Lithium-ion battery

Abstract

To provide a lithium-ion battery in which deterioration of a resin member is not accelerated even though a nonaqueous electrolyte containing fluorine is used.SOLUTION: A battery 1 according to the present disclosed technology is a lithium-ion battery including: a case 2; an electrode body 3 and an electrolyte contained which are inside the case 2; and a resin member 10 that is fixed to the case and has an inner exposed surface 11 which is exposed inside the case 2. The electrolytic solution is a nonaqueous electrolytic solution containing fluorine. The resin member 10 contains a glass filler formed of glass which contains silicon oxide as a main body and added with group 2 elements. A number of atoms ratio of the group 2 elements to silicon in component elements of the glass filler is 0.12% or more and 65% or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The disclosed technology relates to lithium-ion batteries. [Background technology]

[0002] In a lithium-ion battery, an electrode assembly and an electrolyte are housed inside a case. A resin member is fixed to a part of the case of such a battery for the purpose of installing terminal members and for other purposes. A part of the resin member is an internally exposed surface that is exposed inside the case. A resin member containing a glass filler can be used. For example, the resin described in Patent Document 1 can be used as such a filler-containing resin. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-035950 Summary of the Invention [Problem to be solved by the invention]

[0004] In some cases, non-aqueous electrolytes containing fluorine are used as the electrolyte in these types of batteries. In such cases, the filler-containing resin may deteriorate. The deterioration of the filler-containing resin occurs when moisture is mixed into the non-aqueous electrolyte. This is because hydrogen fluoride is produced by the reaction between the fluorine in the non-aqueous electrolyte and the mixed moisture. Hydrogen fluoride dissolves glass, so the glass filler dissolves and is lost.

[0005] An object of the present disclosure is to provide a lithium ion battery in which deterioration of resin members is not accelerated even when a non-aqueous electrolyte containing fluorine is used. [Means for solving the problem]

[0006] A lithium-ion battery according to one aspect of the disclosed technology is a battery having a case, an electrode assembly and an electrolyte housed inside the case, and a resin member fixed to the case and having an internally exposed surface exposed inside the case, wherein the electrolyte is a non-aqueous electrolyte containing fluorine, and the resin member contains a glass filler formed of glass mainly composed of silicon oxide with a Group 2 element added, and the atomic ratio of the Group 2 element to silicon among the component elements of the glass filler is 0.12% or more and 65% or less.

[0007] In the lithium-ion battery of the above embodiment, the resin member contains a glass filler, which adjusts its linear expansion coefficient and elastic modulus. This allows the resin member's linear expansion coefficient and elastic modulus to be close to those of the case. Meanwhile, when moisture is mixed into the electrolyte, hydrogen fluoride produced by the reaction between fluorine in the electrolyte and water attempts to dissolve the glass filler. However, the Group 2 element added to the glass filler inhibits this dissolution. Therefore, the properties of the resin member are maintained even when moisture is mixed in.

[0008] In the lithium-ion battery of the above aspect, at least a part of the Group 2 element may be magnesium, and the mass ratio of magnesium to silicon in the component elements of the glass filler may be 0.1% or more and 25% or less. Using magnesium as the Group 2 element more effectively inhibits dissolution of the glass filler by hydrogen fluoride.

[0009] In the lithium-ion battery of the above aspect, at least a part of the Group 2 element may be calcium, and the mass ratio of calcium to silicon among the component elements of the glass filler may be 0.17% or more and 81% or less. Even if the Group 2 element is calcium, the effect of suppressing dissolution of the glass filler by hydrogen fluoride is still available.

[0010] The lithium ion battery of any of the above aspects may further include a terminal member connected to the electrode assembly inside the case, penetrating the case and partially exposed to the outside of the case, and the resin member insulates the case from the terminal member, thereby maintaining the insulating and sealing properties of the resin member between the case and the terminal member for a long period of time. [Effects of the Invention]

[0011] According to the disclosed technique, a lithium ion battery is provided in which deterioration of resin members is not accelerated even when a non-aqueous electrolyte containing fluorine is used. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view of a battery according to an embodiment. [Figure 2] FIG. 2 is a partially enlarged view showing a part of FIG. 1. [Figure 3] 1 is a graph showing the maximum depth at which corrosion of a glass filler occurs due to immersion in an electrolyte. [Figure 4] 10 is a graph showing a change in the elastic modulus of a resin member due to immersion in an electrolyte solution. [Figure 5] 1 is a graph showing the relationship between the temperature and the penetration depth of fluorine due to immersion in an electrolyte solution. DETAILED DESCRIPTION OF THE INVENTION

[0013] This embodiment embodies the disclosed technology as a battery 1 shown in Figs. 1 and 2. The battery 1 has an electrode assembly 3 housed in a case 2. The case 2 is an exterior member that forms the exterior of the battery 1. In this embodiment, the case 2 is made of metal (e.g., aluminum). The case 2 is composed of a box body 4 and a lid body 5. The electrode assembly 3 is made by stacking positive and negative electrode plates.

[0014] The case 2 contains not only the electrode assembly 3 but also an electrolyte 6. The electrolyte 6 is not only present in liquid form in the internal space of the case 2, but also permeates the electrode assembly 3. The battery 1 further includes a terminal member 7. The terminal member 7 penetrates the case 2. Part of the terminal member 7 is exposed to the outside of the case 2. The portion of the terminal member 7 inside the case 2 is connected to the electrode assembly 3. The portion of the terminal member 7 outside the case 2 is connected to an external terminal 8. The battery 1 has two terminal members 7, one for the positive electrode and one for the negative electrode, and two external terminals 8. The terminal members 7 and the external terminals 8 are made of aluminum or copper.

[0015] The lid 5 has a through hole 9 formed therein, through which the terminal member 7 passes. The battery 1 further has a resin member 10. The resin member 10 is fixed to the case 2. The position at which the resin member 10 is fixed in the case 2 is between the lid 5 and the terminal member 7 at the through hole 9. The resin member 10 has two roles: to separate the internal space of the case 2 from the external space, and to insulate the case 2 from the terminal member 7. The resin member 10 has an internal exposed surface 11 that is exposed to the inside of the case 2.

[0016] The electrolyte 6 in the battery 1 of this embodiment will be described. In this embodiment, a non-aqueous electrolyte containing fluorine is used as the electrolyte 6. Examples of materials that can be used as the solvent and electrolyte in the electrolyte 6 of this embodiment include the following. Solvent: polar organic solvent such as ethylene carbonate, propylene carbonate, diethyl carbonate, etc. Electrolyte: fluorine-containing salt such as lithium hexafluorophosphate, lithium tetrafluoroborate, etc.

[0017] The resin member 10 in the battery 1 of this embodiment will be described. The resin member 10 of this embodiment is a composite material in which a glass filler is blended into a base resin. The purpose of blending the glass filler is to adjust the linear expansion coefficient and elastic modulus of the resin member 10. Adjusting the linear expansion coefficient means lowering the linear expansion coefficient of the resin member 10. This is to bring it closer to the linear expansion coefficient of metal parts such as the lid body 5 and terminal member 7. Adjusting the elastic modulus means increasing the elastic modulus of the resin member 10. Both of these contribute to improving the durability of the sealing performance of the resin member 10 in the battery 1.

[0018] The type of resin that can be used as the base resin of the resin member 10 of this embodiment is not particularly limited, but is preferably one that has excellent heat resistance and mechanical strength, such as polyphenylene sulfide resin (hereinafter referred to as PPS resin), polyphenylene oxide resin, and modified polyphenylene ether resin.

[0019] The glass filler of the resin member 10 of this embodiment is made of minute pieces of glass. They are shaped like short fibers or particles. The glass used for the glass filler in this embodiment is mainly made of silicon oxide (such as silicon dioxide) to which a Group 2 element (particularly magnesium or calcium) has been added. The added Group 2 element is thought to be in an oxidized state in the glass. The glass may also contain small amounts of aluminum to improve productivity, and titanium and iron to improve acid resistance, all in an oxidized state.

[0020] In this embodiment, the purpose of adding a Group 2 element to the glass filler is to improve the durability of the resin member 10. In this embodiment, as described above, a fluorine-containing salt is used as the electrolyte of the electrolytic solution 6. Therefore, the electrolytic solution 6 contains fluorine in the form of, for example, hexafluorophosphate ions.

[0021] On the other hand, during the manufacturing process of battery 1, a certain amount of moisture may be mixed into the inside of case 2 due to water vapor in the environment. Also, during the use of battery 1, moisture may penetrate from the outside to the inside if the sealing of case 2 is loose. For this reason, even if electrolyte 6 is based on a non-aqueous solvent, it cannot be said that there is absolutely no moisture present.

[0022] When water is mixed into the electrolyte 6, fluorine in the electrolyte 6 removes hydrogen from water molecules to generate hydrogen fluoride. The generation of hydrogen fluoride is a factor that inhibits the durability performance originally expected of the resin member 10. This is because glass, which is generally a highly chemically stable compound, is decomposed into hydrogen fluoride. Therefore, when the hydrogen fluoride generated in the electrolyte 6 comes into contact with the inner exposed surface 11 of the resin member 10, the glass filler in the resin member 10 is attacked by the hydrogen fluoride. As the glass filler elutes from the resin member 10, the linear expansion coefficient and elastic modulus of the resin member 10 approach those of the original base resin. This results in earlier deterioration of the resin member 10 than expected.

[0023] However, in this embodiment, the Group 2 element added to the glass filler prevents the glass from being dissolved by hydrogen fluoride. This is because hydrogen fluoride attacks Group 2 elements preferentially over silicon oxide. In other words, the Group 2 element traps hydrogen fluoride and protects silicon oxide from attack by hydrogen fluoride. The Group 2 element itself becomes a fluoride by trapping hydrogen fluoride. Water is also produced during this process.

[0024] Therefore, the presence of the Group 2 element suppresses dissolution of the glass by hydrogen fluoride, thereby maintaining the durability of the resin member 10 as originally intended. Therefore, in the battery 1 of this embodiment, even if moisture penetrates into the case 2, there is almost no decrease in the durability of the resin member 10. Therefore, in this embodiment, the insulation and sealing properties between the lid body 5 and the terminal member 7 provided by the resin member 10 are maintained for a long period of time.

[0025] The amount of Group 2 element in the glass filler is preferably such that the atomic ratio of Group 2 element to silicon in the component elements is 0.12% or more and 65% or less. This is the total amount when multiple types of Group 2 elements (e.g., magnesium and calcium) are contained. If the amount of Group 2 element is insufficient, the effect of improving durability will be insufficient. If the amount of Group 2 element is excessive, it will be difficult to mold into short fibers, which will reduce the productivity of the glass.

[0026] When at least a portion of the Group 2 element is magnesium, its content relative to silicon is preferably 0.1% to 25% by mass, and when at least a portion of the Group 2 element is calcium, its content relative to silicon is preferably 0.17% to 81% by mass.

[0027] The inventors of the present invention have conducted tests to evaluate the durability of the resin member 10 of this embodiment, and the results thereof will be described below. The evaluation results for which will be described here are for the following two types. Erosion depth after durability test Change in elastic modulus before and after durability

[0028] The following two types of filled resins were each cut into 1 mm thick plate samples and subjected to these tests. (Example) Base resin: PPS resin Glass filler material: Magnesium blend (1.9% to 25% by mass relative to silicon) Glass filler shape: Short fiber (10 μm diameter x 0.3 mm length) (Comparative Example) Base resin: Same as above Glass filler material: No Group 2 elements Glass filler shape: Same as above

[0029] In the test, samples of these resin members were immersed in an electrolyte solution under the following conditions. Electrolyte solvent type: Ethylene carbonate and diethyl carbonate mixture (mass ratio 1:1) Electrolyte type, concentration: Lithium hexafluorophosphate, 1 mol / L Water content: 1200 ppm (equivalent to 25 years after the battery was first used) Electrolyte temperature during immersion: 25℃, 65℃, 80℃ Soaking time: 20 days

[0030] In the evaluation of corrosion depth after durability testing, the corrosion state of the glass filler in the sample after immersion was evaluated. Specifically, the maximum depth from the surface at which complete disappearance of the glass filler was observed in the cross section of the sample was evaluated. The surface of the sample corresponds to the internal exposed surface 11 of the resin member 10. This evaluation was performed by observing the cross section of the sample with a scanning electron microscope. The results are shown in Figure 3. Figure 3 shows the maximum corrosion depth (vertical axis) after immersion for each of the three levels of immersion temperature, comparing the example and comparative example.

[0031] The following can be said from Figure 3. Overall, the higher the immersion temperature, the deeper the corrosion will progress. Under all temperature conditions, the corrosion depth was smaller in the Example than in the Comparative Example. Note that the corrosion depth in the Example immersed at 25°C was zero.

[0032] 3, it can be seen that in the Examples containing magnesium, corrosion of the glass filler was suppressed under all temperature conditions compared to the Comparative Examples containing no magnesium. This is believed to be because the magnesium added to the Examples suppressed dissolution of the glass by hydrogen fluoride.

[0033] In evaluating the change in elastic modulus before and after durability testing, the degree to which the elastic modulus of the sample after immersion decreased compared to the elastic modulus of the sample before immersion was evaluated. To do this, the elastic modulus of each sample before and after immersion was measured, and the rate of decrease was calculated. The results are shown in Figure 4. The vertical axis in Figure 4 shows the ratio of the decrease in the elastic modulus of the sample after immersion from the reference elastic modulus of the sample before immersion as a negative value. The further down in Figure 4, the more significant the decrease in elastic modulus due to immersion. Figure 4 also shows the results for the Example and Comparative Example for each of three levels of immersion temperature.

[0034] The following can be said from Figure 4. Overall, the higher the immersion temperature, the greater the decrease in elastic modulus due to immersion. Under all temperature conditions, the degree of decrease in elastic modulus is smaller in the examples than in the comparative examples.

[0035] As can be seen from Figure 4, the Examples containing magnesium suppressed the decrease in elastic modulus due to immersion under all temperature conditions compared to the Comparative Examples not containing magnesium. This is believed to be because the magnesium added to the Examples suppressed the dissolution of the glass by hydrogen fluoride. In other words, while the Comparative Examples lost a significant amount of glass filler due to immersion, the Examples maintained a significant amount of glass filler even after immersion.

[0036] The inventors also conducted further tests on the penetration of fluorine by immersing the resin member 10 of this embodiment in an electrolyte solution. For this test, resins containing glass fillers with the four compositions shown in Table 1 were used as samples. The shape of the samples was the same as that described above. In Table 1, the values ​​in the "mass %" column indicate the mass ratio of each element to the mass of the entire glass, including oxygen, etc. The values ​​in the "mass ratio (%)" column indicate the relative mass ratio of only each element in the glass. The values ​​in the "atomic number ratio (%)" column are mass ratio values ​​converted to atomic number ratios based on the atomic weight of each element.

[0037] [Table 1]

[0038] Of the four samples in Table 1, Sample A contains only calcium as a Group 2 element and does not contain magnesium. Samples B to D contain both magnesium and calcium as Group 2 elements. Of these, Sample B has a calcium content near the upper limit of the aforementioned desirable range in terms of mass ratio, and the total content of magnesium and calcium is near the upper limit of the aforementioned desirable range in terms of atomic ratio. Sample C has a magnesium content near the upper limit of the aforementioned desirable range in terms of mass ratio, and the magnesium content and calcium content are approximately equal in terms of atomic ratio. Compared to Sample C, Sample D has a reduced magnesium content and an increased calcium content while maintaining an approximately equal total atomic ratio of the magnesium content and calcium content.

[0039] These four types of samples were immersed in an electrolyte, and the penetration depth of fluorine into the samples after immersion was measured. Multiple samples of each type were used for the measurement. The electrolyte used was the same as that described in the explanation of the test above. A scanning electron microscope equipped with an X-ray elemental analyzer was used to measure the penetration depth of fluorine. That is, while observing the cross section of the sample after immersion with the electron microscope, the fluorine distribution was mapped with the X-ray elemental analyzer, and the maximum depth from the surface at which the presence of fluorine was detected was measured. This is a different indicator from the "erosion depth" mentioned above, and is generally a larger value than the "erosion depth" under the same conditions.

[0040] Figure 5 is a graph showing the relationship between the measured fluorine penetration depth and the temperature of the electrolyte during immersion. The vertical axis in Figure 5 represents penetration depth, with the lower the value, the less penetration there is, indicating better resistance to the electrolyte. For the measurements in Figure 5, the immersion temperature was set to four levels: 25°C, 40°C, 60°C, and 80°C. The immersion time was 20 days. Five samples for each temperature level and sample type were immersed and then measured, and the maximum penetration depth for each sample was recorded.

[0041] Figure 5 shows that the higher the immersion temperature, the greater the penetration depth of fluorine. Furthermore, of the four types of samples, sample A, which does not contain magnesium, tends to have a greater penetration depth than samples B to D, which contain magnesium. This suggests that, among the Group 2 elements, magnesium is even more effective than the other Group 2 elements. However, since fluorine penetrates so deeply into samples that do not contain any Group 2 elements at all that it does not fit within the range of the vertical axis of Figure 5, it can be said that fluorine penetration is suppressed even in sample A by comparison.

[0042] As described above in detail, according to the present embodiment, in a battery 1 in which the electrolyte solution 6 contains fluorine, a composite material containing a glass filler to which a Group 2 element is added is used as the resin member 10 that seals the through-hole 9 through which the terminal member 7 passes. This suppresses deterioration of the resin member 10 due to moisture contamination in the electrolyte solution 6. In other words, the addition of a Group 2 element to the glass filler improves the durability of the resin member 10. Thus, a lithium-ion battery 1 in which deterioration of the resin member 10 is not accelerated even when a nonaqueous electrolyte solution 6 containing fluorine is used is realized.

[0043] The present embodiment and examples are merely illustrative and do not limit the presently disclosed technology in any way. Therefore, the presently disclosed technology can naturally be improved and modified in various ways without departing from the spirit and scope of the presently disclosed technology. For example, in the above embodiment, the battery 1 to which the presently disclosed technology is applied is a flat prismatic battery as shown in FIG. 1 . However, the presently disclosed technology is not limited to this, and can also be applied to batteries with other shapes, such as a cylindrical shape.

[0044] In the above embodiment, the resin member 10 to which the technology disclosed herein is applied is the one that insulates between the terminal member 7 and the lid 5. However, the technology disclosed herein is not limited to this, and can also be applied to resin materials in other locations in the battery. Examples of resin materials in other locations include sealing resins when sealing a liquid inlet with a resin material. Furthermore, the box body 4 of the case 2 may be an insulating material, and therefore the box body 4 itself can be made of a resin member to which the technology disclosed herein is applied. Furthermore, in the case of a cylindrical battery, the resin member disclosed herein can also be used as a sealing resin between a cylindrical case and a circular lid.

[0045] In the above embodiment, the terminal member 7 and the external terminal 8 are connected outside the case 2. However, the terminal member 7 and the external terminal 8 may be integral. Inside the case 2, one end of the terminal member 7 is not limited to being directly connected to the electrode body 3, but may be indirectly connected via another current collecting member. [Explanation of symbols]

[0046] 1 battery 6 electrolyte 2 Case 7 Terminal material 3 Electrode body 10 Resin member 4 Box 11 Internal exposed surface 5 Lid

Claims

1. A lithium ion battery having a case, an electrode assembly and an electrolyte solution housed inside the case, and a resin member fixed to the case and having an inner exposed surface exposed inside the case, the electrolyte is a non-aqueous electrolyte containing fluorine, the resin member contains a glass filler formed of glass containing silicon oxide as a main component and a Group 2 element added thereto; A lithium ion battery, wherein the atomic ratio of the Group 2 element to silicon in the component elements of the glass filler is 0.12% or more and 65% or less.

2. 10. The lithium ion battery of claim 1, At least a portion of the Group 2 elements is magnesium, A lithium ion battery, wherein the mass ratio of magnesium to silicon among the component elements of the glass filler is 0.1% or more and 25% or less.

3. 10. The lithium ion battery of claim 1, At least a portion of the Group 2 elements is calcium, A lithium ion battery, wherein the mass ratio of calcium to silicon among the component elements of the glass filler is 0.17% or more and 81% or less.

4. 4. The lithium ion battery according to claim 1, a terminal member connected to the electrode body inside the case, penetrating the case, and partially exposed to the outside of the case; The resin member insulates the case from the terminal member.

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