JP5895538B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery having a positive electrode plate containing a positive electrode active material in which a part of NiMn spinel is substituted with Fe and Ti.

  In recent years, lithium ion secondary batteries have attracted attention as power sources for vehicles such as hybrid vehicles and electric vehicles. A lithium ion secondary battery has an electrode body in which a positive electrode plate and a negative electrode plate are stacked by winding or flat stacking with a separator interposed therebetween. Further, the positive electrode plate and the negative electrode plate are in the form of a strip formed by forming an active material layer containing an active material on the surface of a current collector.

As a power source for vehicles, a battery pack is used by connecting a large number of lithium ion secondary batteries. This is because a high voltage of several hundred volts is required for the vehicle. For this reason, a lithium ion secondary battery used for a vehicle power source is required to have a high output voltage. In an assembled battery, the higher the output voltage of each lithium ion secondary battery, the smaller the number of connections. That is, it is preferable from the viewpoint of space saving and weight reduction. As a positive electrode active material capable of constructing a lithium ion secondary battery having a high output voltage, spinel-structured LiMn ₂ O ₄ can be mentioned.

In the lithium ion secondary battery using NiMn spinel represented by LiNi _0.5 Mn _1.5 O _{4 in} which a part of Mn of LiMn ₂ O ₄ is replaced with Ni as the positive electrode active material, the output voltage is 4.5V. More than that. Furthermore, a lithium ion secondary battery using NiMn spinel is less likely to cause a decrease in full charge capacity due to repeated charge and discharge, and has excellent cycle characteristics. For this reason, a technology for manufacturing a lithium ion secondary battery having more excellent battery characteristics by replacing a part thereof with a different element based on NiMn spinel has been developed.

  For example, in Patent Document 1, a part of a transition metal site of NiMn spinel is selected from the group consisting of Ti, Cr, Fe, Co, Cu, Zn, Al, and B as a positive electrode active material of a lithium ion secondary battery. It is disclosed to use one substituted with at least one element. Thereby, in a lithium ion secondary battery with an output voltage of 4.5 V or more, it is said that thermal decomposition of the electrolytic solution can be suppressed and high thermal stability can be achieved.

JP 2002-158008 A

  However, any lithium ion secondary battery using a conventional NiMn spinel substituted with a different element is sufficiently sufficient in terms of cycle characteristics to use a NiMn spinel not substituted with a different element. It was not excellent. In particular, when the number of charge / discharge cycles is small, even if the cycle characteristics are excellent, the number of cycles increases beyond a certain number, and the cycle characteristics may deteriorate rapidly. That is, there is a problem that the cycle life is short.

  The present invention has been made for the purpose of solving the problems of the prior art described above. That is, the problem is to provide a lithium ion secondary battery having a long cycle life.

The lithium ion secondary battery of the present invention made for the purpose of solving this problem is a lithium ion secondary battery in which a positive electrode plate, a negative electrode plate, and an electrolyte are accommodated in a battery case, and the positive electrode plate is a positive electrode active material. The active material contained in the positive electrode active material layer has a general formula LiNi _0.5-α Fe _x Mn _1.5-β Ti _Y O ₄ (0.01 ≦ X ≦ 0.10, 0.01 ≦ Y ≦ 0.10, 0 ≦ α, 0 ≦ β, X + Y = α + β) (excluding LiNi _0.45 Fe _0.1 Mn _1.35 Ti _0.1 O ₄ ) It is.

Represented by the general formula LiNi _0.5- αFe _X Mn _1.5- βTi _Y O ₄ (0.01 ≦ X ≦ 0.10, 0.01 ≦ Y ≦ 0.10, 0 ≦ α, 0 ≦ β, X + Y = α + β) The positive electrode active material is obtained by replacing part of Ni and Mn of the NiMn spinel with Fe and Ti. And the lithium ion secondary battery of the invention using this has a high output voltage of 4.5V or higher. Furthermore, the lithium ion secondary battery of the present invention tends to be less likely to reduce the full charge capacity due to repeated charge and discharge than those using NiMn spinel that is not substituted with a different element as the positive electrode active material. This tendency is not reversed even when the number of cycles, which is repeated charging and discharging, increases. That is, it is a lithium ion secondary battery with a long cycle life.

  According to the present invention, a lithium ion secondary battery having a long cycle life is provided.

It is sectional drawing of the secondary battery which concerns on embodiment. It is a perspective view of the electrode body which concerns on embodiment. It is sectional drawing before winding of the positive electrode plate, negative electrode plate, and separator which comprise the electrode body which concerns on embodiment. It is a graph which shows the comparison of the capacity | capacitance maintenance factor of an Example and each comparative example. It is a graph which shows the comparison of the transition of the capacity | capacitance maintenance factor of an Example and each comparative example.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view of a secondary battery 10 in this embodiment. As shown in FIG. 1, the secondary battery 10 is a lithium ion secondary battery in which an electrode body 20 and an electrolytic solution 30 are accommodated in a battery case 40. The battery case 40 includes a battery case main body 41 and a sealing plate 42. In addition, the sealing plate 42 includes an insulating member 43.

The electrolytic solution 30 is obtained by dissolving an electrolyte in an organic solvent. Although not specifically limited, the organic solvent in this embodiment is a mixture of methyl trifluoroethyl carbonate (MFEC) and ethyl methyl carbonate (EMC). Moreover, in the electrolyte solution 30, these organic solvents are mixed by the following volume ratio.
MFEC: 5
EMC: 5
Furthermore, the electrolytic solution 30 is an organic electrolytic solution in which lithium hexafluorophosphate (LiPF ₆ ) is added as a lithium salt as an electrolyte to the above mixed organic solvent to make the concentration of Li ions 1 mol / l.

  FIG. 2 is a perspective view of the electrode body 20. As shown in FIG. 2, the electrode body 20 is a flat wound electrode body. FIG. 3 is a cross-sectional view of the positive electrode plate 50, the negative electrode plate 60, and the separator 70 constituting the electrode body 20 before winding. The positive electrode plate 50, the negative electrode plate 60, and the separator 70 are all in the form of strips that are long in the depth direction of the paper in FIG.

  As shown in FIG. 3, the positive electrode plate 50 is formed by forming a positive electrode active material layer 52 on both surfaces of an aluminum foil 51 that is a positive electrode current collector. The negative electrode plate 60 is formed by forming a negative electrode active material layer 62 on both surfaces of a copper foil 61 that is a negative electrode current collector. Both the positive electrode active material layer 52 and the negative electrode active material layer 62 contain an active material capable of inserting and extracting lithium ions. This point will be described in detail later.

  The separator 70 is a porous member that can transmit lithium ions while preventing a short circuit between the positive electrode plate 50 and the negative electrode plate 60. As the porous member, a porous film made of polypropylene (PP), polyethylene (PE) or the like can be used alone, or a composite material in which a plurality of these are laminated in the thickness direction can be used. Although not particularly limited, in this embodiment, a composite material made of PE / PP / PE is used as the separator 70. The width of the separator 70 (the length in the left-right direction in FIG. 3) is narrower than that of the positive electrode plate 50 and the negative electrode plate 60.

  Here, as shown in FIG. 3, in the positive electrode plate 50 and the negative electrode plate 60, the positive electrode active material layer 52 and the negative electrode active material layer 62 are formed in a range of about the same width as the separator 70. However, in practice, the width of the separator 70 is slightly wider. This is for reliably preventing a short circuit between the positive electrode plate 50 and the negative electrode plate 60.

  Also, as shown in FIG. 3, the positive electrode plate 50 and the negative electrode plate 60 have portions where the positive electrode active material layer 52 and the negative electrode active material layer 62 are not formed, respectively. The aluminum foil 51 is exposed at a portion of the positive electrode plate 50 where the positive electrode active material layer 52 is not formed. Furthermore, the portion where the aluminum foil 51 is exposed protrudes to the right in FIG. 3 from the negative electrode plate 60 and the separator 70. On the other hand, the copper foil 61 is exposed at a portion of the negative electrode plate 60 where the negative electrode active material layer 62 is not formed. Further, the portion where the copper foil 61 is exposed protrudes to the left in FIG. 3 from the positive electrode plate 50 and the separator 70.

  The electrode body 20 is obtained by winding a positive electrode plate 50, a negative electrode plate 60, and a separator 70 into a flat shape as shown in FIG. 2 while overlapping them as shown in FIG. Further, as shown in FIG. 2, the electrode body 20 includes a power storage unit 21, a positive electrode end 22, and a negative electrode end 23. The positive electrode end portion 22 and the negative electrode end portion 23 are both end portions of the electrode body 20 in the width direction (left-right direction in FIG. 2). The power storage unit 21 is a central portion in the width direction of the electrode body 20 sandwiched between the positive electrode end 22 and the negative electrode end 23.

  The power storage unit 21 is a portion where the positive electrode plate 50, the negative electrode plate 60, and the separator 70 are alternately overlapped at the center in the width direction in FIG. Therefore, the electrical storage part 21 is a part which can contribute to charging / discharging. On the other hand, the positive electrode end portion 22 is a portion made of an aluminum foil 51 protruding to the right end in FIG. Further, the negative electrode end portion 23 is a portion made of the copper foil 61 protruding to the left end in FIG.

  In the secondary battery 10 shown in FIG. 1, a positive terminal 80 is connected to the positive end 22. A negative electrode terminal 90 is connected to the negative electrode end portion 23. In the positive electrode terminal 80 and the negative electrode terminal 90, ends 81 and 91 on the side not connected to the electrode body 20 are protruded to the outside of the battery case 40 through an insulating member 43 provided on the sealing plate 42. The secondary battery 10 performs charging and discharging in the power storage unit 21 of the electrode body 20 via the positive electrode terminal 80 and the negative electrode terminal 90.

Here, as described above, both the positive electrode active material layer 52 and the negative electrode active material layer 62 contain an active material capable of inserting and extracting lithium ions. In this embodiment, as the positive electrode active material contained in the positive electrode active material layer 52, Ni and Mn of NiMn spinel represented by the general formula LiNi _0.5 Mn _1.5 O ₄ are partially substituted with Fe and Ti. It was. Specifically, a material represented by the general formula LiNi _0.475 Fe _0.025 Mn _1.475 Ti _0.025 O ₄ was used. However, the present invention is not limited to this, and the general formula LiNi _0.5- αFe _X Mn _1.5- βTi _Y O ₄ (0.01 ≦ X ≦ 0.10, 0.01 ≦ Y ≦ 0.10, 0 ≦ α, Any material represented by 0 ≦ β, X + Y = α + β) can be preferably used as the positive electrode active material. Further, by using such a positive electrode active material, the output voltage of the secondary battery 10 is as high as 4.5 V or more.

  In addition to the positive electrode active material, the positive electrode active material layer 52 includes various positive electrode materials. In this embodiment, a conductive additive and a binder are included as positive electrode materials other than the positive electrode active material. The conductive assistant is a component for increasing the conductivity in the positive electrode active material layer 52. The binder is a component for binding the positive electrode active material layer 52 to the surface of the aluminum foil 51 while binding the components in the positive electrode active material layer 52 to each other. Although it does not necessarily limit, acetylene black (AB) was used as a conductive support agent, and the polyvinylidene fluoride (PVdF) was used as a binder.

The positive electrode active material layer 52 is formed by applying a slurry obtained by dispersing the positive electrode material in a solvent onto the surface of the aluminum foil 51 and then drying it. As a solvent, N-methylpyrrolidone (NMP) was used. Moreover, the compounding ratio in the slurry of a positive electrode material is shown below.
LiNi _0.475 Fe _0.025 Mn _1.475 Ti _0.025 O ₄ : 85 wt%
AB: 10 wt%
PVdF: 5 wt%

On the other hand, the negative electrode active material layer 62 of this embodiment includes a negative electrode active material and a binder as a negative electrode material other than the negative electrode active material. Although not particularly limited, in this embodiment, graphite is used as the negative electrode active material, and carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) are used as the binder. The negative electrode active material layer 62 is formed by applying a slurry obtained by dispersing these negative electrode materials in a solvent to the surface of the copper foil 61 and then drying the slurry. Water was used as the solvent. Moreover, the compounding ratio in the slurry of said negative electrode material is shown below.
Graphite: 98wt%
CMC: 1wt%
SBR: 1wt%

[Confirmation of effect]
The inventor used the secondary battery 10 as described above as an example, and conducted an experiment for comparison with the lithium ion secondary batteries of Comparative Examples 1 to 6 in which only the secondary battery 10 and the positive electrode active material were different. In this experiment, the capacity maintenance rate and its transition were compared by conducting experiments according to the following procedure using Examples and Comparative Examples 1 to 6.
1. Conditioning2. 2. Measurement of initial full charge capacity Cycle test

  First, the secondary batteries of Examples and Comparative Examples 1 to 6 used in the experiment will be described. As described above, the embodiment is the secondary battery 10 of this embodiment. Moreover, all of Comparative Examples 1 to 6 are lithium ion secondary batteries having the same configuration manufactured by the same method as the secondary battery 10 except for the positive electrode active material used. Table 1 below shows the positive electrode active materials used in Examples and Comparative Examples 1 to 6, respectively.

As shown in Table 1,
As described in this embodiment, the positive electrode active material used in the examples is obtained by replacing part of Ni and Mn in the NiMn spinel with Fe and Ti.
The positive electrode active material used in Comparative Example 1 is NiMn spinel that is not substituted with a different element.
The positive electrode active material used in Comparative Example 2 is obtained by substituting a part of Mn of NiMn spinel with Ti.
The positive electrode active material used in Comparative Example 3 is obtained by replacing a part of Mn of NiMn spinel with Fe.
The positive electrode active material used in Comparative Example 4 is obtained by replacing part of Ni in the NiMn spinel with Mg.
The positive electrode active material used in Comparative Example 5 is obtained by replacing part of Ni and Mn in the NiMn spinel with Mg and Ti.
The positive electrode active material used in Comparative Example 6 is obtained by replacing a part of Ni in the NiMn spinel with Fe and Mg.
That is, the positive electrode active materials used in Examples and Comparative Examples 2 to 6 are based on NiMn spinel, and a part thereof is replaced with a different element (Fe, Ti, Mg).

  Next, experiments conducted using these Examples and Comparative Examples 1 to 6 will be described along the procedure. “1. Conditioning” is a process of performing initial charge / discharge of a lithium ion secondary battery that has been assembled. And it is a process for stabilizing the battery performance of a lithium ion secondary battery. In this step, CC (Constant Current) charge and CC discharge were repeated three times each in an environment of a temperature of 25 ° C. In CC charging, charging was performed at a constant current value of 1/3 C at a C rate with a current value that can be charged or discharged in 1 hour as a full charge capacity of 1 C until the voltage reached 4.9 V. In CC discharge, discharge was performed at a constant current value of 1/3 C until the voltage reached 3.5V. It should be noted that there was a 10 minute interval after CC charge and after CC discharge until the next CC discharge or CC charge.

  Next, in “2. Measurement of initial full charge capacity”, initial full charge capacity is obtained by performing CC-CV (Constant Voltage) charge and CC-CV discharge once each in an environment at a temperature of 25 ° C. Was measured. That is, in CC-CV charging, charging is performed at a constant current value of 1/3 C until the voltage reaches 4.9 V, and after the voltage reaches 4.9 V, the voltage becomes constant at 4.9 V. The battery was charged while lowering the current value. In CC-CV discharge, discharge is performed at a constant current value of 1/3 C until the voltage reaches 3.5 V, and after the voltage reaches 3.5 V, the current is set to be constant at 3.5 V. The battery was discharged while lowering the value. In addition, after CC-CV charge, the space | interval of 10 minutes was left | separated by the next CC-CV discharge.

  In “3. Cycle test”, CC charge and CC discharge were repeated 200 times in an environment of a temperature of 60 ° C. (200 cycles). In CC charging, charging was performed at a constant current value of 2C until the voltage reached 4.9V. In CC discharge, discharge was performed at a constant current value of 2C until the voltage reached 3.5V. It should be noted that there was a 10 minute interval after CC charge and after CC discharge until the next CC discharge or CC charge.

  In addition, in “3. Cycle test”, the full charge capacity was periodically measured during the cycle test by charging and discharging under the same conditions as in “2. Measurement of initial full charge capacity” above. . The full charge capacity during the cycle test was measured every 50 cycles in the cycle test. Furthermore, the full charge capacity was measured even after the cycle test was completed for 200 cycles, and this was defined as the full charge capacity after the cycle test.

  The results of this experiment are shown in FIG. FIG. 4 is a graph showing a comparison of capacity retention ratios after the cycle test of Examples and Comparative Examples 1-6. The capacity maintenance ratio after the cycle test is the ratio of the full charge capacity after the cycle test to the initial full charge capacity. In FIG. 4, the capacity retention rate after the cycle test of the example and the comparative examples 1 to 6 is shown by the ratio to the capacity retention rate after the cycle test of the comparative example 1. In Comparative Example 1, NiMn spinel not substituted with a different element was used, and in the other Examples and Comparative Examples 2 to 6, the NiMn spinel was partially substituted with a different element. This is because the.

  As shown in FIG. 4, the capacity retention rate after the cycle test of Comparative Examples 2, 3, 4, and 6 is lower than the capacity retention rate after the cycle test of Comparative Example 1. On the other hand, it was confirmed that the capacity retention rate after the cycle test of Example and Comparative Example 5 was higher than the capacity retention rate after the cycle test of Comparative Example 1. Further, in the comparison between the example and the comparative example 5, it was confirmed that the capacity retention rate after the cycle test of the example was higher than the capacity retention rate after the cycle test of the comparative example 5.

  Here, in Comparative Example 2 and Comparative Example 3, the capacity retention rate after the cycle test is lower than that in Comparative Example 1 using NiMn spinel not substituted with a different element. That is, in a lithium ion secondary battery using a part of the NiMn spinel substituted with only one of Fe or Ti, the capacity maintenance rate does not increase. On the other hand, a lithium ion secondary battery having a high capacity retention rate can be constructed by using a NiMn spinel partially substituted with two elements of Fe and Ti as in the embodiment.

  FIG. 5 is a graph showing a comparison of the transition of the capacity retention rate during the cycle test of the example and the comparative examples 1, 5, and 6. In FIG. 5, the vertical axis represents the capacity maintenance ratio, and the horizontal axis represents the square root of the number of cycles. The capacity maintenance rate during the cycle test is the ratio of the full charge capacity measured every 50 cycles in the cycle test to the initial full charge capacity. In FIG. 5, the transition of the capacity maintenance ratios of the example and the comparative examples 1, 5, and 6 are shown by approximate curves based on the capacity maintenance ratios measured every 50 cycles. FIG. 5 also shows the transition of the capacity maintenance ratio after 200 cycles (two-dot chain line in the figure) obtained by extrapolation based on the transition of the capacity maintenance ratio during the cycle test.

  As shown in FIG. 5, the capacity retention rates of the example and comparative examples 5 and 6 are both higher than the capacity retention rate of comparative example 1 before 100 cycles. That is, it can be said that both the example and the comparative examples 5 and 6 have better cycle characteristics than the comparative example 1 before 100 cycles.

  However, as shown in FIG. 5, the capacity retention rate of Comparative Example 6 decreases rapidly as the number of cycles increases from near 100 cycles. As described above in FIG. 4, the capacity retention rate of Comparative Example 1 is lower at the 200th cycle when the cycle test is completed. That is, Comparative Example 6 has a shorter cycle life than Comparative Example 1.

  On the other hand, the capacity retention rate of the example and the comparative example 5 is higher than the capacity retention rate of the comparative example 1 even at the 200th cycle as described above with reference to FIG. However, as shown in FIG. 5, the capacity retention rate of Comparative Example 5 is not as high as that of Comparative Example 6, but the rate of decrease is higher as the number of cycles increases from around 100 cycles. Then, at the 200th cycle, the capacity maintenance rate of Comparative Example 1 is reduced to the same level. For this reason, the capacity retention rate of Comparative Example 5 may be lower than the capacity retention rate of Comparative Example 1 as shown by the two-dot chain line in FIG. 5 after 200 cycles based on the tendency to 200 cycles. Conceivable. That is, even in Comparative Example 5, the cycle life is shorter than in Comparative Example 1.

  On the other hand, the capacity retention rate of the example is gradually lower than the capacity retention rate of Comparative Example 1 in the cycle test. For this reason, it is considered that the capacity maintenance rate of the example does not become lower than the capacity maintenance rate of Comparative Example 1 even after 200 cycles. That is, in the example, the cycle life is longer than that in Comparative Example 1.

  Furthermore, in the embodiment, as shown in FIG. 5, the rate of decrease in the capacity maintenance rate is substantially constant. For this reason, even in the transition of the capacity maintenance ratio after 200 cycles indicated by the two-dot chain line in FIG. 5, it is considered that the prediction can be accurately made by extrapolation based on the transition of the capacity maintenance ratio during the cycle test. As a result, in the embodiment, the cycle life can be accurately predicted.

Here, the positive electrode active material used in the examples is represented by the general formula LiNi _0.475 Fe _0.025 Mn _1.475 Ti _0.025 O ₄ . In other words, the values of X, Y, α, and β are all set to 0.025 in what is represented by the general formula LiNi _0.5- αFe _X Mn _1.5- βTi _Y O ₄ . However, when the same experiment was performed using different values of X, Y, α, and β, the values of X and Y were both in the range of 0.01 or more and less than 0.10. , Α and β are both 0 or more, and the same X + Y value and α + β value were confirmed to have the same effect as in the example. That is, the general formula LiNi _0.5- αFe _X Mn _1.5- βTi _Y O ₄ (0.01 ≦ X ≦ 0.10, 0.01 ≦ Y ≦ 0.10, 0 ≦ α, 0 ≦ β, X + Y = α + β) It was confirmed that a lithium ion secondary battery with a long cycle life could be constructed by using the indicated positive electrode active material.

As described above in detail, the secondary battery 10 of the present embodiment includes the electrode body 20 formed by winding the positive electrode plate 50 and the negative electrode plate 60 with the separator 70 interposed therebetween, the electrolytic solution 30, and these electrode bodies. 20 and a battery case 40 that accommodates the electrolytic solution 30. The positive electrode plate 50 is formed by forming a positive electrode active material layer 52 containing a positive electrode active material on the surface of an aluminum foil 51. The negative electrode plate is formed by forming a negative electrode active material layer 62 containing a negative electrode active material on the surface of a copper foil 61. As a positive electrode active material, the general formula LiNi _0.5- αFe _X Mn _1.5- βTi _Y O ₄ (0.01 ≦ X ≦ 0.10, 0.01 ≦ Y ≦ 0.10, 0 ≦ α, 0 ≦ β, X + Y = α + β) is used. As a result, a lithium ion secondary battery with a long cycle life has been realized.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the present invention is not limited to the flat type lithium ion secondary battery, but can be applied in the same manner as long as it uses a wound electrode body. Further, for example, the present invention can be applied to a lithium ion secondary battery having a stacked electrode body in which a positive electrode plate and a negative electrode plate are stacked without interposing a separator therebetween.

  Further, for example, various materials including a positive electrode material and a negative electrode material other than the positive electrode active material are merely examples, and can be selected from various materials conventionally used in lithium ion secondary batteries.

DESCRIPTION OF SYMBOLS 10 ... Secondary battery 30 ... Electrolytic solution 40 ... Battery case 50 ... Positive electrode plate 51 ... Aluminum foil 52 ... Positive electrode active material layer 60 ... Negative electrode plate 61 ... Copper foil 62 ... Negative electrode active material layer

Claims (1)

In a lithium ion secondary battery in which a positive electrode plate, a negative electrode plate, and an electrolyte are housed in a battery case,
The positive electrode plate has a positive electrode active material layer;
The active material contained in the positive electrode active material layer has a general formula of LiNi _0.5-α Fe _X Mn _1.5-β Ti _Y O ₄ (0.01 ≦ X ≦ 0.10, 0.01 ≦ Y ≦ 0.10, 0 ≦ α, 0 ≦ β, X + Y = α + β) (excluding LiNi _0.45 Fe _0.1 Mn _1.35 Ti _0.1 O ₄ ) .

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