JP2016219223A - Lithium secondary battery and method for charging lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery capable of being charged at a high current density while preventing a short circuit, and a method for charging the lithium secondary battery.SOLUTION: A lithium secondary battery comprises: a negative electrode layer containing Li metal or Li alloy; a positive electrode layer containing a positive electrode active material; and a solid electrolyte layer provided between the negative electrode layer and the positive electrode layer and containing a lithium ion conductive ceramic material including Li, La, Zr, and O and having a garnet type crystal structure or a crystal structure similar to the garnet type crystal structure. The lithium secondary battery is charged at a current density (Ie/Sc) of 300 μA/cmor higher indicating current Ie with respect to the contact area Sc between the solid electrolyte layer and the negative electrode layer at 50°C or higher.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium secondary battery and a method for charging a lithium secondary battery.

  In recent years, with the spread of electronic devices such as personal computers and mobile phones, the development of natural energy storage technology, and the spread of electric vehicles and the like, the demand for safe and high energy density secondary batteries is increasing. Some secondary batteries use an organic electrolyte as an electrolyte responsible for ion transfer between a positive electrode and a negative electrode. However, in a secondary battery using an organic electrolyte, there is a risk of leakage, ignition, explosion, etc. of the organic electrolyte, which may not be preferable in terms of safety. Therefore, in recent years, in order to ensure high safety, development of an all-solid secondary battery in which a solid electrolyte is used in place of the organic electrolyte and all other battery elements are made of solid has been promoted.

  Since the electrolyte is ceramic, the all-solid-state secondary battery is safe without leakage or ignition. In addition, the all-solid-state secondary battery can simplify the exterior provided in the secondary battery using the organic electrolyte, and can be downsized by stacking each battery element. The energy density per unit weight can be improved. Among all solid state secondary batteries, all solid state lithium secondary batteries containing lithium metal in the electrode are expected to have higher energy density. In an all-solid lithium secondary battery, since the reactivity of lithium metal is high, it is necessary to use an electrolyte made of a specific material that is stable against lithium metal.

As a material constituting such an electrolyte, Li ₇ La ₃ Zr ₂ O ₁₂ (hereinafter referred to as LLZ), which is a ceramic material having a garnet-type crystal structure, is expected.

For example, Patent Document 1 discloses an all-solid lithium secondary battery comprising “a positive electrode, a negative electrode, and a solid electrolyte containing a ceramic having a garnet-type or garnet-type crystal structure composed of Li, La, Zr, and O”. Secondary battery "(Claim 1 of Patent Document 1) is disclosed. Examples of the negative electrode active material contained in the negative electrode include metallic lithium, Li metal compound, and the like (Column 0045 of Patent Document 1), and Li-La-Zr-based ceramics are shown to have good metal Li resistance. (Column 0065 to Column 0067 of Patent Document 1). In addition, an all-solid battery using a Li-La-Zr-based ceramic pellet as a solid electrolyte, a metal Li as a negative electrode, and LiCoO ₂ as a positive electrode is prepared, and a charge / discharge test is performed at a current density of 5 μA / cm ^2. It has been confirmed that the solid state battery is operating (Columns 0068 and 0069 of Patent Document 1).

Patent Document 2 discloses that “... a negative electrode having a negative electrode active material containing a lithium alloy containing at least one predetermined element of Mg, Al, Si, In, Ag and Sn, the positive electrode and the negative electrode. Interstitial composition formula Li _{5 + X} La ₃ (Zr _X , A _2−X ) O ₁₂ (wherein A is made of Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga and Ge) An all-solid-state lithium secondary battery comprising one or more elements selected from the group, and a solid electrolyte of a garnet-type oxide represented by X = 1.4 ≦ X <2 ”(Patent Document 2) Claim 1) is disclosed.

JP 2010-45019 A JP 2011-70939 A

By the way, when the inventors of the present invention fabricated a lithium secondary battery using LLZ as a solid electrolyte and lithium metal as a negative electrode and conducted a charge / discharge test at room temperature, a relatively high current density of several mA / cm ² was obtained. However, it was found that the battery was short-circuited at a current density of about several tens of μA / cm ² when charged. The lithium secondary battery in which the short circuit has occurred becomes in a state where the negative electrode and the positive electrode are energized and does not function as a battery. In addition, if the lithium secondary battery is short-circuited, a large current flows through the short-circuited portion at a time, so heat generation is considered to occur. That is, if a lithium secondary battery using LLZ as the solid electrolyte and lithium metal as the negative electrode is charged at a high current density, there is a risk of short-circuiting, and if short-circuited, there is a risk of heat generation. On the other hand, if the lithium secondary battery is prevented from being short-circuited by charging at a low current density, it takes a long time for charging. Lithium secondary batteries used for electronic devices such as personal computers and mobile phones, and electric vehicles are required to be able to be charged in a short time. Therefore, it is desirable that they can be charged at a high current density.

  An object of this invention is to provide the charging method of the lithium secondary battery and lithium secondary battery which can be charged with high current density, preventing a short circuit.

Means for solving the problems are as follows:
[1] a negative electrode layer containing Li metal or Li alloy;
A positive electrode layer containing a positive electrode active material;
Contains a lithium ion conductive ceramic material containing Li, La, Zr, and O and having a garnet-type crystal structure or a crystal structure similar to a garnet-type crystal structure, provided between the negative electrode layer and the positive electrode layer A solid electrolyte layer,
Lithium having a current density (Ie / Sc) indicating a current Ie with respect to a contact area Sc between the solid electrolyte layer and the negative electrode layer at 50 ° C. or higher and charged to 300 μA / cm ² or higher. It is a secondary battery.

Preferred embodiments of the above [1] are as follows.
[2] The solid electrolyte layer after charging protrudes from the surface of the negative electrode layer to the solid electrolyte layer, and the protruding precipitate containing Li is a cross section in the stacking direction of the negative electrode layer and the solid electrolyte layer. In the above, the protruding deposit has a length of 5 μm or more on the straight line formed by the negative electrode layer and the solid electrolyte layer, and the total length of the protruding deposit on the straight line with respect to the total length of the straight line The lithium secondary battery according to the above [1], wherein the existence ratio of the protruding precipitates indicated by a ratio of length is 20% or less.
[3] The solid electrolyte layer according to [1] or [2], wherein the lithium ion conductivity at room temperature is 10 ⁻⁵ S / cm or more and the relative density is 86% or more. It is a lithium secondary battery.
[4] The negative electrode layer contains at least one selected from the group consisting of Li metal, Li—Al alloy, Li—Sn alloy, and Li—Si alloy. 3]. The lithium secondary battery according to any one of 3).
[5] The lithium secondary battery according to any one of [1] to [4], wherein each of the negative electrode layer and the positive electrode layer is solid.

Means for solving the another problem is as follows.
[6] a negative electrode layer containing Li metal or Li alloy;
A positive electrode layer containing a positive electrode active material;
A lithium ion conductive ceramic material containing Li, La, Zr, and O and having a garnet-type crystal structure or a crystal structure similar to a garnet-type crystal structure is provided between the negative electrode layer and the positive electrode layer. A solid electrolyte layer;
A lithium secondary battery having a current density of 50 μC or higher at a current density (Ie / Sc) indicating a current Ie with respect to a contact area Sc between the solid electrolyte layer and the negative electrode layer is 300 μA / cm ² or higher. And a charging method of the lithium secondary battery.

According to the present invention, it is possible to provide a lithium secondary battery that can be charged at a high current density of 300 μA / cm ² or more while preventing a short circuit, and a method for charging the lithium secondary battery.

FIG. 1 is a schematic sectional view showing a lithium secondary battery which is an embodiment of the lithium secondary battery according to the present invention.

1. Lithium Secondary Battery A lithium secondary battery which is an embodiment of a lithium secondary battery according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing a lithium secondary battery which is an embodiment of the lithium secondary battery according to the present invention. The lithium secondary battery 10 includes a battery element unit 18 having a solid electrolyte layer 11, a positive electrode layer 12, and a negative electrode layer 13, a pair of current collectors 14 and 15, and an exterior body 19. The lithium secondary battery 10 can also be called an all-solid lithium secondary battery because the solid electrolyte layer 11, the positive electrode layer 12, and the negative electrode layer 13 are all solid.

The negative electrode layer 13 contains Li metal or Li alloy as a negative electrode active material. Examples of the Li alloy include a lithium-aluminum alloy (Li-Al alloy), a lithium-tin alloy (Li-Sn alloy), a lithium-silicon alloy (Li-Si alloy), and a lithium-magnesium alloy (Li-Mg alloy). Etc. Among these, the negative electrode layer 13 is made of a Li metal, a Li—Al alloy, a Li—Sn alloy, a Li—Si alloy, and a Li—Mg alloy in that it can be a high energy density lithium secondary battery. It is preferable to contain at least one selected from the group, and it is more preferable that the material is composed only of these Li metals or Li alloys. The negative electrode layer 13 may further contain a solid electrolyte. The solid electrolyte contained in the negative electrode layer 13 is not particularly limited as long as it is a material having Li ion conductivity. For example, the solid electrolyte contained in the negative electrode layer 13 includes a lithium ion conductive ceramic material, Li (Zr, Nb) ₂ (PO ₄ ) ₃ (referred to as LZNP), Li (Al, Ge) contained in the solid electrolyte layer 11. ) ₂ (PO ₄ ) ₃ (referred to as LAGP), Li (Al, Ti) ₂ (PO ₄ ) ₃ (referred to as LATP), Li (Zr, Nb) ₂ (PO ₄ ) ₃ (referred to as LZNP), Li (Zr, Ca) ₂ (PO ₄ ) ₃ (referred to as LZCP), La 2 / 3-xLi 3xTiO 3 (referred to as LLT), Li ₂ S—P ₂ S ₅ , Li ₃ BO ₃ , LiPO _{3 and the} like. In addition, when the electronic conductivity of a negative electrode active material is inadequate, a conductive support agent may be contained with a negative electrode active material and a solid electrolyte. The conductive auxiliary agent is not particularly limited, and any material having electronic conductivity may be used. For example, examples of the conductive assistant include conductive carbon, nickel (Ni), platinum (Pt), silver (Ag), and the like.

The positive electrode layer 12 contains a positive electrode active material. The positive electrode active material is not particularly limited, and examples thereof include LiCoO ₂ , LiMnO ₃ , LiNiO ₂ , LiFePO ₄ , sulfur, LiS, FeS ₂ , NiS, and TiS ₂ . The positive electrode layer 12 may further contain a solid electrolyte. The solid electrolyte contained in the positive electrode layer 12 is not particularly limited as long as the material has lithium ion conductivity. Examples of the solid electrolyte contained in the positive electrode layer 12 include substances exemplified as the solid electrolyte contained in the negative electrode layer 13. In addition, when the electronic conductivity of a positive electrode active material is inadequate, a conductive support agent may be contained with a positive electrode active material and a solid electrolyte. The conductive auxiliary agent is not particularly limited, and any material having electronic conductivity may be used. Examples of the conductive aid include the substances exemplified as the conductive aid contained in the negative electrode layer 13.

  The solid electrolyte layer 11 is disposed between the negative electrode layer 13 and the positive electrode layer 12. The solid electrolyte layer 11 contains a lithium ion conductive ceramic material containing at least Li, La, Zr, and O and having a garnet-type crystal structure or a crystal structure similar to a garnet-type crystal structure. The lithium ion conductive ceramic material may be in a powder form or a sintered body (bulk body) having a predetermined size. The solid electrolyte layer 11 is preferably composed of a sintered body of a lithium ion conductive ceramic material. Moreover, the solid electrolyte layer 11 may be comprised by the sintered compact formed by shape | molding and sintering a powdery lithium ion conductive ceramic material individually or with another material in a suitable shape. This lithium ion conductive ceramic material is less likely to react with lithium metal or a lithium alloy than, for example, an oxide having a NASICON type structure and a perovskite type oxide. Therefore, the negative electrode layer 13 may contain lithium metal or a lithium alloy. it can. In the lithium secondary battery 10 of this embodiment, since the solid electrolyte layer 11 hardly reacts with lithium metal or lithium alloy, the negative electrode layer 13 containing lithium metal or lithium alloy can be used, and as a result, high energy density. Have

The said lithium ion conductive ceramic material is obtained by baking the raw material which mix | blended the material containing Li component, La component, and Zr component by a predetermined ratio. Examples of the lithium ion conductive ceramic material include compounds represented by the following general formula (I). The compound represented by the following general formula (I) includes a site where Li is disposed (referred to as Li site), a site where La is disposed (referred to as La site), and a site where Zr is disposed (referred to as Zr site). ). In the lithium ion conductive ceramic material, it is preferable that at least one of the Li site, La site, and Zr site in the compound represented by the general formula (I) is partially substituted with another element. . In the compound represented by the general formula (I), when a part of the Li site, La site, or Zr site is substituted with another element, the compound has a garnet crystal structure or a crystal structure similar to a garnet crystal structure. In some cases, the lithium ion conductivity may be increased, and it may be advantageous for the lithium ion conduction path, and the lithium ion conductivity may be increased by selecting an appropriate substitution element and setting an appropriate substitution amount. Examples of the other elements include Al, Mg, Ca, Sr, Ba, K, Y, Pr, Nd, Sm, Gd, Lu, Sc, Ti, V, Ga, Nb, In, Sn, Hf, Ta, and W. , Pb, Bi, Si, Ge, Sb, Te, and the like. Among these, in the compound represented by the general formula (I), elements contained other than Li, La, and Zr are Al, Mg, Sr, Nb, Ta, and Bi in that lithium ion conductivity is increased. preferable.
Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ): General formula (I)

  The types of elements contained in the solid electrolyte layer 11 and their contents can be measured by ICP emission spectroscopy (high frequency inductively coupled plasma emission spectroscopy). Specifically, composition analysis is performed by applying a solution obtained by dissolving powder obtained by pulverizing the solid electrolyte layer 11 in a solvent such as an acid to an ICP emission spectroscopic analyzer.

The fact that the solid electrolyte layer 11 contains a lithium ion conductive ceramic material having a garnet-type crystal structure or a crystal structure similar to a garnet-type crystal structure is obtained by analyzing the pulverized powder of the solid electrolyte layer 11 with an X-ray diffractometer (XRD). This can be confirmed. Specifically, first, the powder obtained by pulverizing the solid electrolyte layer 11 is analyzed by an X-ray diffractometer (XRD) to obtain an X-ray diffraction pattern. The substance contained in the solid electrolyte layer 11 is identified by comparing the obtained X-ray diffraction pattern with an ICDD (International Center for Diffraction Data) card. The X-ray diffraction patterns are compared using an ICDD card (01-080-4947) (Li ₇ La ₃ Zr ₂ O ₁₂ ) corresponding to LLZ. A lithium ion conductive ceramic material having a garnet-type crystal structure or a crystal structure similar to a garnet-type crystal structure is an ICDD card (01-080-4947 (Li ₇ La ₃ Zr ₂ O ₁₂ )) depending on the presence and type of additives. Since the composition is different, the diffraction angle of the diffraction peak and the diffraction intensity ratio may be different. A garnet-type crystal structure or a crystal structure similar to a garnet-type crystal structure allows a deviation in diffraction angle and diffraction intensity ratio of diffraction peaks when elements other than Li, La, and Zr are contained.

  The solid electrolyte layer 11 is analyzed by ICP emission spectroscopy (high frequency inductively coupled plasma emission spectroscopy) to confirm the presence of each element such as Li, La, and Zr. When XRD analysis is performed, the garnet type is used. What is necessary is that a peak indicating a metal oxide having a crystal structure or a crystal structure similar to a garnet-type crystal structure can be detected. It is preferable that the intensity of the three peaks showing the above substance is larger than the intensity of the three peaks having a large intensity in order to obtain a desired lithium ion conductivity.

The solid electrolyte layer 11 preferably has a lithium ion conductivity at room temperature of 10 ⁻⁵ S / cm or more, and more preferably 10 ⁻⁴ S / cm or more. When the lithium ion conductivity of the solid electrolyte layer 11 is in the above range, the lithium secondary battery 10 having a small internal resistance and desired performance can be provided.

  As a method for increasing the lithium ion conductivity of the solid electrolyte layer 11, the proportion of the lithium ion conductive ceramic material having a garnet-type crystal structure or a crystal structure similar to the garnet-type crystal structure contained in the solid electrolyte layer 11 is increased. Methods and the like. As a method of increasing the proportion of the lithium ion conductive ceramic material, for example, when the solid electrolyte layer 11 is manufactured, it is arranged at the Li site, La site, and Zr site in addition to the Li component, La component, and Zr component. The method etc. which sinter the compounding material which mix | blended predetermined amount the component containing the element which can be mentioned can be mentioned.

  The lithium ion conductivity can be determined as follows. First, after polishing both surfaces of the solid electrolyte layer 11 and applying a gold coating to the polished surface, the specific resistance of the solid electrolyte layer 11 is measured at room temperature by the AC impedance method. The ionic conductivity can be calculated as the reciprocal of the specific resistance.

  The solid electrolyte layer 11 is preferably dense. Specifically, the relative density with respect to the theoretical density of the solid electrolyte layer 11 is preferably 86% or more, and more preferably 90% or more. When the relative density of the solid electrolyte layer 11 is 86% or more, particularly 90% or more, it is possible to suppress a short circuit from occurring inside the lithium secondary battery 10. The short circuit is considered to occur when the Li dendride passes through the grain boundaries and pores in the solid electrolyte layer 11, and it is preferable that the grain boundaries and pores are less dense.

Examples of a method for increasing the relative density of the solid electrolyte layer 11 include a method for improving the sinterability of the solid electrolyte layer 11. As a method for improving the sinterability of the solid electrolyte layer 11, for example, by sintering a blended material in which the Zr component is added in excess of the composition ratio represented by the general formula (1), Examples thereof include a method for forming a lithium ion conductive ceramic material and Li ₂ ZrO ₃ . When a lithium ion conductive ceramic material and Li ₂ ZrO ₃ are formed on the solid electrolyte layer 11, a substance that is likely to precipitate at the grain boundary, such as an oxide containing Al, an oxide containing La and Al, etc. Is considered to be difficult to precipitate, thereby suppressing the growth of grain boundaries, and it is considered difficult to form large grain boundaries. As a result, the relative density can be increased.

  The relative density can be determined as follows. First, the dry mass of the solid electrolyte layer 11 is measured with an electronic balance, for example, and the volume of the solid electrolyte layer 11 is measured with a caliper. The measured density of the solid electrolyte layer 11 is calculated by dividing the measured dry mass by the volume. On the other hand, the theoretical density of the solid electrolyte layer 11 is calculated. The relative density (%) can be obtained by dividing the measured density by the theoretical density and multiplying by 100.

Interfacial resistance at room temperature and the solid electrolyte layer 11 and negative electrode layer 13 is preferably at 3000 ohms / cm ² or less, more preferably 500 [Omega / cm ² or less. Interfacial resistance 3000 ohms / cm ² or less, especially when is 500 [Omega / cm ² or less, a lithium metal at the interface between the solid electrolyte layer 11 and negative electrode layer 13 during the charging can be inhibited from locally deposited It is possible to suppress a short circuit caused by a large current flowing through the deposited lithium metal.

Examples of a method for reducing the interface resistance include a method for improving the bonding state between the solid electrolyte layer 11 and the negative electrode layer 13. As a method for improving the bonding state between the solid electrolyte layer 11 and the negative electrode layer 13, the surface of the solid electrolyte layer 11 is formed flat by polishing or the like when the lithium secondary battery 10 is manufactured. A method for forming the negative electrode layer 13, a method for melting and bonding the negative electrode layer or the solid electrolyte layer, a method for performing pressure bonding by softening the negative electrode layer or the solid electrolyte layer with heat, and Li ₂ having a low Young's modulus. Examples thereof include a method of pressure bonding or thermocompression bonding of a solid electrolyte layer such as S—P ₂ S ₅ and a method of providing an intermediate layer between the solid electrolyte layer and the negative electrode layer, as will be described later.

  The interface resistance between the solid electrolyte layer 11 and the negative electrode layer 13 can be obtained as follows. First, a symmetric cell having a structure in which the solid electrolyte layer 11 to be measured is sandwiched between electrodes having the same composition is prepared. The symmetrical cell is produced by pressing and fixing an electrode containing Li metal or Li alloy constituting the negative electrode layer 13 to the solid electrolyte layer 11. Next, the interface resistance of the symmetric cell is measured by the AC impedance method.

  The pair of current collectors 14 and 15 includes a first current collector 14 and a second current collector 15. The first current collector 14 is disposed on the side of the positive electrode layer 12 opposite to the side on which the solid electrolyte layer 11 is disposed. The second current collector 15 is disposed on the opposite side of the negative electrode layer 13 from the side on which the solid electrolyte layer 11 is disposed. As long as the pair of current collectors 14 and 15 can collect current from the negative electrode layer 13 and the positive electrode layer 12, the shape and the material to be formed are not particularly limited. The shape of the pair of current collectors 14 and 15 is set as appropriate according to the use of the lithium secondary battery 10, and examples thereof include a foil shape, a plate shape, and a mesh shape. The material forming the pair of current collectors 14 and 15 is a conductive material, for example, stainless steel (SUS), nickel (Ni), titanium (Ti), iron (2), copper (Cu), Examples thereof include conductive metal materials selected from aluminum (Al), and alloys thereof, carbon materials, and the like. The pair of current collectors 14 and 15 may be, for example, a bulk body made of the above-described material, or may be a compact body obtained by molding the above-described material powder.

  The battery element portion 18 and the pair of current collectors 14 and 15 are accommodated in the exterior body 19. The shape of the exterior body 19 is not particularly limited as long as the battery element portion 18 and the pair of current collectors 14 and 15 can be covered, and is appropriately set according to the use of the lithium secondary battery 10 and the like. Examples of the shape of the exterior body 19 include a laminate type, a coin type, and a cylindrical type. The material forming the exterior body 19 is not particularly limited as long as it has insulating properties, and examples thereof include an epoxy resin and a polybutadiene resin. In addition, by putting an insulator (including gas) between the electronic element portion and the exterior body, the exterior body may be a metal, such as stainless steel (SUS), iron (2), aluminum (Al), and these. Mention may be made of materials selected from alloys.

  The exterior body 19 is preferably formed airtight. The inside of the outer package 19 is preferably an atmosphere in which the battery element portion 18 hardly reacts. Examples thereof include an inert gas such as argon gas, a dry air, and a gas atmosphere such as nitrogen. When the negative electrode layer 13 is made of lithium metal, the exterior body 19 is replaced with an inert gas such as argon gas in order to prevent the reaction between lithium and nitrogen or oxygen. preferable.

  As shown in FIG. 1, the lithium secondary battery 10 is not limited to a single battery in which the number of battery element portions 18 accommodated in the exterior body 19 is one, and the battery element portion 18 is a current collector. A stacked battery in which a plurality of layers are stacked via 14 and 15 may be used. The laminated battery may have a bipolar structure in which a plurality of battery element portions 18 are connected in series, or may have a monopolar structure in which a plurality of battery element portions 18 are connected in parallel.

  The lithium secondary battery 10 accommodated in the exterior body 19 may be used alone, or a plurality of lithium secondary batteries 10 may be connected in series or in parallel. Further, the lithium secondary battery 10 of this embodiment includes the exterior body 19, but may not include the exterior body 19.

The lithium secondary battery 10 is charged at 50 ° C. or higher with a current density (Ie / Sc) indicating a current Ie with respect to the contact area Sc between the solid electrolyte layer 11 and the negative electrode layer 13 being 300 μA / cm ² or higher. The lithium secondary battery 10 is short-circuited when charged at a high current density of, for example, 300 μA / cm ² or more at room temperature, but has a high current density of 300 μA / cm ² or more when charged at a temperature of 50 ° C. or higher. Even if it is charged, it is possible to prevent a short circuit. Therefore, since this lithium secondary battery 10 is charged at a high current density of 300 μA / cm ² or more at a temperature of 50 ° C. or higher, it can be charged in a short time while preventing a short circuit. The lithium secondary battery 10 can prevent a short circuit even if it is charged with a higher current density as the temperature of the lithium secondary battery 10 is higher. However, when the negative electrode layer 13 is formed of lithium metal, the negative electrode layer 13 may be melted when the temperature exceeds 180 ° C., and therefore, it is preferable that the negative electrode layer 13 is charged at 180 ° C. or less. The lithium secondary battery 10 is short-circuited even when charged at 170 ° C. with a maximum of 60000 μA / cm ² , although the upper limit value of the current density that can prevent a short circuit varies depending on the material and structure of the lithium secondary battery 10. Can be prevented. What is necessary is just to set suitably the temperature and current density of the lithium secondary battery 10 at the time of the lithium secondary battery 10 being charged according to the material which comprises the lithium secondary battery 10, a use, etc.

The lithium secondary battery 10 can be prevented from being short-circuited even when charged with a higher current density as the temperature of the lithium secondary battery 10 increases. When charging the lithium secondary battery 10, lithium ions usually move from the positive electrode layer 12 to the negative electrode layer 13. For example, when charged at a high current density at room temperature, lithium ions moving from the positive electrode layer 12 to the negative electrode layer 13 are formed on the interface between the solid electrolyte layer 11 and the negative electrode layer 13, in other words, on the surface of the negative electrode layer 13 on the solid electrolyte layer 11 side. It is thought that it becomes easy to precipitate locally as a projection-like deposit. When lithium metal or a metal containing Li is deposited as a protrusion-like precipitate on the interface, current concentration occurs here, and it is considered that the current density becomes excessively high and short-circuiting easily occurs. On the other hand, the higher the temperature of the lithium secondary battery 10, the better the interface state between the solid electrolyte layer 11 and the negative electrode layer 13, and a lithium metal or a metal containing Li is locally deposited as protruding deposits at the interface. It is thought that instead of being dispersed, precipitation occurs. Alternatively, it is considered that the deposited lithium metal or the metal containing Li is softened or melted and is not easily formed into a projecting precipitate. For this reason, it is considered that the current density does not become excessively high due to current concentration, and a short circuit can be prevented even if charging is performed by increasing the current density as the temperature increases.
That is, the solid electrolyte layer 11 after charging protrudes from the surface of the negative electrode layer 13 to the solid electrolyte layer 11, and a protruding precipitate containing Li is formed between the negative electrode layer 13 and the solid electrolyte layer 11. In the cross section in the stacking direction, the protruding deposit has a length of 5 μm or more on the straight line formed by the negative electrode layer 13 and the solid electrolyte layer 11, and the straight line of the protruding deposit with respect to the total length of the straight line. It is preferable that the ratio of the protrusion-like precipitates indicated by the ratio of the total length in the upper part is 20% or less. The proportion of the protrusion-like precipitate is more preferably 5% or less, and most preferably, the protrusion-like precipitate does not exist after charging, that is, the proportion of the protrusion-like precipitate is 0%. It is preferable that

The ratio of the protrusion-like precipitates can be measured by the following method.
First, in the lithium secondary battery 10, the lithium secondary battery 10 is cut so that a cross-sectional image parallel to the stacking direction of the solid electrolyte layer 11 and the negative electrode layer 13 is obtained.
Next, in the cut lithium secondary battery 10, the cross-sectional SEM image in the stacking direction is captured so that the bonding interface between the solid electrolyte layer 11 and the negative electrode layer 13 can be imaged with a scanning electron microscope (SEM). It is not preferable that the imaging magnification is too large or too large. For example, the magnification is preferably about 500 to 5000 times. However, it is not limited to this magnification, and can be appropriately changed depending on the size of the lithium secondary battery 10.
Next, in the captured SEM image, the length of the entire straight image showing the interface between the negative electrode layer 13 and the solid electrolyte layer 11 is measured as the total length of the straight line formed by the negative electrode layer 13 and the solid electrolyte layer 11. The “total length of the straight line formed by the negative electrode layer 13 and the solid electrolyte layer 11” herein is the total length of the interface between the negative electrode layer 13 and the solid electrolyte layer 11 in the acquired cross-sectional SEM image. The interface is shown as a substantially straight line. In the cross-sectional SEM image, even when irregularities or the like exist at the interface between the negative electrode layer 13 and the solid electrolyte layer 11, the presence of these irregularities is ignored and the negative electrode layer 13 and the solid electrolyte layer 11 are flat. In the cross-sectional SEM image, it is assumed that the interface between the negative electrode layer 13 and the solid electrolyte layer 11 is a straight line.
Further, in the same image, among the precipitates deposited on the surface of the negative electrode layer 13, that is, the deposits protruding from the surface of the negative electrode layer 13 toward the solid electrolyte layer 11, the length on the straight line is 5 μm or more. Calculate the total length of the precipitates.
Finally, “the total length of the lengths of the precipitates having a length of 5 μm or more on the straight line” is divided by “the total length of the straight line formed by the negative electrode layer 13 and the solid electrolyte layer 11” and expressed as a percentage. Thus, the existence ratio of the protrusion-like precipitate is calculated.
In this way, it is possible to measure the abundance of protruding precipitates.

  The contact area Sc is an area when it is assumed that the solid electrolyte layer 11 and the negative electrode layer 13 are bonded to each other by a surface. That is, when viewed with a magnifying glass or the like, even when irregularities or the like exist at the interface between the solid electrolyte layer 11 and the negative electrode layer 13, the presence of these irregularities is ignored and the solid electrolyte layer 11 and the negative electrode layer 13 are ignored. The bonding area Sc is measured on the assumption that they are bonded in a plane. That is, the bonding area Sc is synonymous with the area of the planar figure when the negative electrode layer 13 is viewed from the stacking direction.

  The current Ie is an average current value supplied to the lithium secondary battery 10. The charging method of the lithium secondary battery 10 is not particularly limited as long as the average current value can be set to a desired current density (Ie / Sc). The pulse charging method is a constant current voltage charging method. May be.

  The method for adjusting the temperature of the lithium secondary battery 10 is not particularly limited, and examples thereof include a method for adjusting the temperature of the lithium secondary battery using a heating unit and / or a cooling unit. Examples of the heating means include a heater and a Peltier element. A method of installing a heater or the like directly on the surface of the lithium secondary battery 10, a method of placing the lithium secondary battery 10 in a container, and the inside or outside of the container The method of installing a heater etc. in can be mentioned. Examples of the heating means include a method in which the lithium secondary battery 10 is placed in a container and a gas or liquid having a predetermined temperature is allowed to flow inside or outside the container. In addition, examples of the heating means include factory exhaust heat, automobile exhaust heat, geothermal heat, solar heat, and the like, and these may be used in combination. Examples of the cooling means include a method in which the lithium secondary battery 10 is placed in a container and a gas or liquid having a predetermined temperature is allowed to flow inside or outside the container. Further, a method of taking outside air with a cooling fan and blowing outside air to the lithium secondary battery 210 can be mentioned.

  The temperature of the lithium secondary battery 10 can be obtained as follows. For example, the temperature measurement device is installed on the surface of the lithium secondary battery 10, the inner wall surface of the container in which the lithium secondary battery is stored, and the like. Examples of the temperature measuring device include a thermocouple, a contact temperature sensor such as a platinum resistance thermometer, a non-contact temperature sensor such as a radiation thermometer, and the like.

  Next, an example of the manufacturing method of the lithium secondary battery 10 which is one Example of the lithium secondary battery which concerns on this invention is demonstrated below.

  First, the manufacturing method of the solid electrolyte layer 11 in the lithium secondary battery 10 of this embodiment is demonstrated. The solid electrolyte layer 11 has a blending step of blending raw materials to obtain a blended material and a firing step of firing the obtained blended material.

  In the blending step, as a raw material, a material containing at least a Li component, a La component, and a Zr component is blended to obtain a blended material. Each component to be blended is blended at a component ratio that provides a lithium ion conductive ceramic material having a garnet-type crystal structure or a crystal structure similar to a garnet-type crystal structure. Since Li is easily volatilized during firing, it is contained in a larger amount than the composition ratio shown in the general formula (1). In addition to the Li component, La component, and Zr component, the compounding material preferably contains a predetermined amount of a component containing an element that can be arranged at the Li site, La site, or Zr site. By firing the obtained blended material as described later, a sintered body of the lithium ion conductive ceramic material represented by the general formula (I) or a part of the crystal phase represented by the general formula (I) A sintered body of a lithium ion conductive ceramic material substituted with the above element can be obtained.

The material containing each component is not particularly limited as long as it is a material that is converted into each component by firing, and includes, for example, an oxide, a complex oxide, a hydroxide, each component including Li, La, and Zr. Examples thereof include carbonates, chlorides, sulfates, nitrates, and phosphates. Specific examples of the material containing each component include powders such as Li ₂ O, LiOH, Li ₂ CO ₃ , La ₂ O ₃ , La (OH) ₃ , and ZrO ₂ . The material containing each component may or may not contain an oxygen (O) component. In the case where the material containing each component does not contain an oxygen (O) component, at least Li, La, Zr, and O can be set by appropriately setting the firing atmosphere, such as performing a firing step described later in an oxidizing atmosphere. A lithium ion conductive ceramic material can be obtained.

  For the preparation of the blending material, a known raw material powder preparation method in the synthesis of ceramics can be appropriately employed. For example, the material containing the above components is put into a pot together with zirconia balls, ground and mixed in a ball mill for 8 to 20 hours in an organic solvent, and further dried to obtain a blended material. Examples of the organic solvent include alcohols such as ethanol and butanol, acetone, and the like.

  Prior to the firing step, it is preferable to have a step of temporarily firing the compounded material. In this step, for example, the compounded material is calcined at 900 to 1100 ° C. for 2 to 15 hours in a crucible to obtain a calcined material. By performing the pre-baking step, a material having a garnet-type crystal structure or a garnet-type similar crystal structure is easily obtained after the baking step.

  Before the firing step, it is preferable to include a step of adding a binder to the temporary firing material and crushing and mixing. In this step, for example, a binder is added to the temporarily fired material, and the mixture is pulverized and mixed in an organic solvent with a ball mill for 8 to 100 hours, and further dried to obtain an unfired material. By further pulverizing and mixing the temporarily fired material, a uniform crystal phase can be easily obtained after the firing step. Examples of the binder include methyl cellulose, ethyl cellulose, polyvinyl alcohol, and polyvinyl butyral. Examples of the organic solvent include ethanol, butanol, and acetone.

In the firing step, the blended material obtained through the blending step described above is fired. Specifically, the compounded material is put into a mold having a desired shape and size, press-molded, and then subjected to, for example, a cold isostatic pressing machine (CIP: Cold Isostatic Pressing). A hydrostatic pressure of ² t / cm ² is applied to obtain a molded body. A sintered body of a lithium ion conductive ceramic material is obtained by firing this molded body at 1000 to 1250 ° C. for 3 to 36 hours.

  When the blending material does not contain an oxygen component, the molded body is preferably fired in an oxygen atmosphere, and when the blending material contains an oxygen component, an inert gas such as nitrogen is used. The molded body may be fired in an active gas atmosphere or a reducing atmosphere. In addition, when the process of carrying out temporary baking further is implemented after the said mixing | blending process, the said baking process is performed with respect to the said temporary baking material. When a step of adding a binder and crushing after the blending step is performed, the firing step is performed on the unfired material.

  According to the method for manufacturing the solid electrolyte layer 11, a sintered body of a lithium ion conductive ceramic material containing Li, La, Zr, and O and having a garnet-type crystal structure or a crystal structure similar to a garnet-type crystal structure can be easily obtained. Can be manufactured. The obtained sintered body can be used as the solid electrolyte layer 11 of the lithium secondary battery 10 as it is or after being appropriately processed.

  The positive electrode layer 12 and the negative electrode layer 13 can be manufactured by appropriately adopting a known method for manufacturing a ceramic molded body. For example, first, the above-described positive electrode active material, solid electrolyte, and optionally a powder of a compound that becomes a conductive aid are mixed at a predetermined ratio to obtain a mixed powder. Subsequently, this mixed powder is put into a cylindrical mold capable of being pressure-molded. For example, a SUS base material used as the first current collector 14 and the obtained mixed powder are stacked in this order in the cylindrical mold and press molded to obtain a positive electrode pellet. The negative electrode pellet is produced in the same manner as the positive electrode pellet.

  Next, the positive electrode pellet, the solid electrolyte layer, and the negative electrode pellet are stacked in this order so that the positive electrode pellet and the current collectors 14 and 15 of the negative electrode pellet are arranged on the outer side to obtain a stacked body. Next, each member is fixed by sandwiching the laminated body with a predetermined pressure via the first current collector 14 and the second current collector 15. In this way, the lithium secondary battery 10 is obtained.

  In addition to the method described above, the method for manufacturing the lithium secondary battery 10 is a method of laminating each of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer in this order in an unfired state, and simultaneously firing them. There are a method in which the positive electrode layer and the negative electrode layer are baked on the solid electrolyte layer, a method in which pressure is applied when baking the positive electrode layer and the negative electrode layer on the plate-shaped solid electrolyte layer (hot press method), and the like.

2. Lithium Secondary Battery Charging Method A lithium secondary battery charging method, which is an example of a lithium secondary battery charging method according to the present invention, will be described below. Hereinafter, the method for charging the lithium secondary battery 10 according to the embodiment will be described as an example.

The charging method of the lithium secondary battery 10 of this embodiment is such that the current density (Ie / Sc) indicating the current Ie with respect to the contact area Sc between the solid electrolyte layer 11 and the negative electrode layer 13 is 50 ° C. or higher. Charge at 300 μA / cm ² or more. Charging method of a lithium secondary battery 10, the lithium secondary battery 10 at 80 ° C. or higher 180 ° C. or less, it is preferable to charge by the current density to 300 .mu.A / cm ² or more 6000μA / cm ² or less, 0.99 ° C. or higher 170 ° C. In the following, it is more preferable to charge at a current density of 1000 μA / cm ² or more and 3000 μA / cm ² or less. When the negative electrode layer 13 in the lithium secondary battery 10 is formed of lithium metal, the negative electrode layer 13 may be dissolved when the temperature exceeds 180 ° C. Therefore, it is preferable to charge at 180 ° C. or lower for safety. It is more preferable to charge at 170 degrees C or less from a point. Further, the lithium secondary battery 10 can prevent a short circuit even when charged with a higher current density as the temperature of the lithium secondary battery 10 is higher. Therefore, the temperature of the lithium secondary battery 10 is preferably 80 ° C. or higher, more preferably 150 ° C. or higher, and the maximum current density at which the short circuit can be prevented at the temperature of the lithium secondary battery 10. It is preferable to charge. The lithium secondary battery 10 can be charged in a shorter time as it is charged at a higher current density. In the lithium secondary battery 10, since the upper limit value of the current density that can prevent a short circuit is different depending on the material, structure, etc. constituting the lithium secondary battery 10, the current depends on the material, structure, etc. constituting the lithium secondary battery 10. The density is set as appropriate.

According to the lithium secondary battery and the charging method of the lithium secondary battery according to the present invention, the battery can be charged at a high current density of 300 μA / cm ² or more while preventing a short circuit by charging at a temperature of 50 ° C. or more. As a result, charging can be completed in a short time. Therefore, the lithium secondary battery and the method for charging the lithium secondary battery according to the present invention are used for electronic devices such as personal computers and mobile phones, electric vehicles, and the like, and are required to be charged in a short time. It is suitably used as the charging method.

  The lithium secondary battery according to the present invention is not limited to the above-described embodiment, and various modifications can be made within a range in which the object of the present invention can be achieved.

  For example, the lithium secondary battery according to the present invention may be configured to include an intermediate layer formed of gold or the like between the negative electrode layer and the electrolyte layer, or formed of gold or the like between the positive electrode layer and the electrolyte layer. It is good also as a structure provided with the intermediate | middle layer.

The lithium secondary battery according to the present invention may be a lithium-air battery in which the negative electrode active material is lithium metal or a lithium alloy and the positive electrode active material is oxygen. The lithium secondary battery according to the present invention may contain an ionic liquid or an organic electrolyte having lithium ion conductivity in the positive electrode layer or the negative electrode layer. Examples of the organic electrolyte include a solution in which an electrolyte such as LiPF ₆ is dissolved in a solvent such as EC (ethylene carbonate) and DEC (diethyl carbonate). The positive electrode layer may contain an aqueous electrolyte. For example, an aqueous lithium hydroxide solution, an aqueous lithium fluoride solution, an aqueous lithium chloride solution, an aqueous lithium bromide solution, an aqueous lithium iodide solution, an aqueous lithium acetate solution, an aqueous lithium sulfate solution, Examples include lithium acid aqueous solution.

1. Evaluation of lithium ion conductive ceramic materials (Sample 1)
[Production of lithium ion conductive ceramic materials]
The ratio of each component of Li, La, and Zr is Li: La: Zr = 7: 3: 2 (molar ratio) in the raw material powder, Li ₂ CO ₃ , La (OH) ₃ , ZrO ₂ In addition, since Li easily volatilizes during firing, 10% by mass of Li ₂ CO ₃ was added to the weighed Li ₂ CO ₃ in consideration of the volatile content of lithium. This was put into an alumina pot together with zirconia balls, ground and mixed in a ball mill for 15 hours in ethanol, and further dried to obtain a blended material.

The obtained blended material was calcined at 1100 ° C. for 10 hours in an alumina crucible to obtain a calcined material. A binder was added to the temporarily fired material, and the mixture was pulverized and mixed with a ball mill in an organic solvent for 15 hours and further dried to obtain an unfired material. The green material is put into a mold having a diameter of 10 mm, press-molded, and then a hydrostatic pressure of 1.5 t / cm ² is applied using a cold isostatic press (CIP) to obtain a molded body. It was. The compact was covered with a calcined powder having the same composition as the compact and fired at 1200 ° C. for 16 hours in an air atmosphere to obtain a sintered body of a lithium ion conductive ceramic material having a diameter of 10 mm and a thickness of 1 mm. .

[XRD analysis of lithium ion conductive ceramic materials]
The powder obtained by pulverizing the sintered body was analyzed with an X-ray diffractometer (XRD) to obtain an X-ray diffraction pattern. As a result of comparing the obtained X-ray diffraction pattern with the ICDD card, it was confirmed that the sintered body substantially matched with the LLZ cubic ICDD card. Therefore, it can be determined that the sintered body of the lithium ion conductive ceramic material has a garnet-type crystal structure or a garnet-type similar crystal structure.

[Ionic conductivity]
After polishing both surfaces of the sintered body and coating the polished surface by gold sputtering, the specific resistance and ionic conductivity of the sintered body were measured at room temperature by the AC impedance method. For this measurement, a Solartron 1255B type frequency response analyzer was connected to a Solartron 1470E type multistat. The measured resistance R (specific resistance) is the sum of the intragranular resistance ra and the grain boundary resistance rb (R = ra + rb). Further, the ionic conductivity Ic is obtained as the reciprocal of the resistance R (Ic = 1 / R). As a result, the ionic conductivity of the sintered body was 4 × 10 ⁻⁴ S / cm.

[Relative density]
The dry mass of the sintered body was measured with an electronic balance, and the volume was measured with a caliper. The measured density of each sample was calculated by dividing the dry mass by the volume. Moreover, the theoretical density of each composition was calculated. The measured density was divided by the theoretical density, and the value multiplied by 100 was calculated as the relative density. As a result, the relative density of the sintered body was 92%.

[Interface resistance]
A symmetric cell was produced by pressing and fixing Li metal electrodes on both sides of the sintered body. For this measurement, a Solartron 1255B type frequency response analyzer was connected to a Solartron 1470E type multistat. In the joined body of Li metal and the solid electrolyte layer, “ion conductivity” is observed between the Li metal and the solid electrolyte layer in addition to the intragranular resistance ra and the grain boundary resistance rb measured at the time of measurement. The interfacial resistance ri is measured. Measurement of the interfacial resistance ri of the symmetrical cell is 650Ω / cm ² at room temperature (25 ° C.), a 89Ω / cm ² at 80 ° C., it was 0.5 .OMEGA / cm ² at 170 ° C.. From this result, it can be seen that the higher the temperature of the sintered body, the lower the interface resistance of the sintered body.

(Sample 2)
As raw material powder, SrCO ₃ and MgO are added in addition to Li ₂ CO ₃ , La (OH) ₃ and ZrO ₂ , and the ratio of each component of Li, La, Zr, Sr and Mg is Li: La: Zr = 6. .95: 2.75: 2: 0.25: 0.15 (molar ratio), and since Li easily volatilizes during firing, lithium volatilization relative to the weighed Li ₂ CO ₃ In consideration of the amount, it was added in an amount of 14% by mass. This was put into a nylon pot together with zirconia balls, ground and mixed in a ball mill for 15 hours in ethanol, and further dried to obtain a blended material.

The obtained blended material was calcined at 1100 ° C. for 10 hours on a magnesia plate to obtain a calcined material. A binder was added to the temporarily fired material, and the mixture was pulverized and mixed in an organic solvent with a ball mill for 60 hours, and further dried to obtain an unfired material. This unfired material was put into a mold having a diameter of 10 mm, press molded, and then a hydrostatic pressure of 1.5 t / cm ² was applied using a cold isostatic press (CIP) to obtain a molded body. It was. The compact was covered with a calcined powder having the same composition as the compact and fired at 1200 ° C. for 4 hours in a nitrogen atmosphere to obtain a sintered body of a lithium ion conductive ceramic material having a diameter of 10 mm and a thickness of 1 mm. .
The sintered body has an ionic conductivity of 1.4 × 10 ⁻³ S / cm, a relative density of 93%, and an interface resistance of 22.5 Ω / cm ² at room temperature (25 ° C.) and 0.18 Ω / cm at 170 ° C. cm ² .

[Relationship between current density and temperature]
Example 1
A Li metal foil having a diameter of 10 mm and a thickness of 0.1 mm is pressure bonded to both surfaces of the sintered body of sample 1, and this is held at 170 ° C. for 1 hour, and then cooled to form a Li / LLZ / Li bonded body. Obtained. A specimen made of SUS was joined to a Li metal foil in the Li / LLZ / Li joined body.
The test body was placed in a container maintained at a predetermined temperature, and a test was performed in which direct current was continuously applied for 500 seconds.
The average current of the applied direct current is Ie, the contact area between the sintered body and the Li metal foil is Sc, and the value obtained by dividing Ie by Sc is the current density (Ie / Sc). The temperature is 25 ° C., and the current density is 300 μA. As a result of testing at / cm ² , the test specimen was short-circuited. Therefore, as a result of performing the test while raising the temperature to 300 ° C. and 170 ° C. with the current density kept at 300 μA / cm ² , the test body did not short-circuit. Furthermore, as a result of testing at a temperature of 170 ° C. and a current density of 6000 μA / cm ² , the test body did not short-circuit.

(Example 2)
A test body was prepared in the same manner as in Example 1 except that the sintered body of Sample 2 was used. This test specimen was tested in the same manner as Sample 1 at a temperature of 25 ° C. and a current density of 300 μA / cm ^2. As a result, the test specimen was short-circuited. As a result of performing the test by raising the temperature to 80 ° C. and 170 ° C., the test body did not short-circuit. Moreover, as a result of testing at a temperature of 170 ° C. and a current density of 7000 μA / cm ² , the test specimen was not short-circuited. Further, the current density was increased and the test was performed at 8000 μA / cm ^2. As a result, the test specimen was short-circuited.

[Abundance of protruding precipitates]
In Example 1, the test body formed of Sample 1 was tested at a temperature of 25 ° C. and a current density of 300 μA / cm ^2. As a result, the test was short-circuited, and the test was performed at a temperature of 170 ° C. and a current density of 300 μA / cm ^2. The cross section including the interface between the solid electrolyte layer and the negative electrode layer was observed from the SEM image in the test specimen that was not short-circuited as a result of the test.
In the cross section of the test specimen tested at a temperature of 25 ° C. and a current density of 300 μA / cm ² , the negative electrode layer protrudes from the surface of the negative electrode layer toward the solid electrolyte layer at the interface between the negative electrode layer and the solid electrolyte layer. There was a protrusion-like precipitate having a length of 5 μm or more on a straight line formed by the solid electrolyte layer. As described above, the proportion of the protrusion-like precipitate was measured and found to be 36%.
Protruding precipitate having a length of 5 μm or more on the straight line at the interface between the negative electrode layer and the solid electrolyte layer side in the cross section of the test specimen tested at a temperature of 170 ° C. and a current density of 300 μA / cm ² . Did not exist. That is, the proportion of the protruding precipitates was 0%.
From these results, even after charging, the current density is locally increased due to current concentration if the proportion of protruding precipitates at the interface between the negative electrode layer and the solid electrolyte layer is 20% or less. It is considered that a short circuit can be prevented even if charging is performed by increasing the current density as the temperature during charging increases.

As shown in Examples 1 and 2, a solid electrolyte layer containing a lithium ion conductive ceramic material containing Li, La, Zr, and O and having a garnet-type crystal structure or a crystal structure similar to a garnet-type crystal structure Li / LLZ / Li bonded body with Li metal foil bonded to both sides of the wire is short-circuited when a relatively high direct current of 300 μA / cm ² is supplied at 25 ° C., but is not short-circuited at 50 ° C. or higher. It was.

2. Evaluation of lithium secondary battery [Preparation of lithium secondary battery]
(Sample A)
The positive electrode mixture used as the positive electrode layer is obtained by mixing FeS ₂ as a positive electrode active material and 80Li ₂ S-20P ₂ S ₅ as a sulfide-based solid electrolyte glass at a mass ratio of 6: 4 to obtain a compact. Obtained.
The compact and the sintered compact of the lithium ion conductive ceramic material of Sample 1 were superposed and heated at 190 ° C. for 1 hour to join them. Next, a Li metal foil is pressure-bonded as a negative electrode layer to the surface of the sintered body to which the powder of the positive electrode mixture is not bonded, and this is held at 170 ° C. for 1 hour, so that the positive electrode layer and the solid electrolyte layer And a negative electrode layer were laminated to produce a battery element part.

(Sample B)
Sulfur as a positive electrode active material, 80Li ₂ S-20P ₂ S ₅ as a sulfide-based solid electrolyte glass, and ketjen black, which is conductive carbon as a conductive auxiliary agent, are mixed at a mass ratio of 6: 6: 1. A battery element portion was produced in the same manner as Sample A, except that the positive electrode mixture obtained by forming a compact was used.

(Sample C)
The same positive electrode composite as the positive electrode layer as Sample B was prepared. As the sintered body to be the solid electrolyte layer, the sintered body of the lithium ion conductive ceramic material of Sample 1 was prepared. The negative electrode composite material to be the negative electrode layer is a mass ratio of 1: 1 of a Li—Al alloy (in molar ratio: Li: Al = 1: 1) and 80Li ₂ S-20P ₂ S ₅ as a sulfide-based solid electrolyte glass. To obtain a green compact. Two current collectors made of SUS were prepared. The current collector, the negative electrode mixture, the sintered body, the positive electrode mixture, and the current collector are laminated in this order, and are fixed and bonded by sandwiching them with a pressure fixture at 50 MPa without heating. A battery element portion in which a layer, a solid electrolyte layer, a negative electrode layer, and a current collector were laminated was produced.

(Sample D)
Using a positive electrode mixture obtained by mixing LiCoO ₂ as a positive electrode active material and 80Li ₂ S-20P ₂ S ₅ as a sulfide-based solid electrolyte glass at a mass ratio of 6: 4 to obtain a compact. A battery element portion was produced in the same manner as Sample C except for the above.

[Charge / discharge test]
(Comparative Example 1)
The battery element parts of Samples A to D were each put in a thermostatic bath maintaining an argon atmosphere, and a charge / discharge test was performed. The constant temperature bath has a temperature detection unit, a heating unit, and a cooling unit, and the constant temperature bath is set by the heating unit or the cooling unit acting according to the difference between the set temperature and the temperature detected by the temperature detection unit. Can be maintained at temperature. A Solartron 1470E multistat was used as a charge controller for charging and discharging the battery element. The temperature detection unit, heating means, cooling means, and 1470E type multistat of the thermostatic bath are connected to a personal computer, and the temperature and current density of the thermostatic bath can be changed as appropriate. In Comparative Example 1, one cycle of charge / discharge was performed with the current density supplied to the battery element portion being 12.8 μA / cm ² in a state where the temperature of the thermostatic chamber was kept constant at 25 ° C. As a result, all the battery element portions of Samples A to D were able to be charged / discharged without being short-circuited, but it is considered that charging requires a long time because the current density is small.

(Comparative Example 2)
A charge / discharge test of the battery element portions of Samples A to D was performed in the same manner as in Comparative Example 1 except that the current density was set to 300 μA / cm ² . As a result, all the battery element portions of Samples A to D were able to be discharged, but were short-circuited when charged.

(Comparative Example 3)
A charge / discharge test of the battery element portions of Samples A to D was performed in the same manner as in Comparative Example 1 except that the temperature of the thermostatic chamber was 185 ° C. and the current density was 300 μA / cm ² . As a result, in all the battery element parts of Samples A to D, the Li metal in the negative electrode layer was melted, and the battery side part was short-circuited with the positive electrode layer and could not be discharged and charged.

(Example 11)
A charge / discharge test of the battery element portions of Samples A to D was performed in the same manner as in Comparative Example 1 except that the temperature of the thermostatic bath was 80 ° C. and the current density was 300 μA / cm ² . As a result, all the battery element parts of Samples A to D were not short-circuited in any process of discharging and charging.

(Example 12)
The battery element part of Sample B was discharged at a current density of 128 μA / cm ² in a state where the temperature of the thermostatic chamber was kept constant at 25 ° C., and then the current density was set to 128 while the temperature was kept constant at 120 ° C. When charging was performed at intervals of 1000 seconds in the order of 256, 348, 256, and 128 μA / cm ² , the battery could be charged without being short-circuited.

(Example 13)
The battery element part of Sample B was discharged at a current density of 128 μA / cm ² in a state where the temperature of the constant temperature bath was kept constant at 25 ° C., and then the current density was set to 64 while the temperature was kept constant at 170 ° C. When charging was performed at intervals of 1000 seconds in the order of 128, 256, 640, 1280, 2000, 1280, 640, 256, 128, 64 μA / cm ² , the battery could be charged without being short-circuited.

(Example 14)
The battery element of the sample B, and while the constant temperature of the thermostatic bath to 25 ° C., in a state to discharge at a current density of 128μA / cm ^2, then, that a constant current density of 300 .mu.A / cm ^2, a thermostat The temperature was changed in the order of 80, 120, 150, 170, 150, 120, and 80 ° C., and charging was performed while maintaining each temperature for 1000 seconds. As a result, charging was possible without short-circuiting at all temperatures.

(Example 15)
The battery element of the sample B, and while the constant temperature of the thermostatic bath to 25 ° C., in a state to discharge at a current density of 128μA / cm ^2, then, that a constant current density of 640μA / cm ^2, a thermostat The temperature was changed in the order of 150, 170, 150, and 170 ° C., and charging was performed while maintaining each temperature for 1000 seconds. As a result, charging was possible without short-circuiting at all temperatures.

(Example 16)
The battery element part of Sample B was discharged at a current density of 128 μA / cm ² with the temperature of the thermostat kept constant at 25 ° C., and the temperature was maintained at 80 ° C.
(1) Current density of 300 μA / cm ² , maintained at a temperature of 80 ° C. for 1000 seconds,
(2) Current density of 300 μA / cm ² , temperature rise from 80 ° C. to 120 ° C. in 1000 seconds,
(3) Current density of 450 μA / cm ² , maintained at a temperature of 120 ° C. for 1000 seconds,
(4) Current density is 450 μA / cm ² , temperature is raised from 120 ° C. to 150 ° C. in 1000 seconds,
(5) Current density of 450 μA / cm ² , maintained at a temperature of 150 ° C. for 1000 seconds,
(6) Current density is 450 μA / cm ² , temperature is raised from 150 ° C. to 170 ° C. in 1000 seconds,
(7) Current density 1500 μA / cm ² , maintained at 170 ° C. for 1000 seconds,
(8) Current density 450 μA / cm ² , cooling from temperature 170 ° C. to 120 ° C. in 1000 seconds,
When the battery was charged in the order of, it was possible to charge without short-circuiting under all conditions.

As shown in Comparative Examples 1 to 3 and Examples 11 to 16, a lithium ion conductive ceramic material containing Li, La, Zr, and O and having a garnet-type crystal structure or a crystal structure similar to a garnet-type crystal structure When a battery element part was prepared by providing a positive electrode layer and a negative electrode layer made of various materials on both surfaces of a solid electrolyte layer containing A, and a charge / discharge test was performed, the same test results as in Examples 1 and 2 were obtained. Results are shown.
As shown in Comparative Example 1, there is no short circuit when charged at a relatively low current density of 12.8 μA / cm ² at 25 ° C., but as shown in Comparative Example 2, a relatively high current density of 300 μA / cm ^2. Shorted when charged with. In addition, as shown in Comparative Example 3, when the temperature reached 185 ° C. or higher, the Li metal portion contained in the negative electrode layer was melted and shorted with the positive electrode layer from the battery side surface. On the other hand, as shown in Example 11, even when charging was performed at a relatively high current density of 300 μA / cm ² , no short circuit occurred when the temperature was set to 80 ° C. Further, as shown in Examples 12 to 16, when the current density is changed in a state where the temperature is maintained at a relatively high constant temperature, the comparison is performed at 50 ° C. or higher while charging at a relatively high constant current density. No short circuit occurred when the temperature was changed at a relatively high temperature and when charging was performed while changing these values at a relatively high temperature and a relatively high current density.
In the present invention, the relatively high temperature can be expressed as 50 ° C. or more, and the relatively low temperature can be expressed as less than 50 ° C. Further, the relatively high current density can be expressed as 300 μA / cm ² or more, and the relatively low current density can be expressed as less than 300 μA / cm ² .

From the above, a negative electrode layer containing Li metal or Li alloy, a positive electrode layer containing various positive electrode active materials, Li, La, Zr, and O, and a garnet crystal structure or a garnet crystal structure similar A lithium secondary battery having a solid electrolyte layer containing a lithium ion conductive ceramic material having a crystal structure is charged at a temperature of 50 ° C. or higher, thereby preventing a short circuit and a high current density of 300 μA / cm ² or higher. It turns out that it can charge with. Therefore, this lithium secondary battery can be charged in a short time.

DESCRIPTION OF SYMBOLS 10 Lithium secondary battery 11 Solid electrolyte layer 12 Positive electrode layer 13 Negative electrode layer 14 1st electrical power collector 15 2nd electrical power collector 18 Battery element part 19 Exterior body

Claims (6)

A negative electrode layer containing Li metal or Li alloy;
A positive electrode layer containing a positive electrode active material;
Contains a lithium ion conductive ceramic material containing Li, La, Zr, and O and having a garnet-type crystal structure or a crystal structure similar to a garnet-type crystal structure, provided between the negative electrode layer and the positive electrode layer A solid electrolyte layer,
Lithium having a current density (Ie / Sc) indicating a current Ie with respect to a contact area Sc between the solid electrolyte layer and the negative electrode layer at 50 ° C. or higher and charged to 300 μA / cm ² or higher. Secondary battery.   The solid electrolyte layer after charging protrudes from the surface of the negative electrode layer to the solid electrolyte layer, and the projecting precipitate containing Li has a cross section in the stacking direction of the negative electrode layer and the solid electrolyte layer. The protruding deposit has a length of 5 μm or more on the straight line formed by the negative electrode layer and the solid electrolyte layer, and the total length of the protruding deposit on the straight line with respect to the total length of the straight line is 2. The lithium secondary battery according to claim 1, wherein a ratio of the protruding precipitates expressed as a ratio is 20% or less. The lithium secondary battery according to claim 1, wherein the solid electrolyte layer has a lithium ion conductivity at room temperature of 10 ⁻⁵ S / cm or more and a relative density of 86% or more.   The said negative electrode layer contains at least 1 type selected from the group which consists of Li metal, a Li-Al alloy, a Li-Sn alloy, and a Li-Si alloy, The any one of Claims 1-3 characterized by the above-mentioned. The lithium secondary battery as described in.   The lithium secondary battery according to claim 1, wherein each of the negative electrode layer and the positive electrode layer is solid. A negative electrode layer containing Li metal or Li alloy;
A positive electrode layer containing a positive electrode active material;
A lithium ion conductive ceramic material containing Li, La, Zr, and O and having a garnet-type crystal structure or a crystal structure similar to a garnet-type crystal structure is provided between the negative electrode layer and the positive electrode layer. A solid electrolyte layer;
A lithium secondary battery having a current density of 50 μC or higher at a current density (Ie / Sc) indicating a current Ie with respect to a contact area Sc between the solid electrolyte layer and the negative electrode layer is 300 μA / cm ² or higher. A method for charging a lithium secondary battery.

Images