Device for determining the mechanical properties of a material

Abstract

The invention relates to a device 1 for determining the mechanical properties of a material, comprising a sample carrier 4, a penetration determination unit 13 and an actuation unit 8, wherein the sample carrier 4 has at least one pore 5, wherein the sample carrier 4 is configured to receive a sample 9 of the material to be examined on a first side 19, wherein the actuation unit 8 is configured to exert a force on a sample 9 arranged in the sample carrier 4, so that the sample 9 is pressed towards the first side 19, and wherein the penetration determination unit 13 is configured to determine a degree of penetration of the pore 5 by the sample 9.

Description

[0001] The invention relates to a device and a method for determining the mechanical properties of a material. State of the art

[0002] The development of batteries, particularly lithium batteries, is driven, among other things, by the development of new materials and the acquisition of knowledge about their mechanical properties. In investigating material properties, the length-scale dependence of these mechanical properties is of considerable importance. Nano- or micro-identification methods are currently used to examine these materials. These investigations are carried out using a microindenter. Here, the material under investigation is clamped onto a support surface, and a point on the surface of the material is pressed into it using a probe tip, causing the affected area to deform. The probe tip is significantly smaller than the surface of the material under investigation. The probe tip can have different geometries, for example, round, flat, or pointed.The material of the probe tip is harder than the material being tested. The penetration force and the penetration depth of the probe tip into the material are measured. From this information, the mechanical properties of the material are determined.

[0003] For a material to be suitable for use in batteries, especially lithium batteries, its tendency to form dendrites is crucial. Knowledge of the material's mechanical properties, as required to determine this tendency, can only be partially derived using microindentation. Furthermore, the high reactivity of alkali metals, which are particularly well-suited for use in batteries and are therefore preferred for investigation, complicates the use of a conventional microindenter. Disclosure of the invention

[0004] The device according to the invention for determining the mechanical properties of a material allows for a repeatable and reliable determination of these properties. In particular, the viscoplastic properties of the material are investigated at small lengths. Thus, the length-scale dependencies of the mechanical properties of the material under investigation can be reliably and reproducibly obtained using this device. Especially in the field of battery technology, this improves the predictability of the material's behavior when used in a battery. In particular, the mechanical properties of the material under investigation obtained using this device can be used to determine the material's tendency to form dendrites.

[0005] The device for determining the mechanical properties of a material comprises a sample holder, a penetration detection unit, and an application unit. The sample holder has at least one pore of any dimension or shape. The sample holder is configured to receive a sample of the material to be tested on a first side. The application unit is configured to exert a force on a sample arranged in the sample holder, pressing the sample toward the first side. The penetration detection unit is configured to determine the degree of penetration of the pore by the sample.

[0006] The applied force is set so that the sample undergoes viscoplastic deformation in the pore area. As the force increases, the sample begins to deform and penetrate the pore. This process also causes viscoplastic deformation of the surrounding material around the pore. After the force is applied, the penetration of the sample into the pore is determined using a penetration tester. Based on the temperature, the applied force, the size of the area of ​​the sample under force, the duration of the force application, the size of the plastically deformed area, and the degree of penetration, the length-scale dependencies of the mechanical properties of the material under investigation can be reliably determined. Furthermore, the pressure applied to the sample can be determined based on the force applied, the area of ​​the sample under force, and the duration of the force application.Based on the pressure, a mechanical stress in the sample can be determined.

[0007] The determined length-scale-dependent mechanical properties can be used to improve simulations of the behavior of the investigated material. This allows for more accurate predictions of the material's behavior at small dimensions, such as those found and relevant in battery cell chemistry, particularly in lithium batteries.

[0008] The device has a small number of components and enables a reproducible determination of the mechanical properties and a reproducible determination of the length scale dependence of the mechanical properties of the material under investigation.

[0009] The dependent claims describe preferred embodiments of the invention.

[0010] Preferably, the penetration determination unit is based on an optical and / or an electrical device. Using an optical or electrical device, the degree of penetration of the sample in the pore can be determined precisely and reliably. At the same time, a large number of easily controllable optical and electrical devices exist, making the devices simple and reliable to use.

[0011] Preferably, the sample holder is made of an electrically insulating material. The penetration detection unit has a first electrical contact and a second electrical contact. The first electrical contact is located at an end of the pore opposite the first side. The second electrical contact is configured to make electrical contact with the sample.

[0012] By designing the sample holder from an electrically insulating material, a direct short circuit between the first and second electrical contacts is avoided. Thus, an electrical resistance and an electric field exist between the first and second electrical contacts. The properties of the electric field are determined by the material between the first and second electrical contacts. The properties of the electric field change depending on the proportion of the path between the first and second electrical contacts filled by air, vacuum, and the sample. As the sample penetrates the pore, this ratio changes, and consequently, so does the property of the electric field.This change in the electric field between the first and second electrical contacts allows the length of the sample to be determined before and after the force is applied, and thus the degree of penetration of the sample into the pore to be precisely determined. Similarly, a change in the length of the sample, and therefore the degree of penetration, can be determined capacitively. This is a particularly simple and cost-effective implementation of an electrical device as a penetration determination unit.

[0013] Advantageously, the penetration detection unit is designed to detect complete penetration of the pore by means of the electrical connection between the first and second electrical contacts by the electrically conductive sample. If the conductive sample completely penetrates the pore and touches the first electrical contact, a short circuit exists between the first and second electrical contacts. This allows for a reliable determination of whether the sample has completely penetrated the pore.

[0014] The penetration measurement unit is particularly advantageously equipped, especially with imaging techniques, to determine the size of a plastically deformed area of ​​the sample. Based on the size of this plastically deformed area, direct comparisons between the mechanical properties of different materials can be made. Furthermore, the imaging technique allows for a more precise determination of the shape and other properties of the plastically deformed area, enabling direct comparison with other samples. This allows for more accurate conclusions to be drawn about the mechanical properties of the materials under investigation.

[0015] Advantageously, the penetration determination unit is configured to determine the size of the plastically deformed area of ​​the sample through simulation. Using initial values, the penetration determination unit performs a first simulation and determines the penetration of the pore by the sample. This results in the identification of a plastically deformed area within the sample. The simulation's boundary conditions are then modified until the calculated pore penetration by the sample matches the penetration determined by the penetration determination unit. The size of the plastically deformed area determined in this way is then accepted as the actual size of the plastically deformed area present in the sample.

[0016] Preferably, the device comprises a housing. The housing includes a gas-tight sealed compartment. This gas-tight compartment encloses the sample holder and the application unit. The gas-tight compartment is filled with an inert gas. This allows the investigation of highly reactive materials, such as alkali metals, which would otherwise react chemically with substances in the ambient air, such as oxygen, nitrogen, other particles, or moisture, thereby distorting and / or compromising the investigation of their mechanical properties.

[0017] The pore is preferably designed as a through-opening. A through-opening is easy to produce and allows for simple and residue-free removal of the sample from the device after the experiments.

[0018] Advantageously, the sample holder has a large number of pores. This allows the behavior of the material with a large number of pores to be compared with its behavior with a single pore, and conclusions to be drawn about the mechanical properties of the sample material.

[0019] The device advantageously comprises at least one temperature element and at least one temperature sensor. The temperature element is configured to set a temperature within the device. The temperature sensor is configured to determine a temperature within the device, particularly within the sample. Determining the temperature of the device and the sample allows for a more precise determination of the mechanical properties and the length-scale dependence of the mechanical properties of the sample. By setting the temperature of the device, the mechanical properties of the sample can be determined at different temperatures. This allows for a more comprehensive determination of the mechanical properties of the material under investigation.

[0020] Preferably, the specimen holder has a higher strength than the specimen. The device is designed to cause a deformation of the specimen, particularly a plastic one, by applying force to the specimen via the loading unit, without deforming the specimen holder. The higher strength of the specimen holder compared to the specimen prevents deformation of the specimen holder during the tests. Minor deformations that have no influence on the test results, or whose influence on the test results is within the tolerance range of the penetration testing unit, can be disregarded. This reduces aging of the specimen holder. Furthermore, the higher strength of the specimen holder compared to the specimen ensures reproducibility of the tests and the mechanical properties of the material under investigation.

[0021] Preferably, the pore can have a cylindrical, nozzle-shaped, or conical form. This allows for a variety of investigations. In particular, the sample holder has a multitude of pores, each with a different shape. This enables a large number of different tests to be carried out in a single operation.

[0022] The invention further comprises a method for determining a mechanical property of a material using a device according to one of the preceding embodiments. In a first step, a sample of the material to be tested is placed on a first side of the sample carrier. In a second step, a force is applied to the sample so that the sample is pressed onto the first side of the sample carrier and into the pore. In a third step, the degree of penetration of a pore of the sample carrier by the sample is determined while applying the force. In a fourth step, a mechanical property of the sample is determined by the duration of the force application to the sample, the size of the area of ​​the sample subjected to the force, the magnitude of the force, the diameter of the pore, the size of the plastically deformed area, and the degree of penetration of the pore by the sample.This approach offers the advantages of the device's design as used. Furthermore, this approach allows for easy handling.

[0023] Preferably, the temperature is kept at a constant value during the test. The sample is subjected to a constant force throughout the test. These conditions allow for a simple evaluation of the test.

[0024] Preferably, the temperature is kept constant during the test. The sample is subjected to a variable force during the test. The applied force is measured. This condition allows for further investigation of the mechanical properties under different force applications.

[0025] Advantageously, the sample holder is designed in multiple parts. The bridge and the base plate are designed as separate components and are assembled to form the sample holder. This allows for easy replacement of the bridge and thus simple investigation of the mechanical properties at different sample heights, without the sample swelling beyond the bridge when subjected to force. Furthermore, this design allows for the easy replacement of a damaged bridge.

[0026] The rotationally symmetric design and coaxial arrangement of the sample holder and the application unit are particularly advantageous. This allows a rotationally symmetric sample to be inserted coaxially into the sample holder. This rotationally symmetrical design of the sample holder and the application unit simplifies the determination of the sample's mechanical properties.

[0027] Preferably, the sample holder and the application unit are designed as polygons. This allows polygonal samples to be inserted into the sample holder and examined. Furthermore, rotation of a polygonal sample within the sample holder is prevented.

[0028] Further details, features and advantages of the invention will become apparent from the following description and the figures. These show: Fig. 1 a schematic representation of a device according to a first embodiment, and Fig. 2 a schematic representation of a method according to the first embodiment of the invention.

[0029] The Fig. Figure 1 shows a schematic representation of a device 1 according to a first embodiment.

[0030] The device 1 for determining the mechanical properties of a material comprises a sample holder 4, a penetration determination unit 13, and an actuation unit 8. The sample holder 4 has a pore 5. The sample holder 4 is configured to receive a sample 9 of the material to be tested on a first side 19. The actuation unit 8 is configured to exert a force on a sample 9 arranged in the sample holder 4, such that the sample 9 is pressed towards the first side 19. The penetration determination unit 13 is configured to determine the degree of penetration of the pore 5 by the sample 9.

[0031] The sample carrier 4 and the pore 5 are rotationally symmetrical and arranged coaxially with each other. The pore 5 is cylindrical. The sample carrier 4 has a base plate 4a and a web 4b. The web 4b prevents the sample 9 from slipping and oozing out of the sample carrier 4. The actuation unit 8 is designed as a rotationally symmetrical plunger and is arranged coaxially with the sample carrier 4. An outer diameter 20 of the plunger corresponds to an inner diameter 10 of the sample carrier 4, so that the plunger can be inserted between the web 4b with minimal friction. The sample 9 is inserted between the web 4b as a rotationally symmetrical component. This rotationally symmetrical design of the sample carrier 4, the pore 5, the plunger, and consequently the sample 9, results in a symmetrical load on the sample 9 when the force is applied to the sample 9 by the plunger.

[0032] The device 1 has a small number of components and enables a reproducible determination of the mechanical properties and a reproducible determination of the length scale dependence of the mechanical properties of the material under investigation.

[0033] Pore ​​5 is designed as a through-hole. A through-hole is easy to produce and allows for simple and residue-free removal of sample 9 from apparatus 1 after the tests.

[0034] The pore diameter 6 is smaller than the sample diameter 10. In particular, the pore diameter 6 is one-tenth or less than one-tenth of the sample diameter 10. When the sample 9 is deformed, a plastically deformed region 12 forms in and around the pore 5 in the sample 9. A mechanical property of the sample 9 can be inferred from the size of the plastic region 12. For a reliable and comparable determination of the size of the plastic region 12 in the sample 9, a quasi-hydrostatic stress state of the plastic region 12 is preferred. This is achieved by plasticizing the investigated sample 9 far from its upper surface. The upper surface is opposite and facing the punch.

[0035] The smaller pore diameter 6 compared to the sample diameter 10 ensures that the plastic area 12 forms far away from the upper surface of the sample 9.

[0036] In particular, the sample height 11 is less than the height 4c of the web 4b and the sample diameter 10 corresponds to the web inner diameter 4d.

[0037] The sample holder 4 is made of an electrically insulating material. The penetration detection unit 13 has a first electrical contact 15 and a second electrical contact 16. The first electrical contact 15 is located at the end of the pore 5 opposite the first side. The second electrical contact 16 is configured to make electrical contact with the sample 9. The penetration detection unit 13 is configured to detect complete penetration of the pore 5 by the electrical connection between the first and second electrical contacts through the electrically conductive sample 9.

[0038] By designing the sample holder 4 from an electrically insulating material, a direct short circuit between the first electrical contact 15 and the second electrical contact 16 is avoided. Thus, an electrical resistance exists between the first electrical contact 15 and the second electrical contact 16. If the conductive sample 9 completely penetrates the pore 5 and touches the first electrical contact 15, a short circuit occurs between the first electrical contact 15 and the second electrical contact 16. From this, a reliable conclusion can be drawn regarding the complete penetration of the pore 5 by the sample 9. This represents a particularly simple and cost-effective implementation of an electrical device as a penetration detection unit 13.An evaluation unit 14 is electrically connected to the first electrical contact 15 and the second electrical contact 16 and is configured to determine an electrical resistance between the first electrical contact 15 and the second electrical contact 16.

[0039] Additionally or alternatively, the penetration determination unit 13 can be set up, in particular by means of an imaging method 100, to determine the size of a plastically deformed area 12 of the sample 9.

[0040] The device 1 has a housing 2 which gas-tightly encloses the sample carrier 4, the application unit 8, and the sample 9 inserted therein. The gas-tight area 3 is filled with an inert gas.

[0041] A temperature element 17 and a temperature sensor 18 are arranged on the device 1. The temperature element 17 is configured to set a temperature in the device 1. The temperature sensor 18 is configured to determine a temperature in the device 1, in particular in the sample 9. Determining the temperature of the device 1 and the sample 9 allows for a more precise determination of the mechanical properties and the length-scale dependence of the mechanical properties of the sample 9. By setting the temperature of the device 1, the mechanical properties of the sample 9 can be determined at different temperatures. This allows for a more comprehensive determination of the mechanical properties of the material under investigation.

[0042] The temperature element 17 is arranged on a subside 4e of the device 1 and is rotationally symmetrical. The temperature element 17 is arranged coaxially with the device 1 on the base plate 4a. This allows for uniform and large-area temperature control of both the sample carrier 4 and the sample 9.

[0043] The sample holder 4 has a higher strength than the sample 9. The device 1 is designed to cause plastic deformation of the sample 9 by applying force to the sample 9 via the loading unit 8, without causing any deformation, particularly plastic deformation, of the sample holder 4. Due to the higher strength of the sample holder 4 compared to the sample 9, plastic deformation of the sample holder 4 is prevented during the tests. This reduces aging of the sample holder 4. Furthermore, the higher strength of the sample holder 4 compared to the sample 9 ensures reproducibility of the tests and the mechanical properties of the material under investigation.

[0044] This embodiment enables the determination of the mechanical properties and the length-scale dependence of the mechanical properties of sample 9. Here, alkali metals, despite their highly reactive chemical reaction with air, can be examined as sample 9 with low risk.

[0045] The Fig. Figure 2 shows a schematic representation of a method 100 according to the first embodiment of the invention.

[0046] Method 100 for determining a mechanical property of a material is carried out using a device 1 according to the first embodiment. In a first step, a sample 9 of the material to be investigated is placed on a first side 19 of the sample carrier 4 101. In a second step, a force is applied to the sample 9 so that the sample 9 is pressed onto the first side 19 of the sample carrier 4 and into the pore 5 102. In a third step, the degree of penetration of a pore 5 of the sample carrier 4 by the sample 9 is determined under the application of the force 103. In a fourth step, a mechanical property of the sample 9 is determined by means of the duration of the application of the force to the sample 9, the magnitude of the force, the area of ​​the force-affected area of ​​the sample 9, the diameter 6 of the pore 5, and the degree of penetration of the pore 5 by the sample 9 104.

[0047] The applied force is adjusted to cause viscoplastic deformation of sample 9 in the region of pore 5. As the force increases, sample 9 begins to deform and penetrate pore 5. This process also causes viscoplastic deformation of the surrounding material around pore 5. After a specific duration of force application, the penetration of sample 9 into pore 5 is determined using the penetration detection unit 13. Based on the temperature, the magnitude of the applied force, the area of ​​the sample subjected to the force, the duration of force application, and the degree of penetration, the length-scale dependencies of the mechanical properties of the material under investigation can be reliably determined. Furthermore, the pressure exerted on the sample can be determined based on the force applied to the sample, the area of ​​the sample subjected to the force, and the duration of force application.Based on the pressure, a mechanical stress in the sample can be determined.

[0048] The determined length-scale-dependent mechanical properties can be used to improve simulations of the behavior of the investigated material. This allows for improved predictions of the material's behavior at small dimensions, such as those found in battery cell chemistry, particularly in lithium batteries.

[0049] In particular, the behavior, such as the size of the plastically deformed area 12 and the time required for penetration of pore 5 at a given force, can be predicted using a simulation. This prediction can then be compared with the actual experimental results. If the predictions deviate from the experimental results, the newly acquired knowledge from the experiment can be incorporated into the simulation. This process is repeated until the simulation predictions match the experimental results. Reference symbol list: 1 Device 2 cases 3 gas-tight area 4 sample carriers 4a Base plate 4b Bridge 4c Bridge height 4d inner web diameter 4e bottom 5 pores 6 pore diameters 7 Base plate height 8 operating units 9 Sample 10 sample diameters 11 Sample height 12. Plastically deformed area of ​​the sample 13 Penetration determination unit 14 evaluation units 15 first electrical contact 16 second electrical contact 17 Temperature element 18 Temperature sensor 19 first page 20 Outer diameter of the punch 100 procedures 101 Insert 102 Pressurize 103 Determine 104 Determine

Claims

[1] Device (1) for determining mechanical properties of a material, comprising - a sample carrier (4), - a penetration determination unit (13) and - a loading unit (8), - wherein the sample carrier (4) has at least one pore (5), - wherein the sample carrier (4) is arranged to receive a sample (9) of the material to be examined on a first side (19), - wherein the application unit (8) is arranged to exert a force on a sample (9) arranged in the sample carrier (4) so ​​that the sample (9) is pressed towards the first side (19), and - wherein the penetration determination unit (13) is configured to determine a degree of penetration of the pore (5) by the sample (9). [2] Device (1) according to claim 1 characterized bythat the penetration determination unit (13) is based on an optical device and / or on an electrical device. [3] Device (1) according to one of the preceding claims characterized by , that - the sample carrier (4) is made of an electrically insulating material, and - the penetration determination unit (13) has a first electrical contact (15) and a second electrical contact (16), - wherein the first electrical contact (15) is arranged at an end of the pore (5) opposite the first side (19), and - wherein the second electrical contact (16) is arranged to be electrically contacted with the sample (9). [4] Device (1) according to one of the preceding claims characterized byin that the penetration determination unit (13) is configured to detect complete penetration of the pore (5) by the electrically conductive sample (9) on the basis of the electrical connection between the first electrical contact (15) and the second electrical contact (16). [5] Device (1) according to one of the preceding claims characterized by that the penetration determination unit (13) is configured to determine the size of a plastically deformed region of the sample (9), in particular by imaging methods. [6] Device (1) according to one of the preceding claims characterized by , - a housing (2), - wherein the housing (2) has a gas-tight enclosed area (3), - wherein the gas-tight enclosed area (3) encloses the sample carrier (4) and the loading unit (8), and - wherein the gas-tight region (3) is filled with an inert gas. [7] Device (1) according to one of the preceding claims characterized by that the pore (5) is designed as a through opening (5). [8] Device (1) according to one of the preceding claims characterized by that the sample carrier (4) has a plurality of pores (5). [9] Device (1) according to one of the preceding claims characterized by , - at least one temperature element (17) and at least one temperature sensor (18), - wherein the temperature element (17) is arranged to set a temperature in the device (1), and - wherein the temperature sensor (17) is configured to determine a temperature in the device (1). [10] Device (1) according to one of the preceding claims characterized by , that - the sample carrier (4) has a higher strength than the sample (9), - wherein the device (1) is designed to cause a deformation of the sample (9) without a deformation of the sample carrier (4) by applying a force to the sample (9) by the application unit. [11] Method (100) for determining a mechanical property of a material by means of a device (1) according to one of the preceding claims, the method (100) comprising the steps: - placing (101) a sample (9) of the material to be examined on a first side of the sample carrier (4), - applying (102) a force to the sample (9) so that the sample (9) is pressed onto the first side of the sample carrier (4) and into the pore (5), - determining (103) a degree of penetration of a pore (5) of the sample carrier (4) by the sample (9) under application of the force, and - Determining (104) a mechanical property of the sample (9) by means of the duration of application of the force to the sample (9), the magnitude of the force, the size of the force-actuated area of ​​the sample, the size of the plastically deformed region, the diameter (6) of the pore (5) and the degree of penetration of the pore (5) by the sample (9).

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