prepared, and the battery is assembled. Thereafter, an electrolytic solution is injected into the battery case 110 from the electrolytic solution injection port 113d, and the electrolytic solution injection port 113d is sealed.
Next, the lithium secondary battery 100 is initially charged and discharged to operate as a battery.

  Next, a Li deposition resistance improving method for improving resistance related to Li deposition (dendrites) in which Li metal is deposited on the negative electrode plate 131 is applied to the charged lithium secondary battery 100. That is, in the Li resistance improvement step, the charging step for charging the lithium secondary battery 100 and the discharging step for discharging the lithium secondary battery 100 are performed under the environment of 25 ° C. with a charging current of 4C (5 Ah × 4 = 20 A). ), And the discharge current is set to 20C (5 Ah × 20 = 100 A), and alternately performed 43200 times.

Specifically, the discharge process is performed at 20 C (100 A) for 10 seconds, and then paused for 10 seconds. Then, a charge process is performed for 50 seconds at 4C (20A), and it rests for 50 seconds. Thereafter, 43200 times are performed as one cycle. In the present embodiment, the amount of charge to charge the lithium secondary battery 100 in one charging step is the same as the amount of discharge to discharge the lithium secondary battery 100 in one discharge step (0.28 ( Ah) = 100 × 10/3600 = 20 × 50/3600). Moreover, since it takes 120 seconds to perform one cycle, this Li tolerance improvement process takes 60 days.
Thus, the lithium secondary battery 100 of this embodiment is completed.

  As described above, in the Li precipitation resistance improving method of the present embodiment, the charging process and the discharging process are performed in an environment of −15 to 65 ° C., and the magnitude of at least one of the charging current and the discharging current is set to 8C or more. , Alternately 500 times or more. By performing such a charge / discharge cycle, even in the lithium secondary battery 100 having the negative electrode plate 131 containing the carbon-based negative electrode active material, it is possible to improve the resistance regarding Li deposition (dendrites).

  Furthermore, in the present embodiment, the charging current and the discharging current are different from each other, and the difference between the charging current and the discharging current is 5 C or more, so that the Li precipitation resistance can be further improved. Moreover, since the discharge current is made larger than the charging current, the Li precipitation resistance can be further improved. Moreover, since the discharge time in the discharge step is 2 to 50 seconds, the Li precipitation resistance can be further improved. Moreover, since the charge process and the discharge process are performed in an environment of 45 ° C. or lower, the Li precipitation resistance can be further improved.

  In the present embodiment, since the amount of charge to charge the lithium secondary battery 100 in the charging step is equal to the amount of discharge to discharge the lithium secondary battery 100 in the discharging step, the charging step and the discharging step Is performed once, the state of charge of the lithium secondary battery 100 can be returned to the original state before performing these steps. Therefore, it is easy to repeat the charging process and the discharging process many times.

(Example)
Subsequently, the result of the test conducted in order to verify the effect of this invention is demonstrated.
As the lithium secondary batteries of Examples 1 to 5 of the present invention, the lithium secondary battery 100 and the like are changed by changing the magnitude of the discharge current and the charge current and the energizing time of the discharge process and the charge process in the above-described Li resistance improvement process. (See Table 1). In addition, as lithium secondary batteries of Comparative Examples 1 and 2, two types of lithium secondary batteries described later were manufactured.

  Specifically, in Example 4, as described in the above embodiment, for the lithium secondary battery 100, the discharging process was performed at 20C (100A) for 10 seconds, then paused for 10 seconds, and the charging process was performed at 4C ( 20A) was performed for 50 seconds, and a charge / discharge cycle (one cycle for 120 seconds) was performed for 60 seconds in an environment of 25 ° C. for 60 days (43200 times).

Moreover, in Example 1, the discharge process was performed at 12C (60A) for 10 seconds, then paused for 10 seconds, the charge process was performed at 12C (60A) for 10 seconds, and paused for 90 seconds (120 per cycle). Second), the Li resistance improvement process was performed.
Moreover, in Example 2, the discharge process was performed at 20C (100A) for 10 seconds, then paused for 10 seconds, and the charge process was performed at 20C (100A) for 10 seconds and paused for 90 seconds (120 per cycle). Second), the Li resistance improvement process was performed.

Moreover, in Example 3, the discharge process was performed at 12C (60A) for 10 seconds, then paused for 10 seconds, the charge process was performed at 4C (20A) for 30 seconds, and paused for 70 seconds (120 per cycle). Second), the Li resistance improvement process was performed.
In Example 5, the discharging process was performed at 4C (20A) for 50 seconds, then paused for 10 seconds, and the charging process was performed at 20C (100A) for 10 seconds, and rested for 50 seconds (120 per cycle). Second), the Li resistance improvement process was performed.

On the other hand, in Comparative Example 1, a lithium secondary battery was manufactured in the same manner as in the above embodiment, except that the Li tolerance improving step was not performed.
Moreover, in the comparative example 2, in the Li tolerance improvement process, after performing the discharge process for 10 seconds at 4C (20A), it is paused for 10 seconds, the charge process is performed for 10 seconds at 4C (20A), and is charged and discharged for 90 seconds. The cycle (one cycle for 120 seconds) was performed for 60 days (43200 times).

  And about the lithium secondary battery 100 etc. of these Examples 1-5 and Comparative Examples 1 and 2, the low temperature large current cycle process which produces Li precipitation (dendrites) compulsorily was performed. That is, in an environment of −15 ° C., after charging at 150 A (about 30 C) for 0.1 to 0.5 seconds, discharging at 1.5 A (about 0.3 C) for 10 to 50 seconds, Then, rest for 29.5 to 29.9 seconds. This is one cycle and is repeated 10,000 cycles.

After performing the above-described low-temperature, high-current cycle treatment, the battery capacity Q2 was determined for each lithium secondary battery 100 and the like. That is, the lithium secondary battery 100 or the like is placed in an environment of 25 ° C., charged to SOC 100% with 1C (5A), and then suspended for 10 minutes. Thereafter, the battery is discharged at 0.2 C (1 A) to SOC 0%, and the energized charge amount at this time is defined as the battery capacity Q2 after the low temperature large current cycle process. In addition, after assembling the lithium secondary battery 100 and the like, the battery capacity (initial battery capacity) Q1 is obtained in the same manner at the stage before performing the above-described Li resistance improvement process. Then, the capacity reduction rate At (%) is obtained by the following equation.
Capacity reduction rate At = {1− (battery capacity Q2 / battery capacity Q1)} × 100

  In addition, the above-mentioned low temperature large current cycle process and the measurement of the battery capacity Q2 are prepared for each of the samples for performing the Li resistance improvement step for each of Examples 1 to 5 and Comparative Examples 1 and 2, respectively. In addition to measuring the battery capacity Q2 as described above after performing the Li tolerance improving process for 60 days, the low temperature high current was also obtained for each sample that was subjected to the Li tolerance improving process for 3, 7, 14, and 30 days. The battery capacity Q2 was measured by performing cycle treatment. These results are shown in the graph of FIG.

  From the graph of FIG. 7, in the lithium secondary battery of Comparative Example 1 in which the Li tolerance improving process was not performed, no change was observed in the capacity decrease rate At even after 60 days had passed (left). Moreover, in the lithium secondary battery of Comparative Example 2, no change was observed in the capacity decrease rate At even when the Li resistance improvement step was performed for 60 days. That is, it can be seen that in the Li resistance improvement process to the extent performed in this comparative example, the resistance related to Li precipitation is not improved even if it is carried out for 60 days.

On the other hand, in the lithium secondary batteries of Examples 1 to 5, when the Li tolerance improving process was performed, the capacity reduction rate At of the lithium secondary battery was reduced with the implementation time. That is, the tolerance regarding Li precipitation was improved by performing the Li tolerance improving step.
Specifically, when the Li resistance improvement process was carried out for 60 days, the capacity reduction rate At of the lithium secondary battery of Example 4 was greatly reduced, and the Li precipitation resistance was most improved. Moreover, in the lithium secondary battery of Example 4, the capacity reduction rate At can be lowered at an early stage of the Li precipitation resistance process as compared with the lithium secondary batteries of other Examples 1 to 3 and 5. I understand. Specifically, it can be seen that if the Li precipitation resistance step of Example 4 is performed for about 30 days (number of cycles: 21600 times), the capacity reduction rate At = 4% that can be improved in Example 4 can be reached. .

  In addition, it was the lithium secondary battery of Example 2 in which the capacity reduction rate At decreased after the lithium secondary battery of Example 4 and the Li precipitation resistance improved. In addition, it was the lithium secondary battery of Example 5 in which the capacity reduction rate At decreased after the lithium secondary battery of Example 2 and the Li precipitation resistance improved. In addition, the capacity reduction rate At of the lithium secondary battery of Example 3 was reduced substantially the same as that of the lithium secondary battery of Example 5, and the Li precipitation resistance was improved. Further, among the lithium secondary batteries of Examples 1 to 5, it was the lithium secondary battery of Example 1 that had the smallest decrease in the capacity reduction rate At.

  From the comparison between the result of Comparative Example 2 in which the charging current (4C) and the discharge current (4C) are small and the results of Examples 1 to 5, the result of Example 11 (discharge current is 10C) described later (FIG. 8). In view of (see also), it can be understood that the Li precipitation resistance is improved by charging / discharging at least one of the charging current and the discharging current to 8 C or more. Furthermore, it turns out that Li precipitation tolerance can further be improved by performing the charging / discharging which makes the magnitude | size of at least one of a charging current and a discharge current 15 C or more.

Further, from the comparison between the results of Examples 1 and 2 in which the charging current and the discharging current are the same magnitude and the results of Examples 3 to 5 in which the charging current and the discharging current are different from each other, When the discharge current and the discharge current are different from each other, it is understood that the Li precipitation resistance can be further improved as compared with the case where the charge current and the discharge current are made the same. Moreover, it turns out that Li precipitation tolerance can further be improved by making the difference of a charging current and a discharge current into 5 C or more.
Further, from the comparison between the result of Example 5 in which the charging current (20C) is larger than the discharging current (4C) and the result of Example 4 in which the discharging current (20C) is larger than the charging current (4C), It can be seen that when the current is made larger than the charging current, the Li precipitation resistance can be further improved.

  Further, in consideration of the results of Examples 1 to 5 in which the capacity decrease rate At decreases with time (see FIG. 7) and the results of Example 11 (number of cycles: 930 times) described later (see FIG. 8), the charging step It can be seen that the Li precipitation resistance can be sufficiently improved by alternately performing the discharge process and the discharge process 500 times or more. Furthermore, according to the result of Example 12 described later (see FIG. 9), it is inferred that the capacity reduction rate At can be reduced to around 4% even if the number of implementation days is about 20 days (cycle number: 14400 times). Therefore, it can be seen that the Li precipitation resistance can be particularly improved by alternately performing the charging step and the discharging step 15000 times or more.

Next, as the lithium secondary batteries of Examples 6 to 11, lithium secondary batteries in which the discharge time of the discharge process was changed in the above-described Li resistance improvement process were manufactured (see Table 1).
Specifically, in Example 6, after the discharge process was performed for 1 second, the charge process was performed for 5 seconds, and then the charge / discharge cycle (40 seconds in one cycle) was stopped for 14 days (30240). Times). In Examples 6 to 10, the discharge current was 20C (100A), the charge current was 4C (20A), and the environmental temperature was 25 ° C.
Further, in Example 7, after performing the discharging process for 5 seconds, the charging process is performed for 25 seconds, and then the charging / discharging cycle (75 seconds for one cycle) is performed for 14 days (16128 times). It was.

Further, in Example 8, after performing the discharging process for 10 seconds, the charging process is subsequently performed for 50 seconds, and then the charging / discharging cycle (75 seconds in one cycle) is performed for 14 days (16128 times). It was.
Further, in Example 9, after performing the discharging process for 20 seconds, the charging process is performed for 100 seconds, and then the charging / discharging cycle (180 seconds for one cycle) is performed for 14 days (6720 times). It was.
In Example 10, after performing the discharging process for 100 seconds, the charging process is subsequently performed for 500 seconds, and then the charging / discharging cycle (1200 seconds for one cycle) is performed for 14 days (1008 times). It was.

Further, in Example 11, after performing the discharging process for 200 seconds, the charging process is performed for 500 seconds, and then the charging / discharging cycle (1300 seconds in one cycle) is performed for 14 days (924 times). It was. In Example 11 only, the discharge current was 10 C (50 A) and the charge current was 4 C (20 A).
And about each of the lithium secondary battery of each Example 6-11, after performing a Li tolerance improvement process, the above-mentioned low temperature large current cycle process and measurement of battery capacity Q2 are performed, and the capacity | capacitance reduction rate of a lithium secondary battery At was determined. These results are shown in the graph of FIG.

  From the graph of FIG. 8, the lithium secondary battery of Example 8 in which the discharge time of the discharge process was 10 seconds had the lowest capacity reduction rate At and the best Li precipitation resistance. In addition, the lithium secondary battery of Example 7 in which the discharge time of the discharge process is 5 seconds and the lithium secondary battery of Example 9 in which the discharge time of the discharge process is 20 seconds are also sufficiently low in the capacity reduction rate At. , Li precipitation resistance was good. In comparison with these, in the lithium secondary battery of Example 6 in which the discharge time of the discharge process was 1 second, and the lithium secondary battery of Examples 10 and 11 in which the discharge time of the discharge process was 100 seconds and 200 seconds, The decrease rate At was slightly high. From these facts, it can be seen that when the discharge time in the discharge step is 2 to 50 seconds, the Li precipitation resistance can be further improved.

Subsequently, the lithium secondary battery which changed the environmental temperature which performs the above-mentioned Li tolerance improvement process was manufactured as a lithium secondary battery of Examples 12-15 (refer Table 1).
Specifically, Example 12 is in an environment of 0 ° C, Example 13 is in an environment of 25 ° C, Example 14 is in an environment of 45 ° C, and Example 15 is in an environment of 60 ° C. The Li tolerance improvement process was performed. In Examples 12 to 15, the Li resistance improving step was performed for 30 days in the same manner as in Example 4 except for the environmental temperature and the number of days (30 days).
Furthermore, after preparing the same lithium secondary battery as used in Examples 12 to 15 and carrying out the Li resistance improvement process for only 7 days, the above-described low-temperature high-current cycle treatment and measurement of the battery capacity Q2 were performed, respectively. The capacity reduction rate At of the lithium secondary battery was determined. These results are shown in the graph of FIG.

  From the graph of FIG. 9, when the Li resistance improvement step was performed for 30 days, the lithium secondary battery of Example 12 in which the environmental temperature was 0 ° C. and the lithium secondary battery of Example 13 in which the environmental temperature was 25 ° C. In both cases, the capacity decrease rate At was low and the Li precipitation resistance was good. In particular, in the lithium secondary battery of Example 12, the capacity decrease rate At is greatly reduced at the early stage (7 days) of the Li resistance improvement process as compared with the lithium secondary battery of Example 13, and Li precipitation resistance is increased. Improved. Compared to these, Example 14 in which the environmental temperature was 45 ° C. had a slightly higher capacity reduction rate At, and Example 15 in which the environmental temperature was 60 ° C. had a higher capacity reduction rate At. From these results, it is understood that the Li precipitation resistance can be further improved when the environmental temperature for performing the Li resistance improvement step is −15 to 45 ° C., and further −15 to 25 ° C.

Next, as Examples 16 to 18, in Examples 3 to 5 described above, the number of days of implementation of the Li resistance improving process that was 60 days (number of cycles: 43200) was changed to 30 days (number of cycles: 21600), respectively. It changed and manufactured the lithium secondary battery (refer Table 1).
When the lithium secondary batteries according to Examples 16 to 18 were stored (leaved) for 7 days, 14 days, or 30 days after finishing the Li resistance improvement step, the above-described low-temperature high-current cycle treatment and The battery capacity Q2 was measured to determine the capacity reduction rate At of the lithium secondary battery. These results are shown in the graph of FIG.

  From the graph of FIG. 10, it can be seen that in any of the lithium secondary batteries of Examples 16 to 18, the capacity decrease rate At hardly changes after the Li resistance improvement step. Specifically, even after 30 days have elapsed from the end of the Li tolerance improving process, the capacity decrease rate At only increases by about 0.2%. From these, it can be seen that the Li deposition resistance can be satisfactorily maintained over a long period of time by subjecting the lithium secondary battery to the aforementioned Li resistance improvement step. In particular, in the lithium secondary battery of Example 17, it can be seen that a state in which the capacity decrease rate At is low (for example, 5% or less) can be stably maintained over a long period of time.

  In the above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.

100 lithium secondary battery 120 wound electrode body 121 positive electrode plate (positive electrode body)
122 positive electrode current collector foil 123 positive electrode active material layer 131 negative electrode plate (negative electrode body)
132 Negative Electrode Current Foil 133 Negative Electrode Active Material Layer

Claims (9)

About a lithium secondary battery having a negative electrode body containing a carbon-based negative electrode active material, a Li precipitation resistance improving method for improving resistance related to Li precipitation in which Li metal is deposited on the negative electrode body,
The charging step for charging the lithium secondary battery and the discharging step for discharging the lithium secondary battery are performed under an environment of −15 to 65 ° C., and at least one of the charging current and the discharging current is set to 8C or more. A method for improving Li precipitation resistance, which is alternately performed 500 times or more alternately. The Li precipitation resistance improving method according to claim 1,
A method for improving Li precipitation resistance, wherein the charging current and the discharging current are different from each other. The Li precipitation resistance improving method according to claim 2,
A method for improving Li precipitation resistance, wherein a difference between the charging current and the discharging current is 5 C or more. The Li precipitation resistance improving method according to claim 2 or 3,
A method for improving Li deposition resistance, wherein the discharge current is larger than the charging current. A method for improving Li precipitation resistance according to any one of claims 1 to 4,
The Li precipitation tolerance improvement method which makes discharge time in the said discharge process 2-50 second. It is a Li precipitation tolerance improvement method according to any one of claims 1 to 5,
A method for improving Li precipitation resistance, wherein the charging step and the discharging step are performed in an environment of 45 ° C. or lower. It is Li precipitation tolerance improvement method as described in any one of Claims 1-6, Comprising:
A Li deposition resistance improving method for equalizing a charge electricity amount charged in the lithium secondary battery in the charging step and a discharge electricity amount discharging the lithium secondary battery in the discharge step. A method for producing a lithium secondary battery having a negative electrode body containing a carbon-based negative electrode active material,
The manufacturing method of a lithium secondary battery provided with the Li tolerance improvement process which performs the Li precipitation tolerance improvement method as described in any one of Claims 1-7. A lithium secondary battery having a negative electrode body containing a carbon-based negative electrode active material,
The lithium secondary battery formed by giving the Li precipitation tolerance improvement method as described in any one of Claims 1-7.

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