JP6604479B2 - Lithium ion battery - Google Patents

Description

  The present invention relates to a lithium ion battery including a separator between a positive electrode and a negative electrode.

  A lithium ion battery is disposed between a positive electrode including a lithium transition metal oxide as an active material, a negative electrode including carbon as an active material, an electrolytic solution including an organic solvent in which a lithium salt is dissolved, and the positive electrode and the negative electrode. And a separator.

  In some cases, foreign electrodes such as iron, copper, zinc, tin, cobalt, nickel, and chromium are mixed in the electrode of the lithium ion battery. The mixed metal foreign matter may be mixed into the battery in a solid or ionic state. Lithium ion batteries may have a reduced output voltage or heat generation / ignition failure due to mixed metal foreign matter. In particular, when metal foreign matter is mixed in the vicinity of the positive electrode, the metal foreign matter is ionized by the internal electric field and is induced to the negative electrode side. When these ions are deposited on the negative electrode, a dendride is formed, the dendride grows and reaches the positive electrode from the negative electrode, and the positive and negative electrodes are short-circuited. Such a short circuit causes an OCV (Open Circuit Voltage) failure in which the output voltage is lowered, and further causes a heat generation / ignition failure.

  In the conventional lithium ion battery, in order to suppress such a defect caused by the metal foreign matter, a configuration in which the positive electrode and the negative electrode are handled in close contact with the coating separator has been proposed. With such a structure, there is no gap between the electrode / separator, metal foreign matter mixed during assembly does not touch the electrode, and dendrites caused by metal foreign matter are less likely to occur (see Patent Document 1).

JP 2013-127857 A

  However, in the conventional lithium ion battery, the metal foreign matter mixed at the time of assembly can be inactivated, but the metal foreign matter already mixed into the positive electrode in the source process cannot be removed. Moves to the negative electrode, and dendride is generated at the negative electrode. Due to the generation of dendrites, the positive electrode and the negative electrode are short-circuited, and the output voltage of the lithium ion battery decreases, or the lithium ion battery generates heat and ignites, resulting in a decrease in battery performance and safety. is there.

  This invention solves the said problem, and aims at ensuring the battery performance and safety | security of a lithium ion battery.

In order to achieve the above object, a lithium ion battery according to the present invention includes a positive electrode plate including a lithium metal oxide as a positive electrode active material, a negative electrode plate including carbon as a negative electrode active material, and a first surface having the negative electrode. A separator disposed between the positive electrode plate and the negative electrode plate so that a second surface serving as a back surface of the first surface is in contact with the positive electrode plate; and lithium ion as an electrolyte in an organic solvent The separator is composed of a support layer and a separation functional layer having a smaller pore size and a lower porosity than the support layer, and one of the support layer and the separation functional layer is the first Arranged on one side, the other on the second side, the separation functional layer on the first side of the separator, and the support layer on the second side The average pore diameter of the separation functional layer is And greater than the lithium ions solvated by smaller the electrolyte from polyvalent ions solvated with solution liquid.

  According to this configuration, a separator composed of a separation functional layer and a support layer is used, and the separation functional layer has a dense structure with a small pore diameter and a low porosity as compared with the support layer. Since the movement to the negative electrode side can be suppressed, and the precipitation of metal foreign matters on the negative electrode side is thereby suppressed, battery performance and safety can be ensured.

Sectional drawing shown about the structure of a cylindrical lithium ion battery as one embodiment of this invention Sectional drawing which illustrates typically the principal part structure of the positive electrode plate in one embodiment of this invention, a negative electrode plate, and a separator. The figure which illustrates the structure of the separator in Example 1. The figure which illustrates the structure of the separator in Example 2. The figure which illustrates the structure of the separator in Example 3. The figure which shows the result of the charge-discharge cycle characteristic evaluation of the lithium ion battery in an Example and a comparative example

Embodiments of the present invention will be described below with reference to the drawings.
Note that, in the following description, the same reference numerals are given to components having the same action, and the description is omitted as appropriate.

(Embodiment 1)
FIG. 1 is a cross-sectional view showing a configuration of a cylindrical lithium ion battery as an embodiment of the present invention. The cylindrical lithium ion battery illustrated in FIG. 1 includes a positive electrode plate 1 and a negative electrode plate 2, and the positive electrode plate 1 and the negative electrode plate 2 are alternately stacked. A separator 3 is disposed between the positive electrode plate 1 and the negative electrode plate 2 so as to prevent the positive electrode plate 1 and the negative electrode plate 2 from being in physical contact. The laminated positive electrode plate 1, negative electrode plate 2 and separator 3 are wound in a cylindrical shape and arranged in a case 6 having a positive electrode tab 4, a negative electrode tab 5, an electrolyte solution 7 and the like, and a cylindrical lithium ion battery. Configure. The electrolytic solution 7 is made of, for example, a solution in which a lithium salt is dissolved in an organic solvent, and contains lithium ions as an electrolyte.

Next, the structure of the separator 3 will be described with reference to FIG.
FIG. 2 is a cross-sectional view schematically illustrating main components of a positive electrode plate, a negative electrode plate, and a separator according to an embodiment of the present invention.

  A desirable configuration of the separator 3 of the present invention is formed by laminating a separation functional layer 3a in which pores are formed and a support layer 3b. The separation functional layer 3a has a dense configuration with a small pore diameter and a low porosity, and the support layer 3b has a coarse configuration with a larger pore diameter and a higher porosity than the separation functional layer 3a.

  The pore diameter is a diameter of a cross section perpendicular to the longitudinal direction of the pore portion of the membrane, and the porosity is a ratio of the volume of the pore portion to the volume of the membrane. The larger the pore diameter and the higher the porosity, the higher the liquid permeability, but the mechanical strength decreases. In addition, the smaller the hole diameter, the smaller the size of the metal foreign matter that can be blocked. The blocking rate of a substance by pores is determined by the size of the pore diameter, the density of the pores, and the thickness of the layer. For example, when the mixed foreign metal ions are solvated and the diameter is 0.8 nm or more and 1.0 nm or less, the average diameter of the pores of the separation functional layer 3a is 0.3 nm or more and 0.8 nm or less. The porosity can be made larger than 0% and not larger than 1%.

  Here, for the sake of expression, vacancies having an average diameter of 0.3 nm or more and 0.8 nm or less are used, but at this size, the distance between the bond chains of the molecules constituting the film is the vacancies. This is a size that can be measured by a method of measuring the pore size of the functional layer of the reverse osmosis membrane, such as a positron annihilation method, which is difficult to measure by a method of measuring a normal pore diameter such as a mercury porosimeter.

  In the separator 3, a surface on which the separation functional layer 3a is exposed is a first surface, and a surface on which the support layer 3b is exposed is a second surface. That is, the pore diameter and porosity of the separator 3 on the first surface side are smaller than the pore diameter and porosity of the separator 3 on the second surface side, respectively.

Here, the separation functional layer 3a in the present embodiment is a layer having a function of blocking the transmission of ions and molecules having a certain size or larger and allowing ions having a smaller size to be transmitted.
The average film thickness, which is the thickness of the separation functional layer 3a used in the present embodiment, is not particularly limited, but is preferably 10 nm or more and 100 nm or less. If the thickness is less than 10 nm, there is a high possibility that defects will occur in the film due to insufficient strength. If the thickness is more than 100 nm, the movement of the permeation target necessary for the battery reaction is hindered, resulting in a decrease in battery performance. Moreover, it is preferable that the average film thickness of the isolation | separation functional layer 3a is thinner than the average film thickness of the support layer 3b.

  The material of the separation functional layer 3a is not particularly limited, but regenerated cellulose, cellulose ester, polyacrylonitrile, polytetrafluoroethylene, polyester polymer alloy, polyamide, polyimide, polysulfone, polyethersulfone, polyethylene , Polypropylene, polyvinylidene fluoride, polyvinyl alcohol, ethylene-vinyl copolymer, and polyvinyl chloride are preferable. In particular, aromatic polyamide and cellulose acetate are more preferable.

  Here, the support layer 3b in the present embodiment is a porous layer that supports the separation functional layer 3a. Although it does not specifically limit, a nonwoven fabric, a porous film, etc. are mentioned, for example. Since the support layer 3b has a larger pore diameter and a higher porosity than the separation functional layer 3a, ions that have passed through the separation functional layer 3a permeate the support layer 3b.

  The average film thickness, which is the thickness of the support layer 3b used in the present embodiment, is not particularly limited, but is preferably 15 μm or more and 100 μm or less. If the thickness is less than 15 μm, there is a high possibility that the film breaks due to insufficient strength. If the thickness is more than 100 μm, the ratio of the separator volume in the internal volume of the alkaline battery is high, and the ratio of the positive electrode active material and the negative electrode active material is low. Therefore, the battery capacity is reduced.

  Moreover, it is preferable that the hole diameter formed in the support layer 3b is 100 nm or more and 1 micrometer or less. When the thickness is less than 100 nm, the movement of the permeation target necessary for the battery reaction is hindered, so that the battery performance is deteriorated. When the thickness is larger than 1 μm, there is a high possibility that the insulation between the positive electrode and the negative electrode cannot be secured. The porosity is preferably 50% or more and 80% or less. If it is less than 50%, the movement of the permeation target necessary for the battery reaction is hindered, resulting in a decrease in battery performance. If it is more than 80%, there is a high possibility that the film will break due to insufficient strength.

  The material of the support layer 3b is not particularly limited, but regenerated cellulose, cellulose ester, polysulfone, polyether sulfone, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, vinylon, polyamide, polyimide, polyethylene, polypropylene , Polyester, and polyvinylidene fluoride are preferred.

  As a manufacturing method of the separator 3 of this Embodiment, the support layer 3b is produced first and the isolation | separation functional layer 3a is formed on the support layer 3b after that. The support layer 3b can be produced by a dry stretching method, a wet extraction method, a foaming method or the like after the material of the support layer 3b is melted or dissolved in a predetermined solvent. Next, the separator 3 is obtained by applying and drying a solution of the material of the separation functional layer 3a on the support layer 3b using a die coating method.

  The structures of the positive electrode plate 1 and the negative electrode plate 2 will be described using the cross-sectional structures of the positive electrode plate 1 and the negative electrode plate 2 shown in FIG. The positive electrode plate 1 has a structure in which a positive electrode current collector 1b using an aluminum foil or the like is sandwiched between two positive electrode active materials 1a containing a lithium metal oxide or a binder agent and laminated using a binder agent. Further, the negative electrode plate 2 has a structure in which a negative electrode current collector 2b using a copper foil or the like is sandwiched between two negative electrode active materials 2a containing carbon and a binder agent and laminated using a binder agent.

  Using the positive electrode plate 1, the negative electrode plate 2, and the separator 3 having the above structure, as shown in FIG. 1, the positive electrode plate 1, the separator 3, the negative electrode plate 2, and the separator 3 are laminated in this order and wound. The lithium ion battery is completed by inserting and sealing the product into the case 6 together with the positive electrode tab 4, the negative electrode tab 5, the electrolyte solution 7, and the like.

  In the example shown in FIG. 2, the positive electrode plate 1, the negative electrode plate 2, and the separator 3 are arranged so that the support layer 3 b comes into contact with the positive electrode active material 1 a and the separation functional layer 3 a comes into contact with the negative electrode active material 2 a when wound. It is arranged. However, the separator 3 may be disposed so that the support layer 3b is in contact with the negative electrode active material 2a and the separation functional layer 3a is in contact with the positive electrode active material 1a.

  As described above, the separator 3 composed of the separation functional layer 3a and the support layer 3b is used, and the separation functional layer 3a has a small structure with a small pore diameter and a low porosity as compared with the support layer 3b. The functional layer 3a can have a function of suppressing the permeation of polyvalent metal ions, and the support layer 3b can ensure the mechanical strength of the entire separator 3 without reducing the liquid permeability.

  Here, the separation functional layer 3a has such a pore diameter and porosity that it can sufficiently permeate lithium ions in the electrolytic solution 7 and suppress the permeation of foreign metal ions, and has a film thickness of the electrolytic solution 7 and the lithium ions. In order not to lower the permeability of the film, the film is below a certain level.

  Further, the support layer 3b has a film thickness of a certain level or more in order to ensure the mechanical strength of the separator 3, and has a pore diameter and pores of a certain level or more so as not to affect the permeability of the electrolyte solution 7 and lithium ions. Become a rate. Thus, even if metal foreign matter is mixed into the positive electrode plate 1 in the source process, dendride generation can be prevented, and precipitation of the metal foreign matter on the negative electrode plate 2 can be suppressed. Can be secured.

Hereinafter, specific examples will be described in more detail.
FIG. 3 is a diagram illustrating the configuration of the separator in the first embodiment, FIG. 4 is a diagram illustrating the configuration of the separator in the second embodiment, FIG. 5 is a diagram illustrating the configuration of the separator in the third embodiment, and FIG. It is a figure which shows the result of the charging / discharging cycle characteristic evaluation of the lithium ion battery in a comparative example.

(Example 1)
In Embodiment 1, lithium in which positive electrode active material 1a is mixed with 100 ppm of iron, copper, zinc, tin, cobalt, nickel, and chromium, each having a diameter of 20 μm or more and 30 μm or less, as a metal foreign substance with respect to the mass of positive electrode active material 1a An ion battery is manufactured and is referred to as Example 1. At this time, a separator 3 in which the separation function layer 3a is not disposed on the side wall 10 of the support layer 3b is used.

  That is, as shown in FIG. 3, the separator 3 in Example 1 is in contact with the negative electrode plate 2 only on the first surface 8 of the separator 3 whose surface is the separation functional layer 3a, and the separator 3 whose surface is the support layer 3b. The second electrode 9 is in contact with the positive electrode plate 1 only. Therefore, the separation functional layer 3a is not formed at a position in contact with the side wall 10 facing the positive electrode tab 4 and the negative electrode tab 5 of the support layer 3b.

(Example 2)
In the first embodiment, lithium ions in which 100 ppm of iron, copper, zinc, tin, cobalt, nickel, and chromium having a diameter of 20 μm or more and 30 μm or less are mixed into the positive electrode active material 1a as metal foreign matter with respect to the mass of the positive electrode active material 1a. A battery is manufactured and is referred to as Example 2. At this time, as shown in FIG. 4, a separator 3 in which the separation functional layer 3a is disposed in contact with the side wall 10 of the support layer 3b is used. That is, the separation functional layer 3a is formed at a position in contact with the negative electrode plate 2 and the side wall 10 of the support layer 3b.

Example 3
In the first embodiment, lithium ions in which 100 ppm of iron, copper, zinc, tin, cobalt, nickel, and chromium having a diameter of 20 μm or more and 30 μm or less are mixed into the positive electrode active material 1a as metal foreign matter with respect to the mass of the positive electrode active material 1a. A battery is produced and is referred to as Example 3. At this time, the separation functional layer 3a is also disposed on the side wall 10 of the support layer 3b as the separator 3, and the thickness of the central portion of the separation functional layer 3a is smaller than the thickness of both ends (positive electrode tab side and negative electrode tab side). Is used. That is, the film thickness T3a of the separation functional layer 3a is set so that the film thickness of the central portion between the positive electrode tab 4 (see FIG. 1) and the negative electrode tab 5 (see FIG. 1) is the outer peripheral side. Reference), and the thickness is made larger than the film thickness on the negative electrode tab 5 (see FIG. 1) side. In order to avoid local concentration of stress at this time, the film thickness is gradually changed. In the third embodiment, the configuration in which the separation function layer 3a is also disposed on the side wall 10 of the support layer 3b has been described as an example. However, the separation function layer 3a is also disposed in the configuration in which the separation function layer 3a is not disposed on the side wall 10 of the support layer 3b. The film thickness of the center part of the layer 3a can also be made thinner than the film thickness of both ends.

(Comparative Example 1)
In contrast to the first embodiment, a conventional separator that does not include a separation functional layer is used, and iron, copper, zinc, tin, cobalt, nickel, and chromium having a diameter of 20 μm or more and 30 μm or less are used as the positive electrode active material 1a. A lithium ion battery in which 100 ppm was mixed with respect to the mass of the substance 1a was produced.

  For the lithium ion batteries of Examples 1 to 3 and Comparative Example 1 manufactured under the above conditions, a constant current / constant electric charge / discharge test (upper limit) with a charging current of 1.8 mA and an electric charge of 5.4 mAh in an atmosphere at 25 ° C. Voltage 4.2V, lower limit voltage 3.0V). The result is shown in FIG.

  As is apparent from the results of FIG. 6, Examples 1 to 3 have better charge / discharge cycle characteristics than Comparative Example 1. That is, in the lithium ion batteries according to Examples 1 to 3 configured by the separator including the separation function layer 3a as compared with Comparative Example 1 according to the lithium ion battery including the separator having the conventional configuration, charging and discharging are repeated. Battery capacity decrease is small.

  In Comparative Example 1, the positive active material 1a was charged with 100 ppm of iron, copper, zinc, tin, cobalt, nickel, and chromium, each having a diameter of 20 μm or more and 30 μm or less, as a foreign metal. The performance is greatly reduced. This is because the metal foreign matter ionized on the positive electrode side moves to the negative electrode side, and the metal foreign matter is deposited on the surface of the negative electrode plate 2, and this precipitate grows toward the positive electrode plate 1. 1 and the negative electrode plate 2 are considered to have caused an internal short circuit.

  On the other hand, in the lithium ion batteries according to Examples 1 to 3 using the separator 3 provided with at least the separation functional layer 3a, the average pore diameter of the separation functional layer is smaller than the polyvalent ions solvated with the electrolytic solution. Bigger than. The separation functional layer 3a includes pores having a pore diameter of 0.6 nm to 2 nm and a porosity of 10% to 30%. Various ions in the electrolytic solution are in a solvated state in which the solvent is adsorbed according to the amount of charge, and ions having a larger valence tend to have a larger solvated size.

  For this reason, ions such as iron, copper, zinc, tin, cobalt, nickel, and chromium that are divalent or higher ions are larger than lithium ions that are monovalent ions in a solvated state. For this reason, it is possible to suppress the movement of foreign metal ions by transmitting lithium ions from the positive electrode side to the negative electrode side, and the output voltage of the lithium ion battery decreases or the lithium ion battery generates heat and ignites. It can suppress that performance and safety fall, and can secure battery performance and safety of a lithium ion battery.

Next, the charge / discharge cycle characteristics in Examples 1 to 3 will be described in the order of Example 1, Example 2, and Example 3.
In Example 1, the separation functional layer 3a is disposed only between the support layer 3b and the negative electrode plate 2, and the separation functional layer 3a is not disposed on the side wall 10 of the support layer 3b. If the positive electrode plate 1 contains a large amount of metal impurities, it is suppressed that ionized metal impurities diffuse near the positive electrode plate 1 and pass through the separation functional layer 3a to reach the negative electrode plate 2. However, between the side wall 10 of the support layer 3b of the separator 3 and the positive electrode tab 4 and the negative electrode tab 5, it penetrates by the capillary effect and reaches the negative electrode plate 2, and ionized metal impurities are deposited on the negative electrode plate 2. it is conceivable that.

  On the other hand, in Example 2, since the separation functional layer 3a is also disposed on the side wall of the support layer 3b, the metal impurities permeate between the side wall 10 of the support layer 3b of the separator 3 and the positive electrode tab 4 and the negative electrode tab 5. It is considered that almost no permeation of the ionized metal foreign matter as occurred in Example 1 occurred. For this reason, it is thought that Example 2 has better charge / discharge cycle characteristics than Example 1.

  In addition, since the separation functional layer 3a has a small pore size and a low porosity, the membrane is dense, so that it is difficult for the electrolytic solution to pass through compared to the support layer 3b. For this reason, the separation functional layer 3a has a thickness that does not hinder the flow of the electrolyte and suppresses the passage of foreign metal ions. In the case of Example 2, as shown in FIG. 4, the film thickness T3av of the separator 3 with respect to the direction in which the electrolytic solution flows in the separation function layer 3a disposed on the side wall of the support layer 3b is sufficient as the film thickness T3a of the separation function layer 3a. Therefore, the thickness of the support layer 3b is almost the same as the film thickness T3b. As described above, almost no foreign metal ions are transmitted near the support layer 3b. On the other hand, if the thickness T3ah of the separation functional layer 3a disposed on the side wall 10 of the support layer 3b in the direction perpendicular to the electrolyte flow direction is thick, the width of the support layer 3b in the direction perpendicular to the flow of the electrolyte is reduced. The flow of the electrolyte is inhibited. Therefore, the thickness T3ah of the separation functional layer 3a disposed on the side wall of the support layer 3b is preferably smaller than the film thickness T3a of the separation functional layer 3a disposed on the surface of the support layer 3b.

  Here, it describes about the change of the electrode shape accompanying charging / discharging in a general lithium ion battery. When the lithium ion battery is charged, the value varies depending on the electrode plate specifications, but the negative electrode plate 2 expands by about 10% and the positive electrode plate 1 expands by about 2%. On the other hand, at the time of discharging, both the positive electrode plate 1 and the negative electrode plate 2 return to the original state. However, the electrolyte does not return immediately after being extruded. Due to such expansion of the electrode plate during charging, the innermost central part of the electrode plate group is subjected to a pressure that halves the amount of electrolyte contained, and this non-uniformity of stress and electrolyte amount deteriorates the charge / discharge cycle characteristics. It is one of the causes.

  By the way, the separation functional layer 3a of Example 3 has a film thickness at the center portion smaller than the film thickness at both ends (positive electrode tab side and negative electrode tab side). For this reason, compared with Example 2, since the obstruction | occlusion of the liquid permeation by the layer with a low porosity in a center part from both ends becomes small, the electrolyte solution of a center part permeate | transmits easily, and the nonuniformity of the amount of electrolyte solution is suppressed. Yes. For this reason, it is thought that Example 3 has better charge / discharge cycle characteristics than Example 2.

  As Embodiment 1, the positive electrode plate 1, the negative electrode plate 2, and the separator 3 are arranged so that the support layer 3b touches the positive electrode active material 1a and the separation functional layer 3a touches the negative electrode active material 2a when wound. The positive electrode plate 1, the negative electrode plate 2, and the separator 3 are arranged in such a direction that the separation functional layer 3a touches the positive electrode active material 1a and the support layer 3b touches the negative electrode active material 2a when wound. However, the effect of suppressing the movement of foreign metal ions as in Examples 1 to 3 is obtained.

  However, when the separation functional layer 3a is in contact with the positive electrode active material 1a in which the metal foreign matter is easily ionized, the separation functional layer 3a is locally in contact with the high-concentration metal foreign matter ions, and the metal foreign matter in the separation functional layer 3a. Even if the ion rejection is high, the amount of foreign metal ions that permeate the separation function layer 3a increases. On the other hand, when the support layer 3b is in contact with the positive electrode active material 1a, and the metal foreign matter ions permeate the support layer 3b and reach the separation function layer 3a, the metal foreign matter ions diffuse and pass through the support layer 3b. Since the concentration is increased, the amount of foreign metal ions is relatively small. Therefore, since there are few metal foreign substances deposited on the surface of the negative electrode plate 2, good charge / discharge cycle characteristics and safety can be obtained.

  Next, the separator 3 used in Example 3 was evaluated for the rejection rate of iron, copper, zinc, tin, cobalt, nickel, and chromium, which are lithium and metal foreign matters, and the results are shown in [Table 1].

  The evaluation of the rejection rate is defined by the concentration C1 of the target substance on the supply liquid side and the concentration C2 of the target substance on the permeate side through the separator, using the rejection rate R of the separation target by the separator as an index. R = (1−C2 ÷ C1) × 100. Here, lithium trifluoromethanesulfonate, iron trifluoromethanesulfonate, copper trifluoromethanesulfonate, zinc trifluoromethanesulfonate, tin trifluoromethanesulfonate, cobalt trifluoromethanesulfonate, nickel trifluoromethanesulfonate as ethylene carbonate to the supply liquid A solution containing a certain amount of chromium trifluoromethanesulfonate was added.

  The solution which permeated by applying a pressure of about 0.3 MPa to the supply liquid side through the separator was used as the permeate. Thereafter, the concentrations of lithium, iron, copper, zinc, tin, cobalt, nickel, and chromium contained in the supply liquid and permeate were measured, and the rejection rate (%) of each substance was calculated using the above formula. The rejection rate of each substance was RLi, RFe, RCu, RCn, RSn, RCo, RNi, RCr.

As is apparent from [Table 1], with respect to the separator 3 used in Example 1, the rejection rate RFe, RCu, RZn of iron, copper, zinc, tin, cobalt, nickel, and chromium with respect to the rejection rate RLi of lithium. It can be seen that RSn, RCo, RNi, and RCr are higher. This is because lithium, which is a monovalent ion, iron, copper, zinc, tin, cobalt, nickel, and chromium are polyvalent ions, and the ion size when solvated differs greatly. Yes. Separator 3 used in the lithium ion battery of the present embodiment utilizes the above difference in ion size, lithium necessary for the battery reaction permeates the separator, and movement of the metal foreign object to be separated is blocked by separator 3. This result also shows that it has the function to do.

Next, the separator separation function and the rejection rate will be described.
Compared with the separator 3 used in Examples 1 to 3, when the pore diameter is small and the porosity is small (less than 50%) and the inhibition size is small, the lithium rejection rate RLi and metallic foreign substances such as iron, copper, zinc, The rejection ratios RFe, RCu, RZn, RSn, RCo, RNi, and RCr of tin, cobalt, nickel, and chromium are larger than the values in [Table 1]. That is, not only the metal foreign matter but also the movement of lithium necessary for the battery reaction is hindered between the positive and negative electrodes, so that it is not suitable as a separator for a lithium ion battery.

  Further, in comparison with the separators used in Examples 1 to 3, when the pore diameter is large and the porosity is large (greater than 80%) and the inhibition size is large, the lithium rejection rate RLi and metallic foreign objects such as iron and copper Zinc, tin, cobalt, nickel, chromium rejection rate RFe, RCu, RZn, RSn, RCo, RNi, RCr are smaller than the values in [Table 1]. In other words, not only lithium but also foreign metal particles pass through the separator, so that the intended effect of the present invention cannot be obtained.

  From the above, the rejection rate RFe, RCu, RZn, RSn, RCo, RNi, RCr of iron, copper, zinc, tin, cobalt, nickel and chromium must be sufficiently larger than the rejection rate RLi of lithium. Understand.

  INDUSTRIAL APPLICABILITY The present invention can ensure battery performance and safety, and is useful for a lithium ion battery or the like that includes a separator between a positive electrode and a negative electrode.

DESCRIPTION OF SYMBOLS 1 Positive electrode plate 1a Positive electrode active material 1b Current collector for positive electrodes 2 Negative electrode plate 2a Negative electrode active material 2b Current collector for negative electrodes 3 Separator 3a Separation functional layer 3b Support layer 4 Positive electrode tab 5 Negative electrode tab 6 Case 7 Electrolytic solution 8 First surface 9 Second side 10 Side wall

Claims (7)

A positive electrode plate containing a lithium metal oxide as a positive electrode active material;
A negative electrode plate containing carbon as a negative electrode active material;
A separator disposed between the positive electrode plate and the negative electrode plate such that a first surface is in contact with the negative electrode plate and a second surface which is the back surface of the first surface is in contact with the positive electrode plate;
An electrolyte solution in which lithium ions are dissolved as an electrolyte in an organic solvent,
The separator is composed of a support layer and a separation functional layer having a pore size smaller than that of the support layer and a low porosity.
One of the support layer and the separation functional layer is disposed on the first surface side, and the other is disposed on the second surface side ,
The separation functional layer is disposed on the first surface side of the separator, and the support layer is disposed on the second surface side;
The average pore diameter of the separation functional layer is smaller than multivalent ions solvated with the electrolyte solution and larger than lithium ions solvated with the electrolyte solution ,
Lithium ion battery. The average film thickness of the separation functional layer is smaller than the average film thickness of the support layer,
The lithium ion battery according to claim 1 . The material of the separation functional layer is regenerated cellulose, cellulose ester, polyacrylonitrile, Teflon, polyester polymer alloy, polyamide, polyimide, polysulfone, polyethersulfone, polyethylene, polypropylene, polyvinylidene fluoride, polyvinyl alcohol, ethylene-vinyl. It is one of a copolymer and polyvinyl chloride,
The lithium ion battery according to claim 1 or 2. The material of the support layer is regenerated cellulose, cellulose ester, polysulfone, polyether sulfone, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, vinylon, polyamide, polyimide, polyethylene, polypropylene, polyester, and polyvinylidene fluoride. Any one of them,
The lithium ion battery according to any one of claims 1 to 3 . The separation functional layer is also formed in a region in contact with the side wall of the support layer,
The lithium ion battery according to any one of claims 1 to 4 . The separation functional layer is characterized in that the thickness of the portion in contact with the side wall of the support layer is smaller than the thickness of the portion in contact with the positive electrode plate or the negative electrode plate.
The lithium ion battery according to claim 4 . The thickness of the portion of the separation functional layer in contact with the positive electrode plate or the negative electrode plate is thicker toward the side wall side of the support layer ,
The lithium ion battery according to claim 1 .