JP2015153727A - lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery superior in cycle durability.SOLUTION: A lithium ion secondary battery comprises a housing 500, a wind-type electrode body 400 and an electrolytic solution which are included in the housing 500, and a positive electrode collector terminal 120 and a negative electrode collector terminal 220 which are connected to the electrode body 400. The electrode body 400 has a bottom-end part BT immersed in the electrolytic solution. Supposing that the distance from the bottom-end part BT of the electrode body 400 to a top-end part TP of the electrode body 400 in a height direction of the battery is X, the distance from the bottom-end part BT to the liquid level EL of the electrolytic solution is Y, and at least one distance of the distance from the bottom-end part BT to a connection part 120a of the positive electrode collector terminal 120 and the electrode body 400, and the distance from the bottom-end part BT to a connection part 220a of the negative electrode collector terminal 220 and the electrode body 400 is Z, X, Y and Z satisfies the following conditions: 0.11≤Y/X≤0.33; and 0≤Z/X≤0.39.

Description

  The present invention relates to a lithium ion secondary battery.

  Japanese Patent Laying-Open No. 2013-232425 (Patent Document 1) discloses a non-aqueous secondary battery in which a wound electrode body is housed in a case together with a non-aqueous electrolyte.

JP2013-232425A

In the lithium ion secondary battery, the electrolytic solution is held by the electrode body and functions as a medium that promotes the movement of Li ⁺ between the positive and negative electrodes. However, when the charge / discharge cycle is repeated, the electrolyte solution should be held between the positive and negative electrodes because the electrolyte solution flows out of the electrode body as the electrode body expands and contracts, or the electrolyte solution decomposes. Insufficient quantity may occur. Such a phenomenon is generally called “liquid drainage” and is considered to be one of the factors affecting the cycle life of the battery.

  As a measure against the liquid withering, it is conceivable that an excessive amount of the electrolytic solution is accommodated in the battery in advance and the electrode body is immersed in the electrolytic solution to some extent. This prevents the electrolyte solution from flowing out of the electrode body, and can compensate for a shortage of the electrolyte amount in the electrode body. However, in applications that are expected to be used for a long time, such as in-vehicle applications, further improvement in cycle durability is desired.

In view of this, the present inventor conducted a detailed investigation of the cause of the capacity decrease associated with the charge / discharge cycle in a battery having a configuration in which the wound electrode body was immersed in the electrolytic solution, and the portion of the electrode body immersed in the electrolytic solution. In the negative electrode, it was newly found that the Li ⁺ acceptability was locally reduced, which contributed to the capacity reduction.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a lithium ion secondary battery having excellent cycle durability.

The inventor measured the temperature distribution in the battery during charging / discharging by thermography. As a result, the temperature of the portion of the wound electrode body that was immersed in the electrolyte solution was locally low, and this was the Li ⁺ acceptance. It was found that it was the cause of sex decline. The inventor has further researched based on this finding, and has found a battery configuration capable of efficiently relaxing the temperature distribution generated in the battery being charged and discharged, and has completed the present invention. That is, the lithium ion secondary battery of the present invention has the following configuration.

  (1) A lithium ion secondary battery includes a housing, a wound electrode body and an electrolytic solution built in the housing, a positive current collector terminal and a negative current collector terminal connected to the electrode body, Is provided. Here, the lower end of the electrode body is immersed in the electrolytic solution.

  In the height direction of the battery, X is the distance from the lower end of the electrode body to the upper end of the electrode body, Y is the distance from the lower end to the liquid surface of the electrolyte, and the positive current collector terminal from the lower end Of at least one of the distance from the lower end to the connection between the negative electrode current collector terminal and the electrode body is 0.11 ≦ Y / The relationship of X ≦ 0.33 and 0 ≦ Z / X ≦ 0.39 is satisfied.

  In a lithium ion secondary battery provided with said structure, the temperature distribution which arises in the electrode body during charging / discharging is relieve | moderated, and the outstanding cycle durability can be shown. The reason is presumed as follows.

The reason why the temperature of the portion of the electrode body that is immersed in the electrolytic solution is considered to be that the heat of the electrode body is taken away by the electrolytic solution. Then, it is considered that the reaction field is lowered by deprivation and local Li ⁺ acceptability is lowered.

  In the above configuration, X is an index representing the volume of the electrode body, and Y is an index representing the volume of the portion of the electrode body that is immersed in the electrolytic solution. Therefore, Y / X can be regarded as an index representing the proportion of the electrode body that is immersed in the electrolyte.

Here, according to the experimental results obtained by the present inventors, when Y / X exceeds 0.33, the temperature difference (hereinafter referred to as “temperature unevenness”) generated in the height direction of the electrode body due to the heat removal action of the electrolyte solution. And the Li ⁺ acceptability decreases in the lower part of the electrode body. On the other hand, when Y / X is less than 0.11, sufficient cycle durability cannot be exhibited due to liquid erosion. Therefore, in the present invention, Y / X is restricted to a range of 0.11 ≦ Y / X ≦ 0.33.

  Furthermore, in the present invention, in addition to the regulation of the liquid level, the portion of the electrode body that is immersed in the electrolytic solution is heated using Joule heat and heat conduction of the current collecting terminal connected to the electrode body. That is, by providing a connecting portion between the current collecting terminal and the electrode body in a lower portion of the electrode body, Joule heat generated in the current collecting terminal is conducted to the lower portion of the electrode body through the connecting portion. As a result, the portion of the electrode body that has been immersed in the electrolyte and the electrolyte are heated, and in combination with the effect of suppressing heat removal due to the restriction of the height of the liquid surface, temperature unevenness that occurs in the electrode during charge / discharge Is significantly reduced, and the cycle durability is remarkably improved.

  Here, according to the experimental results obtained by the present inventors, the distance from the lower end of the electrode body to the connection portion between the positive electrode current collector terminal and the electrode body, and the connection between the lower end portion and the negative electrode current collector terminal and the electrode body. When at least one of the distances to the part is Z, Z / X is restricted to a range of 0 ≦ Z / X ≦ 0.39, thereby preventing temperature unevenness generated in the electrode body during charging and discharging. Can be significantly reduced.

  Here, the “connecting portion” indicates a portion where the positive electrode current collecting terminal and the negative electrode current collecting terminal are electrically connected to the electrode body, and specifically indicates, for example, a welding portion, a welding portion, or the like. Further, in the present specification, the positive current collecting terminal and the negative current collecting terminal may be collectively referred to simply as “current collecting terminal” or “each current collecting terminal”.

  The “battery height direction” indicates the height direction in a posture in which the lithium ion secondary battery should be normally used.

  (2) It is preferable that Z / X satisfies the relationship of 0 ≦ Z / X ≦ 0.39 at least at the connection portion between the positive electrode current collecting terminal and the electrode body.

  In general, aluminum (Al) is used as the material for the positive electrode current collector terminal, and copper (Cu) is used as the material for the negative electrode current collector terminal. Here, Al is a material having a lower thermal conductivity than Cu. In other words, it can be said that the positive electrode current collector terminal has a larger amount of Joule heat generated by charging and discharging than the negative electrode current collector terminal. Therefore, when at least the positive electrode current collecting terminal satisfies the above relationship, the lower part of the electrode body can be efficiently heated.

  More preferably, both the positive electrode current collector terminal and the negative electrode current collector terminal satisfy the relationship of 0 ≦ Z / X ≦ 0.39. This is because when both the positive electrode current collector terminal and the negative electrode current collector terminal satisfy the above relationship, the lower part of the electrode body can be more efficiently heated, and the cycle durability is further improved.

  (3) Z / X preferably satisfies 0 ≦ Z / X ≦ 0.28. Thereby, the temperature nonuniformity which arises in an electrode body becomes still smaller, and cycling durability improves further. From the same viewpoint, it is more preferable that Z / X satisfies 0 ≦ Z / X ≦ 0.17.

  (4) The wound electrode body has a connection portion with a current collecting terminal at both ends of the winding shaft. It is preferable that they are arranged so as to be in a direction substantially orthogonal to the vertical direction.

  By adopting such a configuration, it is possible to efficiently extract electricity from the electrode body that is a power generation element, and to provide a battery that is excellent in high-rate performance.

  According to the present invention, a lithium ion secondary battery excellent in cycle durability is provided.

It is typical sectional drawing which shows an example of a structure of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is typical sectional drawing which shows the structure of the modification of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a schematic diagram which shows an example of a structure of the winding type electrode body concerning one Embodiment of this invention. It is a graph which shows an example of the influence which the ratio of the part immersed in electrolyte solution has on cycle durability among electrode bodies. It is a graph which shows an example of the influence which the height of the connection position of a current collection terminal has on cycle durability. It is a graph which shows an example of the relationship between the ratio of the part immersed in electrolyte solution among electrode bodies, the height of the connection position of a current collection terminal, and cycle durability.

  Hereinafter, an embodiment of the present invention (hereinafter also referred to as “the present embodiment”) will be described in detail, but the present embodiment is not limited thereto.

[Lithium ion secondary battery]
FIG. 1 is a schematic cross-sectional view showing an example of the configuration of the lithium ion secondary battery of the present embodiment. Referring to FIG. 1, battery 1000 includes a housing 500. The housing 500 has a bottomed rectangular housing body 500a and a lid 500b. The material of the housing 500 is, for example, Al or an Al alloy.

  The casing 500 contains a wound electrode body 400 and an electrolytic solution (not shown). Inside the housing 500, the electrode body 400 is disposed such that the direction of the winding axis AW is substantially perpendicular to the height direction of the battery 1000. The lower end portion BT of the electrode body 400 is immersed in the electrolytic solution.

  FIG. 3 is a schematic diagram showing a configuration of a wound electrode body 400. Referring to FIG. 3, electrode body 400 is wound so that positive electrode plate 100 and negative electrode plate 200 face each other with separator 300 interposed therebetween. Although the electrode body 400 shown in FIG. 3 has a flat shape, the electrode body 400 does not necessarily have a flat shape as long as it is a wound electrode body. Even when the electrode body 400 has a flat shape, the thickness and the aspect ratio (the dimensional ratio in the height direction and the winding axis direction) of the electrode body 400 are not particularly limited.

  The positive electrode plate 100 is a long belt-like sheet member, and a positive electrode mixture portion 100a in which a positive electrode mixture is fixed on a current collector core material (for example, an Al foil), and a positive electrode non-combination where the current collector core material is exposed. Material part 100b. In the positive electrode plate 100, the positive electrode unmixed material portion 100 b is continuously formed on one side of the positive electrode plate 100 in the short direction (width direction). In the electrode body 400, the positive electrode unmixed material portion 100b is disposed so as to be exposed from one end portion of the winding shaft AW.

  The negative electrode plate 200 is also a long belt-like sheet member, and a negative electrode composite portion 200a in which the negative electrode composite material is fixed onto a current collector core material (for example, Cu foil), and a negative electrode non-bonded material in which the current collector core material is exposed. And a material part 200b. In the negative electrode plate 200, the negative electrode unmixed material portion 200 b is continuously formed on one side of the negative electrode plate 200 in the short direction (width direction). In the electrode body 400, the negative electrode unmixed material portion 200b is arranged so as to be exposed from an end portion different from the end portion where the positive electrode non-mixed material portion 100b is exposed on the winding axis AW.

  Referring again to FIG. 1, positive electrode unmixed material portion 100 b exposed from electrode body 400 is welded to positive electrode current collector terminal 120 at connection portion 120 a so as to be bundled by positive electrode current collector terminal 120. Further, the negative electrode unmixed material portion 200 b exposed from the electrode body 400 is welded to the negative electrode current collector terminal 220 at the connection portion 220 a so as to be bundled by the negative electrode current collector terminal 220. Here, it is preferable that the connecting portions 120a and 220a are provided at the tip portions of the current collecting terminals. This is to generate efficient heat conduction.

  Furthermore, the positive electrode current collecting terminal 120 is connected to a positive electrode external terminal 140 provided on the lid 500b. Similarly, the negative electrode current collecting terminal 220 is connected to a negative electrode external terminal 240 provided on the lid 500b.

  In the height direction of the battery 1000, when the distance from the lower end BT to the upper end TP of the electrode body 400 is X and the distance from the lower end BT to the electrolyte surface EL is Y, Y / X is The relationship of 0.11 ≦ Y / X ≦ 0.33 is satisfied. Thereby, it is possible to suppress the heat removal action by the electrolytic solution while preventing the liquid from withstanding.

  Furthermore, in battery 1000, when the distance from lower end portion BT of electrode body 400 to connecting portion 120a between positive electrode current collector terminal 120 and electrode body 400 is Z, Z / X is 0 ≦ Z / X ≦ 0.39. Satisfies the relationship. Further, when the distance from the lower end portion BT to the connecting portion 220a between the negative electrode current collector terminal 220 and the electrode body 400 is Z, the relationship that Z / X satisfies 0 ≦ Z / X ≦ 0.39 is satisfied. . Thereby, Joule heat generated at each current collecting terminal at the time of charging / discharging is transmitted to the lower part of the electrode body 400 and the electrolytic solution through each current collecting terminal, and the part can be heated.

  In this way, by controlling the height of the liquid surface EL and the height of the connection position between the current collector terminal and the electrode body 400, the temperature of the portion of the electrode body 400 immersed in the electrolytic solution is suppressed. Can do. That is, in the battery 1000, the temperature unevenness of the electrode body 400 during charge / discharge is alleviated, and the charge / discharge reaction can be allowed to proceed substantially uniformly over the entire area of the electrode body 400. Therefore, the battery 1000 can exhibit excellent cycle durability.

Here, a modification of the present embodiment will be described.
[Modification]
FIG. 2 is a schematic cross-sectional view showing a configuration of a modified example of the present embodiment. In the present embodiment, as in the battery 2000 shown in FIG. 2, a plurality of connection portions between the current collecting terminals and the electrode body 400 may be provided. In this case, in the height direction of the battery 2000, the distance from the lower end portion BT to the connection portions 120b and 220b located closest is assumed to be Z.

  In the battery 2000, the connection parts 120b and 220b are located below the liquid level EL of the electrolytic solution. That is, the connection parts 120b and 220b are located in the electrolytic solution. As a result, not only the electrode body 400 but also the electrolytic solution can be directly heated. Therefore, the temperature unevenness generated in the electrode body 400 can be efficiently reduced.

Hereinafter, each member constituting the battery 1000 will be described.
<Positive electrode plate>
The positive electrode plate 100 is formed, for example, by forming a positive electrode mixture portion 100a by coating and drying a positive electrode mixture slurry containing a positive electrode active material, a conductive material, a binder, a solvent, and the like on a current collector core material. The positive electrode mixture portion 100a can be compressed to adjust its thickness.

The positive electrode active material may be any material that can act as the positive electrode of the lithium ion secondary battery. For example, LiCoO ₂ , LiNiO ₂ , LiNi _a Co _b O ₂ (where a + b = 1, 0 <a <1, 0 <b <1), LiMnO ₂ , LiMn ₂ O ₄ , LiNi _a Co _b A positive electrode active material such as Mn _c O ₂ (where a + b + c = 1, 0 <a <1, 0 <b <1, 0 <c <1) or LiFePO ₄ can be used. These positive electrode active materials may be used independently and may use 2 or more types together. The content rate of the positive electrode active material in a positive electrode compound material is about 80-99 mass%, for example, Preferably it is about 85-95 mass%.

  As the conductive material, for example, acetylene black (AB) can be used, and as the binder, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), or the like can be used. In addition, as a solvent used in the case of slurrying, N-methyl-2-pyrrolidone (NMP) etc. are suitable, for example.

<Negative electrode plate>
The negative electrode plate 200 was formed by applying a negative electrode mixture slurry containing, for example, a negative electrode active material, a thickener, a binder, a solvent, and the like onto a current collector core and drying, thereby forming a negative electrode mixture portion 200a. Then, it can produce by compressing the negative electrode compound-material part 200a and adjusting the thickness.

  The negative electrode active material should just be what can act as a negative electrode of a lithium ion secondary battery. For example, carbon-based negative electrode active materials such as graphite and coke, and alloy-based negative electrode active materials such as silicon and tin can be used. These negative electrode active materials may be used independently and may use 2 or more types together. The content rate of the negative electrode active material in a negative electrode compound material is about 90-99 mass%, for example, Preferably it is about 95-99 mass%.

  As the thickening material, for example, carboxymethyl cellulose (CMC) or the like can be used, and as the binding material, styrene butadiene rubber (SBR) or the like can be used. In addition, as a solvent used in the case of slurrying, water etc. are suitable, for example.

<Separator>
Separator 300 allows Li ⁺ to pass therethrough and prevents electrical contact between positive electrode plate 100 and negative electrode plate 200. The separator 300 is preferably a microporous film made of a polyolefin-based material from the viewpoint of mechanical strength and chemical stability. For example, a microporous film such as polyethylene (PE) or polypropylene (PP) is suitable. The thickness of the separator 300 can be about 5-40 micrometers, for example. What is necessary is just to adjust suitably the hole diameter and porosity of the separator 300 so that the air permeability may become a desired value.

<Electrolyte>
The electrolytic solution is obtained by dissolving a solute (Li salt) in an aprotic solvent. Examples of the aprotic solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (GBL) and vinylene carbonate (VC), and dimethyl carbonate (DMC). ), Chain carbonates such as ethyl methyl carbonate (EMC) and diethyl carbonate (DEC). These aprotic solvents can be used in an appropriate combination of two or more from the viewpoint of electrical conductivity and electrochemical stability. In particular, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate, and the volume ratio of the cyclic carbonate to the chain carbonate is preferably about 1: 9 to 5: 5. If a specific example is given, 3 types, EC, EMC, and DMC, can be mixed and used, for example.

As the Li salt, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO _{3 and the} like can be used. Moreover, you may use 2 or more types together about these Li salts. The concentration of the Li salt in the electrolytic solution is not particularly limited, but is preferably about 0.5 to 2.0 mol / L from the viewpoint of discharge characteristics and storage characteristics.

  Hereinafter, although this embodiment is described in detail using an example, this embodiment is not limited to these.

[Production of lithium ion secondary battery]
Various lithium ion secondary batteries were manufactured by changing the height of the electrolyte surface and the height of the connection position of the current collector terminal as follows, and the cycle durability was evaluated.

  In this experiment, the height from the lower end portion BT of the electrode body 400 to the connecting portion 120a of the positive electrode current collecting terminal 120 and the height from the connecting portion 220a of the negative electrode current collecting terminal 220 are the same.

<Example 1>
(Preparation of positive electrode plate)
A positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), a conductive additive (AB), and a binder (PVdF) are mixed with LiNi _1/3 Co _1/3 Mn _1/3. The mixture was mixed so that O ₂ : AB: PVdF = 93: 4: 3 (mass ratio), and further kneaded in NMP to obtain a positive electrode mixture slurry. Next, using a die coater, the positive electrode mixture slurry was coated on both main surfaces of the long strip-shaped Al foil (current collector core material) and dried to form the positive electrode mixture portion 100a. Furthermore, the positive electrode plate 100 was obtained by rolling the positive electrode mixture part 100a using a roll mill. The positive electrode plate 100 had a positive electrode non-mixed material portion 100b continuously on one side in the short direction (width direction).

(Preparation of negative electrode plate)
A negative electrode active material (natural graphite powder), a thickener (CMC), and a binder (SBR) are mixed so that natural graphite: CMC: SBR = 98: 1: 1 (mass ratio). Furthermore, the negative electrode mixture slurry was obtained by kneading in water. Next, using a die coater, the negative electrode mixture slurry was applied on both main surfaces of a long strip of Cu foil (current collector core material) and dried to form the negative electrode mixture portion 200a. Furthermore, the negative electrode plate 200 was obtained by rolling the negative electrode mixture part 200a using a roll mill. The negative electrode plate 200 had the negative electrode non-mixing material part 200b continuously on one side in the width direction.

(Preparation of electrolyte)
EC, EMC, and DMC were mixed so that EC: EMC: DMC = 3: 4: 3 (volume ratio) to obtain a mixed solvent. Next, an electrolytic solution was prepared by dissolving LiPF ₆ (1.0 mol / L) in this mixed solvent. The density of this electrolytic solution was 1.23 g / cm ³ .

(assembly)
A separator 300 having a three-layer structure of PP / PE / PP was prepared. Referring to FIG. 3, winding was performed so that positive electrode plate 100 and negative electrode plate 200 face each other with separator 300 interposed therebetween, so that an elliptical wound body was obtained. Next, a wound electrode body 400 was obtained by pressing the wound body into a flat shape using a flat plate press. At this time, the length dimension of the electrode body 400 in the height direction [dimension to be the distance (X) in the finished battery] was 90 mm.

  With reference to FIG. 1, a housing body 500a and a lid body 500b provided with a current collecting terminal and an external terminal in advance were prepared.

  Next, the positive electrode current collector terminal 120 made of Al is welded to the positive electrode non-mixed material portion 100b so that the positive electrode non-mixed material portion 100b exposed from one end portion of the winding axis AW of the electrode body 400 is bundled. Connected. Similarly, the negative electrode current collector terminal 220 made of Cu is welded and electrically connected to the negative electrode non-mixed material portion 200b so as to bundle the negative electrode non-mixed material portion 200b exposed from the other end of the winding shaft AW. . At this time, the distance (Z) from the lower end portion BT of the electrode body 400 to the connection portions 120a and 220a of the current collecting terminals was set to 35 mm.

  Next, the electrode body 400 was inserted into the housing body 500a, and the housing body 500a and the lid body 500b were joined by laser welding. Further, the electrolytic solution (142 g) prepared above was injected from an injection hole (not shown) provided in the lid 500b. After the injection, the distance (Y) from the lower end BT of the electrode body 400 to the liquid level EL was 30 mm.

  The liquid injection hole was sealed with a sealing plug to obtain a prismatic lithium ion secondary battery (design capacity: 25 Ah).

<Examples 2-8 and Comparative Examples 1-5>
As shown in Table 1, the distance (Y) is changed by changing the injection amount of the electrolytic solution, and the distance (Z) is changed by changing the shape (length dimension) and welding position of the current collecting terminal. Except this, using the same conditions as in Example 1, prismatic lithium ion secondary batteries according to Examples 2 to 8 and Comparative Examples 1 to 5 were obtained.

[Evaluation]
Each battery obtained above was evaluated as follows. In the following description, “CC” represents a constant current, and “CV” represents a constant voltage.

(Measurement of initial capacity)
For each battery, CC-CV charge (CC current: 25 A, CV voltage: 4.1 V, total charge time: 2 hours) and CC-CV discharge (CC current: 25 A, CV voltage) in a 25 ° C. environment. : 3.0 V, total discharge time: 2 hours), and the initial capacity (discharge capacity) was measured.

(Cycle durability test)
In a thermostat set to 0 ° C., a charge / discharge cycle of 1000 cyc was performed with one cycle being the sequential execution of the operations [1] to [4] for each battery.

[1] Pulse charging (current value: 130 A, time: 17 seconds)
[2] Rest (time: 10 minutes)
[3] Pulse discharge (current value: 130 A, time: 30 seconds)
[4] Rest (time: 10 minutes).

  And after 1000 cyc execution, the capacity | capacitance after a cycle was measured on the same conditions as an initial stage capacity | capacitance, and the capacity | capacitance maintenance factor was computed by remove | dividing a post-cycle capacity | capacitance by an initial stage capacity | capacitance. The results are shown in Table 1.

<Results and discussion>
(1) Effect of liquid level FIG. 4 shows the ratio of the distance (Y) from the lower end BT to the liquid level EL and the distance (X) from the lower end BT to the upper end TP, that is, the electrode body. It is a graph which shows the influence which the parameter | index (Y / X) showing the ratio of the part immersed in electrolyte solution among 400 has on a capacity | capacitance maintenance factor. In FIG. 4, the index (Z / X) representing the height of the connection position of the current collecting terminal is fixed at 0.39.

  As can be seen from FIG. 4, in the range where Y / X is 0.22 to 0.44, the capacity retention rate is improved as Y / X becomes smaller (that is, the liquid level EL becomes lower). This is presumably because, in the electrode body 400, the amount of heat removal decreases and the temperature unevenness is suppressed by reducing the contact volume with the electrolytic solution.

  However, when Y / X is less than 0.11, the capacity retention rate decreases rapidly. This is considered to be because the progress of liquid withering was accelerated by the liquid level EL becoming excessively low. Therefore, from this result, Y / X needs to be at least 0.11 or more.

(2) About the influence of the height of the connection position of the current collector terminal FIG. 5 shows the distance (Z) from the lower end portion BT to the connection portions 120a, 220a between the current collector terminals and the electrode body 400, and the lower end portion BT. It is a graph which shows the influence which the ratio (Z / X) showing the ratio with the distance (X) to upper end part TP, ie, the height of the connection position of a current collection terminal, has on the capacity maintenance rate. In FIG. 5, the index (Y / X) indicating the ratio of the portion of the electrode body that is immersed in the electrolytic solution is fixed to 0.22.

  As can be seen from FIG. 5, the smaller the Z / X is, that is, the lower the connecting portions 120a and 220a between the current collector terminals and the electrode body 400 in the height direction of the battery 1000, the higher the capacity retention rate. ing. This is presumably because the lower portions of the electrode body 400 and the electrolytic solution are heated by the lower positions of the connecting portions 120a and 220a, and temperature unevenness is suppressed. Therefore, Z / X is preferably as small as possible, and most preferably 0 (zero).

  Further, when Z / X is reduced from 0.50 to 0.39, the capacity retention ratio is greatly improved, and the effect is slightly reduced with 0.39 as a boundary. Therefore, Z / X needs to be at least 0.39 or less.

(3) Regarding the synergistic effect of the height of the liquid level and the height of the connection position of the current collecting terminal FIG. 6 shows an index (Y / X) indicating the ratio of the portion of the electrode body immersed in the electrolyte, and the current collector. It is a graph which shows transition of the capacity | capacitance maintenance factor at the time of changing both of the parameter | index (Z / X) showing the height of the connection position of an electrical terminal. The dotted line in FIG. 6 is attached in an auxiliary manner so that the transition tendency of the capacity maintenance rate can be easily understood.

  FIG. 6 shows that the capacity retention ratio is remarkably improved in the region where 0.11 ≦ Y / X ≦ 0.33 and 0 ≦ Z / X ≦ 0.39. The reason for such a result is that the heat removal suppression effect by reducing the height of the liquid surface EL and the heating effect by reducing the height of the connection portions 120a and 220a of the current collecting terminal are synergistic. It is thought that.

From the above experimental results, it can be said that the following items were proved.
That is, it includes a housing 500, a wound electrode body 400 and an electrolytic solution built in the housing 500, and a positive electrode current collecting terminal 120 and a negative electrode current collecting terminal 220 connected to the electrode body 400. The lower end portion BT of the body 400 is immersed in the electrolyte, and in the height direction of the battery, the distance from the lower end portion BT of the electrode body 400 to the upper end portion TP of the electrode body 400 is X, and the electrolyte solution from the lower end portion BT Y is the distance to the liquid surface EL, the distance from the lower end BT to the connecting portion 120a between the positive electrode current collecting terminal 120 and the electrode body 400, and the connecting portion between the lower end portion BT and the negative electrode current collecting terminal 220 and the electrode body 400. A lithium ion secondary battery satisfying a relationship of 0.11 ≦ Y / X ≦ 0.33 and 0 ≦ Z / X ≦ 0.39, where at least one of the distances up to 220a is Z, To cycle durability It is.

  Although the present embodiment and examples have been described as above, the embodiment and examples disclosed this time are illustrative in all points and are not restrictive. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 100 Positive electrode plate, 100a Positive electrode mixture part, 100b Positive electrode non-mixing part, 120 Positive electrode current collection terminal, 120a, 120b, 220a, 220b Connection part, 140 Positive electrode external terminal, 200 Negative electrode plate, 200a Negative electrode mixture part, 200b Negative electrode Non-mixed material part, 220 negative electrode current collector terminal, 240 negative electrode external terminal, 300 separator, 400 electrode body, TP upper end part, BT lower end part, 500 housing, 500a housing body, 500b lid body, 1000, 2000 battery, X , Y, Z distance, EL liquid level, AW winding axis.

Claims (1)

A housing,
A wound electrode body and electrolyte contained in the housing;
A positive electrode current collector terminal and a negative electrode current collector terminal connected to the electrode body,
The lower end of the electrode body is immersed in the electrolytic solution,
In the height direction of the battery,
The distance from the lower end of the electrode body to the upper end of the electrode body is X,
The distance from the lower end to the liquid level of the electrolyte is Y,
At least one of the distance from the lower end to the connecting portion between the positive electrode current collector terminal and the electrode body and the distance from the lower end to the connecting portion between the negative electrode current collector terminal and the electrode body Is Z,
A lithium ion secondary battery satisfying 0.11 ≦ Y / X ≦ 0.33 and 0 ≦ Z / X ≦ 0.39.

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