Conformity assessment method for negative electrode active materials

Abstract

The present invention relates to a method for evaluating a negative electrode active material for a lithium secondary battery and a negative electrode for a lithium secondary battery including a negative electrode active material judged to be suitable according to the method. The evaluation method can quantify the degree of side reactions that may occur in a negative electrode active layer after activation in a non-destructive manner, and can judge with high reliability the material suitability of a negative electrode active material contained inside a secondary battery. The negative electrode active material judged in this way has the advantages of excellent high-temperature stability and excellent life characteristics when used in a negative electrode.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0137191, filed on October 24, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to an evaluation method capable of evaluating the suitability of a negative electrode active material for a secondary battery, and to a negative electrode that has been judged to be suitable using the evaluation method. [Background technology]

[0003] Conventionally, lithium metal has been used as the negative electrode active material in lithium-ion secondary batteries. However, when lithium metal is used, there is a risk of explosion due to the formation of dendrites, which can cause a short circuit in the battery. Therefore, instead of lithium metal, carbon materials, which have advantages in terms of charge / discharge cycle life and cost, are often used as the negative electrode active material.

[0004] Such carbon materials include graphite. Charging graphite has a layered structure in which lithium ions are inserted, while discharging graphite has a layered structure in which the inserted lithium ions are released. A battery cell in a stable state after the initial activation process maintains a constant lithium ion concentration within the charged graphite. However, if the solid electrolyte interphase (SEI) layer of the battery cell is not fully formed during the initial activation process, or if active materials and / or additives other than the carbon material are present in the electrode, side reactions that reduce the lithium ion concentration within the graphite may occur. In particular, in recent years, to improve energy density, silicon materials containing silicon (Si) are often mixed with graphite at a suitable ratio and used as a negative electrode active material. The degree of side reactions that reduce the lithium ion concentration within the graphite varies depending on the mixing ratio and particle shape of the silicon material mixed with the carbon material, which in turn affects the battery's degradation tendency.

[0005] Therefore, in order to develop batteries with excellent performance, such as high-temperature stability and lifespan characteristics, research must be conducted to quantify the degree of side reactions that occur in negative electrode active materials and develop negative electrode active materials that satisfy the quantified degree of side reactions. However, to achieve this, technology must exist that can quantify the degree of side reactions in negative electrode active materials in batteries and evaluate the performance of the developed negative electrode active materials. However, because such technology has not yet been developed, it is difficult to develop negative electrode active materials that reflect the degree of side reactions of the negative electrode active materials. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6264299 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-098089 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide an evaluation method capable of non-destructively evaluating the material compatibility of a negative electrode active material contained in a secondary battery by quantifying the degree of side reactions occurring in the negative electrode, specifically, the negative electrode active layer, in a secondary battery, and a negative electrode for a secondary battery that has been determined to be compatible by the evaluation method. [Means for solving the problem]

[0008] To solve the above-mentioned problems, In one embodiment, the present invention comprises: measuring X-ray diffraction of the charged and stored battery cell; extracting X-ray diffraction peaks corresponding to the carbon intercalation compound and its decomposition products contained in the negative electrode active layer of the negative electrode from the measured X-ray diffraction, and calculating intensity integral values of the extracted diffraction peaks; From the calculated intensity integral, the reaction rate constant k1 for the carbon intercalation compound or the reaction rate constant k for its decomposition product -1 and calculating and evaluating the material compatibility of the negative electrode active material contained in the negative electrode active layer based on the calculated reaction rate constant.

[0009] At this time, the reaction rate constant k1 and the reaction rate constant k -1 may depend on the reaction represented by the following reaction scheme 1:

[0010] [ka]

[0011] In the above reaction formula 1, x is an integer of 2 to 10.

[0012] The reaction rate constant k1 for the carbon intercalation compound can be calculated by fitting the intensity integral value of the diffraction peak for the carbon intercalation compound to the following formula 1.

[0013]

number

[0014] In Equation 1, c6(0) represents the initial concentration of carbon intercalation compounds; c6(t) represents the concentration of carbon intercalation compounds at time t; a and b represent constants over time, t represents the elapsed storage time, k represents the effective reaction rate constant.

[0015] In addition, the reaction rate constant k for the decomposition product of the carbon intercalation compound is -1 can be calculated by fitting the intensity integral of the diffraction peak for the decomposition product to the following formula 2.

[0016]

number

[0017] In Equation 2, c 12 (0) represents the initial concentration of the degradant, c 12 (t) represents the concentration of the degradant at time t, a and b represent constants over time, t represents the elapsed storage time, k represents the effective reaction rate constant.

[0018] In this case, a and b in Formula 1 and Formula 2 can be 0 to 1 and 0 to 10, respectively.

[0019] In addition, the step of evaluating the material compatibility of the negative electrode active material includes: The calculated reaction rate constant k1 or k -1 comparing the values with their respective reference values and determining that the negative electrode active material of the negative electrode active layer is a suitable material if the reference values are satisfied; The calculated reaction rate constant k1 or k -1 Calculating the equilibrium constant K from The method may further include comparing the calculated equilibrium constant K with a reference equilibrium constant value, and when the reference value is satisfied, determining that the negative electrode active material of the negative electrode active layer is a suitable material.

[0020] At this time, the reference value of the reaction rate constant k1 and the reaction rate constant k -1 The standard values are 0.1 hours -1 It can be the following:

[0021] Also, the reference value of the equilibrium constant K may be 10 or less.

[0022] On the other hand, the carbon intercalation compound may be a compound in which 5 to 7 moles of carbon atoms are bonded to 1 mole of lithium atoms.

[0023] As an example, the carbon intercalation compound is LiC6, Li2C 12 , Li3C18 , Li4C 24 , Li5C 30 and Li6C 36 It may be one or more selected from the group consisting of:

[0024] The negative electrode is made of one or more carbon-based active materials selected from the group consisting of graphite, graphene, carbon nanotubes, carbon black, acetylene black, ketjen black, and carbon fiber, and Si, SiC, and SiO x (where 0.8≦x≦2.5) and one or more silicon-based active materials.

[0025] Furthermore, the battery cell can be stored at 150°C or less.

[0026] Furthermore, the negative electrode active material may have a specific range for the reference value of the reaction rate constant k1 and the reference value of the equilibrium constant K depending on the content of the silicon-based active material.

[0027] As an example, when the silicon-based active material is contained in an amount of 50% by weight or less based on the weight of the entire negative electrode active material, the reaction rate constant k1 reference value is 0.1 hour -1 and the equilibrium constant K can be 10 or less.

[0028] As another example, when the silicon-based active material is contained in an amount of 20% by weight or less based on the total weight of the negative electrode active material, the reaction rate constant k1 reference value is 0.05 hours. -1 and the equilibrium constant K reference value can be 5 or less.

[0029] Furthermore, in one embodiment, the present invention provides The negative electrode active material includes a carbon-based active material and a silicon-based active material, and the negative electrode active material is determined to be suitable through the evaluation method according to the present invention.

[0030] At this time, the negative electrode active material provided in the negative electrode has a reaction rate constant k -1and the equilibrium constant K, the compatibility can be judged in the above-described evaluation method of the present invention.

[0031] Specifically, when the negative electrode active material contains 50% by weight or less of a silicon-based active material based on the total weight, the negative electrode active material can be used for 0.1 hours. -1 It may have a reaction rate constant k of less than or equal to 10 and an equilibrium constant K of less than or equal to 10.

[0032] More specifically, when the negative electrode active material contains 20% by weight or less of a silicon-based active material based on the total weight, the negative electrode active material can be used for 0.05 hours. -1 It may have a reaction rate constant k of 1 or less and an equilibrium constant K of 5 or less. [Effects of the Invention]

[0033] The method for evaluating a negative electrode active material according to the present invention quantifies the degree of side reactions that may occur in a negative electrode active layer after activation in a non-destructive manner, and can reliably determine the material suitability of a negative electrode active material contained in a secondary battery with high reliability. The negative electrode active material thus determined has advantages such as excellent high-temperature stability and excellent life characteristics when used in a negative electrode. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a graph obtained by fitting the change in concentration ratio (c6(t) / c6(0)) of a carbon intercalation compound as a function of time t in Example 1 and Comparative Example 1 carried out according to the present invention. [Figure 2] 1 is a graph obtained by fitting the change in concentration ratio (c6(t) / c6(0)) of a carbon intercalation compound as a function of time t in Example 1 and Comparative Example 1 carried out according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] Because the present invention is susceptible to various modifications and may have various embodiments, specific embodiments are described in detail in the detailed description.

[0036] However, this is not intended to limit the invention to any particular embodiment, but rather to be understood as including all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0037] In the present invention, terms such as "comprise" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts or combinations thereof described in the specification, and may be understood as not precluding the presence or possibility of addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0038] Furthermore, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion therebetween. Conversely, when a layer, film, region, plate, or other portion is described as being "under" another portion, this includes not only the case where it is "directly below" the other portion, but also the case where there is another portion therebetween. Furthermore, in this application, being "located on" can include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0039] Furthermore, in the present invention, "contained as a main component" can mean 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or 97.5% by weight or more of the total weight of the composition such as a slurry or the specific component, and in some cases can mean 100% by weight when constituting the entire composition or specific component.

[0040] The present invention will now be described in more detail.

[0041] <Evaluation method for negative electrode active materials for secondary batteries> In one embodiment, the present invention comprises: measuring X-ray diffraction of the charged and stored battery cell; extracting X-ray diffraction peaks corresponding to the carbon intercalation compound and its decomposition products contained in the negative electrode active layer of the negative electrode from the measured X-ray diffraction, and calculating intensity integral values of the extracted diffraction peaks; The reaction rate constants k1 and k2 for the carbon intercalation compound and its decomposition products were calculated from the calculated intensity integrals. -1 and calculating and evaluating the material compatibility of the negative electrode active material contained in the negative electrode active layer based on the calculated reaction rate constant.

[0042] The method for evaluating a negative electrode active material for a secondary battery according to the present invention is a method for evaluating the suitability of a negative electrode active material for use in a secondary battery, and may evaluate an "negative electrode active material" that exhibits electrochemical activity in a negative electrode and / or an "negative electrode active layer" that contains the same as a main component. The "negative electrode active material" may be in the form of one or more single substances and / or a composition containing such substances that undergo an electrochemical reaction in the negative electrode active layer to induce electrical activity.

[0043] The evaluation method is characterized in that a negative electrode including a negative electrode active layer is manufactured using the negative electrode active material to be evaluated, and the degree of side reaction that occurs is quantified after the manufactured negative electrode is fully charged and stored at high temperature. Specifically, the evaluation method is characterized in that the reaction rate constants (k1, k2) for the carbon intercalation compound and its decomposition products are determined through the change in concentration of the carbon intercalation compound contained in the active layer of the negative electrode over time during storage of a charged battery cell. -1 The degree of side reactions in the negative electrode active layer can be quantified in the form of an equilibrium constant (K), etc., and the negative electrode active material can be evaluated through these. Therefore, the above evaluation method has the advantage of being able to evaluate the material compatibility of the negative electrode active material contained in the negative electrode of a battery cell with high reliability in a non-destructive manner.

[0044] A method for evaluating a negative electrode active material for a secondary battery according to the present invention includes measuring X-ray diffraction of a battery cell that has been charged and stored. The step of measuring X-ray diffraction of the battery cell involves non-destructively analyzing the negative electrode active layer of a negative electrode provided inside a fully charged battery cell, and may be performed by measuring X-ray diffraction of the stored battery cell at regular time intervals, for example, every 0.5 to 24 hours, more specifically, every 5 to 7 hours. In this case, the X-ray diffraction of the battery cell may not include information about the separator or electrolyte of the electrode assembly, which does not have crystallinity, but may include information about the positive and / or negative electrode active materials, which have crystallinity.

[0045] Furthermore, the temperature at which the battery cells are stored may be 150°C or lower, specifically 5°C to 150°C, 10°C to 150°C, 20°C to 150°C, 20°C to 120°C, 25°C to 100°C, 25°C to 80°C, 50°C to 100°C, 50°C to 80°C, 50°C to 70°C, 55°C to 65°C, or 58°C to 62°C.

[0046] The storage may be performed for 1 to 10 days, more specifically, for 1 to 9 days, 1 to 7 days, 2 to 6 days, 4 to 8 days, 6 to 8 days, 1 to 5 days, or 2 to 4 days. By storing the battery cell for the above-mentioned period, the present invention can induce equilibrium between the carbon intercalation compound contained in the battery cell and its decomposition products.

[0047] In addition, the method for evaluating a negative electrode active material for a secondary battery according to the present invention includes the steps of extracting X-ray diffraction peaks for a carbon intercalation compound and its decomposition products contained in a negative electrode active layer from the measured X-ray diffraction, and calculating the intensity integral values of the extracted diffraction peaks.

[0048] The above step can be performed by extracting, from the measured X-ray diffraction results, X-ray diffraction peaks of the carbon intercalation compound into which lithium has been inserted and X-ray diffraction peaks of decomposition products resulting from lithium desorption from the carbon intercalation compound, confirming the diffraction peak intensities that change with time, and calculating and displaying the integral values of the confirmed peak intensities over time.

[0049] Here, the intensity of the X-ray diffraction peak can correspond to the relative concentrations of the carbon intercalation compound and its decomposition products contained in the negative electrode active layer, and the value showing the intensity of the diffraction peak as a function of time can indicate the change in such relative concentrations.

[0050] In addition, the evaluation method of the negative electrode active material for a secondary battery according to the present invention is also a method for calculating the reaction rate constants k1 and k2 for the carbon intercalation compound and its decomposition products from the calculated intensity integral value. -1 The method includes a step of calculating each of the following:

[0051] Here, the reaction rate constants k1 and k -1 can be obtained by fitting the previously calculated intensity integral value to the following equations 1 and 2, respectively.

[0052]

number

[0053]

number

[0054] In Equation 1 and Equation 2, c6(0) represents the initial concentration of carbon intercalation compounds; c6(t) represents the concentration of carbon intercalation compounds at time t; c 12 (0) represents the initial concentration of the degradant, c 12 (t) represents the concentration of the degradant at time t, a and b represent constants over time, t represents the elapsed storage time, k represents the effective reaction rate constant.

[0055] The above formulas 1 and 2 may quantify the degree of side reactions that may occur in the negative electrode active layer during the activation process of a charged battery cell, respectively, in terms of the reaction rate of the carbon intercalation compound and its decomposition products.

[0056] Specifically, carbon-based active materials used as negative electrode active materials for secondary batteries include graphite having a layered structure, and the carbon-based active materials have a carbon intercalation compound structure in which lithium ions are inserted into the layered structure during battery charging, and the inserted lithium ions are released during battery discharge.

[0057] At this time, in a battery cell in a stable state after the initial activation process, the concentration of lithium ions in the graphite is maintained constant in a charged state. However, if a silicon-based active material is contained in the electrode as an active material other than a carbon-based active material, a side reaction that reduces the concentration of lithium ions and / or lithium in the graphite may occur during the initial activation process. More specifically, in a battery cell in a charged state after the initial activation process, a carbon intercalation compound (Li) into which lithium ions are inserted is formed. x C 6x ) is decomposed into a decomposition product (Li x-1 C 6x ) and the carbon intercalation compound. Here, lithium is released from the carbon intercalation compound over time under charged conditions. Some of the released lithium participates in side reactions, and a significant portion of these side reactions are converted into irreversible reactions that reduce the concentration of the carbon intercalation compound and cause degradation of the negative electrode active material. The concentration of the carbon intercalation compound may vary depending on the composition of the negative electrode active material, for example, the type and / or content ratio of the silicon-based active material contained with the carbon-based active material. The present invention can quantify the side reactions induced in the negative electrode active layer through changes in the concentration of the carbon intercalation compound depending on the composition of the negative electrode active material, and the quantified form may be the reaction rate constant for the carbon intercalation compound and decomposition products resulting from lithium being released from the layered structure.

[0058] [ka]

[0059] In the above reaction formula 1, x is an integer of 2 to 10.

[0060] More specifically, the present invention can calculate the change in concentration of a carbon intercalation compound over time from the decomposition reaction of the carbon intercalation compound that occurs in the negative electrode active layer during use and / or storage of a battery cell that is fully charged after initial activation, as represented by Reaction Scheme 1 above, in other words, the amount of decomposition product produced by lithium desorption from the carbon intercalation compound, which can be expressed mathematically as shown in Equation 3 below.

[0061]

number

[0062] In the above formula 3, dc6 / dt represents the derivative of the carbon intercalation compound concentration with respect to time t, k1 is the rate constant of the forward reaction in which lithium ions are released from the carbon intercalation compound to produce decomposition products of the carbon intercalation compound and lithium ions, k -1 is the rate constant of the reverse reaction of the decomposition product of the carbon intercalation compound and lithium ions to form the carbon intercalation compound, c 12 represents the concentration of decomposition products produced by decomposition of lithium ions in the carbon intercalation compound, c Li represents the concentration of lithium ions decomposed from the carbon intercalation compound, c6 represents the concentration of carbon intercalation compounds.

[0063] Next, to calculate the amount of side reactions in the anode during use and / or storage from Equation 3, which quantifies the reaction of Reaction Scheme 1 in terms of the change in concentration of the carbon intercalation compound and its decomposition products, integration and calculation of Equation 3 can be performed to derive Equation 1, which can predict the concentration change corresponding to the reaction rate of the carbon intercalation compound contained in the anode active layer during storage of a battery cell that has been fully charged after activation. The derived Equation 1 expresses the extent of side reactions that may occur in the anode active layer of a charged battery cell during use and / or storage after the initial activation process as the reaction rate for the carbon intercalation compound. In this case, k1, the lithium desorption reaction rate, is derived from the effective reaction rate constant k for the carbon intercalation compound, and the derived k1 can be used as an indicator that quantifies the side reactions occurring in the anode active layer.

[0064]

number

[0065] In Equation 1, c6(0) represents the initial concentration of carbon intercalation compounds; c6(t) represents the concentration of carbon intercalation compounds at time t; a and b represent constants over time, t represents the elapsed storage time, k represents the effective reaction rate constant.

[0066] As described above, the present invention has a configuration in which peaks (or spectra) for a carbon intercalation compound and its decomposition products are extracted from X-ray diffraction, and then the intensity integral value of the extracted peak is calculated, and the calculated intensity integral value is fitted to Equation 1 to obtain a reaction rate constant. This allows for a method that extracts diffraction peaks of a carbon intercalation compound from X-ray diffraction, calculates integral values for the intensity of the extracted peaks, and obtains a peak integral value (I LiC6 (t)) for the initial peak integral (I LiC6 This has the advantage that the accuracy of the reaction rate constant is significantly higher than when the reaction rate constant is calculated from the ratio of (0).

[0067] In the same manner, the change in concentration of the decomposition product resulting from the desorption of lithium from the carbon intercalation compound over time can be calculated using Reaction Formula 1, and by performing integration and calculation on the calculated formula, Equation 2 can be derived, which can predict the change in concentration of the decomposition product contained in the negative electrode active layer during storage of a battery cell that has been fully charged after activation, depending on the reaction rate.

[0068]

number

[0069] In Equation 2, c 12 (0) represents the initial concentration of the degradant, c 12 (t) represents the concentration of the degradant at time t, a and b represent constants over time, t represents the elapsed storage time, k represents the effective reaction rate constant.

[0070] In the above formulas 1 and 2, a and b are constants relative to time, and a can be 0 to 1, and b can be 0 to 10. Specifically, a can be 0 to 1, and b can be 0 to 10, more specifically, a can be 0 to 0.9, 0.1 to 0.8, or 0.1 to 0.6, and b can be 1 to 9, 2 to 8, or 4 to 6.

[0071] As one example, the negative electrode active layer provided in the battery cell according to the present invention may contain, as the negative electrode active material, 50 to 99 wt % and 1 to 50 wt % of a carbon-based active material and a silicon-based active material, respectively, based on the total weight of the negative electrode active material, in which case a and b may be 0.05 to 1.0 and 1 to 10, respectively. Specifically, a in the above formula 1 may be 0.1 to 0.6, more specifically 0.1 to 0.5, 0.1 to 0.4, 0.2 to 0.6, 0.2 to 0.5, 0.25 to 0.4, 0.25 to 0.45, 0.3 to 0.42, 0.28 to 0.42, or 0.31 to 0.39. Furthermore, b in the above formula 1 can be 2 to 9, and more specifically can be 3 to 9, 3 to 7, 4 to 8, 5 to 10, 3 to 8, 1 to 6, 4.5 to 6.0, or 5.0 to 5.5.

[0072] The above a and b may vary depending on the components, content, composition, and stabilization state of the negative electrode active layer where the lithium side reaction occurs. By controlling a and b within the above ranges, the concentration of lithium that has undergone the irreversible reaction, i.e., the extent of the side reaction in the negative electrode active layer, can be quantified with higher reliability depending on the components, content, composition, and stabilization state of the negative electrode active layer.

[0073] The method for evaluating a negative electrode active material for a secondary battery according to the present invention also includes evaluating the material compatibility of the negative electrode active material based on the calculated reaction rate constant.

[0074] The above step is a step of determining that a negative electrode active material that induces fewer side reactions in the negative electrode active layer after the activation process is a material with high material compatibility, and the determination may be made by evaluating the material compatibility based on the previously calculated reaction rate constant.

[0075] More specifically, the step is carried out by using the calculated reaction rate constant k1 or k -1 a step of comparing the calculated reaction rate constant k1 or k2 with the respective standard values and determining that the negative electrode active material of the negative electrode active layer is a suitable material if the standard values are met; -1and comparing the calculated equilibrium constant K with a reference equilibrium constant value, and if the reference value is satisfied, determining that the negative electrode active material of the negative electrode active layer is a suitable material.

[0076] The effective reaction rate constant k1 for the carbon intercalation compound calculated previously in Equation 1 and the effective reaction rate constant k for the decomposition product of the carbon intercalation compound calculated in Equation 2 are -1 The k1 and k2 can vary depending on the degree of stabilization of the carbon intercalation compound contained in the negative electrode active layer and the components contained in the negative electrode active layer, particularly the type and / or content ratio of components other than the carbon-based active material, such as the silicon-based negative electrode active material. -1 may vary depending on the components, content, composition, and stabilization state of the negative electrode active layer where the irreversible reaction of lithium occurs. Therefore, the reaction rate constants k1 and / or k2 may vary depending on the composition of the negative electrode active material (specifically, the components and content ratios). -1 The reaction rate constants k1 and / or k2 were investigated, and the values were compared to determine whether the negative electrode was in a stable state, i.e., whether there were few side reactions. -1 The reference value k1 and / or k -1 Then, the reaction rate constants k1 and k2 calculated from the X-ray diffraction results of the battery cell that was previously fully charged and stored are set to -1 is the reference value k1 and / or k -1 If the above condition is satisfied, it can be primarily determined that the negative electrode active material inside the battery cell measured by X-ray diffraction is suitable as a negative electrode material.

[0077] In this case, the reaction rate constant reference value for the carbon intercalation compound (i.e., reference value k1) is 0.1 hour when the negative electrode active material contains a carbon-based active material and a silicon-based active material in an amount of 50 to 100 wt % and 0 to 50 wt % based on the total weight of the negative electrode active material. -1 More specifically, the reference value of the reaction rate constant for the carbon intercalation compound is 0.0001 to 0.005 hour when the carbon-based active material and the silicon-based active material are contained in an amount of 50 to 100 wt % and 0 to 50 wt % based on the total weight of the negative electrode active material, respectively. -1, 0.0001~0.001hour -1 , 0.0005~0.002hour -1 , 0.005~0.1hour -1 , 0.005~0.07hours -1 , 0.005~0.05hours -1 , 0.005~0.03hours -1 , 0.005~0.02hour -1 , 0.005~0.015hours -1 , 0.005~0.009hours -1 , 0.01~0.015hours -1 , 0.025~0.04hours -1 , or 0.030~0.035 hours -1 It could be.

[0078] In addition, the reaction rate constant reference value for the decomposition product of the carbon intercalation compound (i.e., the reference value k -1 ) is a negative electrode active material containing a carbon-based active material and a silicon-based active material in an amount of 50 to 100% by weight and 0 to 50% by weight, respectively, based on the total weight of the negative electrode active material. -1 More specifically, it can be 0.0001 to 0.005 hours. -1 , 0.0001~0.001hour -1 , 0.0005~0.002hour -1 , 0.001~0.05hours -1 , 0.001~0.02hour -1 , or 0.002 to 0.01 hours -1 , 0.005~0.1hour -1 , 0.005~0.07hours -1 , 0.005~0.05hours -1 , 0.005~0.03hours -1 , 0.005~0.02hour -1 , 0.005~0.015hours -1 , 0.005~0.009hours -1 , 0.01~0.015hours -1 , 0.025~0.04hours -1 , or 0.030~0.035 hours -1It could be.

[0079] In addition, the above reference values k1 and k -1 The value at which the negative electrode is highly stabilized and side reactions are minimized may be predicted through simulation or may be determined by actually measuring the value in advance for each composition of the negative electrode active material, but is not limited thereto.

[0080] Further, the step of evaluating the material compatibility may optionally include determining the reaction rate constants k1 and / or k -1 The equilibrium constant K can be calculated from the reaction rate constant k and the calculated equilibrium constant K can be applied to make a secondary judgment. The secondary judgment can be understood as a step of verifying the primary judgment. In addition, the equilibrium constant K can be calculated by the reaction rate constant k and k -1 The ratio (k1 / k -1 ) and the reference value of the equilibrium constant K can be obtained from the reaction rate constants k1 and k -1 can be obtained from the standard value ratio.

[0081] In this case, the equilibrium constant reference value (i.e., reference value K) may be 10 or less when the negative electrode active material contains a carbon-based active material and a silicon-based active material in an amount of 50 to 100 wt %, or 0 to 50 wt %, relative to the total weight of the negative electrode active material, and more specifically may be 0.1 to 10, 0.1 to 5, 0.1 to 3, 0.5 to 2, 1 to 4.5, 5 to 10, 5.5 to 9, or 6 to 9.

[0082] As an example, when the silicon-based active material is contained in an amount of more than 0% by weight and less than 10% by weight based on the weight of the entire negative electrode active material, the reference value of the reaction rate constant k1 is 0.005 hours. -1 Less than or equal to 0.001 hours -1 The standard value of the equilibrium constant K can be 1 or less, or 0.1 or less. More specifically, the standard value of the reaction rate constant k1 is 0.0001 to 0.001 hour. -1 and the standard value of the equilibrium constant K can be 0.001 to 0.1.

[0083] As another example, when the silicon-based active material is contained in an amount of more than 10 wt% and less than 20 wt% based on the total weight of the negative electrode active material, the reaction rate constant k1 reference value is more than 0.005 and less than 0.05 hour -1 Less than or equal to 0.005, 0.03hour -1 Less than or equal to 0.001 hours -1 Excess 0.03hour -1 The standard value of the equilibrium constant K can be greater than 0.1 and less than 6, greater than 0.1 and less than 3, greater than 1 and less than 5, greater than 1 and less than 6, greater than 1 and less than 3, or greater than 0.1 and less than 5. More specifically, the standard value of the reaction rate constant k1 is 0.005 to 0.01 hour -1 and the standard value of the equilibrium constant K can be 0.1 to 3.

[0084] As another example, when the silicon-based active material is contained in an amount of more than 20% by weight and less than 50% by weight based on the total weight of the negative electrode active material, the reaction rate constant k1 reference value is more than 0.05 and less than 0.1 hour. -1 Less than or equal to 0.03, 0.1hour -1 The standard value of the equilibrium constant K can be more than 3 and less than 10, or more than 5 and less than 10. More specifically, the standard value of the reaction rate constant k1 is 0.05 to 0.09 hours. -1 and the standard value of the equilibrium constant K can be 6-9.

[0085] As another example, when the silicon-based active material is contained in an amount of more than 0% by weight and less than 20% by weight based on the weight of the entire negative electrode active material, the reaction rate constant k1 reference value is 0.05 hours. -1 Less than 0.00001~0.05hour -1 , or 0.00001 to 0.03 hours -1 and the reference value of the equilibrium constant K can be 5 or less, 0.5 to 5, or 0.5 to 3.

[0086] Meanwhile, the negative electrode for a secondary battery according to the present invention includes a carbon-based active material containing carbon as a main component as a negative electrode active material. As described above, the carbon-based active material may be formed by inserting positive electrode metal ions, which react reversibly when the battery cell is charged, into the negative electrode, for example, one or more positive electrode metal ions selected from Li, Na, Mg, Ca, K, Rb, Cs, and Al. That is, in the case of a secondary battery, the carbon intercalation compound is a compound that acts as a catalyst between the carbon-based active material and lithium ions (Li + ) can refer to a material in which sodium ions (Na) are bonded to a carbonaceous active material in the case of sodium secondary batteries or aluminum secondary batteries. + ) or aluminum ions (Al 3+ ) may refer to the substance to which the bond is attached.

[0087] The carbon-based active material may be any material commonly used in the art as a negative electrode active material without any particular limitation. Specifically, the carbon-based active material may include one or more carbon-based active materials selected from the group consisting of graphite, graphene, carbon nanotubes, carbon black, acetylene black, ketjen black, and carbon fiber.

[0088] Furthermore, the carbon intercalation compound may have one or more metal ions of Li, Na, Mg, Ca, and Al contained in the positive electrode inserted into the interlayer structure of the carbon-based active material at a certain molar fraction during charging of the battery cell. Specifically, in the case of a secondary battery, the carbon intercalation compound in which lithium is inserted into the interlayer structure of the carbon-based active material during charging of the battery cell may have 5 to 7 molar fractions of carbon atoms bonded to 1 mole of lithium atoms, specifically 5.5 to 6.5 molar fractions of carbon atoms bonded to 1 mole of lithium atoms.

[0089] As an example, the carbon intercalation compound is LiC6, Li2C 12 , Li3C 18 , Li4C 24 , Li5C 30 and Li6C 36 and the material may comprise one or more selected from the group consisting of Li 2x C 12x (However, it can also be expressed as 2≦x≦10).

[0090] In the case of a sodium secondary battery, the carbon intercalation compound may have 5 to 7 molar fractions of carbon atoms bonded to 1 mole of sodium atoms, specifically 5.5 to 6.5 molar fractions of carbon atoms bonded to 1 mole of sodium atoms.

[0091] As an example, the carbon intercalation compound is NaC6, Na2C 12 , Na3C 18 , Na4C 24 , Na5C 30 and Na6C 36 The substance may comprise one or more selected from the group consisting of Na 2x C 12x (However, it can also be expressed as 2≦x≦10).

[0092] The negative electrode active layer may further contain a silicon-based active material as a negative electrode active material. Examples of such silicon-based active materials include Si, SiC, and SiO x (where 0.8≦x≦2.5). In this case, the silicon material may contain one or more metals selected from Li, Na, Mg, and Ca in an amount of 0 to 50 molar parts per 100 molar parts of silicon (Si) contained in the silicon material. In addition, the silicon-based active material may have a composite form in which the silicon material is coated with or composited with carbon.

[0093] As an example, the silicon-based active material may be a material in which Si and SiO2 are uniformly mixed.

[0094] In another example, the silicon-based active material is SiO x (where 0.8≦x≦2.5) Li is added to SiO x The doping material may be 10 molar parts or less per 100 molar parts of silicon (Si) contained in the silicon dioxide.

[0095] As another example, the silicon-based active material is SiO x (where 0.8≦x≦2.5) Al is added to SiOx The alloy compound may be contained in an amount of 20 to 40 parts by mole relative to 100 parts by mole of silicon (Si) contained in the alloy.

[0096] As another example, the silicon-based active material may be a composite in which Si is coated with carbon (ie, a Si / C composite).

[0097] The silicon-based active material may have a certain content ratio with the carbon-based active material, which is the main component of the negative electrode active material. Specifically, the silicon-based active material may be included in an amount of 0 to 50 wt % based on the total weight of the negative electrode active material, with the remainder being the carbon-based active material. Specifically, the silicon-based active material may be included in an amount of 0 to 10 wt %, 5 to 10 wt %, 10 to 20 wt %, 10 to 15 wt %, 15 to 20 wt %, 20 to 50 wt %, 20 to 40 wt %, 20 to 30 wt %, or 30 to 50 wt % based on the total weight of the negative electrode active material.

[0098] <Anode active material evaluation system for secondary batteries> In one embodiment, the present invention further comprises: A negative electrode active material evaluation system is provided to which the above-described method for evaluating a negative electrode active material for a secondary battery is applied.

[0099] The negative electrode active material evaluation system according to the present invention is adapted to the above-described negative electrode active material evaluation method, and can evaluate the material compatibility of the negative electrode active material contained in the negative electrode of a battery cell in a non-destructive manner with high reliability.

[0100] To this end, the evaluation system includes a chamber into which a fully charged battery cell is inserted, an input unit provided outside the chamber for inputting the type and content ratio of the negative electrode active material contained in the battery cell inserted into the chamber, an X-ray diffraction detector mounted in the chamber for irradiating X-rays onto the battery cell and detecting X-rays diffracted from the battery cell, and an X-ray diffraction detector electrically connected to the X-ray diffraction detector for extracting X-ray diffraction peaks for a carbon intercalation compound and / or its decomposition products from the X-ray diffraction spectrum transmitted from the battery cell by the X-ray diffraction detector, calculating intensity integrals of the extracted diffraction peaks, and calculating a reaction rate constant k1 for the carbon intercalation compound and / or its decomposition products from the calculated intensity integrals. -1 and a control unit that calculates:

[0101] In this case, the control unit may include a database that stores reference values of reaction rate constants for carbon intercalation compounds and their decomposition products according to the type and content ratio of the negative electrode active material, and may compare the reference value of the reaction rate constant according to the type and content ratio of the negative electrode active material input via the input unit with the reaction rate constant calculated from the value measured by the X-ray diffraction detection unit to determine the material suitability of the negative electrode active material included in the battery cell.

[0102] The control unit also calculates the calculated reaction rate constant k1 for the carbon intercalation compound and / or the reaction rate constant k for its decomposition product. -1 The equilibrium constant K can be additionally calculated from the reaction rate constant reference value, and the calculated equilibrium constant K can be compared to the equilibrium constant reference value obtained from the reaction rate constant reference value to further verify the material compatibility results evaluated using the reaction rate constant.

[0103] The negative electrode active material evaluation system for a secondary battery according to the present invention has the above-described configuration, and can evaluate the material compatibility of the negative electrode active material included in a battery cell in a non-destructive manner with high accuracy.

[0104] <Anode for lithium secondary batteries> Furthermore, in one embodiment, the present invention provides The negative electrode for a lithium secondary battery includes a negative electrode active material that has been determined to be suitable through the above-described evaluation method for a negative electrode active material for a secondary battery.

[0105] The negative electrode according to the present invention has a structure in which a negative electrode active layer is located on a negative electrode current collector, and the negative electrode composite layer has a reaction rate constant k1 and an equilibrium constant K of 0.1 hour for the carbon intercalation compound, which are calculated by fitting the intensity integrals of the X-ray diffraction peaks of the carbon intercalation compound and its decomposition products during X-ray diffraction of the negative electrode composite layer. -1 The reaction rate constant k1 and the equilibrium constant K can be calculated by the same procedure as in the evaluation method of the negative electrode active material according to the present invention after obtaining an X-ray diffraction spectrum.

[0106] Here, the negative electrode active material contained in the negative electrode active layer includes a carbon-based active material and a silicon-based active material, and the reaction rate constant k1 and the equilibrium constant K for the carbon intercalation compound calculated by X-ray diffraction analysis may vary depending on the content and / or content ratio of the silicon-based active material.

[0107] Specifically, the X-ray diffraction analysis results of the negative electrode active layer may vary depending on the composition (e.g., components and content) of the negative electrode active material, the form of the negative electrode active material, the combination of components other than the negative electrode active material, the conditions for forming the negative electrode active layer, etc., and therefore the peaks corresponding to the carbon intercalation compound and its decomposition products present in the negative electrode active layer may vary. The present invention is characterized in that, when the negative electrode active layer contains a carbon-based active material and a silicon-based active material, the reaction rate constant k1 and equilibrium constant K for the carbon intercalation compound fall within specific ranges depending on the content and / or content ratio of the silicon-based active material.

[0108] For example, when the negative electrode active material contained in the negative electrode active layer according to the present invention contains 0 to 50 wt % of a silicon-based active material with respect to the weight of the entire negative electrode active material, the reaction rate constant k1 with respect to a carbon intercalation compound is 0.1 hour -1 More specifically, it can be 0.0001 to 0.005 hours. -1, 0.0001~0.001hour -1 , 0.0005~0.002hour -1 , 0.001~0.05hours -1 , 0.001~0.02hour -1 , 0.002~0.01hour -1 , 0.005~0.1hour -1 , 0.005~0.07hours -1 , 0.005~0.05hours -1 , 0.005~0.03hours -1 , 0.005~0.02hour -1 , 0.005~0.015hours -1 , 0.005~0.009hours -1 , 0.01~0.015hours -1 , 0.025~0.04hours -1 , or 0.030~0.035 hours -1 It could be.

[0109] Furthermore, the negative electrode active material contained in the negative electrode active layer according to the present invention may have an equilibrium constant K of 10 or less, more specifically 0.1 to 10, 0.1 to 5, 0.1 to 3, 0.5 to 2, 1 to 4.5, 5 to 10, 5.5 to 9, or 6 to 9, when the negative electrode active material contains 0 to 50 wt % of a silicon-based active material relative to the total weight of the negative electrode active material.

[0110] As an example, when the negative electrode active material contains 10 wt % or less of a silicon-based active material based on the total weight, the negative electrode active material has a resistance of 0.005 hours. -1 Less than or equal to 0.001 hours -1 It may have a reaction rate constant k1 of 1 or less, or an equilibrium constant K of 0.1 or less.

[0111] In another example, when the negative electrode active material contains more than 10 wt % and not more than 20 wt % of a silicon-based active material based on the total weight, the negative electrode active material has a sintering time of more than 0.005 to 0.05 hours. -1 Less than or equal to 0.005, 0.03hour -1 Less than or equal to 0.001 or more than 0.03 hours -1and an equilibrium constant K of greater than 0.1 and less than or equal to 6, greater than 0.1 and less than or equal to 3, greater than 1 and less than or equal to 5, greater than 1 and less than or equal to 6, greater than 1 and less than or equal to 3, or greater than 0.1 and less than or equal to 5.

[0112] In another example, when the negative electrode active material contains more than 20 wt % and not more than 50 wt % of a silicon-based active material based on the total weight, the negative electrode active material has a temperature of more than 0.05 to 0.1 hour. -1 Less than or equal to 0.03 or more than 0.1 hour -1 and an equilibrium constant K of greater than 3 and less than or equal to 10 or greater than 5 and less than or equal to 10.

[0113] In another example, when the negative electrode active material contains more than 0 wt % and 20 wt % or less of a silicon-based active material, -1 Less than 0.00001~0.05hour -1 , or 0.00001 to 0.03 hours -1 and an equilibrium constant K of 5 or less, 0.5 to 5, or 0.5 to 3.

[0114] Meanwhile, the negative electrode active layer may be prepared by coating a negative electrode slurry containing a negative electrode active material and a binder that helps bind the negative electrode active material on a negative electrode current collector, followed by drying and pressing.

[0115] In this case, the negative electrode active material includes a negative electrode active material that has been determined to be suitable by the evaluation method of the present invention. Therefore, a negative electrode including the negative electrode has an advantage of being excellent in high-temperature stability since side reactions in the negative electrode active layer are significantly reduced during high-temperature storage in a fully charged state.

[0116] The negative electrode active material includes a carbon-based active material mainly composed of carbon atoms. The carbon-based active material may be any carbon-based active material commonly used in the art without any particular limitation. Specifically, the carbon-based active material may include one or more carbon-based active materials selected from the group consisting of graphite, graphene, carbon nanotubes, carbon black, acetylene black, ketjen black, and carbon fiber.

[0117] The negative electrode active material may further include a silicon-based active material in addition to the carbon-based active material. Examples of the silicon-based active material include Si, SiC, and SiO. x (where 0.8≦x≦2.5). In this case, the silicon material may contain one or more metals selected from Li, Na, Mg, and Ca in an amount of 0 to 50 molar parts per 100 molar parts of silicon (Si) contained in the silicon material. In addition, the silicon-based active material may have a composite form in which the silicon material is coated with or composited with carbon.

[0118] As an example, the silicon-based active material may be a material in which Si and SiO2 are uniformly mixed.

[0119] In another example, the silicon-based active material is SiO x (where 0.8≦x≦2.5) Li is added to SiO x The doping material may be 10 molar parts or less per 100 molar parts of silicon (Si) contained in the silicon dioxide.

[0120] As another example, the silicon-based active material is SiO x (where 0.8≦x≦2.5) Al is added to SiO x The alloy compound may be contained in an amount of 20 to 40 parts by mole relative to 100 parts by mole of silicon (Si) contained in the alloy.

[0121] As another example, the silicon-based active material may be a composite in which Si is coated with carbon (ie, a Si / C composite).

[0122] The silicon-based active material may have a certain content ratio with the carbon-based active material, which is the main component of the negative electrode active material. Specifically, the silicon-based active material may be included in an amount of 0 to 50 wt % based on the total weight of the negative electrode active material, with the remainder being the carbon-based active material. Specifically, the silicon-based active material may be included in an amount of 0 to 10 wt %, 5 to 10 wt %, 10 to 20 wt %, 10 to 15 wt %, 15 to 20 wt %, 20 to 50 wt %, 20 to 40 wt %, 20 to 30 wt %, or 30 to 50 wt % based on the total weight of the negative electrode active material.

[0123] The negative electrode for a secondary battery according to the present invention has the above-described structure, and therefore has excellent life characteristics. In addition, it has the advantage of excellent high-temperature stability due to significantly reduced side reactions in the negative electrode active layer during high-temperature storage.

[0124] The present invention will be described in more detail below with reference to examples and experimental examples.

[0125] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0126] <Examples 1 and 2 and Comparative Example 1. Evaluation of material compatibility of negative electrode active materials assembled into battery cells>

[0127] <Battery cell manufacturing> A negative electrode active material was prepared by mixing natural graphite, which is a carbon-based active material, and silicon particles (SiO, purity: >99.8%), which is a silicon-based active material. The content of the silicon particles (i.e., silicon-based active material) in the negative electrode active material was adjusted as shown in Table 1 based on the weight of the total negative electrode active material.

[0128] Next, 100 parts by weight of the negative electrode active material was mixed with 3 parts by weight of styrene-butadiene rubber (SBR) as a binder and 0.5 parts by weight of an additive to prepare a negative electrode slurry. Additives A and B were used as additives in the example and comparative example, respectively. The prepared negative electrode slurry was coated on the entire surface of a 10 cm x 20 cm copper current collector and dried to form a negative electrode composite layer (average thickness: 120 μm). The circulating air temperature was 80°C. The mixture was then rolled and dried in a vacuum oven at 130°C for 12 hours to prepare a negative electrode.

[0129] Separately, N-methylpyrrolidone solvent was poured into a homomixer, and the positive electrode active material, LiNi 0.8 Co 0.1 Mn 0.1 To prepare a cathode slurry, 100 parts by weight of O2 were mixed with 2 parts by weight of carbon black (a conductive material) and 2 parts by weight of PVDF (a binder) at 3,000 rpm for 60 minutes. The cathode slurry was coated onto a 10 cm x 20 cm aluminum current collector and dried to form a cathode composite layer (average thickness: 150 μm). The circulating air temperature was 80°C. The mixture was then rolled and dried in a vacuum oven at 130°C for 12 hours to prepare a cathode.

[0130] Then, a separator (thickness: about 16 μm) made of a porous polyethylene (PE) film was interposed between the fabricated positive electrode and each of the previously prepared negative electrodes, and E2DVC was injected as an electrolyte to fabricate a pouch cell in the form of a full cell.

[0131] Here, "E2DVC" refers to a type of carbonate-based electrolyte solution, which is a solution obtained by mixing lithium hexafluorophosphate (LiPF6, 1.0 M) and vinylene carbonate (VC, 2 wt %) with a mixture of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) = 1:1:1 (volume ratio).

[0132] The prepared battery cells were charged at a constant current (CC) of 0.3C to a voltage of 4.25V at a temperature of 25°C, then charged at a constant voltage (CV) of 0.05C, and then discharged at a constant current (CC) of 0.3C to 2.5V. This process was repeated three times. The discharged battery cells were then fully charged to 4.25V to 100% SOC.

[0133] <Initial judgment of compatibility of negative electrode active material> Each charged battery cell was then fixed in a fixture inside a high-temperature chamber for pouch cell transmission X-ray diffraction, and the X-ray diffraction was aligned to the current collector peak position through 2θ scanning on the X-ray diffraction stage. The sample reference was adjusted so that the diffraction peaks for the copper and aluminum current collectors matched their positions in the database, and in this state, the oven temperature was set to 60°C to induce a high-temperature environment. X-ray diffraction measurements of the pouch cells were taken when the internal oven temperature reached 60°C, and then every 6 hours thereafter.

[0134] The diffraction peaks of the carbon intercalation compound (specifically, LiC6) were extracted from the measured X-ray diffraction data, and the integral values of the extracted peak intensities were calculated. The calculated values were then plotted against time. Then, Equation 1 was used to fit the ratio (c6(t) / c6(0)) of the initial concentration of the carbon intercalation compound (c6(t)) to the concentration of the carbon intercalation compound at time t (c6(t)). In this case, a in Equation 1 was adjusted to 0.36 ± 0.06, and b was adjusted to 5.3 ± 2.0. The reaction rate constant k1 of the carbon intercalation compound was calculated from the fitted results, and the results are shown in Figures 1 and 2 and Table 1. In Figure 1, the concentration ratio (c6(t) / c6(0)) calculated from the X-ray diffraction results is represented by dots over time, and the graph based on Equation 1 is represented by a line.

[0135]

number

[0136] In Equation 1, c6(0) represents the initial concentration of carbon intercalation compounds; c6(t) represents the concentration of carbon intercalation compounds at time t; a and b represent constants over time, t represents the elapsed storage time, k is the effective reaction rate constant.

[0137] [Table 1]

[0138] The calculated reaction rate constant k1 was compared with the reaction rate constant reference value to determine the suitability of the negative electrode active material. The reference value was applied according to the content of silicon monoxide (SiO), a silicon-based active material, as shown in Table 2 below.

[0139] [Table 2]

[0140] As a result of the initial evaluation of the negative electrode active materials, it was confirmed that the negative electrode active materials of Examples 1 to 3 and Comparative Example 1 had reaction rate constant values for the carbon intercalation compound that satisfied the reference value.

[0141] <Secondary compatibility assessment of negative electrode active materials> The equilibrium constant K was calculated using the reaction rate constant k1 calculated in each of the examples and comparative examples, as shown in Table 3 below. The calculated equilibrium constant K was compared with the equilibrium constant reference value to secondarily determine the suitability of the negative electrode active material.

[0142] [Table 3]

[0143] At this time, the reference value K was applied according to the content of silicon monoxide (SiO) which is a silicon-based active material, as shown in Table 4 below.

[0144] [Table 4]

[0145] As a result of the secondary evaluation of the negative electrode active materials, the negative electrode active materials used in the battery cells of Examples 1 to 3 met the standard value for the equilibrium constant K and were therefore evaluated as "suitable" as negative electrode materials for lithium secondary batteries. On the other hand, the negative electrode active material used in the battery cell of Comparative Example 1 did not meet the standard value for the equilibrium constant. Failure to meet the standard value, as with the negative electrode active material of Comparative Example 1, means that a side reaction that reduces the concentration of lithium ions in the graphite during the charge / discharge process after activation may occur, which may lead to a strong tendency for battery degradation. Therefore, the negative electrode active material used in the battery cell of Comparative Example 1 was evaluated as "unsuitable" as a negative electrode material for lithium secondary batteries.

[0146] <Experimental Example>

[0147] To verify the results obtained in the examples and comparative examples, the battery cells used in example 2 and comparative example 1, which contain the same silicon-based active material, were subjected to 100 charge-discharge cycles at 45°C and 0.3C, and the charge-discharge capacity retention was measured. The results are shown in Table 5 below.

[0148] [Table 5]

[0149] As can be seen from Table 5 above, the battery cells of the examples judged to be suitable as anode materials for lithium secondary batteries according to the present invention exhibited a high capacity retention rate of about 92% or more even after 100 charge-discharge cycles, whereas the battery cells of the comparative examples judged to be unsuitable as anode materials exhibited a low capacity retention rate of less than about 87% after 100 charge-discharge cycles.

[0150] These results show that the method for assessing a negative electrode active material for a lithium secondary battery according to the present invention can quantify the degree of side reactions that may occur in the negative electrode active layer after activation and assess the degradation tendency of the negative electrode active material with high reliability, and that a negative electrode that is assessed as suitable through the above assessment method has excellent life characteristics and high-temperature stability.

[0151] Although the present invention has been described above with reference to preferred embodiments, it will be understood that a person skilled in the art or having ordinary knowledge in the art can make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention as set forth in the claims below.

[0152] Therefore, the technical scope of the present invention is not limited to the content described in the Summary of the Invention of the specification, but is defined by the claims.

Claims

1. measuring X-ray diffraction of the charged and stored battery cell; extracting X-ray diffraction peaks corresponding to the carbon intercalation compound and its decomposition products contained in the negative electrode active layer of the negative electrode from the measured X-ray diffraction, and calculating intensity integral values of the extracted diffraction peaks; The reaction rate constant k for the carbon intercalation compound was calculated from the calculated intensity integral value. １ or the reaction rate constant k for the decomposition product of the carbon intercalation compound －１ and calculating and evaluating the material compatibility of the negative electrode active material contained in the negative electrode active layer based on the calculated reaction rate constant.

2. Reaction rate constant k １ and the reaction rate constant k －１ The method for evaluating a negative electrode active material for a secondary battery according to claim 1 , wherein: 【Chemical 1】 In the above reaction scheme 1, x is an integer of 2 to 10.

3. Reaction rate constant k for carbon intercalation compounds １ The method for evaluating a negative electrode active material for a secondary battery according to claim 1 , wherein the value of the diffraction peak intensity integral for the carbon intercalation compound is calculated by fitting the value of the diffraction peak intensity integral for the carbon intercalation compound to the following formula 1: [Equation 1] In Formula 1, c ６ (0) represents the initial concentration of carbon intercalation compound; c ６ (t) represents the concentration of carbon intercalation compounds at time t; a and b represent constants with respect to time; t represents the elapsed storage time; k represents the effective reaction rate constant.

4. Reaction rate constant k for the decomposition product of the carbon intercalation compound －１ The method for evaluating a negative electrode active material for a secondary battery according to claim 1 , wherein the value of the diffraction peak intensity integral for the decomposition product is calculated by fitting the value of the diffraction peak intensity integral for the decomposition product to the following formula 2: [Equation 2] In Equation 2, c １２ (0) represents the initial concentration of the decomposition product, c １２ (t) represents the concentration of the decomposition product at time t; a and b represent constants with respect to time; t represents the elapsed storage time; k represents the effective reaction rate constant.

5. 5. The method for evaluating a negative electrode active material for a secondary battery according to claim 3, wherein a and b in Formula 1 and Formula 2 are 0 to 1 and 0 to 10, respectively.

6. The step of evaluating the material compatibility of the negative electrode active material includes: The calculated reaction rate constant k １ or k －１ comparing the values with their respective reference values and determining that the negative electrode active material of the negative electrode active layer is a suitable material if the reference values are satisfied; The calculated reaction rate constant k １ or k －１ Calculating the equilibrium constant K from and comparing the calculated equilibrium constant K with a reference equilibrium constant value, and if the reference value is satisfied, determining that the negative electrode active material of the negative electrode active layer is a suitable material.

7. Reaction rate constant k １ The reference value of and the reaction rate constant k －１ The reference values are 0.1 hours, respectively. －１ The method for evaluating a negative electrode active material for a secondary battery according to claim 6, wherein:

8. 7. The method for evaluating a negative electrode active material for a secondary battery according to claim 6, wherein the reference value of the equilibrium constant K is 10 or less.

9. 2. The method for evaluating a negative electrode active material for a secondary battery according to claim 1, wherein the carbon intercalation compound is a compound in which 5 to 7 moles of carbon atoms are bonded to 1 mole of lithium atoms.

10. The carbon intercalation compound is LiC ６ , Li ２ C １２ , Li ３ C １８ , Li ４ C ２４ , Li ５ C ３０ and Li ６ C ３６ The method for evaluating a negative electrode active material for a secondary battery according to claim 1 , wherein the negative electrode active material is one or more selected from the group consisting of:

11. The method for evaluating a negative electrode active material for a secondary battery according to claim 1 , wherein the storage is carried out at 150° C. or less.

12. The negative electrode is one or more carbonaceous active materials selected from the group consisting of graphite, graphene, carbon nanotubes, carbon black, acetylene black, ketjen black, and carbon fibers; Si, SiC and SiO ｘ and one or more silicon-based active materials selected from the group consisting of (where 0.8≦x≦2.5).

13. When the silicon-based active material is contained in an amount of 50% by weight or less based on the weight of the entire negative electrode active material, Reaction rate constant k １ The standard value is 0.1 hours －１ is less than or equal to, and 2. The method for evaluating a negative electrode active material for a secondary battery according to claim 1, wherein the reference value of the equilibrium constant K is 10 or less.

14. When the silicon-based active material is contained in an amount of 20% by weight or less based on the weight of the entire negative electrode active material, Reaction rate constant k １ The standard value is 0.05 hours －１ is less than or equal to, and 2. The method for evaluating a negative electrode active material for a secondary battery according to claim 1, wherein the reference value of the equilibrium constant K is 5 or less.

15. The negative electrode active material includes a carbon-based active material and a silicon-based active material, A negative electrode for a secondary battery, comprising a negative electrode active material that has been determined to be suitable through the evaluation method of claim 1.

16. When the negative electrode active material contains 50% by weight or less of a silicon-based active material based on the total weight, the negative electrode active material is －１ The reaction rate constant k １ The negative electrode for a secondary battery according to claim 15 , wherein the negative electrode has an equilibrium constant K of 10 or less.

17. When the silicon-based active material is contained in an amount of 20% by weight or less based on the weight of the entire negative electrode active material, Reaction rate constant k １ The standard value is 0.05 hours －１ is less than or equal to, and 16. The negative electrode for a secondary battery according to claim 15, wherein the reference value of the equilibrium constant K is 5 or less.

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